On the relation between experimental results for SASD type crystals and the two-sublattice model

摘要

The mechanism of ferroelectric phase transitions taking place in sodium ammonium sulphate dihydrate and sodium ammonium selenate dihydrate is suggested. It is found that SO4 (SeO4) groups contribute predominantly to the phase transitions taking place in these crystals. The modified Mitsui-type model, which includes both long- and short-range correlations is tested. The cluster form of the hamiltonian is formulated and its two-sublattice variant is analysed. It is shown that the assumed approach yields the results, which are quantitatively in very good agreement with experiment data. (C) 2002 Elsevier Science B.V. All rights reserved. [References: 18]