= Phase transition
{wiki}
A phase transition is a change between equilibrium phases associated with nonanalytic thermodynamic behavior in an appropriate infinite-system limit. Melting, liquid–vapor coexistence and magnetic ordering illustrate different kinds. A <phase diagram> specifies the control parameters and the boundaries between phases.
At a <first-order phase transition>, a first derivative of the relevant <thermodynamic potential> changes discontinuously; thermal examples can have <latent heat> and <phase coexistence>. At a <continuous phase transition>, an order parameter can develop continuously while response functions and a <correlation length> become singular. Real finite systems show rounded signatures, so measurements usually compare <heat capacity>, density, structural scattering or an <order parameter> across a controlled scan. Hysteresis is evidence of delayed conversion or <metastability>, rather than the definition of an equilibrium transition.
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