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{{short description|Physical process of transition between basic states of matter}}
{{Use dmy dates|date=October 2014}}
[[File:Phase change - en.svg|thumb|upright=1.45|This diagram shows the nomenclature for the different phase transitions.]]

In [[chemistry]], [[thermodynamics]], and other related fields, a '''phase transition''' (or '''phase change''') is the [[physical process]] of transition between one state of a medium and another. Commonly the term is used to refer to changes among the basic [[State of matter|states of matter]]: [[solid]], [[liquid]], and [[gas]], and in rare cases, [[plasma (physics)|plasma]]. A phase of a [[thermodynamic system]] and the states of matter have uniform [[physical property|physical properties]]. During a phase transition of a given medium, certain properties of the medium change as a result of the change of external conditions, such as [[temperature]] or [[pressure]]. This can be a discontinuous change; for example, a liquid may become gas upon heating to its [[boiling point]], resulting in an abrupt change in volume. The identification of the external conditions at which a transformation occurs defines the phase transition point.

==Types of phase transition==

===States of matter===
[[File:Phase diagram of water simplified.svg|thumb|250px|A simplified phase diagram for [[water]], showing whether solid ice, liquid water, or gaseous water vapor is the most stable at different combinations of temperature and pressure.]]
{{See also|vapor pressure|phase diagram}}

Phase transitions commonly refer to when a substance transforms between one of the four [[state of matter|states of matter]] to another. At the phase transition point for a substance, for instance the [[boiling point]], the two phases involved - liquid and [[vapor]], have identical free energies and therefore are equally likely to exist. Below the boiling point, the liquid is the more stable state of the two, whereas above the boiling point the gaseous form is the more stable. 

Common transitions between the solid, liquid, and gaseous phases of a single component, due to the effects of temperature and/or [[pressure]] are identified in the following table:
{{Table of Phase Transitions}}

For a single component, the most stable phase at different temperatures and pressures can be shown on a [[phase diagram]]. Such a diagram usually depicts states in equilibrium. A phase transition usually occurs when the pressure or temperature changes and the system crosses from one region to another, like water turning from liquid to solid as soon as the temperature drops below the [[freezing point]]. In exception to the usual case, it is sometimes possible to change the state of a system [[diabatic]]ally (as opposed to [[adiabatic invariant|adiabatic]]ally) in such a way that it can be brought past a phase transition point without undergoing a phase transition. The resulting state is [[metastable]], i.e., less stable than the phase to which the transition would have occurred, but not unstable either. This occurs in [[superheating]] and [[supercooling]], for example. Metastable states do not appear on usual phase diagrams.

===Structural===
{{See also|Polymorphism (materials science)}}
[[File:Pure iron phase diagram (EN).svg|thumb|250px|A phase diagram showing the [[allotropes of iron]], distinguishing between different several different [[crystal structure]]s including [[Allotropes of iron|ferrite]] (α-iron) and [[austenite]] (γ-iron).]]

Phase transitions can also occur when a solid changes to a different structure without changing its chemical makeup. In elements, this is known as [[allotropy]], whereas in compounds it is known as [[polymorphism (materials science)|polymorphism]]. The change from one [[crystal structure]] to another, from a crystalline solid to an [[amorphous solid]], or from one amorphous structure to another ([[polyamorphism|{{not a typo|polyamorphs}}]]) are all examples of solid to solid phase transitions.

The [[martensitic transformation]] occurs as one of the many phase transformations in carbon steel and stands as a model for [[displacive phase transformations]]. Order-disorder transitions such as in alpha-[[titanium aluminide]]s. As with states of matter, there are also a [[metastable]] to equilibrium phase transformation for structural phase transitions. A metastable polymorph which forms rapidly due to lower surface energy will transform to an equilibrium phase given sufficient thermal input to overcome an energetic barrier.

===Magnetic===
{{See also|Magnetic structure}}
[[File:MnSi magnetic phase diagram.png|thumb|250px|A phase diagram showing different [[magnetic structure]]s in the same crystal structure of [[Manganese monosilicide]].]]

Phase transitions can also describe the change between different kinds of [[magnetic ordering]]. The most well-known is the transition between the [[ferromagnetism|ferromagnetic]] and [[paramagnetism|paramagnetic]] phases of [[magnet]]ic materials, which occurs at what is called the [[Curie point]]. Another example is the transition between differently ordered, [[ANNNI model|commensurate]] or [[commensurability (mathematics)|incommensurate]], magnetic structures, such as in cerium [[antimonide]].

===Mixtures===
[[File:Binary phase diagram of NiTI (phase and temperature).JPG|thumb|250px|A binary phase diagram showing the most stable chemical compounds of [[titanium]] and [[nickel]] at different [[mixing ratio]]s and [[temperature]]s.]]

Phase transitions involving [[Solution (chemistry)|solution]]s and [[mixture]]s are more complicated than transitions involving a single compound. While chemically pure compounds exhibit a single temperature [[melting point]] between solid and liquid phases, mixtures can either have a single melting point, known as [[congruent melting]], or they have different [[liquidus and solidus|liquidus and solidus temperatures]] resulting in a temperature span where solid and liquid coexist in equilibrium. This is often the case in [[solid solution]]s, where the two components are isostructural.

There are also a number of phase transitions involving three phases: a [[eutectic]] transformation, in which a two-component single-phase liquid is cooled and transforms into two solid phases. The same process, but beginning with a solid instead of a liquid is called a [[eutectoid]] transformation. A [[peritectic]] transformation, in which a two-component single-phase solid is heated and transforms into a solid phase and a liquid phase. A [[peritectoid]] reaction is a peritectoid rection, except involving only solid phases. A [[monotectic]] reaction consists of change from a liquid and to a combination of a solid and a second liquid, where the two liquids display a [[miscibility gap]].<ref>{{cite book | last1=Askeland | first1=Donald R. | last2=Haddleton | first2=Frank | last3=Green | first3=Phil | last4=Robertson | first4=Howard | title=The Science and Engineering of Materials | date=1996 | isbn=978-0-412-53910-7 | page=286| publisher=Chapman & Hall }}</ref>

Separation into multiple phases can occur via [[spinodal decomposition]], in which a single phase is cooled and separates into two different compositions.

Non-equilibrium mixtures can occur, such as in [[supersaturation]].

