Ln3 M 1 − δ TX 7 – quasi-isostructural compounds: stereochemistry and silver-ion motion in the Ln3Ag1 − δGeS7 (Ln = La–Nd, Sm, Gd–Er and Y; δ = 0.11–0.50) compounds

2009 ◽  
Vol 65 (2) ◽  
pp. 126-133 ◽  
Author(s):  
Marek Daszkiewicz ◽  
Lubomir D. Gulay ◽  
Olga S. Lychmanyuk
Keyword(s):  
Crystal Structures ◽  
Large Family ◽  
Silver Ions ◽  
Structural Effect ◽  
Inorganic Crystal Structure Database ◽  
Single Crystal Diffraction ◽  
Ion Motion ◽  
Space Group ◽  
Inorganic Crystal ◽  
Crystal Structure Database

The crystal structures of the Ln3Ag1 − δGeS7 (Ln = La–Nd, Sm, Gd–Er, Y; δ = 0.11–0.50, space group P63) compounds were determined by means of X-ray single-crystal diffraction and the similarities among the crystal structures of all Ln3 M 1 − δ TX 7 (space group P63; Ln – lanthanide element, M – monovalent element; T – tetravalent element and X – S, Se) compounds deposited in the Inorganic Crystal Structure Database (ICSD) are discussed. Substitutions of each element in Ln3 M 1 − δ TX 7 result in a different structural effect. On the basis of the data deposited in the ICSD the large family of the Ln3 M 1 − δ TX 7 compounds was divided into three groups depending on the position of the monovalent element in the lattice. This position determines what kind of stereoisomer is present in the structure, either the ++ enantiomer or the +− diastereoisomer. Since the silver ions can occupy a different position and the energy barriers between positions are low the ions can move through the channel. It was shown that this movement is not a stochastic process but a correlated one.

Systematic prediction of new ferroelectrics in space group R3. II

2007 ◽  
Vol 63 (2) ◽  
pp. 257-269 ◽  
Author(s):  
S. C. Abrahams
Keyword(s):  
Inorganic Crystal Structure Database ◽  
Additional Structure ◽  
Stability Range ◽  
Acta Cryst ◽  
Space Group ◽  
Structure Database ◽  
Inorganic Crystal ◽  
Crystal Class ◽  
Thermal Stability Range ◽  
Crystal Structure Database

Release 2006/1 of the Inorganic Crystal Structure Database contains 155 entries under space group R3. Atomic coordinate analysis of the first 81 structures, with 52 different structure types, in Part I [Abrahams (2006). Acta Cryst. B62, 26–41] identified a total of 18 new types that satisfy the structural criteria for ferroelectricity, five that are more likely to have or undergo a transition to 3m symmetry, 19 more likely to be or undergo a transition to nonpolar symmetry and ten with a lower property predictability. Coordinate analysis of the remaining 71 entries with 54 different structure types in Part II leads to 11 materials including Al4B6O15, PbTa3(PO4)(P2O7)3.5, the KCd4Ga5S12 family, the LiZnPO4 family, Ca3Nb1.95O8V0.05 and Mn4Ta2O9 as new candidates which satisfy the structural criteria, together with the three known ferroelectrics Na3MoO3F3, Pb2ScTaO6, and RbTi2(PO4)3 at 6.2 GPa. Two additional ferroelectric predictions are at a lower level of confidence. The analysis also reveals nine materials, two of which are isostructural, that more likely belong or are capable of undergoing a transition to crystal class 3m. There are 14 additional structure types which are more likely to be nonpolar or undergo a transition to nonpolarity, ten have reduced predictive properties, with a further nine for which the space group is expected to remain R3 over the full thermal stability range. The increasing use of methods for identifying overlooked inversion centers in structural determinations may be extended by using coordinate analysis for detecting additional commonly overlooked symmetry elements.

