A Model for Elastic Anomalies in K2Pt(CN)4Br0.3·3H2O

Abstract
A “spin-lattice” model is proposed for K 2 Pt(CN) 4 Br 0.3 ·3H 2 O (KCP) to solve the puzzling problem of the apparent complete softening of shear modulus C 66 without any structural phase transition at low temperatures. Our model emphasizes the importance of the site II water molecules lying between bromine ions and Pt(CN) 4 complexes. Each water molecule is assumed to have three configurations, which are represented by an S =1 Ising spin. An almost complete agreement is obtained between calculation and experimental data. A marked “hardening” of C 66 at low temperatures ( T e.g. external pressure. Ultrasonic attenuation coefficient α 66 , and also C 44 , α 44 , are calculated.