Zeitschrift für Kristallographie - Crystalline Materials

Published by De Gruyter (O)

Volume 221 Issue 5-7 - Crystal Chemistry of Intermetallic Compounds

Issue of Zeitschrift für Kristallographie - Crystalline Materials

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Journal Overview

Publicly Available September 25, 2009

Editorial: Crystal Chemistry of Intermetallic Compounds

Yuri Grin

Page range: VI-VII

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September 25, 2009

Fritz H. Laves – 100 years young

Erwin Parthé

Page range: 301-304

Abstract

This year Fritz Laves, professor for crystallography and petrography and head of the Mineralogical Department at the University and the Eidgenössische Technische Hochschule in Zurich from 1954 to 1976, an accomplished leading scientist and outstanding pioneer in crystal chemistry, would be 100 years old.

September 25, 2009

Fritz H. Laves – an ideal for generations

Werner Fischer

Page range: 305-310

Abstract

Fritz Laves' 100th birthday is an excellent reason to recollect his merits for the German and the international crystallography in general. This, however, would be a task too difficult for me though I consider myself a scientific grandson of him. Laves' crystallographic oeuvre ( cf. Hellner, 1980) is almost too comprehensive to be valued by a single person of my generation. Accordingly, I will confine myself mainly on our common field of interest, i.e. on Mathematical Crystallography.

September 25, 2009

Gustav E. R. Schulze's pioneering work on Laves phases

Peter Paufler

Page range: 311-318

Abstract

There are several reasons to recollect the merits of Gustav Ernst Robert Schulze on the occasion of Fritz Laves' anniversary. Firstly, he had been a good friend of Laves and shared his interest in intermetallic compounds. Secondly, his work on Laves phases, though containing important early results, is less well known for some reasons. Thirdly, Schulze was the founder of a very efficient research centre on intermetallics in Dresden which is still active today. Finally, he introduced Metal Physics at the TU Dresden as a broad subject of bringing together structure and properties of the metallic state from a more fundamental point of view. Later on, this had a clustering effect for the development of materials research institutes in Dresden.

Publicly Available September 25, 2009

Preparation, phase stability and structure of the C36 Laves phase Nb_1–xCo_2+x

Daniel Grüner, Frank Stein, Martin Palm, Joachim Konrad, Alim Ormeci, Walter Schnelle, Yuri Grin, Guido Kreiner

Page range: 319-333

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Abstract

The C36 Laves phase Nb 1–x Co 2+x has been re-investigated in order to study phase stability and structure. Constitutional data have been obtained by investigating homogenized single- and two-phase samples and from diffusion couples. The C36 phase Nb 1–x Co 2+x crystallizes with hexagonal MgNi 2 structure type ( Z = 8, space group P 6 3 / mmc , a = 4.7414(4) Å and c = 15.458(1) Å at x = 0.265(4)). The homogeneity range extends from 24.6(2) to 25.3(5) at% Nb. The temperature range of the phase field is limited by a eutectoid (C36 Nb 1–x Co 2+x = Nb 2 Co 7 + C15 NbCo 2 ) and a peritectic (L + C15 NbCo 2 = C36 Nb 1–x Co 2+x ) reaction at ∼ 1050 °C and 1264 °C, respectively. In addition, the title phase is involved in the peritectoid reaction Co(Nb) + C36 Nb 1–x Co 2+x = Nb 2 Co 7 at 1086 °C and in the eutectic reaction L = Co(Nb) + C36 Nb 1–x Co 2+x at 1239 °C. The C36 and C15 Laves phases of the Nb—Co system are separated by an extremely small two-phase field (<0.5 at%). The crystal structure exhibits pronounced deviations from ideal parameters obtained from a hard sphere model. The Co network displays a type of distortion known from many hexagonal Laves phases. Kagom, layers display an elongation of the Co—Co edges of the basal triangles of Co 5 trigonal bipyramids and a contraction of Co—Co edges of the uncapped triangles. The Nb atoms are also displaced from their idealized sites. In the crystal structure of C36 Nb 1–x Co 2+x excess Co atoms randomly substitute Nb atoms — (Nb 1–x Co x )Co 2 . The excess Co atoms occupy preferentially the Nb2 site approximately twice as much as Nb1. These positions differ mainly in the conformation of the corresponding Nb 6 Nb 2 fragments (Nb1—Nb1 eclipsed and Nb2–Nb2 staggered). In addition, Co atoms are displaced from the original Nb positions. The distortion of the Co and the Nb network is a consequence of the bonding situation of the defect-free crystal structure. The preferential site occupation of excess Co atoms is triggered by interactions with atoms beyond the first coordination shell. The C36 phase Nb 1–x Co 2+x exhibits Pauli-paramagnetic behavior ( χ P = +1.31 · 10 –3 emu mol –1 ). The temperature dependent part of the electrical resistivity ρ (300 K) – ρ 0 is only 17 μΩ cm whereas the residual resistivity is very large with ρ 0 = 140 μΩ cm indicating strong structural disorder.