===Other examples===
[[File:Argon ice 1.jpg|thumb|A small piece of rapidly melting solid [[argon]] shows two concurrent phase changes. The transition from solid to liquid, and gas to liquid (shown by the white condensed water vapour).]]
Other phase changes include:

* Transition to a [[mesophase]] between solid and liquid, such as one of the "[[liquid crystal]]" phases.
* The dependence of the [[adsorption]] geometry on coverage and temperature, such as for [[hydrogen]] on iron (110).
* The emergence of [[superconductivity]] in certain metals and ceramics when cooled below a critical temperature.
* The emergence of [[metamaterial]] properties in artificial photonic media as their parameters are varied.<ref>{{cite journal|author=Rybin, M.V.|title= Phase diagram for the transition from photonic crystals to dielectric metamaterials|journal=Nature Communications|page=10102 |year=2015|doi=10.1038/ncomms10102|pmid= 26626302 |display-authors=etal|volume=6|pmc=4686770|arxiv= 1507.08901|bibcode= 2015NatCo...610102R}}</ref><ref>Eds. Zhou, W., and Fan. S., [https://www.sciencedirect.com/bookseries/semiconductors-and-semimetals/vol/100/suppl/C Semiconductors and Semimetals. Vol 100. Photonic Crystal Metasurface Optoelectronics''], Elsevier, 2019</ref>
* Quantum condensation of [[boson]]ic fluids ([[Bose–Einstein condensate|Bose–Einstein condensation]]). The [[superfluidity|superfluid]] transition in liquid [[helium]] is an example of this.
* The [[Symmetry breaking|breaking of symmetries]] in the laws of physics during the early history of the universe as its temperature cooled.
* [[Isotope fractionation]] occurs during a phase transition, the ratio of light to heavy isotopes in the involved molecules changes. When [[water vapor]] condenses (an [[equilibrium fractionation]]), the heavier water isotopes (<sup>18</sup>O and <sup>2</sup>H) become enriched in the liquid phase while the lighter isotopes (<sup>16</sup>O and <sup>1</sup>H) tend toward the vapor phase.<ref>{{cite web
 | year=2004
 | author= Carol Kendall|author-link=Carol Kendall (scientist)
 | title= Fundamentals of Stable Isotope Geochemistry
 | url= http://wwwrcamnl.wr.usgs.gov/isoig/res/funda.html
 | publisher= USGS
 | access-date= 10 April 2014
}}</ref>

Phase transitions occur when the [[thermodynamic free energy]] of a system is [[analytic function|non-analytic]] for some choice of thermodynamic variables (cf. [[phase (matter)|phases]]). This condition generally stems from the interactions of a large number of particles in a system, and does not appear in systems that are small. Phase transitions can occur for non-thermodynamic systems, where temperature is not a parameter. Examples include: quantum phase transitions, dynamic phase transitions, and topological (structural) phase transitions. In these types of systems other parameters take the place of temperature. For instance, connection probability replaces temperature for percolating networks.
{{Condensed matter physics|expanded=States of matter}}

==Classifications==

===Ehrenfest classification===
[[Paul Ehrenfest]] classified phase transitions based on the behavior of the [[thermodynamic free energy]] as a function of other thermodynamic variables.<ref name="ReferenceA">{{cite journal|last1=Jaeger|first1=Gregg|title=The Ehrenfest Classification of Phase Transitions: Introduction and Evolution|journal=Archive for History of Exact Sciences|date=1 May 1998|volume=53|issue=1|pages=51–81|doi=10.1007/s004070050021|s2cid=121525126}}</ref> Under this scheme, phase transitions were labeled by the lowest derivative of the free energy that is discontinuous at the transition. ''First-order phase transitions'' exhibit a discontinuity in the first derivative of the free energy with respect to some thermodynamic variable.<ref name = Blundell>{{Cite book | last = Blundell | first = Stephen J. |author2=Katherine M. Blundell | title = Concepts in Thermal Physics | publisher = Oxford University Press | year = 2008 | isbn = 978-0-19-856770-7}}</ref> The various solid/liquid/gas transitions are classified as first-order transitions because they involve a discontinuous change in density, which is the (inverse of the) first derivative of the free energy with respect to pressure. ''Second-order phase transitions'' are continuous in the first derivative (the [[#order parameters|order parameter]], which is the first derivative of the free energy with respect to the external field, is continuous across the transition) but exhibit discontinuity in a second derivative of the free energy.<ref name = Blundell/> These include the ferromagnetic phase transition in materials such as iron, where the [[magnetization]], which is the first derivative of the free energy with respect to the applied magnetic field strength, increases continuously from zero as the temperature is lowered below the [[Curie temperature]]. The [[magnetic susceptibility]], the second derivative of the free energy with the field, changes discontinuously. Under the Ehrenfest classification scheme, there could in principle be third, fourth, and higher-order phase transitions. For example, the Gross–Witten–Wadia phase transition in 2-d lattice quantum chromodynamics is a third-order phase transition.<ref>{{Citation |last1=Gross |first1=David J. |title=Possible third-order phase transition in the large N lattice gauge theory |date=1980 |doi=10.1103/PhysRevD.21.446}}</ref><ref>{{Cite journal |last1=Majumdar |first1=Satya N |last2=Schehr |first2=Grégory |date=2014-01-31 |title=Top eigenvalue of a random matrix: large deviations and third order phase transition |url=https://iopscience.iop.org/article/10.1088/1742-5468/2014/01/P01012 |journal=Journal of Statistical Mechanics: Theory and Experiment |volume=2014 |issue=1 |pages=P01012 |doi=10.1088/1742-5468/2014/01/P01012 |issn=1742-5468|arxiv=1311.0580 |bibcode=2014JSMTE..01..012M |s2cid=119122520 }}</ref> The Curie points of many ferromagnetics is also a third-order transition, as shown by their specific heat having a sudden change in slope.<ref>{{Cite book |last=Pippard |first=Alfred B. |title=Elements of classical thermodynamics: for advanced students of physics |date=1981 |publisher=Univ. Pr |isbn=978-0-521-09101-5 |edition=Repr |location=Cambridge |pages=140–141}}</ref><ref>{{Cite journal |last=Austin |first=J. B. |date=November 1932 |title=Heat Capacity of Iron - A Review |journal=Industrial & Engineering Chemistry |volume=24 |issue=11 |pages=1225–1235 |doi=10.1021/ie50275a006 |issn=0019-7866}}</ref>

The Ehrenfest classification implicitly allows for continuous phase transformations, where the bonding character of a material changes, but there is no discontinuity in any free energy derivative. An example of this occurs at the [[supercritical liquid–gas boundaries]].

