E. Parthé

TYPIX : standardized data and crystal chemical characterization of inorganic structure types

This major reference contains condensed crystal chemical information about individual structure types as well as an extensive section on the crystal chemistry of particular structure families. It clarifies and classifies published data on intermetallic and other inorganic structures.

Equiatomic ternary rare earth-transition metal silicides, germanides and gallides

Abstract Over 100 new equiatomic ternary rare earth (R)-transition metal (T) silicides, germanides and gallides were synthesized and structurally analysed either by evaluating powder diffraction photographs or in the case of ScRhSi, ScPtSi, YNiSi, ScRuGe and PrPtGe by refining single-crystal diffraction data. The hexagonal ZrNiAl type, an Fe2P-type derivative, was found for ScRuSi and ScTGe (T ≡ Ru, Rh, Pd, Os). The orthorhombic TiNiSi type, a PbCl2-type derivative, was assigned to RRhGa (R ≡ Er, Y), RPdGa (R ≡ La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Lu, Y, Sc), RIrGa (R ≡ Er, Y), RPtGa (R ≡ La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y, Sc), YNiSi, RRhSi (R ≡ Er, Y, Sc), ScPdSi, RIrSi (R ≡ Gd, Er, Y, Sc), RPtSi (R ≡ Tb, Dy, Ho, Er, Tm, Lu, Y, Sc), RRhGe (R ≡ Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Y, Sc), RIrGe (R ≡ Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Y, Sc) and RPtGe (R ≡ Sm, Gd, Tb, Dy, Ho, Er, Tm, Y, Sc). The CeCu2 type, which is related to TiNiSi, was found for R(Pd0.5Ge0.5)2 (R ≡ La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Y) and R(Pt0.5Ge0.5)2 (R ≡ Ce, Pr, Nd) where the palladium or platinum and germanium atoms are arranged at random on the copper sites. The tetragonal LaPtSi type, a ThSi2-type derivative, was found for RPtSi (R ≡ La, Ce, Pr, Nd, Sm, Gd), LaIrGe and LaPtGe. Finally the cubic LaIrSi type, an SrSi2-type derivative, was found for LaIrSi. The occurrence and structural features of these five structure types together with the tetragonal PbFCl type, an Fe2As-type derivative found earlier for RFeSi and RCoSi compounds, are discussed.

Diffusionless phase transformations of Ru2Si3, Ru2Ge3 and Ru2Sn3: I. Crystal structure investigations☆

Abstract The title compounds have been examined by X-ray methods in the temperature range between -170 °C and 1000 °C. They transform from an orthorhombic centrosymmetric (low-temperature, Ru2Ge3 type) to a tetragonal non-centrosymmetric (high-temperature, Ru2Sn3 type) crystal structure. These transformations are reversible, result from the displacement of Si, Ge, and Sn atoms, and occur gradually over a wide temperature range.

Zinkblende- und Wurtzitüberstrukturen bei ternären Chalkogeniden der Zusammensetzung 12463

Earlier literature data on the structure of Cu2GeSe3 and the low temperature modification of Cu2GeS3 could not be corroborated. Both compounds crystallize in an orthorhombic superstructure of zincblende with 2 formula units per cell (space group Imm2). The point positions for Cu2GeSe3 were obtained from single crystal intensity data collected on an automatic diffractometer. An orthorhombic superstructure of wurtzite was found with the high temperature modification of Cu2SiS3 (space group Cmc21 with 4 formula units per cell). The two new structures belong to the normal tetrahedral structures. According to the tetrahedral structure rules these structures might occur not only with 12463 but with 14253 compounds as well.ZusammenfassungFrühere Literaturangaben über die Struktur von Cu2GeSe3 und der Tieftemperaturmodifikation von Cu2GeS3 wurden als unrichtig befunden. Beide Verbindungen kristallisieren in einer orthorhombischen Zinkblendeüberstruktur mit 2 Formeleinheiten pro Zelle (Raumgruppe Imm2). Die Punktpositionen für Cu2GeSe3 wurden erhalten unter Verwendung von Einkristallintensitäten, die auf einem automatischen Diffraktometer gemessen wurden. Eine orthorhombische Wurtzitüberstruktur wurde bei der Hochtemperaturmodifikation von Cu2SiS3 aufgefunden (Raumgruppe Cmc21 mit 4 Formeleinheiten pro Zelle). Die beiden neuen Strukturen gehören zu den normal tetraedrischen Strukturen und könnten entsprechend den Tetraederstrukturregeln nicht nur bei 12463−, sondern auch bei 14253− Verbindungen auftreten.