September 25, 2009

Atom order and thermodynamic properties of the ternary Laves phase Ti(Ti_yNi_xAl_1–x–y)₂

Andriy Grytsiv, Xing-Qiu Chen, Viktor T. Witusiewicz, Peter Rogl, Raimund Podloucky, Vladimir Pomjakushin, Daniele Maccio, Adriana Saccone, Gerald Giester, Ferdinand Sommer

Page range: 334-348

Abstract

Combined refinement of neutron powder, X-ray single crystal and powder diffraction data allows precise evaluation of symmetry and atom site occupation for the MgZn 2 -type Laves phase. For compositions Ti(Ni 1–x ,Al x ) 2 titanium atoms were found to fully occupy the 4 f site, whilst Ni- and Al-atoms randomly share the 2 a and 6 h sub-lattice sites of space group P 6 3 / mmc . At higher Ti-concentrations, Ti-atoms tend to enter the 2 a and 6 h site. Compositional dependences of the site occupations were used to explain the curved shape of the homogeneity region of the Laves phase. Investigation of the phase relations around the Ti-rich side of the ternary Laves phase was based on LOM, EPMA and X-ray diffraction experiments on argon arc-melted bulk alloys, which were annealed at 1000 °C in vacuum-sealed silica capsules for 100 h. The Ti-rich end of the homogeneity region of the ternary Laves phase at 1000 °C was derived from EMPA to be at Ti 0.463 Ni 0.273 Al 0.264 . Heat of formation data, derived from adiabatic drop calorimetry, were Δ 298 H 0 = –57.9 ± 3.5 kJ/mol for Ti 0.34 Ni 0.18 Al 0.48 and –61.6 ± 3.3 kJ/mol for Ti 0.36 Ni 0.24 Al 0.40 . For the ab initio density functional theory applications a large number of structural models were investigated in order to calculate the concentration dependent heats of formation, structural stabilities, lattice parameters, bulk moduli and site occupancies, which are in good agreement with experiment. The theoretical analysis revealed that there are no Ni—Ni nearest neighbours when the concentration of Ni is smaller than that of Al. With increasing Al concentration, Al starts to fill 2 a sites, and then continues occupying 6 h sites. In compounds with Ti concentration larger than 33.3 at% the 4 f sites are fully occupied by Ti, and the excessive Ti prefers 6 h sites. The Al concentration of the Al-rich end of the homogeneity region of the ternary Laves phase was predicted to be 57 at%.

September 25, 2009

Atomic ordering in the Laves phases L1 V(Co_1–xSi_x)₂ (x = 0.43 and 0.56)

Matthias Conrad, Christoph Pohling, Holger Webert, Bernd Harbrecht

Page range: 349-356

Abstract

The synthesis, phase relations, and crystal structures of two truly ternary, partially ordered Laves phases occurring in the V—Co—Si system are reported. The phases termed L1 V(Co 1–x Si x ) 2 are found in two distinct phase fields next to TiMnSi-type VCoSi. This so-called E-phase emerges in the centre of the miscibility gap which separates the Co- and Si-rich Laves phase fields. Both fields accommodate several structurally distinct L-phases. The L1-phases V(Co 1–x Si x ) 2 ( x = 0.43 and 0.56) crystallise in √3 a × √3 a superstructures of the hexagonal MgZn 2 structure type. A rigorous symmetry-based analysis reveals that, at the given compositions, this type of superstructure affords sufficient structural degrees of freedom for ordering of Co and Si atoms on 4 different sites in a manner that enables tuning of hetero-atomic Co—Si interactions to an optimum.

March 20, 2008

Microscopic structures of Laves phases and structurally related compounds: a transmission electron microscopy study

Tadahiro Yokosawa, Karin Söderberg, Magnus Boström, Daniel Grüner, Guido Kreiner, Osamu Terasaki

Page range: 357-374

Abstract

We present microstructural investigations of Laves phases AB 2 and structurally related compounds using transmission electron microscopy. Convergent-beam electron diffration in combination with selected-area diffraction has been used to determine uniquely the space group symmetry of the respective phases from very small illuminated regions. In addition stacking faults, domain boundaries, and intergrowth have been studied by HREM images. By electron beam irradiation intermetallic phases have been transformed in-situ into phases of different compositions. Polar intermetallic phases in the systems Ca—Al—Zn, Ba—Al and Ba—Al—Zn, as well as transition metal based Nb-Co phases have been chosen for this case study. In the Ca—Al—Zn system, the C15- and C36-type crystals did not show orderliness but a randomly mixed occupation of the B-net by Al and Zn atoms. Starting from C36, a C15 phase of constant Ca and lower Zn content as well as a new C36 phase with higher Ca content could be synthesized by means of electron beam irradiation. In the case of CaAlZn no ordering of Al and Zn were observed, i.e. , Al and Zn randomly mixed occupy the Cu-site in the CeCu 2 structure type. By electron beam irradiation of CaAlZn, a novel hexagonal phase with a hitherto unknown crystal structure is formed. The crystal structures of Ba 21 Al 40 and Ba 14 Al 22+x Zn 5–x are derived from Laves-type structures by omitting and modifying some of the triangular and Kagom, layers. In the case of Ba 21 Al 40 , intergrowth of motifs from the crystal structures of Ba 3 Al 5 and Ba 4 Al 5 were observed, whereas for Ba 14 Al 22+x Zn 5–x the bulk phase displays a domain structure. Adjacent domains are misoriented by ∼120°, the specific angle resulting from the pseudo-trigonal symmetry of the Ba-net. Therefore, only the (Al,Zn)-net is disordered. No superstructure formation were detected for the three polytypes C36, C15 and C14 in the Nb—Co system. However, TEM images of C36-Nb 1–x Co 2+x reveal a high stacking fault density with intergrowth of stacks of C36 and C15 sequence. When the C15 phase is rich in Nb, stacking faults seem to be more important than for Co-rich C15 phases, whereas stacking faults have seldom been observed for the Co-rich C14 phase.

