Karin Cenzual

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.

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.

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.

Structure of Gd3Ru4Al12, a new member of the EuMg5.2 structure family with minority-atom clusters

Gd 3 Ru 4+x All2-x [x = 0.13 (2)], Mr = 1209.44, hexagonal, hP38, P6 3 /mmc – kh 2 g f ba (No. 194), a = 8.8142 (6), c = 9.5692 (9) A, V= 643.8 (1) A 3 , Z = 2, D x =6.239Mgm -3 , A(Mo Ka)=0.71073A, u= 20.330 mm -1 , F(000) = 1056 (1), T= 293 K, wR=0.023 for 338 contributing unique reflections. Gd 3 Ru 4 AI 12 is a substitution variant of the Sc 3 Ni 11Ge 4 structure which is a partly disordered variant of the Sc 3 Ni 11 Si 4 type, all three structures being ternary substitution derivatives of the EuMg 5.2 or ErZn 5 types. Contrary to the related structure types, in Gd 3 Ru 4 AI 12 both Wyckoff sites 2(a) and 2(b) have full occupation, i.e. an ordered arrange- ment of alternate Ru and AI atoms is observed along the c axis. The structure of Gd 3 Ru 4 AI 12 is built up of two kinds of layers perpendicular to [001]: planar layers of composition Gd 3 Al 4 and puckered layers of composition Ru 4 AI 5 . Similar layers are found in cubic Hf 6 Ni 7 AI 16 , a ternary substitution variant of Th 6 Mn 23 , as well as in hexagonal Sr 9 Mg 38 and BaLi 4 .

Y2Co3Al9 with Y2Co3Ga9 type structure: an intergrowth of CsCl- and Th3Pd5-type slabs

Abstract The structure of Y2Co3Al9 was determined by the single-crystal diffraction method (ψ( Mo K α ) = 0.71073 A , μ = 19.931 mm−1, F(000) = 1104, T = 293 K, ωR = 0.037 for 555 unique reflections). This new aluminide has an orthorhombic structure of Y2Co3Ga9 type, oS56, (63) Cmcm − hg2feca, a = 12.740(2)A, b = 7.4635(9) A , c = 9.321(1) A , V = 886.3(2) A 3 , Z = 4, Mr = 597.44, Dx = 4.478 mg mm−3. The Y2Co3Al9 structure can be interpreted as being built up of two kinds of slabs cut from the simple structures CsCl (composition CoAl) and Th3Pd5 (composition Y2Al5): Co3Al3+Y2Al8=Y2Co3Al9. The cobalt atoms are surrounded by eight aluminium atoms at contact distances, forming a distorted cube, and four yttrium atoms at relatively longer distances, the 12 atoms together forming an icosahedron. The yttrium atoms centre capped hexagonal prisms, the coordination numbers for the aluminium atoms are 10 or 11.

Y2Rh3Ge, a rhombohedral substitution variant of the MgCu2 type

The structure of Y2Rh3Ge has been determined and refined from single-crystal X-ray diffraction data (R = 0.042). It is a rhombohedral, ternary, ordered variant of the cubic Laves structure type MgCu2, with space group R3m, Z = 3, a = 5.552(3) and c = 11.82(1)A for the triple hexagonal cell. The ca ratio (2.13) is significantly lower than the value for the triple hexagonal cell of the cubic lattice of the parent structure type (2.45), resulting in shorter distances between Rh and Ge atoms than between Rh atoms. The isotypy of Pr2Rh3Si, Er2Rh3Si, Pr2Rh3Ge, and Er2Rh3Ge has been established from Guinier films. The Y2Rh3Ge structure is compared with the binary compound YRh2, crystallizing with the MgCu2 structure, and with three other simple, ternary, ordered substitution derivatives of the Laves phase types MgZn2 and MgCu2.

Ce5RuGe2 with a Y2HfS5 anti-type structure, an ordered substitution variant of orthorhombic β-Yb5Sb3

Crystallization in Pnma - d 2 c 4 with a=12.255, b=8.898, c=8.008 A, wR=0.051.The Ce 5 RuGe 2 structure is an ordered ternary substitution variant of the β-Yb 5 Sb 3 type and can be considered as an anti-type of the Y 2 HfS 5 structure.

Zr3Rh5 with Pu3Pd5-type structure, a structure geometrically related to the CsCl type

Etude par diffraction de rayons X de la structure de Zr 3 Rh 5 . Analyse des relations geometrique avec les types de structure CsCl et Pu 3 Pd 5