Dielectric, Electromechanical, and Elastic Properties of [Rb.sub.1-x]

The longitudinal dielectric, piezoelectric, and elastic characteristics of ferroelectric Rb[H.sub.2]P[O.sub.4] and antiferroelectric N[H.sub.4][H.sub.2]P[O.sub.4] crystals are calculated in terms of the modified model of proton ordering with allowance for the piezoelectric coupling in an approximation of a four-particle cluster. The results obtained agree well with known experimental data. Along with this, the electromechanical properties of a [Rb.sub.0.2][(N[H.sub.4]).sub.0.8][H.sub.2]P[O.sub.4] single crystal undergoing an antiferroelectric phase transition have been studied experimentally over a wide temperature range. The model predictions and the experimental data agree qualitatively.