DIMENSIONALITY CROSSOVER AND THE NONLINEAR DIELECTRIC RESPONSE IN BETAINE PHOSPHATE ARSENATE MIXED-CRYSTALS/

Dielectric properties of quasi-one-dimensional hydrogen-bonded chains are studied for mixed crystals of antiferroelectric betaine phosphate and ferroelectric betaine arsenate at three different mixing concentra tions, x = 0.1, 0.3, and 0.4 (x being the concentration of arsenate). For mixed crystals with x = 0.3 and 0.4 dielectric study revealed dime nsionality crossover at around 82 K, where the quasi-one-dimensional n ature was turned into three-dimensional Curie-Weiss behaviour on lower ing the temperature, well above the antiferroelectric transition point . For x = 0.1 mixed crystal, on the other hand, the crossover point wa s almost coincident with the antiferroelectric transition point, showi ng still too-weak interchain coupling and strong one-dimensionality, a lmost to the point of antiferroelectric transition. For this system, t he electric bias field effect revealed temperature-dependent nonlinear ity of the dielectric constant, which may be ascribed to a development of competition between antiferroelectric and ferroelectric interchain couplings, the latter growing with increasing bias held and lowering temperature.