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A novel ternary compound, UMo3B7, has been synthesized by arc melting and annealing at 900 °C. Its crystal structure was determined from X-ray single crystal diffraction data (YMo3B7-type structure, space group Pnma; a = 1.10310(8) nm, b = 0.30995(2) nm, c = 1.2792(1) nm, RF2 = 0.0205). The structure is composed of boron filled trigonal prisms as well as unfilled tetrahedra and tetragonal pyramids formed by metal atoms. With respect to boron atoms aggregation, it exhibits a well-developed two-dimensional boron network revealing infinite bands of edge linked boron hexagons. The relationship with the members of the structural series within the V-B system: VnBn+1 = (n-1)VB (CrB-type) + VB2 (AlB2-type) (n = 1, 2, 3, 5) is discussed. Specific heat, magnetic susceptibility and electrical resistivity measurements characterize UMo3B7 as a spin fluctuating system.

Skutterudites are considered to be good thermoelectrics with high figures of merit, ZT. After synthesis, electrodes are created by grinding and hot pressing the resulting powder. Materials such as NdFe4Sb12 exhibit a significantly greater figure of merit, ZT, (about 43%) when it is ball milled to produce fine powders (inital powder 160 nm; after hot pressing ∼330 nm). This enhancement is typically attributed to the reduced particle size, which in turn decreases the mean free path of phonons, and consequently decreases the thermal conductivity. This work aims to investigate whether there is any damage to the crystal structure in the particles formed by ball milling, which could also affect its thermal conductivity. Using a temperature dependent, Extended X-ray Absorption Fine Structure (EXAFS) analysis of a hand ground and ball milled sample of the skutterudite NdyFe4Sb12, we have determined that ball milling causes no significant damage to the local structure around any site. Consequently further improvements in ZT may be possible with smaller particles.

Cu2Ge1-xInxSe3 (x = 0, 0.05, 0.1, 0.15) compounds were prepared by a solid state synthesis. The powder X-ray diffraction pattern of the undoped sample revealed an orthorhombic phase. The increase in doping content led to the appearance of additional peaks related to cubic and tetragonal phases along with the orthorhombic phase. This may be due to the substitutional disorder created by Indium doping. Scanning Electron Microscopy micrographs showed a continuous large grain growth with low porosity, which confirms the compaction of the samples after hot pressing. Elemental composition was measured by Electron Probe Micro Analyzer and confirmed that all the samples are in the stoichiometric ratio. The electrical resistivity (rho) systematically decreased with an increase in doping content, but increased with the temperature indicating a heavily doped semiconductor behavior. A positive Seebeck coefficient (S) of all samples in the entire temperature range reveal holes as predominant charge carriers. Positive Hall coefficient data for the compounds Cu2InxGe1-xSe3 (x = 0, 0.1) at room temperature (RT) confirm the sign of Seebeck coefficient. The trend of rho as a function of doping content for the samples Cu2InxGe1-xSe3 with x = 0 and 0.1 agrees with the measured charge carrier density calculated from Hall data. The total thermal conductivity increased with rising doping content, attributed to an increase in carrier thermal conductivity. The thermal conductivity revealed 1/T dependence, which indicates the dominance of Umklapp phonon scattering at elevated temperatures. The maximum thermoelectric figure of merit (ZT) = 0.23 at 723 K was obtained for Cu2In0.1Ge0.9Se3. (C)2014 Elsevier Ltd. All rights reserved.

The phase relations in the Ge-rich corner of the Sr–Ni–Ge system are investigated at 700 °C by X-ray powder diffraction and electron probe microanalysis. The formation of one ternary compound, SrNiGe 3 , crystallizing in the BaNiSn 3 -structure type, is observed. No clathrate-I compound was detected in as cast or annealed state. Theoretical calculations based on density functional theory (DFT) were performed to gain information on the heat of formation for three different clathrate-I compounds, Sr 8 T 6 Ge 40 (T = Ni, Cu, Zn) and relevant other Ge-rich ternary compounds, namely SrT 2 Ge 2 (T = Cu, Zn) and SrNiGe 3 . Based on these data and the phase relations at 700 °C energies of formation of the clathrate-I phases were calculated and predictions of the phase equilibria at 0 K are provided.