The first example of a phase transition which did not fit into the Ehrenfest classification was the exact solution of the [[Ising model]], discovered in 1944 by [[Lars Onsager]]. The exact specific heat differed from the earlier [[mean-field theory|mean-field]] approximations, which had predicted that it has a simple discontinuity at critical temperature. Instead, the exact specific heat had a logarithmic divergence at the critical temperature.<ref>{{cite book |last= Stanley|first= H. Eugene |date=1971 |title=Introduction to Phase Transitions and Critical Phenomena|location=Oxford |publisher=Clarendon Press}}</ref> In the following decades, the Ehrenfest classification was replaced by a simplified classification scheme that is able to incorporate such transitions.

===Modern classifications===
In the modern classification scheme, phase transitions are divided into two broad categories, named similarly to the Ehrenfest classes:<ref name="ReferenceA"/>

'''First-order phase transitions''' are those that involve a [[latent heat]]. During such a transition, a system either absorbs or releases a fixed (and typically large) amount of energy per volume. During this process, the temperature of the system will stay constant as heat is added: the system is in a "mixed-phase regime" in which some parts of the system have completed the transition and others have not.<ref>Faghri, A., and Zhang, Y., [https://books.google.com/books?id=bxndY2KSuQsC&q=Transport+Phenomena+in+Multiphase+Systems ''Transport Phenomena in Multiphase Systems''], Elsevier, Burlington, MA, 2006,</ref><ref>Faghri, A., and Zhang, Y., [https://www.springer.com/gp/book/9783030221362 ''Fundamentals of Multiphase Heat Transfer and Flow''], Springer, New York, NY, 2020</ref> 

Familiar examples are the melting of ice or the boiling of water (the water does not instantly turn into [[water vapor|vapor]], but forms a [[turbulence|turbulent]] mixture of liquid water and vapor bubbles). [[Yoseph Imry]] and Michael Wortis showed that [[quenched disorder]] can broaden a first-order transition. That is, the transformation is completed over a finite range of temperatures, but phenomena like supercooling and superheating survive and hysteresis is observed on thermal cycling.<ref>{{cite journal | last1 = Imry | first1 = Y. | last2 = Wortis | first2 = M. | year = 1979 | title =  Influence of quenched impurities on first-order phase transitions| journal = Phys. Rev. B | volume = 19 | issue = 7| pages = 3580–3585 | doi=10.1103/physrevb.19.3580|bibcode = 1979PhRvB..19.3580I }}</ref><ref name="KumarPramanik2006">{{cite journal|last1=Kumar|first1=Kranti|last2=Pramanik|first2=A. K.|last3=Banerjee|first3=A.|last4=Chaddah|first4=P.|last5=Roy|first5=S. B.|last6=Park|first6=S.|last7=Zhang|first7=C. L.|last8=Cheong|first8=S.-W.|title=Relating supercooling and glass-like arrest of kinetics for phase separated systems: DopedCeFe2and(La,Pr,Ca)MnO3|journal=Physical Review B|volume=73|issue=18|page=184435|year=2006|issn=1098-0121|doi=10.1103/PhysRevB.73.184435|arxiv = cond-mat/0602627 |bibcode = 2006PhRvB..73r4435K |s2cid=117080049}}</ref><ref name="PasquiniDaroca2008">{{cite journal|last1=Pasquini|first1=G.|last2=Daroca|first2=D. Pérez|last3=Chiliotte|first3=C.|last4=Lozano|first4=G. S.|last5=Bekeris|first5=V.|title=Ordered, Disordered, and Coexistent Stable Vortex Lattices inNbSe2Single Crystals|journal=Physical Review Letters|volume=100|issue=24|page=247003|year=2008|issn=0031-9007|doi=10.1103/PhysRevLett.100.247003|pmid=18643617|bibcode=2008PhRvL.100x7003P|arxiv=0803.0307|s2cid=1568288}}</ref>

'''{{va|Second-order phase transition}}s''' are also called ''"continuous phase transitions"''. They are characterized by a divergent susceptibility, an infinite [[Correlation function (statistical mechanics)|correlation length]], and a [[power law]] decay of correlations near [[Critical point (thermodynamics)|criticality]]. Examples of second-order phase transitions are the [[Ferromagnetism|ferromagnetic]] transition, superconducting transition (for a [[Type-I superconductor]] the phase transition is second-order at zero external field and for a [[Type-II superconductor]] the phase transition is second-order for both normal-state–mixed-state and mixed-state–superconducting-state transitions) and the [[superfluid]] transition. In contrast to viscosity, thermal expansion and heat capacity of amorphous materials show a relatively sudden change at the glass transition temperature<ref name="J. Non-Cryst 2013">{{cite journal | last1 = Ojovan | first1 = M.I. | year = 2013 | title = Ordering and structural changes at the glass-liquid transition | journal = J. Non-Cryst. Solids | volume = 382 | pages = 79–86 | doi = 10.1016/j.jnoncrysol.2013.10.016 |bibcode = 2013JNCS..382...79O }}</ref> which enables accurate detection using [[differential scanning calorimetry]] measurements.  [[Lev Landau]] gave a [[Phenomenology (particle physics)|phenomenological]] [[Landau theory|theory]] of second-order phase transitions.

Apart from isolated, simple phase transitions, there exist transition lines as well as [[multicritical point]]s, when varying external parameters like the magnetic field or composition.

Several transitions are known as ''infinite-order phase transitions''.
They are continuous but break no [[#Symmetry|symmetries]]. The most famous example is the [[Kosterlitz–Thouless transition]] in the two-dimensional [[XY model]]. Many [[quantum phase transition]]s, e.g., in [[two-dimensional electron gas]]es, belong to this class.

The [[glass transition|liquid–glass transition]] is observed in many [[polymers]] and other liquids that can be [[supercooling|supercooled]] far below the melting point of the crystalline phase. This is atypical in several respects. It is not a transition between thermodynamic ground states: it is widely believed that the true ground state is always crystalline. Glass is a ''[[quenched disorder]]'' state, and its entropy, density, and so on, depend on the thermal history. Therefore, the glass transition is primarily a dynamic phenomenon: on cooling a liquid, internal degrees of freedom successively fall out of equilibrium. Some theoretical methods predict an underlying phase transition in the hypothetical limit of infinitely long relaxation times.<ref>Gotze, Wolfgang. "Complex Dynamics of Glass-Forming Liquids: A Mode-Coupling Theory."</ref><ref>{{cite journal | last1 = Lubchenko | first1 = V. Wolynes | last2 = Wolynes | first2 = Peter G. | year = 2007 | title = Theory of Structural Glasses and Supercooled Liquids | journal = Annual Review of Physical Chemistry | volume = 58 | pages = 235–266 | doi=10.1146/annurev.physchem.58.032806.104653| pmid = 17067282 |arxiv = cond-mat/0607349 |bibcode = 2007ARPC...58..235L | s2cid = 46089564 }}</ref> No direct experimental evidence supports the existence of these transitions.