March 20, 2008

Binary rare earth Laves phases — an overview

Karl A. Gschneidner, Jr., Vitalij K. Pecharsky

Page range: 375-381

Abstract

The rare earth metals form the largest subset of the AB 2 Laves phase compounds. The rare earth element ( R ) is always the larger A metal, and they form Laves phases with most of the Group 7–10 elements, plus Mg and Al. As with all Laves phases, the rare earth RB 2 compounds conform with the size rule which had been established in the mid 1930s. Electron concentration effects have also been observed in the RB 2 phases. A number of anomalies and unusual behaviors have been discovered over the years: the La deficiency in “LaNi 2 ” and of R in other “ R Ni 2 ” Laves phase compounds; the crystal structure sequence in the R Mn 2 compound series; the relationship between the Debye temperature and the radius ratio; the Ce valence in the Ce B 2 compounds; and the thermodynamic nature of the magnetic transition in the R Co 2 phases.

September 25, 2009

Binary intermetallic phases formed by Ca, Sr, Ba, Eu and Yb: similarities and differences

Maria L. Fornasini, Franco Merlo

Page range: 382-390

Abstract

The binary intermetallic phases formed by Ca, Sr, Ba, Eu and Yb with Li, Be and group 7 to 15 elements are a family of nearly 570 members, distributed over 50 compositions and 140 structure types. A graphical overview of all phases is given, and they are examined regarding their crystal chemistry, atomic sizes and volume effects in alloying.

September 25, 2009

Complexity of hexagonal approximants in the RE₁₃Zn_~58 system (RE = Ce, Pr, Nd, Sm, Gd, Tb and Dy)

Shuying Piao, Cesar Pay Gómez, Sven Lidin

Page range: 391-401

Abstract

For the RE 13 Zn 58 quasi crystal approximants ( RE = Ce, Pr, Nd, Sm, Gd, Tb, Dy), single crystals were prepared from the elements and their structures were refined from single-crystal X-ray diffraction data. They are derived from the Gd 13 Cd 58 type structure and crystallize in the space group P 6 3 / mmc or its subgroups. The crystal structures of Ce and Pr compounds are identical to that of the archetype, in the Nd compound a pair exchange disorder changes the composition and for Sm a further, partially occupied interstitial position lowers the symmetry to P 6 3 mc . For the compounds with Gd, Tb and Dy, the occupancy may order, lowering the symmetry further. For the case of Tb 13 Zn 59 high quality single crystals allowed us to refine the fully ordered orthorhombic super structure.

Publicly Available September 25, 2009

Reflections on symmetry and formation of axial quasicrystals

Walter Steurer

Page range: 402-411

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Abstract

Some ideas are presented on the geometrical factors governing structure and formation of axial quasicrystals with 5- and 7-fold symmetry, respectively. First, the importance of thin atomic layers is discussed for the growth of decagonal quasicrystals. They are the only long-range ordered structural units carrying information on the local non-crystallographic symmetry of the constituent clusters. Second, the consequences of local polysynthetic twinning for the formation of pentagonal and heptagonal quasicrystals are demonstrated. Third, the special relationship of the β -phase, (Co,Ni) 1–x Al 1+x , to the decagonal phase and its periodic average structure is discussed as well as its role as template for the formation and growth of decagonal Al—Co—Ni.

September 25, 2009

Mosaic-like tilings derivated from o-Co₄Al₁₃ and m-Co₄Al₁₃ crystal structures

Ulrich Burkhardt, Martin Ellner

Page range: 412-419

Abstract

Both well known crystal structures m -Co 4 Al 13 and o -Co 4 Al 13 are described in a simplified two-dimensional representation of regular pentagons and prolate rhombs. The dichromatic tilings differ in the periodic arrangements of prolate rhombs (brick-like and parquet-like, respectively) but show the same matching rules for the regular pentagons. The 2D scheme is used to show the variety in combination of these structural fragments that leads to related periodic as well as cyclical tilings. Starting from different initial nuclei, cyclical tilings with point group symmetry C 5v or C 10 are related to multiple twinned arrangements of the structure m -Co 4 Al 13 . Different decorations of these tilings are compared and characterised by their symmetry.

