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Thermal stability with respect to a structural transformation and the crystal structure of the orthorhombic gadolinium copper phosphide GdCuP 2.16 was investigated using powder diffraction techniques. The structure was refined from the data collected at room temperature to yield Pmm 2 space group, a =5.3284(1), b =5.3868(1) and c =9.7486(2) A. The refinement results agree well with the single crystal results [J. Solid State Chem. 155 (2000) 259]. Although the phosphide preserves the orthorhombic crystal structure up to 700 °C, the thermal expansion along the a axis becomes larger than those along b and c axes above 500 °C, indicating that a structural transformation is likely to occur at higher temperatures.

Variable angle reflectance FTIR was used to investigate the reflectance of thin films of either indium tin oxide (ITO) or fluorine-doped tin oxide (SFO) on glass substrates in the mid-IR. The reflectance was observed to depend on the incident angle, wavenumber, and the polarization used. The Drude model and the Fresnel equations for reflection at a single dielectric boundary were used to interpret these results in terms of the conductivity, reflectivity, skin depth, and plasmon frequency of the metal oxides. The skin depth of thin film ITO electrodes was found to depend on the sheet resistance linearly, while the reflectance varied according to the square root of the sheet resistance. The method shows that an optical probe can be used to determine the electrical properties of metal oxide films in a noninvasive approach.

Fifteen new rare-earth antimonides and bismuthides RE 5 Pt 2 X (see Table 1 ) have been synthesized and characterized by X-ray powder methods. The compounds are isostructural to previously reported RE 5 M 2 X pnictides and adopt the Mo 5 B 2 Si structure (space group I4/mcm , an ordered version of Cr 5 B 3 ). The RE 5 M 2 X series now includes 47 antimonides and bismuthides with M=Ni, Pd, Pt and the heavy rare earths except for ytterbium. Atomic and thermal parameters have been refined and the magnetic susceptibility was measured for Er 5 Pt 2 Bi.

Our studies on the Ge–Nb system reveal the existence of a hexagonal compound with the composition Ge 7 Nb 10 that is stable with respect to disproportionation and which was found to crystallize in the space group P6 3 /mmc . A hexagonal phase of the approximate composition Ge 3 Nb 5 has been mentioned by different authors but has been commonly regarded as C- or N-stabilized and therefore not included in the binary phase diagram. A single crystal X-ray study of the compound revealed a Mn 5 Si 3 -type based structure where half of the 2b interstitial positions are filled with Ge. X-ray powder diffraction studies and electron probe microanalysis were used to determine the composition ranges of the phases. Various experiments were carried out in order to confirm the thermodynamic stability of this compound and to rule out stabilization by hetero-elements. These studies included the use of different starting materials, different sample preparation techniques and different annealing procedures. The results show strong indications, that Ge 7 Nb 10 is formed as a binary phase which is stable with respect to disproportionation and should therefore be included in the binary phase diagram.

The high-temperature modification of Y 5 Sb 3 has been discovered: the Yb 5 Sb 3 structure type, Pnma space group, a =11.867(1), b =9.2247(9) and c =8.0977(8) A. It has been estimated that the first-order structural transition from the low-temperature form (Mn 5 Si 3 type) to the high-temperature form is above 1265°C but below 1400°C. Antimony atoms on one of the two sites can be partially substituted by Ni atoms, which results in a Y 5 Ni x Sb 3− x formula with 0≤ x 5 Ni 0.38 Sb 2.62 crystal, obtained by annealing a sample in an induction furnace for 2 h at 1265°C. All high-temperature nickel-containing phases Y 5 Ni x Sb 3− x with the ordered Yb 5 Sb 3 structure undergo a decomposition to low-temperature Y 5 Sb 3 (Mn 5 Si 3 type) and a nickel-containing phase, when annealed at 800°C. Extended Huckel tight-binding calculations show that substitution of Sb by Ni is unfavorable with respect to the Y–Sb bonding. The structure of Y 5 Ni x Sb 3− x is stabilized by the configurational entropy, resulting from a statistical mixture of Sb and Ni atoms on one site. Choice of an Sb site to be occupied by Ni is dictated by bonding maximization in the substituted structure. The high-temperature Y 5 Sb 3 and Y 5 Ni 0.38 Sb 2.62 phases are weak Pauli paramagnets.

