Phase transitions and the quantum effect in A₂BX₄-type ferroelectric crystals

ABSTRACT

Phase diagrams for modulated phases are constructed based on a competing interactive ISING model. Commensurate phases with the wave number q = 0, 1/6, 1/3 and 1/2 are stable at zero temperature, if the model Hamiltonian is treated classically. On the other hand, the regions of incommensurate wave number as well as high-order commensurate ones extend down to 0 K, if the quantum statistical mechanics is employed. Based on the calculated phase diagram, phase transitions of K₂SeO₄, Rb₂MoO₄, Rb₂SeO₄, and Cs₂WO₄ are discussed.

KEYWORDS:

• incommensurate phase
• phase diagram
• commensurate transition
• quantum effect

Funding

This work was partially supported by a research grant, category A1-2(2015) from the Yamaguchi University Foundation.