September 25, 2009

High-pressure crystal chemistry of binary intermetallic compounds

Roman Demchyna, Stefano Leoni, Helge Rosner, Ulrich Schwarz

Page range: 420-434

Abstract

Effects of high pressure on intermetallic compounds are reviewed with regards to structural stability and phase transitions. Changes of bonding properties and electronic structure are examplified by means of the elemental metals caesium and titanium, the latter forming an internal intermetallic compound at high pressures. After a short systematic overview regarding pressure effects, structural transformations in selected classes of intermetallic compounds like Zintl phases and AlB 2 -type arrangements precedes sections concerning high-pressure synthesis of Laves phases and intermetallic clathrates.

September 25, 2009

Re₃B type intermetallics — crystal chemistry, bonding and properties

Rainer Pöttgen, Mar'yana Lukachuk, Rolf-Dieter Hoffmann

Page range: 435-444

Abstract

The crystal chemistry of binary and ternary intermetallic compounds with orthorhombic Re 3 B or MgCuAl 2 type structure is reviewed. Besides the preparation techniques and crystal chemistry we focus on the structure–property relations and chemical bonding peculiarities. So far about 100 compounds with this structural arrangement have been reported. The large family of intermetallics comprises borides, aluminides, gallides, indides, thallides, and stannides, but also some magnesium and cadmium compounds.

September 25, 2009

Ti₂Rh₆B – a new boride with a double perovskite-like structure containing octahedral Rh₆ clusters

Boniface P. T. Fokwa, Bernhard Eck, Richard Dronskowski

Page range: 445-449

Abstract

Single crystals of Ti 2 Rh 6 B were synthesized by arc-melting the elements in a water-cooled copper crucible under an argon atmosphere. The new silver-like compound with metallic luster crystallizes in space group Fm -3 m (no. 225) with a = 7.8191(5) Å, V = 478.05(5) Å 3 , and Z = 4. The refinement converged to R 1 = 0.0169 and wR 2 = 0.0486 for all 96 unique reflections and 7 parameters. The structure can be described as a defect double perovskite, A 2 BB'O 6 , where the A site is occupied by titanium, the B site by boron, the O site by rhodium but the B' site is vacant leading to the formation of perfectly octahedral Rh 6 clusters and BRh 6 units. Rh—B, Rh—Ti, and Rh—Rh interactions are observed. According to density-functional (LMTO) electronic structure calculations, the strongest bonding occurs for the Rh—B contacts, and the Rh—Rh bonding within the clusters is more than two times stronger than in the BRh 6 units.

September 25, 2009

On the formation and crystal structure of the Pd₆B phase

Tilman Georg Berger, Andreas Leineweber, Eric J. Mittemeijer, Corneliu Sarbu, Viola Duppel, Peter Fischer

Page range: 450-463

Abstract

The crystal structure of the Pd 6 B phase has been elucidated employing selected-area electron diffraction and X-ray and neutron powder diffraction methods. It is based on a cubic close packed arrangement of Pd with B occupying 1/6 of the interstitial octahedral sites in an ordered way, such that a monoclinic ( C 2/ c ) superstructure results. The crystal structure contains isolated [BPd 6 ] octahedral entities providing large distances between nearest neighbour boron atoms. Depending on the way of preparation, the same Pd 6 B phase can occur for the same composition in two different ‘manifestations’ having considerably different lattice parameters, which has a microstructural origin. Various phase equilibria between the ordered Pd 6 B phase and the disordered interstitial solid solution of boron in cubic close packed palladium have been investigated to clarify the corresponding regions in the phase diagram Pd—B.

September 25, 2009

Crystal growth and magnetic properties of rare earth borosilicides

Takao Mori

Page range: 464-471

Abstract

B 12 icosahedra cluster-containing rare earth borosilicides REB 44 Si 2 (RE = Tb, Dy, Ho, Er, Tm, Yb) were grown by the floating zone method and their physical properties were investigated. REB 44 Si 2 compounds are isostructural to REB 50 and they are unique among the newly discovered boron-rich phases in that it is possible to grow large crystals with dimensions exceeding 10 mm. The rare earth atoms form a coupled chain structure like a ladder along the c -axis which is also the axis along which there is a B 12 icosahedral chain. Magnetic properties, resistivity, and specific heat of the compounds were investigated. The conductivity follows the 3D variable range hopping mechanism and it was determined that localization lengths ξ are extremely short, actually close to the distances of the atoms themselves. Magnetic transitions above 4 K are indicated for all the compounds except for TmB 44 Si 2 and it is found that specific heat measurement is the expedient probe of such compounds in which the low temperature susceptibility is influenced by external conditions such as crystal growth rate. Despite dimer-like features to the magnetic transition a spin gap is not observed. The magnetic coupling in these systems is indicated to be different from the conventional mechanisms in f -electron systems of dipole-dipole coupling or RKKY interaction.

