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All elastic stiffness constants have been determined at room temperature in the ferroelectric phase using Brillouin spectroscopy. The temperature dependence of C11, C22, C33 and C66 is measured up to 590 K. Only very weak anomalies are observed for some stiffnesses near Tc = 403 K and T1 = 560 K which are the temperatures of transition between the ferroelectric and the incommensurate phases and the incommensurate and the normal phases, respectively. This behaviour looks quite the same as the one observed in Rb2ZnC14.
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Quilichini et al. (1988) studied this question.
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