The [[gelation]] transition of [[colloids|colloidal particles]] has been shown to be a second-order phase transition under [[nonequilibrium thermodynamics|nonequilibrium]] conditions.<ref>{{cite journal | last1 = Rouwhorst | first1 = J |last2 = Ness | first2 = C. | last3 = Soyanov | first3 = S. | last4=Zaccone | first4=A. | last5=Schall | first5=P | year = 2020 | title = Nonequilibrium continuous phase transition in colloidal gelation with short-range attraction | journal = Nature Communications | volume = 11 | issue = 1| page = 3558 | doi=10.1038/s41467-020-17353-8| pmid = 32678089 | pmc = 7367344 | arxiv = 2007.10691 | bibcode = 2020NatCo..11.3558R | doi-access = free }}</ref>

==Characteristic properties==

===Phase coexistence===
A disorder-broadened  first-order transition occurs over a finite range of temperatures where the fraction of the low-temperature equilibrium phase grows from zero to one (100%) as the temperature is lowered. This continuous variation of the coexisting fractions with temperature raised interesting possibilities. On cooling, some liquids vitrify into a glass rather than transform to the equilibrium crystal phase. This happens if the cooling rate is faster than a critical cooling rate, and is attributed to the molecular motions becoming so slow that the molecules cannot rearrange into the crystal positions.<ref>{{cite journal | year = 1995 | title =  Metallic Glasses| journal = Science | volume = 267 | issue = 5206| pages = 1947–1953 |bibcode = 1995Sci...267.1947G |doi = 10.1126/science.267.5206.1947 | pmid =  17770105| last1 =  Greer| first1 =  A. L.| s2cid = 220105648}}</ref> This slowing down happens below a glass-formation temperature ''T''<sub>g</sub>, which may depend on the applied pressure.<ref name="J. Non-Cryst 2013"/><ref>{{cite journal | last1 = Tarjus | first1 = G. | year = 2007 | title =  Materials science: Metal turned to glass| journal = Nature | volume = 448 | issue = 7155| pages = 758–759 | doi=10.1038/448758a| pmid = 17700684 |bibcode = 2007Natur.448..758T | s2cid = 4410586 | doi-access = free }}</ref> If the first-order freezing transition occurs over a range of temperatures, and ''T''<sub>g</sub> falls within this range, then there is an interesting possibility that the transition is arrested when it is partial and incomplete. Extending these ideas to first-order magnetic transitions being arrested at low temperatures, resulted in the observation of incomplete magnetic transitions, with two magnetic phases coexisting, down to the lowest temperature. First reported in the case of a ferromagnetic to anti-ferromagnetic transition,<ref name="ManekarChaudhary2001">{{cite journal |last1=Manekar |first1=M. A. |last2=Chaudhary |first2=S. |last3=Chattopadhyay |first3=M. K. |last4=Singh |first4=K. J. |last5=Roy |first5=S. B. |last6=Chaddah |first6=P. |title=First-order transition from antiferromagnetism to ferromagnetism inCe(Fe<sub>0.96</sub>Al<sub>0.04</sub>)<sub>2</sub> |journal=Physical Review B |volume=64 |issue=10 |page=104416 |year=2001 |issn=0163-1829 |doi=10.1103/PhysRevB.64.104416 |arxiv=cond-mat/0012472 |bibcode=2001PhRvB..64j4416M|s2cid=16851501 }}</ref> such persistent phase coexistence has now been reported across a variety of first-order magnetic transitions. These include colossal-magnetoresistance manganite materials,<ref>{{cite journal|doi=10.1088/0953-8984/18/49/L02|arxiv = cond-mat/0611152 |bibcode = 2006JPCM...18L.605B |title = Coexisting tunable fractions of glassy and equilibrium long-range-order phases in manganites |journal = Journal of Physics: Condensed Matter |volume = 18 |issue = 49 |pages = L605 |year = 2006 |last1 = Banerjee |first1 = A. |last2 = Pramanik |first2 = A. K. |last3 = Kumar |first3 = Kranti |last4 = Chaddah |first4 = P. |s2cid = 98145553 }}</ref><ref>{{cite journal |author=Wu W. |author2=Israel C. |author3=Hur N. |author4=Park S. |author5=Cheong S. W. |author6=de Lozanne A. | year = 2006 | title =  Magnetic imaging of a supercooling glass transition in a weakly disordered ferromagnet| journal = Nature Materials | volume = 5 | issue = 11| pages = 881–886 |bibcode = 2006NatMa...5..881W |doi = 10.1038/nmat1743 | pmid = 17028576 | s2cid = 9036412 }}</ref> magnetocaloric materials,<ref name="RoyChattopadhyay2006">{{cite journal |last1=Roy |first1=S. B. |last2=Chattopadhyay |first2=M. K. |last3=Chaddah |first3=P. |last4=Moore |first4=J. D. |last5=Perkins |first5=G. K. |last6=Cohen |first6=L. F. |last7=Gschneidner |first7=K. A. |last8=Pecharsky |first8=V. K. |title=Evidence of a magnetic glass state in the magnetocaloric material Gd<sub>5</sub>Ge<sub>4</sub> |journal=Physical Review B |volume=74 |issue=1 |page=012403 |year=2006 |issn=1098-0121 |doi=10.1103/PhysRevB.74.012403 |bibcode = 2006PhRvB..74a2403R }}</ref> magnetic shape memory materials,<ref name="LakhaniBanerjee2012">{{cite journal |last1=Lakhani |first1=Archana |last2=Banerjee |first2=A. |last3=Chaddah |first3=P. |last4=Chen |first4=X. |last5=Ramanujan |first5=R. V. |title=Magnetic glass in shape memory alloy: Ni<sub>45</sub>Co<sub>5</sub>Mn<sub>38</sub>Sn<sub>12</sub> |journal=Journal of Physics: Condensed Matter |volume=24 |issue=38 |year=2012 |page=386004 |issn=0953-8984 |doi=10.1088/0953-8984/24/38/386004 |pmid=22927562 |arxiv = 1206.2024 |bibcode = 2012JPCM...24L6004L |s2cid=206037831 }}</ref> and other materials.<ref name="KushwahaLakhani2009">{{cite journal |last1=Kushwaha |first1=Pallavi |last2=Lakhani |first2=Archana |last3=Rawat |first3=R. |last4=Chaddah |first4=P. |title=Low-temperature study of field-induced antiferromagnetic-ferromagnetic transition in Pd-doped Fe-Rh |journal=Physical Review B |volume=80 |issue=17 |page=174413 |year=2009 |issn=1098-0121 |doi=10.1103/PhysRevB.80.174413 |arxiv=0911.4552 |bibcode=2009PhRvB..80q4413K|s2cid=119165221 }}</ref>
The interesting feature of these observations of ''T''<sub>g</sub> falling within the temperature range over which the transition occurs is that the first-order magnetic transition is influenced by magnetic field, just like the structural transition is influenced by pressure. The relative ease with which magnetic fields can be controlled, in contrast to pressure, raises the possibility that one can study the interplay between ''T''<sub>g</sub> and ''T''<sub>c</sub> in an exhaustive way. Phase coexistence across first-order magnetic transitions will then enable the resolution of outstanding issues in understanding glasses.