September 25, 2009

The effect of transition metal doping on thermal conductivity of YB₆₆

Takaho Tanaka, Koji Kamiya, Takenori Numazawa, Akira Sato, Satoshi Takenouchi

Page range: 472-476

Abstract

The effect of transition metal doping in YB 66 has been studied with respect to increase its thermal conductivity. Single crystals of YB 66 doped with 4th, 5th and 6th group transition metals were grown by floating zone method. A detailed structure analysis suggested that an existing special B—B pair at the (1/4, 1/4, 1/4) site of YB 66 could be attributed to a phonon scattering center that causes the amorphous-like low thermal conductivity. It was found that 5th and 6th group transition metals of V, Cr, Nb and Mo substitute the B—B pair. By contrast 4th group transition metals such as Ti and Zr were found to enter another ( x , x , x ) site with x ∼ 0.135. Thermal conductivity of both Nb-doped and undoped YB 66 was measured in the range 4 K ≤ T ≤ 150 K. Nb doping increased thermal conductivity of YB 66 with a factor of about 2.

September 25, 2009

Structure refinements of iron borides Fe₂B and FeB

Christine Kapfenberger, Barbara Albert, Rainer Pöttgen, Hubert Huppertz

Page range: 477-481

Abstract

Crystals of the iron borides FeB and Fe 2 B were obtained from two different high temperature synthesis routes, viz. in combined copper/gallium flux and under high pressure conditions. Their crystal structures were investigated at room and low temperatures. Structure models from the literature were confirmed. The position of the boron atoms was unambiguously determined. FeB ( Pnma , no. 62) contains zig-zag chains of boron atoms in which the boron atoms are coordinated by seven iron atoms in the form of a mono-capped trigonal prism. Fe 2 B ( I 4 /mcm , no. 140) contains single boron atoms in a square antiprismatic iron atom coordination.

September 25, 2009

Cubic structure types of rare-earth intermetallics and related compounds

Oksana Bodak, Pavlo Demchenko, Yurii Seropegin, Anatolii O. Fedorchuk

Page range: 482-492

Abstract

Cubic structure types of rare-earth intermetallic and related compounds are reviewed and their structural similarities are discussed. The description of the structural relations is based on the ordered substitution or inclusion of atoms or atomic groups starting from the structures of four “aristotypes”: diamond, Cu, CsCl and W. Structural similarities between some types are illustrated by family trees of crystallographic group-subgroup relations.

September 25, 2009

Structural variations in Gd₅Si_4-xSn_x: size vs. electronic effects

Yurij Mozharivskyj, Alexandra O. Tsokol, Gordon J. Miller

Page range: 493-501

Abstract

X-ray single crystal diffraction studies on the Gd 5 Si 4x Sn x series with 0 ≤ x ≤ 3 revealed an increase in the interslab T — T ( T = Si, Sn) dimer distances and transition from Gd 5 Si 4 -type structures for 0 ≤ x ≤ 1.5 ( d T—T = 2.49–2.71 Å) to the Pu 5 Rh 4 -type structure for x = 2 ( d T—T = 3.04 Å). The Ti 5 Ga 4 -type structure, which is a stuffed version of the hexagonal Mn 5 Si 3 structure, was observed for the Gd 5 SiSn 3 sample ( x = 3). Tight-binding linear-muffin-tin-orbital (TB-LMTO) calculations on Gd 5 Si 2 Sn 2 show that the interslab ( T 1— T 1) dimer stretching and the structural transition from the Gd 5 Si 4 -type to the Pu 5 Rh 4 -type results from the influence of the 5 p atomic orbital energy and the larger size of the Sn atoms on the electronic structure, as compared to the Si and Ge atoms in Gd 5 Si 4 and Gd 5 Si 2 Ge 2 .

September 25, 2009

Tin flux synthesis of rare-earth metal silicide compounds RESi_1.7 (RE = Dy, Ho): a novel ordered structure derived from the AlB₂ type

Jérome Roger, Volodymyr Babizhetskyy, Régis Jardin, Roland Guérin, Claude Moinet, Ulrich Burkhardt, Jean-Francois Halet

Page range: 502-510

Abstract

The binary rare-earth metal silicides RESi 1.7 (RE = Dy, Ho) were prepared by tin flux synthesis between 800–1000 °C. Single crystals were obtained after electrochemical dissolving of molten ingots. Their crystal structures were determined from single-crystal X-ray data: orthorhombic symmetry, space group Imm 2; unit cell parameters a = 19.144(1), b = 8.2562(3), c = 6.6571(3) Å and a = 19.063(1), b = 8.2120(2), c = 6.6313(2) Å for DySi 1.7 and HoSi 1.7 , respectively. They represent a new ordered structure type, which is a derivative of the defect AlB 2 type. The main structural feature is the occurrence of a vacancy ordering in the two-dimensional planar network of silicon atoms, leading to rows of edge-shared twelve-membered rings separated by distorted hexagonal rings. Structural comparison with the parent hexagonal silicide Yb 3 Si 5 (Th 3 Pd 5 type), the structure of which has been re-determined on single crystal, is also given.