Standardization of crystal structure data as an aid to the classification of crystal structure types

Abstract Owing to the different ways in which crystal structures may be described, isotypic compounds are often not identified as such. To remedy this situation, crystal structure data can be standardized by means of the structure tidy program. In the standardized data of isotypic structures, occupied sites have the same Wyckoff representation. This makes it possible to use the Wyckoff sequence (the letters of occupied Wyckoff sites) to classify crystal structure types. This classification is much finer than the previously used classification based on the Pearson code and is of great help if one wants to know whether a particular atom arrangement is already known. The standardization has enabled us not only to demonstrate new cases of isotypism, but also to discover structural relationships between different structure types with the same space group, for example substitution, vacancy or filled-in variants.

Er2RhSi3 and R2CoGa3 (R Y, Tb, Dy, Ho, Er, Tm, Yb) with Lu2CoGa3 type structure: new members of the A1B2 structure family

Abstract The structure of Er2RhSi3 was redetermined by X-ray single-crystal diffraction ( λ(Mo Kα)=0.71073 A , μ=42.392 mm −1 , F(000)=892, T=293 K , R=0.037, wR=0.030 for 244 contributing unique reflections). It is shown that this silicide has a hexagonal structure of the Lu2CoGa3 type, hP24, (194) P63/mmc-khfb, a=8.1130(7), c=7.7556(9) A , V=442.09(9) A 3 , Z=4, M r =521.68, D x =7.838 mg mm −3 . The structure of isotypic Er2 Co1.4Ga2.6 (hP24, (194) P63/mmc-khfb, a=8.607(3), c=6.898(3) A , V=442.5(4) A 3 , Z=4, M r =598.30, D x =8.980 mg mm −3 ) was refined by X-ray powder diffraction ( λ(Fe Kα)=1.93735 A , F(000)=1017.6, T=293 K , R=0.092 for 61 reflections). The cell parameters of R2CO1+xGa3−x phases (R  Y, Tb, Dy, Ho, Er, Tm, Yb; x= ±0.4) with the same structure type were obtained from X-ray powder diagrams. The Lu2CoGa3 structure is a distorted substitution variant of the A1B2 type, where the trigonal Lu6 prisms centred by cobalt atoms share triangular faces in infinite columns. The cobalt atoms are displaced away from the prism centres like the mercury atoms in the orthorhombic KHg2 structure type. The distortions in Er2RhSi3 are of a lesser magnitude than those observed in Lu2CoGa3. A progressive substitution of gallium by cobalt along the RGa2-RCoGa cross-sections of the R-Co-Ga systems (R  Y, Tb, Dy, Ho, Er, Tm, Yb, Lu) leads to a step by step deformation of the trigonal prisms. The main features of other deformation and substitution derivatives of the A1B2 type are discussed.

Crystal chemical considerations on rare earth-transition metal compounds RxT with x ≥ 1 (T = Co, Rh, Ni, Pd)

Abstract A survey of the crystal structures of the compounds x T is given. These structures may be grouped into those having exclusively trigonal prisms as coordination polyhedra and those with other polyhedra. For the latter group a crystal chemical interpretation seems difficult. However, the first group (those with only trigonal prisms) may be considered from four different crystal chemical aspects 1. (a) the relationship between the trigonal prism linkage coefficient and the stoichiometry 2. (b) the formation of structural series 3. (c) the concept of structure block stacking 4. (d) the interpretation of structure types based on unit cell twinning of close-packed structures.

