Ferroelectric, piezoelectric, and electro-optic materials

Several interesting developments occurred in 1974. What may well be the final phase diagram on BaO-TiO2 appeared (721-3), with two independent groups in agreement. Interest in holography by laser damage continues to increase, principally in doped LiNbO3 (see Holography); it was reported that (Sr, Ba)Nb2O6 is even more sensitive (620). The ultimate extremes in isotope effects were reported, with PbHPO4 (monoclinic) showing a rise of transition temperature of 142° on deuteration (1603), while the transition of Ca2Sr propionate was lowered on deuteration (1665, 1778). A few new ferroelectrics continue to be discovered, of which PbHPO4 (and possible isomorphs) may well be the most interesting because of the comparisons with the KDP group. In fact, it is my belief that such a comparison may well effect a whole new point of view concerning the mechanism of the ferroelectric phase transition.