Transitions between phases with equal wavenumbers in a double Ising spin model. Application to betaine calcium chloride dihydrate

摘要

A double Ising spin model for uniaxially structurally modulated materials exhibits as a special feature phase transitions between phases with equal wavenumbers but different pseudospin configurations. The character of these 'internal' transitions is investigated in the mean-held approximation, with the mean-field transfer-matrix method, and in Monte Carlo simulations. The structural changes at the transitions are characterized by different strengths of harmonics in a Fourier analysis of the spatial modulation. A dielectric anomaly in the phase diagram of betaine calcium chloride dihydrate (BCCD) and seemingly contradictory structure analyses are explained. [References: 24]