September 25, 2009

Filling the CoSn host-cell: the HfFe₆Ge₆-type and the related structures

Gerard Venturini

Page range: 511-520

Abstract

The crystallographic properties of the CoSn-based MT 6 X 6 compounds (M = alkaline-, alkaline earth-, transition metals, lanthanides and actinides, T = transition metal, X = element of the main group) are reported. The filling scheme and the features of the diffraction patterns are detailed and illustrated by the new LuFe 6 Ge 6–x Ga x series. The members of the hexagonal, orthorhombic and monoclinic series are presented. The crystal chemistry and the structural evolutions as a function of the size of the components and of the valence electron concentration are reported.

September 25, 2009

Synthesis and characterization of Na₂Ba₄Ga₂Sb₆ and Li₁₃Ba₈GaSb₁₂

Iliya Todorov, Slavi C. Sevov

Page range: 521-526

Abstract

The title compounds were synthesized from the elements by heating the corresponding stoichiometric mixtures at high temperature. Their structures were determined from single-crystal X-ray diffraction. Na 2 Ba 4 Ga 2 Sb 6 ( Pnma , Z = 8, a = 12.3468(10) Å, b = 10.6621(10) Å, c = 13.8344(10) Å) contains chains of ∞ [Ga 2 Sb 6 ] 10– . The repeating unit is made of an edge-sharing Ga-centered tetrahedron GaSb 2 (μ-Sb) 2 and another Ga-centered tetrahedron but with additional antimony that is exo-bonded to one of the corners forming Sb–Sb dumbells, i.e. GaSb(Sb–Sb)(μ-Sb) 2 . The unit connects to neighboring units via sharing two corners of the tetrahedra, i.e. [Ga 2 Sb 5 Sb 2/2 ]. Li 13 Ba 8 GaSb 12 ( C 2/ m , Z = 2, a = 18.0650(10) Å, b = 4.9407(10) Å, c = 13.0123(10) Å, β = 126.728(10)°) contains three different types of anions: single-atom anions of Sb 3– , dumbells of Sb 4– , and isolated Ga-centered tetrahedra of GaSb 4 9– . The two compounds are electronically balanced, and this is confirmed by four-probe conductivity and magnetic measurements. Their very narrow band gaps, 0.014 and 0.049 eV for Na 2 Ba 4 Ga 2 Sb 6 and Li 13 Ba 8 GaSb 12 , respectively, make them potential thermoelectric materials.

September 25, 2009

Ge_40.0Te_5.3I₈: synthesis, crystal structure, and properties of a new clathrate-I compound

Kirill A. Kovnir, Nikolay S. Abramchuk, Julia V. Zaikina, Michael Baitinger, Ulrich Burkhardt, Walter Schnelle, Andrei V. Olenev, Oleg I. Lebedev, Gustaaf Van Tendeloo, Evgeny V. Dikarev, Andrei V. Shevelkov

Page range: 527-532

Abstract

A new clathrate phase with the composition Ge 40.0 Te 5.3 I 8 has been prepared and its structure determined from single crystal X-ray data. It crystallizes in the cubic space group Pm -3 n with unit cell parameter a = 10.815(1) Å and Z = 1 ( R = 0.031 for 272 independent reflections and 19 variables). Germanium and tellurium form a cationic clathrate framework hosting the guest iodine anions in cages of two different shapes. The cationic framework features a joint occupation on two of the three independent sites by germanium and tellurium, leading to the formation of Ge—Ge and Ge—Te bonds and vacancies on the third position. Electron diffraction and high-resolution electron microscopy reveal that the bulk material is not uniform; it contains domains showing a tendency for segregation of tellurium and germanium within the 4-fold positions of the space group P 23, which is a subgroup of Pm -3 n . Ge 40.0 Te 5.3 I 8 is a diamagnetic semiconductor with a band gap of about 0.8 eV and its composition agrees with the Zintl formalism for the charge-balanced compounds.

September 25, 2009

Ag₆GeS₄X₂ (X: Cl, Br): surprisingly no filled Laves phases but the first representatives of a new structure type

Michael Wagener, Hans-Jörg Deiseroth, Christof Reiner

Page range: 533-538

Abstract

The two new deeply coloured, air stable, isotypic compounds Ag 6 GeS 4 X 2 (X: Cl, Br) were obtained in the course of a series of experiments to prepare new “non-metallic filled Laves phases (= argyrodites)”. Although the chemical compositions of the new compounds are in accordance with the desired rare type of doubly halide (X) substituted argyrodites Ag 6 GeS 4 X 2 , their crystal structures are not of the argyrodite type. Instead they are the first members of the new family of “non-metallic filled NaHg 2 phases”, i.e. the partial structure of the non-metal atoms S and X (Cl, Br) corresponds to the arrangement of Na and Hg atoms in NaHg 2 (= X 2 S 4 ) with Ge located in tetrahedral holes exclusively and Ag located in tetrahedral as well as octahedral holes. The lattice constants of the new phases are (both space group Pnma , Z = 4): Ag 6 GeS 4 Cl 2 ( a = 643.0(1) pm, b = 761.0(2) pm, c = 2266.0(5) pm), Ag 6 GeS 4 Br 2 ( a = 654.0(1) pm, b = 772.7(2) pm, c = 2289.9(5) pm). High temperature X-ray powder studies show an irreversible loss of halogen resulting in inhomogeneous decomposition products with argyrodite structure.