Ce2Co3Si5 and R2Ni3Si5 (R ≡ Ce, Dy, Y) with the orthorhombic U2Co3Si5-type structure and the structural relationship with the tetragonaL Sc2Fe3Si5-type structure

Abstract The following structural details were determined for Y 2 Ni 3 Si 5 : M r = 494.37 (orthorhombic); space group, Ibam ; a = 9.5651(4) A ; b = 11.1284(6) A ; c = 5.6453(2) A ; V= 600.91(8) A 3 ; Z = 4; D x = 5.465 Mg m −3 ; Mo Kα, λ = 0.71069 A ; μ (Mo Kα ) = 29.8 mm −1 ; F (000) = 928; T = 293 K . The structure was refined to wR = 0.074 for 422 independent reflections. Ce 2 Co 3 Si 5 , Ce 2 Ni 3 Si 5 and Dy 2 Ni 3 Si 5 have the same crystal structure which is known as the U 2 Co 3 Si 5 type. This structure type can be interpreted as an intergrowth of two kinds of structural slabs, one of which is related to the CaBe 2 Ge 2 structure and the other is related to the BaNiSn 3 structure. The U 2 Co 3 Si 5 and the Sc 2 Fe 3 Si 5 structure types are different stacking variants of identical structural columns.

Structure of RNi3Al9 (R = Y, Gd, Dy, Er) with either ordered or partly disordered arrangement of Al‐atom triangles and rare‐earth‐metal atoms

ErNi 3 A1 9 , M r = 586.22, trigonal, new type, hR78, R32 - f 2 edc 4 (No. 155), a = 7.2716 (5), c=27.346 (3) A, V = 1252.2 (2)A 3 , Z = 6, D x = 4.664 Mg m -3 , A(Mo Ka) = 0.71073/k, u = 17.654 mm -1 , F(000) = 1614, T = 293 K, wR = 0.021 for 785 contributing unique reflections. The structure is built up of three kinds of monoatomic layer perpendicular to c: Al-atom layers with triangular mesh, Ni-atom layers with triangular mesh and layers containing two rare-earth-metal atoms for one Al-atom triangle. GdNi 3 A1 9 [a = 7.3006 (9), c = 27.478 (5)/A, wR = 0.020 for 791 reflections] is isotypic. YNi 3 AI 9 [a = 7.2894 (7), c = 27.430 (5) A, wR =0.035 for 635 reflections] and DyNi 3 AI 9 [a = 7.2723 (9), c = 27.344 (6)A, wR = 0.027 for 682 reflections] crystallize in related structures with a partly disordered arrangement of Al-atom triangles and rare-earth-metal atoms. Similar monoatomic layers to those in ErNi 3 AI 9 build up the orthorhombic structure of Y 2 Co 3 AI 9 (Y 2 Co 3 Ga 9 type). The stoichiometry 1:3:9 is related to that of RzT3A19 by replacing every second mixed layer of composition R 2 AI 3 by an Al-atom layer (A1 3 ): 6RT 3 A1 9 = 6R 2 T 3 AI 9 - 3R 2 AI 3 + 3A1 3 .

The crystal structure of orthorhombic Gd3Ni5Al19, a new representative of the structure series R2+mT4+mAl15+4m

The structure of Gd3Ni5Al19 has been determined from single-crystal diffraction data [λ(MoKα) = 0.71073 A, μ = 16.614 mm−1, F(000) = 2316, T = 293 K, wR = 0.023 for 997 contributing unique reflections]. This ternary aluminide crystallizes with a new, orthorhombic structure type, Pearson code oS108, (63) Cmcm, Wyckoff sequence f12c3, a = 4.0893(7), b = 15.993(2), c = 27.092(4) A, V = 1771.8(5) A3, Z = 4, Mr = 1277.95, Dx = 4.790 mg mm−3. The unit cell parameters of GdNiAl4 with orthorhombic YNiAl4 type, Pearson code oS24, (63) Cmcm, a = 4.0863(7), b = 15.520(4), c = 6.612(1)A, were refined from single-crystal diffraction data [λ(MoKα) = 0.71073 A, T = 293K]. The Gd3Ni5Al19 structure can be considered as an intergrowth of two kinds of slab, one cut from the orthorhombic YNiAl4 type and the second one corresponding to the translation unit of a hypothetical monoclinic R2T4Al15 structure. The general formula of this inhomogeneous linear structure series can be expressed as R2+mT4+mAl15+4m, where m is the number of consecutive intergrown YNiAl4-type slabs. The Gd3Ni5Al19 type is the simplest member of this structure series with m = 1. The following member with m = 2 is the monoclinic Y4Ni6Al23 type.