The crystal structure of HfZrP has been determined using single crystal X-ray diffraction data. This compound crystallizes in the orthorhombic space group Cmmm (No.65), with a =19.004(3), b =29.372(4), c =3.565(1) A and the Zr 2 P structure type. The Hf and Zr atoms are disordered on one site with total occupancy of 1.0. X-ray powder patterns indicate that (Hf x Zr 1− x ) 2 P alloys consist of single phase (Zr 2 P-type),two phases and single phase (Hf 2 P-type) corresponding to 0≤ x ≤0.5, 0.5 x x ≤1.0, respectively.

The compounds NdFe 0.45 Ge 2 and HoFe 0.33 Ge 2 have been synthesized and studied by single-crystal X-ray diffraction. They crystallize in the space group D 2 h 17 − C m c m of the orthorhombic system with Z =4 in the unit cell: a =4.091 (2) A, b =15.679(7) A, c =3.985(2) A, V =255.6(4) A 3 ( T =296 K) for HoFe 0.33 Ge 2 ; and a =4.214(2) A, b =16.455(9) A, c =4.070(2) A, V =282.2(4) A 3 (T=296 K) for NdFe 0.45 Ge 2 . The compounds exhibit the defect CeNiSi 2 structure-type.

Hf 5 CoAs 3 was prepared by arc-melting of HfAs, Hf and Co. This new arsenide crystallizes in the orthorhombic space group Pnma with cell dimensions of a =17.327(5)A, b =3.685(4)A, c =10.370(4)A, V =662(1)A 3 . Its crystal structure is isostructural to the structure of Hf 5 CoP 3 . The Co and As atoms both are located in trigonal prismatic voids of the Hf substructure. The Hf atoms form double channels, each of which is filled with an infinite -Co-As- zigzag chain. These double channels are interconnected via bonding Hf–Hf interactions to form the three-dimensional Hf substructure. Since adding more Co occurs with significantly enlarged cell dimensions, it is concluded that the additional Co atoms are included in the structure of Hf 5 CoAs 3 , as Ni is in case of Hf 5 Ni 1+ x P 3 . The densities of states obtained by Extended Huckel calculations and the Pauli paramagnetism experimentally obtained point to metallic behavior of Hf 5 CoAs 3 .

The crystal structure of the λ-Al4Mn phase, considered to be closely related to icosahedral quasicrystalline i-AlMn was determined by X-ray analysis. Metallic, hexagonal needles of the λ-phase were obtained by thermal decomposition of a mixture of Al and MnS. The structure crystallizes in P63/m with a=28.382(9) A and c=12.389(2) A . The volume of the cell is 8643 A3 and contains an average of 568.1 atoms. 106.6 atoms (18.8 at.%) are Mn, corresponding to a calculated density of 3.517(6) g cm−3. The final R-values were Ru=9.2% and Rw=5.9% for 2508 reflections with I>3σ. There are 66 atoms in the asymmetric unit. 104 positions in the unit cell are occupied with Mn and 482 with Al. 102 Mn have icosahedral coordination and two Mn a tri-capped trigonal prismatic coordination (CN 9). 36 Al atoms have icosahedral coordination, 138 Al have a polar bi-capped pentagonal prismatic, 72 Al have a bi-equatorial capped pentagonal prismatic and 168 Al a mixed capped pentagonal prismatic with CN 13 or 14, 4 Al a CN 16 Frank-Kasper polyhedron, and 52 Al an irregular coordination polyhedron. Six Al positions are partly occupied and five Al positions show disorder with small amounts of Mn. The distance ranges are MnMn 2.689–2.784 A, AlMn 2.362–2.949 A and AlAl 2.424–3.414 A. Additionally, one short distance of 2.180 A is between two partly occupied Al sites. The structure of the λ-phase is a member of the I3-family, containing the I3-cluster, a fragment of three vertex connected icosahedra. The structure is composed of six chains of fused truncated 1(2)-tetrahedra in the unit cell, aligned along c. The chains are B-type connected via primitive stacked pseudo I13-clusters. A similar arrangement is found in the structure of μ-Al4.12Mn.

