Dielectric and ultrasonic measurements in CsH2AsO4

The shear elastic constants $c_{44}^E$ and $c_{66}^E$ and both the free and clamped $c$-axis dielectric constant have been measured in the paraelectric phase of single-crystal cesium dihydrogen arsenate. The temperature variation of $c_{66}^E$ is well described by an elastic Curie expression arising from linear piezoelectric coupling. A 20-K difference between the free and clamped Curie temperatures is obtained from an analysis of the elastic measurements and directly from the $c$-axis dielectric measurements. The $a$-axis dielectric constant, which has been measured between 90 and 300 K, shows antiferroelectric characteristics and exhibits a well-defined first-order discontinuity.