Systematic prediction of new ferroelectrics in space groups P31 and P32

2003 ◽  
Vol 59 (5) ◽  
pp. 541-556 ◽  
Author(s):  
S. C. Abrahams
Keyword(s):  
Crystal Structure ◽  
Confidence Level ◽  
Inorganic Crystal Structure Database ◽  
Space Group ◽  
Space Groups ◽  
Structure Database ◽  
Inorganic Crystal ◽  
Atomic Coordinates ◽  
Crystal Structure Database

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 Cu2BaGeS4, Fe3(Fe,Si)O4(OH)5, Se4S5, K2HCr2AsO10, IV-RbNO3, Rb2Sc(NO3)5, Na3ReO5, Nd14(GeO4)2(BO3)6O8, CsHgCl3, Ba2Cu2AlF11, KYF4, SrS2O6·4H2O, Cu3PbTeO6(OH)2, ReH(CO)4, Ni2(NH3)9Mo(CN)8·2H2O and the 6T polytype of Ca1.89Ta1.80Sm0.16Ti0.10O7, in addition to β-LaBSiO5, PbBAsO5 and BaBAsO5 in the stillwellite family.

Systematic prediction of new inorganic ferroelectrics in point group 4

1999 ◽  
Vol 55 (4) ◽  
pp. 494-506 ◽  
Author(s):  
S. C. Abrahams
Keyword(s):  
Crystal Structure ◽  
Point Group ◽  
Inorganic Crystal Structure Database ◽  
Space Group ◽  
Space Groups ◽  
Group 4 ◽  
Structure Database ◽  
Inorganic Crystal ◽  
Crystal Structure Database

The latest release of the Inorganic Crystal Structure Database contains a total of 87 entries corresponding to 70 different materials in point group 4. The structures reported for 11 materials in space group P4 satisfy the criteria for ferroelectricity, as do four in P41, one each in P42 and P43, 12 in I4, including seven that form three families, and another three in I41. Three previously known ferroelectrics were also listed in I4 and one in I41. In addition, the listing for point group 4 contains 22 entries for nonferroelectric materials and three with misassigned space groups. Among the newly predicted ferroelectrics in point group 4, assuming the validity of the underlying structural reports, are Ce5B2C6, modulated NbTe4, Na3Nb12O31F, Ca2FeO3Cl, K4CuV5O15Cl, TlBO2, CrOF3, PbTeO3, VO(HPO3)(H2O).3H2O, MgB2O(OH)6, β-tetragonal boron, CuBi2O4, WOBr4, Na8PtO6, SbF2Cl3, Ba1.2Ti8O16, Ni[SC(NH2)2]4Cl2, Ca2SiO3Cl2, the mineral caratiite, NbAs, β-NbO2 and Ag3BiO3.

Concerning inorganic crystal structure types

1999 ◽  
Vol 55 (2) ◽  
pp. 147-156 ◽  
Author(s):  
G. Bergerhoff ◽  
M. Berndt ◽  
K. Brandenburg ◽  
T. Degen
Keyword(s):  
Crystal Structure ◽  
Crystal Structures ◽  
Structure Type ◽  
Inorganic Crystal Structure Database ◽  
Full Information ◽  
Structure Database ◽  
Inorganic Crystal ◽  
The Difference ◽  
Crystal Structure Database

All representatives of an inorganic crystal structure type can be found systematically in the new database SICS (Standardized Inorganic Crystal Structures). It is derived from the Inorganic Crystal Structure Database (ICSD) by selecting the best determination of each phase. In addition, each entry is given in a standardized description and complemented by searchable descriptors \Delta, which give the difference between all structures of an isopointal set. Because of the large number of structures the full information on relationships present can only be found by means of the new database itself. Some examples are given here in printed form. The limitations and the possibilities of expansion of SICS in terms of the concept of `structure types' are demonstrated.

Prediction of ferroelectricity in recent inorganic crystal structure database entries under space group pba2. Erratum

1996 ◽  
Vol 52 (6) ◽  
pp. 1057-1057
Author(s):  
S. C. Abrahams ◽  
K. Mirsty ◽  
R. M. Nielson
Keyword(s):  
Crystal Structure ◽  
Inorganic Crystal Structure Database ◽  
Acta Cryst ◽  
Space Group ◽  
Structure Database ◽  
Inorganic Crystal ◽  
Crystal Structure Database

The x coordinate for N8 in Table 1 on p. 807 [Abrahams, Mirsky & Nielson, Acta Cryst. (1996), B52, 806–809] was incorrectly quoted as 0.567 (9). The correct value is 0.0567 (9). The correct value is 0.0567 (9).

