Systematic prediction of new ferroelectrics in space group R3.: I

Release 2005/ 1 of the Inorganic Crystal Structure Database contains 158 entries under the space group R3. The first 81 together with 15 related entries include 52 different structure types, 10 of which represent families that have two or more isostructural members. There are 18 types that satisfy the structural criteria for ferroelectricity with a confidence level that necessarily depends upon the reliability of each structural determination. Among them, ( LiTaO3) (9) center dot Ta2O5 and the CsCd( NO2) family are known ferroelectrics. The remaining 16 include the high- intensity higher- order harmonic generator II- BaB2O4, not previously recognized as ferroelectric. The other predicted ferroelectrics are Te( OH)(6) center dot NaF, the MgSO3 center dot 6H(2)O family, Li3P3O9 center dot 3H(2)O, SeNbF9, Al-2( H2PO4) (3)-PO4 center dot 6H(2)O, [ Cr( OCN2H4) (6)] center dot[( Co( NH3) (2)( NO2) (4)] (3) center dot( H2O) (1.5)], NaZnBr3 center dot 5H(2)O, III- Ag3SI, Tl2S, the Ba3Yb4O9 family, the Fe10.7Ru1.3As5 family, Sr17Ta10S42, Pb8Sb3 and the Sc7I12C family. Six structures reported in the space group R3 most likely exhibit mirror symmetry, with three experimental confirmations. The other 19 structures are most likely nonpolar, with six experimental confirmations. The capacity for physical property prediction by the remaining ten structures is shown to be in doubt. Thus, 46% of the present 52 inorganic structure types initially determined in the space group R3 and 35% of those currently assigned to R3 more likely exhibit an additional inversion center, mirror or glide plane, strongly exceeding the recently reported error rate of similar to 11% in organic structures.