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

Abstract

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 In(2)ZnS(4), TlSn(2)F(5), Cu(7)Te(4), NaMnSe(2), Na(2)In(2)(Mo(3)O(8))(MoO(4))(2), Nb(3)Br(7)S, Nb(3)TeI(7), fencooperite, Bi(HCOO)(3), Li(NpO(2))(CO(3))(H(2)O)(2), LiPtD(0.66) and Ag(3)(MoO(3)F(3))(Ag(3)(MoO(4))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 CdI(2), 69 ZnS and 10 SiC polytype structures, together with their low potential for use as possible ferroelectrics, led to their exclusion from fuller analysis.

Designing a Deep-Ultraviolet Nonlinear Optical Material with a Large Second Harmonic Generation Response

“…To isolate the structural displacements hidden in the anionic group theory analysis that produce the acentric charge distribution, we decomposed the polar structure using an approach conceptually similar to that of Abrahams, 17 who examined how polar ferroelectrics could be designed by considering atomic displacement patterns that would drive transitions between nonpolar and polar space groups. The key is that a clear group−subgroup relationship exists.…”

Synthesis, Characterization, and Polymorphism of [H3O][NbF6]: A Polar and Possibly Ferroelectric Oxonium Salt

“…Thus, we confirmed the significance of the polar atomic displacements in [H 3 O][NbF 6 ] compared the possible centrosymmetric super groups Ibam and Ibca by a pseudosymmetry search with the PSEUDO tool of the Bilbao Crystallographic Server [21] . Abrahams defined an empirical limit for the polar displacement of atoms so that a polar structure is unambiguously present in terms of structural chemistry: The largest absolute displacement |ξ i | of an atom i compared to its position in the centrosymmetric supergroup should be significantly larger than 0.1 Å or the root mean square of the amplitude of the thermal displacement of this atom [22,23] . Compared to the supergroup Ibam the largest displacement of 0.62 Å corresponds to the F1 and F6 atoms which is significantly larger than their isotropic thermal displacement of approximately 0.20 Å and 0.22 Å, respectively.…”

“…[21] Abrahams defined an empirical limit for the polar displacement of atoms so that a polar structure is unambigu- ously present in terms of structural chemistry: The largest absolute displacement j ξ i j of an atom i compared to its position in the centrosymmetric supergroup should be significantly larger than 0.1 Å or the root mean square of the amplitude of the thermal displacement of this atom. [22,23] Compared to the supergroup Ibam the largest displacement of 0.62 Å corresponds to the F1 and F6 atoms which is significantly larger than their isotropic thermal displacement of approximately 0.20 Å and 0.22 Å, respectively. In case of the supergroup Ibca, the F2 and F4 atoms have the largest displacement of 0.28 Å (besides the H1 and H3 atoms with 0.5 Å), which is still slightly larger than their thermal displacements of 0.20 Å and 0.22 Å, respectively.…”

Electronic structure and transport in the potential Luttinger liquids CsNb3Br7S and RbNb3Br7S

“…The valence electron count (VEC) in compounds containing triangular Nb 3 clusters compounds is between 6 and 8; for instance, VEC = 6 for Nb 3 Br 7 S 10 and Nb 3 O 2 Cl 5 , 11 VEC = 7 for Nb 3 X 8 (X = Cl, Br, I) and CsNb 3 Br 7 S, 12 and VEC = 8 for NaNb 3 Cl 8 . 9,13,14 The compounds with seven valence electrons can have interesting magnetic behaviour, especially in combination with the two-dimensional polar Kagome lattice structure of Nb 3 X 8 .…”