On the polyhedral volume ratios VA /VB in perovskites ABX 3

2007 ◽  
Vol 63 (3) ◽  
pp. 363-372 ◽  
Author(s):  
Maxim Avdeev ◽  
El'ad N. Caspi ◽  
Sergey Yakovlev
Keyword(s):  
Inorganic Crystal Structure Database ◽  
Coordination Polyhedra ◽  
Space Group ◽  
Space Groups ◽  
Intermediate Space ◽  
Inorganic Crystal ◽  
Cation Coordination ◽  
Analytical Expressions ◽  
Atomic Coordinates ◽  
Crystal Structure Database

This paper presents analytical expressions for the calculation of ratios of cation coordination polyhedra volumes (VA /VB ) for perovskites ABX 3 of the Stokes–Howard diagram directly from atomic coordinates. We show the advantages of quantifying perovskite structure distortion with polyhedral volume ratios rather than with tilting angles, and discuss why space groups with multiple crystallographically inequivalent A or B sites (I4/mmm, Immm, P42/nmc etc.) are much less common than those with a single A and B site (I4/mcm, R\bar 3c, Pnma etc.). Analysis of crystallographic data for approximately 1300 perovskite structures of oxides, halides and chalcogenides from the Inorganic Crystal Structure Database revealed that the most highly distorted perovskites belong to the space group Pnma and formally lower-symmetry perovskites (I2/m, I2/a) are less distorted geometrically. Critical values of the VA /VB ratios for the most common phase transitions Pnma ↔ I4/mcm and Pnma↔ R\bar 3c are estimated to be ∼ 4.85 with the possible intermediate space group Imma stable in the very narrow range of VA /VB ≃ 4.8–4.9. Transitions to post-perovskite CaIrO3-type structures may be expected for VA /VB < 3.8.

Systematic prediction of new ferroelectrics in space group P3

2000 ◽  
Vol 56 (5) ◽  
pp. 793-804 ◽  
Author(s):  
S. C. Abrahams
Keyword(s):  
Crystal Structure ◽  
Confidence Level ◽  
Inorganic Crystal Structure Database ◽  
Structural Determination ◽  
Structural Studies ◽  
Space Group ◽  
Structure Database ◽  
Inorganic Crystal ◽  
Atomic Coordinates ◽  
Crystal Structure Database

The current release of the Inorganic Crystal Structure Database contains a total of 57 entries under space group P3 that correspond to 50 different materials. There are 21 structures reported with this space group that satisfy the criteria for ferroelectricity, at a confidence level that depends on the reliability of the underlying structural determination. One ferroelectric discovered earlier is also listed. In addition, the database contains 19 entries that probably should be assigned to a centrosymmetric space group, seven that are polar but probably not ferroelectric and two that are without atomic coordinates. Seven entries are either duplicates or present additional structural studies of the same material. Structures in space group P3 identified as potentially new ferroelectrics include LiAsCu0.93, Na2UF6, BiTeI, BaGe4O9, α-UMo2O8, Cu2SiS3, Co(IO3)2, Sr7Al12O25, KSn2F5, YbIn2S4, Na5CrF2(PO4)2, Sn(ClO2)2(ClO4)6, Eu3BWO9, Li(H2O)4B(OH)4·2H2O, Mn3V1/2(SiO4)O(OH)2, Ca6(Si2O7)(OH)6, Na6.9(2)[Al5.6(1)Si6.4(1)O24](S2O3)1.0(1)·2H2O, BaCa2In6O12, Ni(H2O)6[Sb(OH)6]2, Sr4Cr3O9 and Cu5O2(VO4)2·CuCl2.

