Review of order-disorder models for KDP-family crystals

Abstract

The various order-disorder-type models for crystals in the KDP (potassium dihydrogen phosphate) family are reviewed, beginning with the Slater-Takagi-Senko model, continuing with tunneling additions by Blinc and Svetina, and analyzing the pressure-induced tricritical point in the Slater-Takagi-Senko model. The possibility of a deuteration-induced tricritical point at atmospheric pressure in RDP (rubidium dihydrogen phosphate) is explored. The Ishibashi model for ADP (ammonium dihydrogen phosphate) is reviewed, and finally various theories and computer simulations for the mixed RDP-ADP crystal system are discussed in terms of their prediction of the observed ferroelectric and antiferroelectric transitions and proton glass behavior.