Y. Ishibashi et V. Dvorak, ON SUCCESSIVE STRUCTURAL PHASE-TRANSITIONS IN LA2MO4 (M=CU, NI ETC) COMPOUNDS, Journal of the Physical Society of Japan, 63(6), 1994, pp. 2202-2205
A Landau-type free energy function is proposed to reproduce the phase
sequences, which are given rise to by the instability of the modes at
the X-point of the I4/mmm phase as seen in La2MO4(M = Cu, Ni etc.) com
pounds. Emphasis is placed on the appearance of the Pccn phase. Typica
l phase diagrams obtained by varying the coefficient values appearing
in the free energy function are presented.