===Critical points===
In any system containing liquid and gaseous phases, there exists a special combination of pressure and temperature, known as the [[Critical point (thermodynamics)|critical point]], at which the transition between liquid and gas becomes a second-order transition. Near the critical point, the fluid is sufficiently hot and compressed that the distinction between the liquid and gaseous phases is almost non-existent. This is associated with the phenomenon of [[critical opalescence]], a milky appearance of the liquid due to density fluctuations at all possible wavelengths (including those of visible light).

===Symmetry===
Phase transitions often involve a [[symmetry breaking]] process. For instance, the cooling of a fluid into a [[crystalline solid]] breaks continuous [[translation symmetry]]: each point in the fluid has the same properties, but each point in a crystal does not have the same properties (unless the points are chosen from the lattice points of the crystal lattice). Typically, the high-temperature phase contains more symmetries than the low-temperature phase due to [[spontaneous symmetry breaking]], with the exception of certain [[accidental symmetry|accidental symmetries]] (e.g. the formation of heavy [[virtual particles]], which only occurs at low temperatures).<ref>{{cite book|last1=Ivancevic|first1=Vladimir G.|last2=Ivancevic|first2=Tijiana, T.|title=Complex Nonlinearity|date=2008|publisher=Springer|location=Berlin|isbn=978-3-540-79357-1|pages=176–177|url=https://books.google.com/books?id=wpsPgHgtxEYC&pg=PA177 |access-date=12 October 2014}}</ref>

===Order parameters<!--'Order parameter' and 'Order parameters' redirect here-->===
An '''order parameter'''<!--boldface per WP:R#PLA--> is a measure of the degree of order across the boundaries in a phase transition system; it normally ranges between zero in one phase (usually above the critical point) and nonzero in the other.<ref>{{cite journal |last1=Clark |first1=J.B. |last2=Hastie |first2=J.W. |last3=Kihlborg |first3=L.H.E. |last4=Metselaar |first4=R. |last5=Thackeray |first5=M.M. |title=Definitions of terms relating to phase transitions of the solid state |journal=Pure and Applied Chemistry |date=1994 |volume=66 |issue=3 |pages=577–594 |doi=10.1351/pac199466030577 |s2cid=95616565 |doi-access=free }}</ref> At the critical point, the order parameter [[susceptibility (disambiguation)|susceptibility]] will usually diverge.

An example of an order parameter is the net [[magnetization]] in a [[ferromagnetic]] system undergoing a phase transition. For liquid/gas transitions, the order parameter is the difference of the densities.

From a theoretical perspective, order parameters arise from symmetry breaking. When this happens, one needs to introduce one or more extra variables to describe the state of the system. For example, in the [[ferromagnetic]] phase, one must provide the net [[magnetization]], whose direction was spontaneously chosen when the system cooled below the [[Curie point]]. However, note that order parameters can also be defined for non-symmetry-breaking transitions.{{cn|date=December 2023}}

Some phase transitions, such as [[superconductivity|superconducting]] and ferromagnetic, can have order parameters for more than one degree of freedom. In such phases, the order parameter may take the form of a complex number, a vector, or even a tensor, the magnitude of which goes to zero at the phase transition.{{citation needed|date=August 2022}}

There also exist dual descriptions of phase transitions in terms of disorder parameters. These indicate the presence of line-like excitations such as [[Quantum vortex|vortex]]- or [[Topological defect|defect]] lines.

===Relevance in cosmology===
Symmetry-breaking phase transitions play an important role in [[physical cosmology|cosmology]]. As the universe expanded and cooled, the vacuum underwent a series of symmetry-breaking phase transitions. For example, the electroweak transition broke the SU(2)×U(1) symmetry of the [[electroweak force|electroweak field]] into the U(1) symmetry of the present-day [[electromagnetic field]]. This transition is important to explain the asymmetry between the amount of matter and antimatter in the present-day universe, according to  [[electroweak baryogenesis]] theory.

Progressive phase transitions in an expanding universe are implicated in the development of order in the universe, as is illustrated by the work of [[Eric Chaisson]]<ref>{{cite book|last = Chaisson|first = Eric J.|title =Cosmic Evolution|url = https://archive.org/details/cosmicevolutionr00chai|url-access = registration|publisher= Harvard University Press|date = 2001|isbn = 978-0-674-00342-2}}</ref> and [[David Layzer]].<ref>David Layzer, ''Cosmogenesis, The Development of Order in the Universe'', Oxford Univ. Press, 1991</ref>

See also [[relational order theories]] and [[order and disorder]].

===Critical exponents and universality classes===
{{main|critical exponent}}
Continuous phase transitions are easier to study than first-order transitions due to the absence of [[latent heat]], and they have been discovered to have many interesting properties. The phenomena associated with continuous phase transitions are called critical phenomena, due to their association with critical points.

Continuous phase transitions can be characterized by parameters known as [[critical exponent]]s. The most important one is perhaps the exponent describing the divergence of the thermal [[correlation length]] by approaching the transition. For instance, let us examine the behavior of the [[heat capacity]] near such a transition. We vary the temperature ''T'' of the system while keeping all the other thermodynamic variables fixed and find that the transition occurs at some critical temperature ''T''<sub>c</sub>. When ''T'' is near ''T''<sub>c</sub>, the heat capacity ''C'' typically has a [[power law]] behavior:
: <math>C \propto |T_\text{c} - T|^{-\alpha}.</math>

The heat capacity of amorphous materials has such a behaviour near the glass transition temperature where the universal critical exponent ''α'' = 0.59<ref>{{cite journal |url= http://eprints.whiterose.ac.uk/1958/1/ojovanmi1_Topologically2.pdf |doi=10.1088/0953-8984/18/50/007 |bibcode = 2006JPCM...1811507O |title=Topologically disordered systems at the glass transition |journal=Journal of Physics: Condensed Matter |volume=18 |issue=50 |pages=11507–11520 |year=2006 |last1=Ojovan |first1=Michael I. |last2=Lee |first2=William E.|s2cid=96326822 }}</ref> A similar behavior, but with the exponent ''ν'' instead of ''α'', applies for the correlation length.

