Systematic prediction of new ferroelectrics in space groups P3₁ and P3₂

Release 2002/2 of the Inorganic Crystal Structure Database (FIZ Karlsruhe, Germany, and Institute Laue–Langevin, Grenoble, France) contains 62 entries in space group P3₁ and ten entries in space group P3₂ for 49 different materials including eight families with two or more isostructural members. The structural criteria for ferroelectricity are satisfied for 16 new structure types at a confidence level that depends on the reliability of each determination. LaBGeO₅, a mineral with stillwellite structure, was previously reported as ferroelectric and forms an additional family with seven other members or related structures that satisfy the criteria. Ten structures reported in space group P3₁ or P3₂ are dubious or incorrect, with atomic coordinates that satisfy supergroup symmetry. One material is probably pyroelectric but is unlikely to become ferroelectric, and three others are either incompletely solved or incom­pletely refined. Among the predicted new ferroelectrics are Cu₂BaGeS_4, Fe₃(Fe,Si)O₄(OH)₅, Se₄S₅, K₂HCr₂AsO₁₀, IV-RbNO₃, Rb₂Sc(NO₃)₅, Na₃ReO₅, Nd₁₄(GeO₄)₂(BO₃)₆O₈, CsHgCl_3, Ba₂Cu₂AlF₁₁, KYF₄, SrS₂O₆·4H₂O, Cu₃PbTeO₆(OH)₂, ReH(CO)₄, Ni₂(NH₃)₉Mo(CN)₈·2H₂O and the 6T polytype of Ca_1.89Ta_1.80Sm_0.16Ti_0.10O₇, in addition to β-LaBSiO₅, PbBAsO₅ and BaBAsO₅ in the stillwellite family.