A "spin-lattice" model is proposed for K2Pt(CN) 4Bro.3·3H2O (KCP) to solve the puzzling problem of the apparent complete softening of shear modulus C66 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 C66 at low temperatures (T<90 K) is predicted. A structural phase transition is possible if the spin-lattice coupling can be enhanced by e.g. external pressure. Ultrasonic attenuation coefficient α66, and also C44, α44, are calculated.
|ジャーナル||Journal of the Physical Society of Japan|
|出版ステータス||Published - 1979 11月|
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