The exponent ''ν'' is positive. This is different with ''α''. Its actual value depends on the type of phase transition we are considering.

The critical exponents are not necessarily the same above and below the critical temperature. When a continuous symmetry is explicitly broken down to a discrete symmetry by irrelevant (in the renormalization group sense) anisotropies, then some exponents (such as <math>\gamma</math>, the exponent of the susceptibility) are not identical.<ref>{{cite journal |last1=Leonard |first1=F. |last2=Delamotte |first2=B. |year = 2015 |title=Critical exponents can be different on the two sides of a transition | journal = Phys. Rev. Lett. | volume = 115 | issue = 20| page = 200601 | arxiv = 1508.07852 |bibcode = 2015PhRvL.115t0601L | doi = 10.1103/PhysRevLett.115.200601 |pmid=26613426|s2cid=22181730 }}</ref>

For −1 &lt; ''α'' &lt; 0, the heat capacity has a "kink" at the transition temperature. This is the behavior of liquid helium at the [[lambda transition]] from a normal state to the [[superfluid]] state, for which experiments have found ''α'' = −0.013 ± 0.003.
At least one experiment was performed in the zero-gravity conditions of an orbiting satellite to minimize pressure differences in the sample.<ref>{{cite journal | doi=10.1103/PhysRevB.68.174518 | title=Specific heat of liquid helium in zero gravity very near the lambda point | year=2003 | last1=Lipa | first1=J. | last2=Nissen | first2=J. | last3=Stricker | first3=D. | last4=Swanson | first4=D. | last5=Chui | first5=T. | journal=Physical Review B | volume=68 | issue=17| page=174518 |arxiv = cond-mat/0310163 |bibcode = 2003PhRvB..68q4518L | s2cid=55646571 }}</ref> This experimental value of α agrees with theoretical predictions based on [[variational perturbation theory]].<ref>{{cite journal | doi=10.1103/PhysRevD.60.085001 | title=Critical exponents from seven-loop strong-coupling φ4 theory in three dimensions | year=1999 | last1=Kleinert | first1=Hagen | journal=Physical Review D | volume=60 | issue=8| page=085001 |arxiv = hep-th/9812197 |bibcode = 1999PhRvD..60h5001K | s2cid=117436273 }}</ref>

For 0 &lt; ''α'' &lt; 1, the heat capacity diverges at the transition temperature (though, since ''α'' &lt; 1, the enthalpy stays finite). An example of such behavior is the 3D ferromagnetic phase transition. In the three-dimensional [[Ising model]] for uniaxial magnets, detailed theoretical studies have yielded the exponent ''α'' ≈ +0.110.

Some model systems do not obey a power-law behavior. For example, mean field theory predicts a finite discontinuity of the heat capacity at the transition temperature, and the two-dimensional Ising model has a [[logarithm]]ic divergence. However, these systems are limiting cases and an exception to the rule. Real phase transitions exhibit power-law behavior.

Several other critical exponents, ''β'', ''γ'', ''δ'', ''ν'', and ''η'', are defined, examining the power law behavior of a measurable physical quantity near the phase transition. Exponents are related by scaling relations, such as
: <math>\beta = \gamma / (\delta - 1),\quad \nu = \gamma / (2 - \eta).</math>
It can be shown that there are only two independent exponents, e.g. ''ν'' and ''η''.

It is a remarkable fact that phase transitions arising in different systems often possess the same set of critical exponents. This phenomenon is known as ''universality''. For example, the critical exponents at the liquid–gas critical point have been found to be independent of the chemical composition of the fluid.

More impressively, but understandably from above, they are an exact match for the critical exponents of the ferromagnetic phase transition in uniaxial magnets. Such systems are said to be in the same universality class. Universality is a prediction of the [[renormalization group]] theory of phase transitions, which states that the thermodynamic properties of a system near a phase transition depend only on a small number of features, such as dimensionality and symmetry, and are insensitive to the underlying microscopic properties of the system. Again, the divergence of the correlation length is the essential point.

===Critical phenomena===
There are also other critical phenomena; e.g., besides ''static functions'' there is also ''critical dynamics''. As a consequence, at a phase transition one may observe ''critical slowing down'' or ''speeding up''. Connected to the previous phenomenon is also the phenomenon of ''enhanced fluctuations'' before the phase transition, as a consequence of lower degree of stability of the initial phase of the system. The large ''static universality classes'' of a continuous phase transition split into smaller ''dynamic universality'' classes. In addition to the critical exponents, there are also universal relations for certain static or dynamic functions of the magnetic fields and temperature differences from the critical value.{{Citation needed|date=November 2023}}

===Phase transitions in biological systems===
Phase transitions play many important roles in biological systems. Examples include the [[lipid bilayer]] formation, the [[Coil–globule transition|coil-globule transition]] in the process of [[protein folding]] and [[DNA melting]], liquid crystal-like transitions in the process of [[DNA condensation]], and cooperative ligand binding to DNA and proteins with the character of phase transition.<ref>{{cite journal | doi=10.1080/07391102.2000.10506578 | pmid=10798534 | title=Long-range interactions between ligands bound to a DNA molecule give rise to adsorption with the character of phase transition of the first kind | year=2000| author = D.Y. Lando and V.B. Teif| journal=J. Biomol. Struct. Dyn. | volume=17 | issue=5 | pages=903–911 | s2cid=23837885 }}</ref>

In ''biological membranes'', gel to liquid crystalline phase transitions play a critical role in physiological functioning of biomembranes. In gel phase, due to low fluidity of membrane lipid fatty-acyl chains, membrane proteins have restricted movement and thus are restrained in exercise of their physiological role. Plants depend critically on photosynthesis by chloroplast thylakoid membranes which are exposed cold environmental temperatures. Thylakoid membranes retain innate fluidity even at relatively low temperatures because of high degree of fatty-acyl disorder allowed by their high content of linolenic acid, 18-carbon chain with 3-double bonds.<ref name="YashRoy_1987">{{cite journal |vauthors=Yashroy RC |year=1987 |title=<sup>13</sup>C NMR studies of lipid fatty acyl chains of chloroplast membranes |url=https://www.researchgate.net/publication/230822408 |journal=Indian Journal of Biochemistry and Biophysics |volume=24 |issue=6 |pages=177–178 |doi=10.1016/0165-022X(91)90019-S |pmid=3428918}}</ref> Gel-to-liquid crystalline phase transition temperature of biological membranes can be determined by many techniques including calorimetry, fluorescence, [[spin label]] [[electron paramagnetic resonance]] and [[NMR]] by recording measurements of the concerned parameter by at series of sample temperatures. A simple method for its determination from 13-C NMR line intensities has also been proposed.<ref>{{cite journal | last1 = YashRoy | first1 = R C | year = 1990 | title = Determination of membrane lipid phase transition temperature from 13-C NMR intensities | url = https://www.researchgate.net/publication/20790042 | journal = Journal of Biochemical and Biophysical Methods | volume = 20 | issue = 4| pages = 353–356 | pmid = 2365951 |doi=10.1016/0165-022X(90)90097-V }}</ref>