The cubic, fluorite-type, structure of zirconia has been found to be stabilized at room-temperature by the substitution of the sulfur for oxygen at 20% of the anion sites in a random way. A major effect of this substitution is to increase the ZrZr distances and thereby to decrease the metal-metal interactions contributing to the structural stability of the monoclinic form.

The Co/P exchange observed in Hf5Co1 + xP3−x is the first example for a statistical disordered Co/P occupancy on one position. In its crystal structure both different kinds of atoms, the late-transition metal atom Co and the nonmetal P, are located in trigonal prismatic voids of the Hf sublattice. The purely Co site has two P neighbours located in neighbouring trigonal prisms, each of which shares a rectangular face with the central Co prism, forming an infinite -Co-P- zigzag chain. The two other P sites have no contact to a Co atom. As a consequence of this, a partial substitution of P by Co on the sites which have shorter distances to the surrounding Hf atoms can take place. This P position can be occupied by up to 50% Co. leading to a significant phase range (0≤x≤0.5 in Hf5Co1+xP3−x). However, increasing the Co to P ratio brings a higher density of states at the Fermi level, corresponding to higher magnetic susceptibilities as determined experimentally. The consequences of the Co/P exchange for the electronic structure are discussed.

Hf 9 Mo 4 SO x and Hf 9 W 4 SO x have been prepared by arc-melting of HfS, Hf and Mo and W respectively and subsequent annealing at 1500°C. Both compounds crystallize in the hexagonal space group P 6, mmc (No. 194), with cell dimensions a = 8.6513(5)A, c = 8.5409(8)A, V = 557.45(8)A, and a = 8.667(1)A, c = 8.583(3)A, V = 558.4(2)A respectively and belong to the general group of κ-phases. The metal sublattice consists of chains of Mo/W centered icosahedra, running along [001], which are interconnected by additional Hf atoms and the non-metal atoms. Oxygen is located in a Hf 6 octahedron and sulfur in a Hf 6 trigonal prism. Apparently, the occupation of the interstitial octahedral position with oxygen could not be totally prevented by carrying out all steps of the synthesis in a glove-box under an argon atmosphere, although its presence should not be necessary to form these κ-phases. Band structure calculations show both materials to be metallic, in agreement with the experimentally determined Pauli paramagnetism.

New κ-phases (P. Rautala and J.T. Norton, Trans. AIME, 194 (1952) 1045; A. Harsta and S. Rundqvist, J. Solid State Chem., 70 (1987) 210) were discovered and crystallographically characterized in the Zr Ta S, Zr Nb S, Zr V S, Hf Nb S, and Hf V S systems, A κ-phase was also identified in the Hf Ta S system through Guinier powder diffraction. These compounds are the first examples of the κ-phase structure containing the Group V transition metals, Ta, Nb, and V. The Ta and Nb κ-phases exhibit the largest volumes (by about 13%) and the largest amounts of second row nonmetal per formula unit of the known κ-phases. X-ray single-crystal diffraction experiments were used to determine metal site occupancies in these κ-phases, and it was found that statistical mixing of the metals primarily on one site occurred for the Ta and Nb compounds. Refinements of the X-ray intensity data indicated that the octahedral nonmetal sites (denoted X2) are less than fully occupied by sulfur in the Ta and Nb κ-phases and less than fully occupied by oxygen in the V κ-phases. Combined neutron and X-ray powder refinements reliably determined that these nonmetal X2 sites are occupied by a mixture of sulfur, oxygen, and vacancies in the Zr Nh S and Zr Ta S κ-phases. The κ-phases in the Zr Nb S (G. Marking et al., Phys. Rev. B, 48 (1993) 16630) and Hf Nb S systems were found to be superconductors with T 2 s of 10.35 K and between 6 and 7 K respectively.