September 25, 2009

Low- and high-temperature structures of YbCuBi

Andriy V. Tkachuk, Yurij Mozharivskyj, Arthur Mar

Page range: 539-542

Abstract

A variable temperature single-crystal X-ray diffraction study was undertaken on the intermetallic compound YbCuBi, which undergoes a phase transition at ∼375 K. At low temperatures ( T = 193 K, a = 4.5821(3) Å, c = 7.8107(8) Å; T = 295 K, a = 4.5825(6) Å, c = 7.8597(10) Å), YbCuBi adopts the LiGaGe-type (ordered CaIn 2 -type) structure (Pearson symbol hP 6, space group P 6 3 mc , Z = 2). At high temperatures ( T = 393 K, a = 4.5885(14) Å, c = 7.913(2) Å; T = 473 K, a = 4.594(4) Å, c = 7.928(6) Å), YbCuBi adopts the ZrBeSi-type (ordered Ni 2 In-type) structure (Pearson symbol hP 6, space group P 6 3 / mmc , Z = 2). The structure consists of Yb atoms separating hexagonal ∞ 2 [CuBi] nets, which are buckled at low temperatures but planar at high temperatures.

September 25, 2009

(La₃Z_x)Al and (Ce₃Z_x)Al with Z = C, N, O: preparation, physical properties and chemical bonding of metal-rich perovskites

Martin Kirchner, Frank Gäbler, Walter Schnelle, Frank R. Wagner, Rainer Niewa

Page range: 543-553

Abstract

The inverse cubic perovskites (La 3 O)Al, (La 3 N)Al, (Ce 3 O)Al, and (Ce 3 N)Al are reported together with the solid solution series (Ce 3 C 1–x N x )Al. The crystal structure of (La 3 N)Al is analyzed in detail based on single crystal X-ray diffraction data (space group Pm -3 m , a = 509.04(1) pm, Z = 1, R gt ( F ) = 0.008, wR ( F 2 ) = 0.018). Combined X-ray powder diffraction and thermal analysis studies on samples with various N and O contents indicate only small tolerance of the ternary compounds towards Z = N, O deficiency and small solubility of Z in hexa gonal α -Ce 3 Al. Indications for the existence of a cubic β -Ce 3 Al with Cu 3 Au structure type could not be derived from any experiment. All studied phases are metals, the Ce compounds contain the rare-earth metal in Ce(4 f 1 ) states according to X-ray absorption spectroscopy and measurements of the magnetic susceptibilities. The Ce moments order antiferromagnetically with T N decreasing and scaling with increasing unit cell dimension of the compounds. Electronic band structure calculations reveal a trend to increased mixing of Z and La states on going from Z = O via N to C. Formation of a band gap even in the formally electronically balanced (La 3 C)Al is mainly prohibited by insufficient charge transfer between the metal species.

September 25, 2009

Geometric variations and electron localizations in intermetallics: PbFCl type compounds

Jürgen Nuss, Ulrich Wedig, Martin Jansen

Page range: 554-562

Abstract

The structural relations of the intermetallic compounds Cu 2 Sb, Mn 2 Sb, Fe 2 As, Mn 2 As, Cr 2 As, Sc 2 Sb as well as of YTiSi and ZrSiS, all adopting the PbFCl structure, are discussed. In the course of these investigations, the crystal structures of Mn 2 Sb, Mn 2 As and Fe 2 As have been redetermined and refined from single crystal data. Bandstructures have been calculated in the framework of Density Functional Theory. The bonding properties are compared on the basis of partial densities of states, of the Crystal Orbital Hamilton Population (COHP) and of the Electron Localization Function (ELF). The trend of the d electrons to become more localized with increasing number leads to different bonding conditions in the compounds discussed.

September 25, 2009

A novel series of sphere packings with arbitrarily low density

Tadeusz E. Dorozinski, Werner Fischer

Page range: 563-566

Abstract

The search for a least dense packing of spheres makes sense only under suitable restrictions because otherwise sphere packings of arbitrarily low density may be constructed. As has been shown before, the condition that all spheres have to be equal as well in their size as in their number of contacts is not such an effective restriction. A sharper condition is the demand that all spheres must have congruent patterns of contacts, i.e. that they must coincide in their first neighbourhood. The example presented here proves that also this restriction is not sufficient to avoid sphere packings with densities approaching zero.

September 25, 2009

Books Received

Page range: 567-569

About this journal

Objective
Zeitschrift für Kristallographie – Crystalline Materials was founded in 1877 by Paul von Groth and is today one of the world’s oldest scientific journals. It offers a place for researchers to present results of their theoretical experimental crystallographic studies. The journal presents significant results on structures and on properties of organic/inorganic substances with crystalline character, periodically ordered, modulated or quasicrystalline on static and dynamic phenomena applying the various methods of diffraction, spectroscopy and microscopy.