It has been proposed that some biological systems might lie near critical points. Examples include [[neural network (biology)|neural networks]] in the salamander retina,<ref>{{cite arXiv|eprint=1407.5946|last1=Tkacik|first1=Gasper|title=Thermodynamics for a network of neurons: Signatures of criticality|last2=Mora|first2=Thierry|last3=Marre|first3=Olivier|last4=Amodei|first4=Dario|last5= Berry II|first5=Michael J.|last6=Bialek|first6=William|class=q-bio.NC|year=2014}}</ref> bird flocks<ref>{{cite journal|last1=Bialek|first1=W|last2=Cavagna|first2=A|last3=Giardina|first3=I|title = Social interactions dominate speed control in poising natural flocks near criticality|journal=PNAS|volume=111|issue=20|pages=7212–7217|year = 2014|bibcode=2014PNAS..111.7212B|doi=10.1073/pnas.1324045111|pmid=24785504|pmc=4034227|arxiv=1307.5563|doi-access=free}}</ref>
gene expression networks in Drosophila,<ref>{{cite journal | last1=Krotov |first1=D|last2=Dubuis|first2=J O|last3=Gregor|first3=T|last4=Bialek|first4=W|title = Morphogenesis at criticality|journal = PNAS|year = 2014|doi=10.1073/pnas.1324186111|pmid=24516161|pmc=3956198|volume=111|issue=10|pages=3683–3688|arxiv=1309.2614|bibcode=2014PNAS..111.3683K|doi-access=free}}</ref> and protein folding.<ref>{{cite journal|last1=Mora|first1=Thierry|last2=Bialek|first2=William|title = Are biological systems poised at criticality?|journal = Journal of Statistical Physics|volume=144|issue=2|pages=268–302|year = 2011 |arxiv=1012.2242 |doi= 10.1007/s10955-011-0229-4|bibcode=2011JSP...144..268M|s2cid=703231}}</ref> However, it is not clear whether or not alternative reasons could explain some of the phenomena supporting arguments for criticality.<ref>{{cite journal |last1=Schwab|first1=David J|last2=Nemenman|first2=Ilya|last3=Mehta|first3=Pankaj|title = Zipf's law and criticality in multivariate data without fine-tuning|journal = Physical Review Letters|volume=113|issue=6|page=068102|year = 2014 |arxiv=1310.0448 |bibcode= 2014PhRvL.113f8102S|doi= 10.1103/PhysRevLett.113.068102|pmid=25148352|pmc=5142845}}</ref> It has also been suggested that biological organisms share two key properties of phase transitions: the change of macroscopic behavior and the coherence of a system at a critical point.<ref>{{Cite journal|last1=Longo|first1=G.|last2=Montévil|first2=M.|date=2011-08-01|title=From physics to biology by extending criticality and symmetry breakings|url=https://www.academia.edu/23155991|journal=Progress in Biophysics and Molecular Biology|series=Systems Biology and Cancer|volume=106|issue=2|pages=340–347|doi=10.1016/j.pbiomolbio.2011.03.005|pmid=21419157|arxiv=1103.1833|s2cid=723820}}</ref> Phase transitions are prominent feature of motor behavior in biological systems.<ref>{{cite book |title=Dynamic Patterns: The Self-Organization of Brain and Behavior (Complex Adaptive Systems) |isbn=978-0-262-61131-2 |author=Kelso, J. A. Scott |year=1995 |publisher=MIT Press }}</ref> Spontaneous gait transitions,<ref>{{cite journal | pmid=7707029 | year=1995 | last1=Diedrich | first1=F. J. | last2=Warren | first2=W. H. Jr. | title=Why change gaits? Dynamics of the walk-run transition | journal=Journal of Experimental Psychology. Human Perception and Performance | volume=21 | issue=1 | pages=183–202 | doi=10.1037/0096-1523.21.1.183 }}</ref> as well as fatigue-induced motor task disengagements,<ref>{{cite journal | pmid=20619908 | year=2010 | last1=Hristovski | first1=R. | last2=Balagué | first2=N. | title=Fatigue-induced spontaneous termination point--nonequilibrium phase transitions and critical behavior in quasi-isometric exertion | journal=Human Movement Science | volume=29 | issue=4 | pages=483–493 | doi=10.1016/j.humov.2010.05.004 }}</ref> show typical critical behavior as an intimation of the sudden qualitative change of the previously stable motor behavioral pattern.

The characteristic feature of second order phase transitions is the appearance of fractals in some scale-free properties.  It has long been known that protein globules are shaped by interactions with water.  There are 20 amino acids that form side groups on protein peptide chains range from hydrophilic to hydrophobic, causing the former to lie near the globular surface, while the latter lie closer to the globular center.  Twenty fractals were discovered in solvent associated surface areas of > 5000 protein segments.<ref>{{cite journal|last1=Moret|first1=Marcelo|last2=Zebende|first2=Gilney|title = Amino acid hydrophobicity and accessible surface area|journal = Physical Review E|date=January 2007|volume=75|issue=1|page=011920|doi=10.1103/PhysRevE.75.011920|pmid=17358197|bibcode=2007PhRvE..75a1920M}}</ref>  The existence of these fractals proves that proteins function near critical points of second-order phase transitions. 
  