The new phosphide Hf5Co1+xP3−x has been prepared by arc melting of HfP, Hf and Co, and subsequent annealing at 1500°C in an induction furnace. It crystallizes in a new structure type, space group Pnma (No. 62), lattice constants a = 16.980(3) A, b = 3.6101(7) A, c = 10.175(1) A, V = 623.8(2) A3. This structure consists of six-membered Hf-channels, condensed to a double channel. Each channel contains one Co and one P atom, which form an infinite CoP zigzag chain. The channels are connected via short HfHf contacts to a three-dimensional network with two further P positions located in trigonal prismatic voids of the Hf sublattice. Unusually, one P site — that with the higher bond order — is partially occupied with Co, indicating that phosphorus is able to take part in delocalized metallic bonds, as well as cobalt. The partial Co/P exchange is related to the similar atomic radii and the expected negative charge for Co and P in this Hf-rich phosphide. A significant phase range is observed.

The phase transition between the NiAs-type structure (P63/mmc) and the troilite structure ( P 6 2c ) in FeS has been examined in synthetic samples in high-temperature X-ray diffraction and DTA experiments, re-examined by Landau theory. The low temperature spin-flip and para- to ferroelectric transition was also studied. It is found experimentally that the NiAs-type to troilite transition is first-order and, by re-examination of Landau theory, that this is required by the Lifshitz condition but not by the Landau conditions. The low-temperature transition is found to occur with no discontinuity in lattice parameters. It is therefore argued that the low-temperature phase, which is known to be ferroelectric, has a trigonal space group symmetry that is a polar subgroup of P 6 2c , namely P31c.

A number of complex metal alloys, including the structure types of λ-Al 4 Mn, Al 10 Mn 3 , Al 5 Co 2 , BHf 9 Mo 4 , C 7 Co 6 W 20 , Zr 6 Ni 6 TiSiO 5 , Al 23 V 4 , μ-Al 4,12 Mn, Al 13 Cr 4 Si 4 , NiTi 2 , CFe 3 W 3 , Al 10 V, Al 18 Cr 2 Mg 3 , Al 45 V 7 , Al 31 Mn 6 Ni 2 , Al 11 Mn 3 Zn 2 , Al 9 Mn 2 Si, Hf 54 Os 17 , Rh 13 Sc 57 , Ag 17 Mg 54 , GaMnSc 9 , Mg 44 Rh 7 , Na 6 Tl, Mg 6 Pd and Fe 11 Zn 39 , representing several hundred different intermetallic structures, are discussed by means of a new cluster concept. The basic building block of the cluster concept consists of 36 atoms in three vertex-connected icosahedra with bi-capped pentagonal coordination polyhedra for the link atoms. Together with a small set of connection types, the structures mentioned above can then be described as being composed of only one building block. This approach enables a good visualization of the structures, points out the similarities of the structural principles between different structures, and is helpful in the structure solution of complex metal alloys. Quasi-crystals for the icosahedral i-AlMnSi and i-TiTM (TM, transition metal) classes are closely related to phases of the above family by similarities in the diffraction pattern and by phase formation. Therefore, we suggest that the structures of the quasi-crystals of both classes have similar underlying structural principles, so contain the basic building block mentioned above. A model for the structure of the quasi-crystals, based on a zonohedral tiling of the Penrose local isomorphism class with four different unit cells, is discussed. The application of the rules of the cluster concept yields atomic decoration of the unit cells with reasonable chemistry in terms of local coordination polyhedra and their three-dimensional arrangement.

The metal atom ordering and oxygen occupancy of four compounds of the filled-Ti2Ni type structure have been determined by single-crystal X-ray diffraction studies. Three additional phases have been identified and indexed from powder X-ray diffraction data. All the phases crystallize in space group Fd 3 m with the following compositions: Zr4Ni2O ( a = 12.1970(9) A ), ZΓ6Ni4Ti2O0.6 ( a = 12.0299(9) A ), Nb6Ni6O ( a = 11.2117(5) A ), and Nb6Ni4Ta2O2 ( a = 11.5813(3) A ). Phases identified using powder data are Nb4Ni2O ( a = 11.5933(3) A ), Zr4Cu2O ( a = 12.2659(7) A ), and Zr6Co4Ti2O ( a = 11.8649(9) A ). A comparison of the structures and oxygen occupancies is presented, as well as tentative explanations based on results of extended Huckel calculations. The role of interstitial oxygen as an electron acceptor and its effect on metal-metal bonding are considered.

