Absolute sign of piezoelectric and pyroelectric coefficients and spontaneous polarization temperature dependence in α-Cu(IO₃)₂, Nd(IO₃)₃.H₂O and LiIO₃

The absolute polarity of single crystals of α-Cu(IO₃)₂ and Nd(IO₃)₃.H₂O, determined by anomalous X-ray scattering techniques, has been related to the sense of the piezoelectric d₂₂ and pyroelectric p₂ coefficients in these monoclinic crystals. The absolute sense of d₂₂ in both cases is predictable from a consideration of the behavior of the spontaneous polarization P_s under stress. P_s was calculated on the basis of a simple point-charge and dipole model. The positive sense of p₂ in α-Cu(IO₃)₂ and Nd(IO₃)₃.H₂O (each with magnitudes of about 2 x 10⁻⁵Cm⁻²deg⁻¹: the secondary pyroelectric coefficients are probably nearly an order of magnitude smaller) allows the inference that |P_s| increases with increasing temperature. The absolute sense of d₃₃ in hexagonal LiIO₃, determined by Morosin [Private communication (1972) quoted as Ref. 25 of Bergman, J. G. & Crane, G. R. (1974). J. Chem. Phys. 60, 2470–2474] is similarly predictable from the calculated P_s. Turner's [J. Appl. Cryst. (1976). 9, 52] measurement of p₃ in LiIO₃ combined with P_s also leads to the inference of increasing |P_s| with temperature.