Inferred Mechanism of the Phase Transformation of a Peculiar Ferroelectric-Ferroelastic Crystal: NaNH₄ Tartrate

抄録

It is hypothesized that the transformation of NaNH₄ tartrate from the prototypic phase to the ferroelectric and ferroelastic phase is caused by instability of a pair of conjugate lattice vibration modes with the wave normal in the orthorhombic b direction and with the wave length equal to 3b. Then the strange dielectric anomaly of NaNH₄ tartrate which has been observed by Jona et al. Takagi et al. is deduced naturally. Also, peculiar elastic and piezoelectric anomalies to be observed are deduced.