The crystal structures of the AgRSb2 (R=Pr, Nd, Gd, Dy, Ho, Er) compounds were determined by X-ray powder diffraction using the Rietveld method. The investigated compounds crystallize in the tetragonal space group P4/nmm (No. 129) with the CuSi2Zr structure type.

The crystal structure of Fe 6 Ge 6 Ho has been determined from single-crystal X-ray data. It crystallizes in the hexagonal, space group P6/mmm (no.191) with the Cu 7 Tb structure type and a =5.102(2) A, c =4.050(2) A, z =0.5, v =91.29(3) A 3 .

During the continuing study of the metal-rich region of the ternary Ta-Nb-S system a new layered compound, Nb x Ta 2− x S ( x ≈0.95), was found using the arc-melting method and characterized by means of X-ray diffraction experiments. The compound crystallizes in the tetragonal space group P 4/ nmm with unit cell dimensions α =333.04(7) pm and c =909.28(94) pm. The tetragonal cell contains two formula units. The structure contains homoatomic layers sequenced S-M2-M1-M1-M2-S (M is a Nb, Ta mixture) generating six-layer sheets stacked along [001] and is closely related to b.c.c. Weak S-S interactions at 319 pm between sheets contrast with the M-M binding within and between the sheets, the former presumably being responsible for the observed graphitic slippage of the samples. Based upon extended Huckel band calculations metallic properties can be expected for this compound. The relative preference of the metal sites for the two metal elements (Ta, Nb) is explained by band calculations.

Two new ternary metal-rich compounds, Nb21-xTaxS8 and NbxTa2-xS, isostructural with the binary metal-rich compounds Nb21S8 and Ta2S respectively, were prepared by means of high temperature techniques in the ternary Ta-Nb-S system. Single-crystal structure refinements were carried out for crystals of Nb21-xTaxS8 (R/Rw=0.027/0.043) and NbαTa2–αS (R/Rw=0.040/0.043), and the compositions were determined as Nb14.8Ta6.2S8 and Nb0.20Ta1.80S respectively from the structure refinements. Stoichiometric ranges of ternary solid-solution-type metal-rich compounds found in the Ta-Nb-S system were determined. Common structural features of these metal-rich compounds are discussed.

The crystal structure of the ternary rare-earth compound Nd 4 Fe 1.3 Ge 7.5 has been determined from single-crystal X-ray data. The compound crystallizes in tetragonal, space group Cmcm, No. 63), with a =4.121(1) A, b =30.446(8) A, c =4.2180(9) A, V =529.2(4) A 3 and Z =2 at room temperature. The structure refinement ( R =0.024, R w =0.031) showed the compound to be a new structure-type.

The structure of Ge 3 Nd 5 has been determined from single-crystal X-ray data. It crystallizes in the hexagonal, space group P6 3 /mcm (No.193) with the Mn 5 Si 3 structure type and a =8.743(2) A, c =6.625(1) A, Z =2, v =438.56(17) A 3 .

The structure of lanthanum rhodium antimonide, La 0.1 Rh 8 Sb 24 , has been determined from single-crystal X-ray data. It crystallizes in the cubic space group Im3 (No.204), with a =9.2213(15) A, V =784.1(2) A 3 and the LaFe 4 P 12 structure type.

The structures of NdNi and NdNi 5 have been determined by single-crystal data. NdNi crystallizes in the orthorhombic space group Cmcm (No. 63), with a =3.8059(5) A, b =10.462(4) A, c =4.3345(12) A, Z =4, V =172.59(8) A 3 and the BCr structure type. NdNi 5 crystallizes with the CaCu 5 structure type, space group P6/mmm (No. 191), a =4.973(2) A, c =4.0124(11) A, Z =1 and V =85.94(5) A 3 .

The structure of NdGe 2 Ni 2 was refined using single-crystal X-ray data. The refinement shows the crystal structure of NdGe 2 Ni 2 is tetragonal with the Al 4 Ba-type structure with the space group I4/mmm (No. 139), a =4.123(4) A, c =9.841(2) A, V =167.3(2) A 3 and Z =2 at room temperature.