Crystal stability and the theory of ferroelectricity part II. Piezoelectric crystals

摘要: Abstract In Part I the dielectric properties of cubic crystals with atoms in special positions were discussed, particular reference to which become unstable against a transverse optic mode vibration long wavelength. These considerations are now extended general symmetry, and it is shown that anomalous temperature dependence certain dielectric, piezoelectric, elastic constants paraelectric phase ferroelectric can be described correlated very natural way terms crystal stability. A formula relating dispersion frequency constant spontaneous polarization displacements transition, previously derived for barium titanate, generalized. The transitions KH2PO4 NH4H2PO4, ordering hydrogen these crystals, discussed qualitatively stability normal modes vibration.