Topics

General Aspects
Inorganic Crystal Structures
Organic and Metalorganic (including Biological)
Crystal Structures
Technological Aspects
Computer Programs
Instrumentation
Material Properties

Article formats
Letters, Reviews, Original Papers, Discussions, Book Reviews

> Information on submission process

Volume 221 Issue 5-7 - Crystal Chemistry of Intermetallic Compounds

Issue of Zeitschrift für Kristallographie - Crystalline Materials

Editorial: Crystal Chemistry of Intermetallic Compounds

Fritz H. Laves – 100 years young

Abstract

Fritz H. Laves – an ideal for generations

Abstract

Gustav E. R. Schulze's pioneering work on Laves phases

Abstract

Preparation, phase stability and structure of the C36 Laves phase Nb1–xCo2+x

Abstract

Atom order and thermodynamic properties of the ternary Laves phase Ti(TiyNixAl1–x–y)2

Abstract

Atomic ordering in the Laves phases L1 V(Co1–xSix)2 (x = 0.43 and 0.56)

Abstract

Microscopic structures of Laves phases and structurally related compounds: a transmission electron microscopy study

Abstract

Binary rare earth Laves phases — an overview

Abstract

Binary intermetallic phases formed by Ca, Sr, Ba, Eu and Yb: similarities and differences

Abstract

Complexity of hexagonal approximants in the RE13Zn~58 system (RE = Ce, Pr, Nd, Sm, Gd, Tb and Dy)

Abstract

Reflections on symmetry and formation of axial quasicrystals

Abstract

Mosaic-like tilings derivated from o-Co4Al13 and m-Co4Al13 crystal structures

Abstract

High-pressure crystal chemistry of binary intermetallic compounds

Abstract

Re3B type intermetallics — crystal chemistry, bonding and properties

Abstract

Ti2Rh6B – a new boride with a double perovskite-like structure containing octahedral Rh6 clusters

Abstract

On the formation and crystal structure of the Pd6B phase

Abstract

Crystal growth and magnetic properties of rare earth borosilicides

Abstract

The effect of transition metal doping on thermal conductivity of YB66

Abstract

Structure refinements of iron borides Fe2B and FeB

Abstract

Cubic structure types of rare-earth intermetallics and related compounds

Abstract

Structural variations in Gd5Si4-xSnx: size vs. electronic effects

Abstract

Tin flux synthesis of rare-earth metal silicide compounds RESi1.7 (RE = Dy, Ho): a novel ordered structure derived from the AlB2 type

Abstract

Filling the CoSn host-cell: the HfFe6Ge6-type and the related structures

Abstract

Synthesis and characterization of Na2Ba4Ga2Sb6 and Li13Ba8GaSb12

Abstract

Ge40.0Te5.3I8: synthesis, crystal structure, and properties of a new clathrate-I compound

Abstract

Ag6GeS4X2 (X: Cl, Br): surprisingly no filled Laves phases but the first representatives of a new structure type

Abstract

Low- and high-temperature structures of YbCuBi

Abstract

(La3Zx)Al and (Ce3Zx)Al with Z = C, N, O: preparation, physical properties and chemical bonding of metal-rich perovskites

Abstract

Geometric variations and electron localizations in intermetallics: PbFCl type compounds

Abstract

A novel series of sphere packings with arbitrarily low density

Abstract

Books Received

Preparation, phase stability and structure of the C36 Laves phase Nb_1–xCo_2+x

Atom order and thermodynamic properties of the ternary Laves phase Ti(Ti_yNi_xAl_1–x–y)₂

Atomic ordering in the Laves phases L1 V(Co_1–xSi_x)₂ (x = 0.43 and 0.56)

Complexity of hexagonal approximants in the RE₁₃Zn_~58 system (RE = Ce, Pr, Nd, Sm, Gd, Tb and Dy)

Mosaic-like tilings derivated from o-Co₄Al₁₃ and m-Co₄Al₁₃ crystal structures

Re₃B type intermetallics — crystal chemistry, bonding and properties

Ti₂Rh₆B – a new boride with a double perovskite-like structure containing octahedral Rh₆ clusters

On the formation and crystal structure of the Pd₆B phase

The effect of transition metal doping on thermal conductivity of YB₆₆

Structure refinements of iron borides Fe₂B and FeB

Structural variations in Gd₅Si_4-xSn_x: size vs. electronic effects

Tin flux synthesis of rare-earth metal silicide compounds RESi_1.7 (RE = Dy, Ho): a novel ordered structure derived from the AlB₂ type

Filling the CoSn host-cell: the HfFe₆Ge₆-type and the related structures

Synthesis and characterization of Na₂Ba₄Ga₂Sb₆ and Li₁₃Ba₈GaSb₁₂

Ge_40.0Te_5.3I₈: synthesis, crystal structure, and properties of a new clathrate-I compound

Ag₆GeS₄X₂ (X: Cl, Br): surprisingly no filled Laves phases but the first representatives of a new structure type

(La₃Z_x)Al and (Ce₃Z_x)Al with Z = C, N, O: preparation, physical properties and chemical bonding of metal-rich perovskites