Landau theory of phase transitions

In the Landau theory of second order phase transitions of Lev Davidovich Landau, the thermodynamic potential takes the form of a power series in the order parameter ($\eta$) (Ref. 1 Eq. 143.1)

$\left.\Phi (P,T,\eta )\right.=\Phi _{0}+\alpha (P,T)\eta +A(P,T)\eta ^{2}+C(P,T)\eta ^{3}+B(P,T)\eta ^{4}+...,$

where P is the pressure and T is the temperature.

References

1. Lev Davidovich Landau "", Physikalische Zeitschrift der Sowjetunion 11 pp. 26-47 (1937)
2. Lev Davidovich Landau "", Physikalische Zeitschrift der Sowjetunion 11 pp. 545-555 (1937)
3. L. D. Landau and E. M. Lifshitz, "Statistical Physics" (Course of Theoretical Physics, Volume 5) 3rd Edition Part 1, Chapter XIV, Pergamon Press (1980)
4. A P Cracknell, J Lorenc and J A Przystawa "Landau's theory of second-order phase transitions and its application to ferromagnetism", Journal of Physics C: Solid State Physics 9 pp. 1731-1758 (1976)