In groups of organisms in stress (when approaching critical transitions), correlations tend to increase, while at the same time, fluctuations also increase. This effect is supported by many experiments and observations of groups of people, mice, trees, and grassy plants.<ref>{{cite journal|last1=Gorban|first1=A.N.|last2=Smirnova|first2=E.V.|last3=Tyukina|first3=T.A.|title=Correlations, risk and crisis: From physiology to finance|journal=Physica A: Statistical Mechanics and Its Applications|date=August 2010|volume=389|issue=16|pages=3193–3217|url=https://www.researchgate.net/publication/222687003|doi=10.1016/j.physa.2010.03.035|arxiv=0905.0129|bibcode=2010PhyA..389.3193G|s2cid=276956}}</ref>

==Experimental==
A variety of methods are applied for studying the various effects. Selected examples are:
* [[Thermogravimetry]] (very common)
* [[X-ray diffraction]] 
* [[Neutron diffraction]]
* [[Raman Spectroscopy]]
* [[SQUID]] (measurement of magnetic transitions)
* [[Hall effect]] (measurement of magnetic transitions)
* [[Mössbauer spectroscopy]] (simultaneous measurement of magnetic and non-magnetic transitions. Limited up to about 800–1000&nbsp;°C)
* [[Perturbed angular correlation]] (simultaneous measurement of magnetic and non-magnetic transitions. No temperature limits. Over 2000&nbsp;°C already performed, theoretical possible up to the highest crystal material, such as [[tantalum hafnium carbide]] 4215&nbsp;°C.)

==See also==
{{Div col}}
* [[Allotropy]]
* [[Autocatalytic reactions and order creation]]
* [[Crystal growth]]
** [[Abnormal grain growth]]
* [[Differential scanning calorimetry]]
* [[Diffusionless transformations]]
* [[Ehrenfest equations]]
* [[Jamming (physics)]]
* [[Kelvin probe force microscope]]
* [[Landau theory]] of second order phase transitions
* [[Laser-heated pedestal growth]]
* [[List of states of matter]]
* [[Micro-pulling-down]]
* [[Percolation theory]]
** [[Continuum percolation theory]]
* [[Superfluid film]]
* [[Superradiant phase transition]]
* [[Topological quantum field theory]]
{{Div col end}}

==References==
{{reflist|30em}}

==Further reading==
* [[Philip Warren Anderson|Anderson, P.W.]], ''Basic Notions of Condensed Matter Physics'', [[Perseus Publishing]] (1997).
* [[Amir Faghri|Faghri, A.]], and [[Yuwen Zhang|Zhang, Y.]], [https://www.springer.com/gp/book/9783030221362 Fundamentals of Multiphase Heat Transfer and Flow], [[Springer Nature]] Switzerland AG, 2020.
* {{cite journal | last1 = Fisher | first1 = M.E. | author-link = Michael E. Fisher | year = 1974 | title = The renormalization group in the theory of critical behavior | journal = Rev. Mod. Phys. | volume = 46 | issue = 4| pages = 597–616 | doi=10.1103/revmodphys.46.597|bibcode = 1974RvMP...46..597F }}
* Goldenfeld, N., ''Lectures on Phase Transitions and the Renormalization Group'', Perseus Publishing (1992).
*{{citation |year=2008 |author=Ivancevic, Vladimir G |author2=Ivancevic, Tijana T |title=Chaos, Phase Transitions, Topology Change and Path Integrals |url=https://books.google.com/books?id=wpsPgHgtxEYC&q=complex+nonlinearity |place=Berlin |publisher=Springer |isbn=978-3-540-79356-4 |access-date=14 March 2013 }}
* M.R.Khoshbin-e-Khoshnazar, ''Ice Phase Transition as a sample of finite system phase transition'', (Physics Education(India)Volume 32. No. 2, Apr - Jun 2016)[http://www.physedu.in/uploads/publication/23/371/4.-Ice-Phase-transition-as-a-sample-of-finite-system-phase--transition.pdf]
* [[Hagen Kleinert|Kleinert, H.]], ''Gauge Fields in Condensed Matter'', Vol. I, "[[:de:Supraflüssigkeit|Superfluid]] and [[vortex|Vortex lines]]; Disorder Fields, [[Phase Transition]]s", pp.&nbsp;1–742, [https://archive.today/20060514143926/http://www.worldscibooks.com/physics/0356.htm World Scientific (Singapore, 1989)]; Paperback {{ISBN|9971-5-0210-0}} (readable online [http://www.physik.fu-berlin.de/~kleinert/kleiner_reb1/contents1.html physik.fu-berlin.de])
* [[Hagen Kleinert|Kleinert, H.]] and Verena Schulte-Frohlinde, ''Critical Properties of φ<sup>4</sup>-Theories'', [https://web.archive.org/web/20080226151023/http://www.worldscibooks.com/physics/4733.html World Scientific (Singapore, 2001)]; Paperback {{ISBN|981-02-4659-5}}'' (readable online here [http://www.physik.fu-berlin.de/~kleinert/b8]).''
* {{cite journal | last1 = Kogut | first1 = J. | author-link2 = Kenneth G. Wilson | last2 = Wilson | first2 = K | year = 1974 | title = The Renormalization Group and the epsilon-Expansion | journal = Phys. Rep. | volume = 12 | issue = 2| pages = 75–199 |bibcode = 1974PhR....12...75W |doi = 10.1016/0370-1573(74)90023-4 }}
* Krieger, Martin H., ''Constitutions of matter : mathematically modelling the most everyday of physical phenomena'', [[University of Chicago Press]], 1996. Contains a detailed pedagogical discussion of [[Lars Onsager|Onsager]]'s solution of the 2-D Ising Model.
* [[Lev Davidovich Landau|Landau, L.D.]] and [[Evgeny Mikhailovich Lifshitz|Lifshitz, E.M.]], ''Statistical Physics Part 1'', vol. 5 of ''[[Course of Theoretical Physics]]'', Pergamon Press, 3rd Ed. (1994).
* Mussardo G., "Statistical Field Theory. An Introduction to Exactly Solved Models of Statistical Physics", Oxford University Press, 2010.
*[[Manfred R. Schroeder|Schroeder, Manfred R.]], ''Fractals, chaos, power laws : minutes from an infinite paradise'', New York: [[W. H. Freeman]], 1991.  Very well-written book in "semi-popular" style—not a textbook—aimed at an audience with some training in mathematics and the physical sciences.  Explains what scaling in phase transitions is all about, among other things.
* H. E. Stanley, ''Introduction to Phase Transitions and Critical Phenomena'' (Oxford University Press, Oxford and New York 1971).
* Yeomans J. M., ''Statistical Mechanics of Phase Transitions'', Oxford University Press, 1992.

==External links==
{{Commons category|Phase changes}}
*[http://www.ibiblio.org/e-notes/Perc/contents.htm Interactive Phase Transitions on lattices] with Java applets
*[https://web.archive.org/web/20160204235430/http://www.sklogwiki.org/SklogWiki/index.php/Universality_classes  Universality classes] from Sklogwiki
{{States of matter}}

{{Authority control}}

{{DEFAULTSORT:Phase Transition}}
[[Category:Phase transitions| ]]
[[Category:Physical phenomena]]
[[Category:Critical phenomena]]