Inorganic structures in space group P3m1; coordinate analysis and systematic prediction of new ferroelectrics

ICSD Release 2007/1 contains 47 families of inorganic crystal structures, some single-member only, within the 311 entries listed under the polar space group P3m1. Coordinate analysis reveals 12 such families to be candidate ferroelectrics, over a range of confidence levels. Selection is based on the detection of an approach to nonpolar supergroup symmetry, within specified limits, by the atomic arrangement as reported in a confirmed polar space group. The primary source of uncertainty in such predictions is the reliability of the underlying structural determination. The candidates include In₂ZnS₄, TlSn₂F₅, Cu₇Te₄, NaMnSe₂, Na₂In₂(Mo₃O₈)(MoO₄)₂, Nb₃Br₇S, Nb₃TeI₇, fencooperite, Bi(HCOO)₃, Li(NpO₂)(CO₃)(H₂O)₂, LiPtD_0.66 and Ag₃(MoO₃F₃)(Ag₃(MoO₄)Cl). A total of 20 structures examined are likely to be nonpolar, a further 20 have reduced predictive properties and three others are more likely to retain P3m1 symmetry over a wide thermal range. Substantial uncertainties associated with many of the listed 163 CdI₂, 69 ZnS and 10 SiC polytype structures, together with their low potential for use as possible ferroelectrics, led to their exclusion from fuller analysis.