Systematic prediction of new ferroelectrics on the basis of structure

An inorganic pyroelectric crystal is predicted to be ferroelectric if it satisfies the structural conditions that no atom within the unit cell be displaced more than about 1 Å from the position it would occupy in the paraelectric state and that the largest such displacement be greater than about 0.1 Å. In addition, the phase transition temperature, as estimated from the AKJ proportionality to the square of the largest critical atomic displacement [Phys. Rev. 172, 551 (1968)], should not exceed about 2000 K. These conditions have been used as successful predictors of ferroelectricity in SrAlF5 and in Pb3(MF6)2 with M = Ti, V, Cr, Fe and Ga. The recent availability of the Inorganic Crystal Structure Database, with its current 2943 entries in polar space groups, offers the possibility of applying these predictors systematically to all structurally determined inorganic pyroelectrics. Eleven of the total 68 polar space groups have now been examined, resulting in the prediction of over 50 new ferroelectric crystals.