Models for the Order—Disorder Transition in NaH3(SeO3)2

Abstract

The entropy of the Makita—Miki model for NaH3(SeO3)2 is shown to be exactly solvable by transformation into a Slater KDPmodel problem. However, arguments are presented to show that the model is unsatisfactory. Two additional models are introduced. The first model is reduced to a dimer problem and is solved exactly. The solution is interesting in the context of critical phenomena, but it indicates that the model is not a good one for NaH3(SeO3)2. The second model is readily solved in the limit of high temperature using results for the two‐dimensional Ising model. Although this model is too difficult to solve exactly at finite temperature except for one limiting case, it is encouraging that analogous models exhibit multiple phase transitions.