Low-Frequency Dielectric Studies of the Ferroelectric Transition in the Hydrogen-Bonded Arsenates and Their Deuterated Isomorphs.

The results are given of a low frequency dielectric investigation of the paraelectric-ferroelectric phase transition in the hydrogen-bonded arsenate family and uses these results both to determine fundamental thermodynamic parameters of the materials and to test the internal self-consistency of the current pseudo-spin theories involving them. For all six materials, the thermodynamic order of the transition is determined to be first-order from the dielectric results and the pressure dependence of the transition temperature is also determined. The dielectric results are used to test the recent pseudo-spin theories of hydrogen-bonded ferroelectric materials. The most important result to emerge is that the pseudo-spin theories do not appear to be internally self-consistent when applied to the hydrogen-bonded arsenate family.