The pressure dependence of the ferroelectric mode and molecular vibrations of the ferroelectric arsenates

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Abstract
Light scattering measurements are reported of the pressure dependence (0-8 kbar), at 295K, of all the Raman-active modes of vibration in RbH2AsO4 and of the coupled-mode spectra for the B2-symmetry phonons in KH2AsO4, RbH2AsO4, CsH2AsO4 and their deuterated isomorphs. The pressure dependence of the ferroelectric mode and its interaction with a B2 optical phonon is determined from fits of the low-frequency y(xy)x spectra to a real-coupled oscillator system. The results reveal a strong dependence on pressure for the ferroelectric mode damping for all the arsenates which causes the mode to become under-damped at quite low pressure. The results are used to discuss the pressure dependence of some of the microscopic parameters characterising the pseudospin model of Kobayashi (1968).