Prediction of ferroelectricity in recent Inorganic Crystal Structure Database entries under space group Pba2

1996 ◽  
Vol 52 (5) ◽  
pp. 806-809 ◽  
Author(s):  
S. C. Abrahams ◽  
K. Mirsky ◽  
R. M. Nielson
Keyword(s):  
Crystal Structure ◽  
Curie Temperature ◽  
Spontaneous Polarization ◽  
Ferroelectric Materials ◽  
Inorganic Crystal Structure Database ◽  
Space Group ◽  
Structure Database ◽  
Inorganic Crystal ◽  
Atomic Coordinates ◽  
Crystal Structure Database

Three new entries in space group Pba2 in the 1995 edition of the Inorganic Crystal Structure Database have been examined in the light of previously developed criteria for the prediction of ferroelectricity. The structural prediction [Abrahams (1989). Acta Cryst. B45, 228–232] that seven of the 21 entries presented under this space group in the 1988 edition most likely corresponded to previously unrecognized ferroelectric materials is thereby updated. The atomic coordinates of [(NH2)2C(NHNH3)]ZrF6, among the new entries, are shown to satisfy the structural criteria; the maximum displacement along the polar axis required of any atom to undergo spontaneous polarization reversal is no larger than ~ 0.9 Å for a C or N atom and ~ 1.4 Å for a H atom, within the aminoguanidinium (2+) cation. By contrast, all atoms in the two independent ZrF6 anions are within 0.1 Å of an arrangement with zero spontaneous polarization. The characteristic force constant of the organic group is presently unknown, hence the Curie temperature for the crystal cannot be estimated. In the second new entry, the only atoms in the structure of the superconductor Ba0.6K0.4BiO23 at 403 K which depart significantly from a centrosymmetric arrangement are three of the four independent O atoms, one of which is at a site only 6% occupied. If these displacements are not artefacts, then this material is ferroelectric with an estimated Curie temperature in the range 410–740 K; a subsequent study, however, reported the structure in space group Pbam. The atomic coordinates of the final 1995 entry, (Cl3PNPCl3)(MoOCl4), do not differ significantly from centrosymmetry, in which case the material is not ferroelectic, apart from unequal occupancy of the Mo-atom sites. If the disorder model is correct and the two Mo sites are unequally occupied, then these sites cannot become equivalent and (Cl3PNPCl3)(MoOCl4) must remain polar without the possibility of becoming ferroelectric.

New ferroelectric inorganic materials predicted in point group 4mm

1996 ◽  
Vol 52 (5) ◽  
pp. 790-805 ◽  
Author(s):  
S. C. Abrahams
Keyword(s):  
Point Group ◽  
Ferroelectric Materials ◽  
Inorganic Materials ◽  
Inorganic Crystal Structure Database ◽  
Space Group ◽  
Group 4 ◽  
Structure Database ◽  
Inorganic Crystal ◽  
Structure Determinations ◽  
Crystal Structure Database

The Inorganic Crystal Structure Database containing a total of 209 entries for 128 different materials reported in point group 4 mm, of which eight are for previously known ferroelectrics. Analysis of the remaining entries, assuming the structure determinations reported are correct, leads to the prediction of an additional 43 new ferroelectric materials. 15 were determined in space group P4mm, 11 in P4bm, one in P42 nm, one in P4cc, two in P42 mc, one in P42 bc, seven in I4mm, two in I4cm, one in I41 md and two in I41 cd. Numerous other structures are shown to have been assigned, most likely, to an incorrect space group. All but one of the materials reported in space group P4bm are predicted to be ferroelectric. New ferroelectrics predicted in point group 4 mm include K2[Pt(CN)4]Br0.3.3H2O, Nd0.33TaO3, YBaCuFeO5+δ, Ba2(TiO)(Si2O7), K2(NbO)2(SiO3)4, Ba6CoNb9O30, Sr2SbMnO6, Hg2AlF5.(H2O)2, Rb5Nb3OF18 and SrNi2(VO4)2.

Systematic prediction of new ferroelectrics in space group R3. I

2006 ◽  
Vol 62 (1) ◽  
pp. 26-41 ◽  
Author(s):  
S. C. Abrahams
Keyword(s):  
Mirror Symmetry ◽  
Physical Property ◽  
The Other ◽  
Inorganic Crystal Structure Database ◽  
Space Group ◽  
Harmonic Generator ◽  
Structure Database ◽  
Inorganic Crystal ◽  
Inorganic Structure ◽  
Crystal Structure Database

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·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·NaF, the MgSO3·6H2O family, Li3P3O9·3H2O, SeNbF9, Al2(H2PO4)3PO4·6H2O, [Cr(OCN2H4)6]·[(Co(NH3)2(NO2)4]3·(H2O)1.5], NaZnBr3·5H2O, 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 ∼ 11% in organic structures.

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