We report on the formation, physical-chemical, as well as elastic and mechanical properties of the novel Half-Heusler (HH) compound TaFeSb that forms during a solid-state reaction from TaSb2 and TaFe2 in the temperature range between 800 and 850 °C. TaFeSb behaves as a semiconductor, and changes the conductivity type either on temperature or composition. Transport properties of TaFeSb and Ta1-xTixFeSb (0 ≤ x ≤ 0.11) were measured in the temperature range from 4.2 to 823 K, and the effect of titanium on thermoelectric and mechanical properties of Ta1-xTixFeSb was investigated. The Ta/Ti substitution results in a significant increase of the thermoelectric power factor to exciting values of above 6 mW/m⋅K2. In combination with a suppressed phonon thermal conductivity, due to a unique role of Ti, an enhanced figure of merit, ZT900K =1.0 (for Ta0.94Ti0.06FeSb) is obtained, close to the highest values reported for Hf-free p-type HH-systems. In addition, experimental results obtained in this study are discussed and analyzed in the context of ab-initio Density Functional Theory (DFT) calculations.

Two novel compounds, EuRh3Ge7 and EuIr3Ge7, have been synthesized by arc melting of the elements and subsequent annealing at 800 °C. X-ray structure analyses confirmed for both compounds isotypism with the crystal structure of the ScRh3Si7-type ( R 3 ¯ c ) : SC-data for EuRh3Ge7 (a = 0.78918(2), c = 2.07179(5) nm, RF = 0.0130) and Rietveld powder data for EuIr3Ge7 (a = 0.788399(5), c = 2.07583 (2) nm, RF = 0.0501). Magnetization, heat capacity, thermal expansion and electrical resistivity at various magnetic fields were measured revealing second order phase transitions at 20 K for EuRh3Ge7, and 87 K for EuIr3Ge7, respectively. While this transition is clearly antiferromagnetic in the case of EuRh3Ge7, the nature of this transition remains unclear for EuIr3Ge7. The evaluation of magnetic susceptibility as well as heat capacity data reveals an intermediate valence state of Eu-ions in both compounds.

Phase relations in the {Si,Ge}-rich part of the three systems Ba–Ir–Ge and Ba–{Rh,Ir}–Si were investigated by means of X-ray single crystal (SC) and powder diffraction (XPD), EPMA and DTA measurements. For Ba–Ir–Ge, partial isothermal sections were constructed at 800 °C and 700 °C. The clathrate solid solution extends from binary Ba8Ge43□3 to Ba8Ir0.4Ge43□2.6 with a slightly enlarged lattice parameter a = 2.13402(2) nm ( I a 3 ¯ d , Ba8Ge43□3-type). Two new ternary stoichiometric compounds were found and their crystal structures were determined by X-ray diffraction: τ1-BaIr2Ge7 (Pmna, own type, a = 3.7782(1), b = 0.64099(2), c = 0.64401(2) nm; RF = 0.0331, SC-data) and τ2-Ba3Ir4Ge16 (P4/mmm, Ba3Rh4Ge16-type, a = 0.653948(6), c = 2.22849(3) nm; RF = 0.0388, XPD-Rietveld analysis). The isothermal sections of the Ba–{Rh,Ir}–Si systems were investigated at 950 °C. Whereas in the Ba–Rh–Si system a clathrate-type I solid solution κI-Ba8RhxSi46−x extends within 2.6 ≤ x ≤ 2.9, the corresponding clathrate-I phase in the Ba–Ir–Si system, κI-Ba8Ir1.8Si44.2 ( P m 3 ¯ n , Na4Si23-type, a = 1.0346(1) nm), is not stable at this temperature, but was clearly observed in the as cast state. The analysis of temperature dependent atomic displacement parameters (100–300 K) of guest and framework atoms for κI-Ba8IrxGe46−x−y□y revealed Debye (θD) and Einstein (θE) temperatures of θD = 244 K, θE,11 = 85 K, and θE,22,33 = 64 K proving the rattling nature of the Ba-atoms in the large Ge-based tetrakaidecahedral cages. A similar analysis for κI-Ba8RhxSi46−x yields significantly higher Debye and Einstein temperatures, θD = 508 K, θE,11 = 115 K, θE,22,33 = 99 K, i.e. a tight bonding of Ba-atoms to the smaller Si-based cages. This behavior is further reflected by the pronounced difference in the thermal expansion coefficients: α100–300 K = 13.7 × 10−6 K−1 (κI-Ba8IrxGe46−x−y□y) and α100–300 K = 7.3 × 10−6 K−1 (κI-Ba8RhxSi46−x).

The structural phase transition in half-Heusler – Heusler stannides ZrNiSn–ZrNi2Sn and HfNiSn–HfNi2Sn was studied using XRD and EPM analyses, electrical and magnetic properties measurement. The influence of the disordering and defects in crystal structure on the physical properties was analyzed. The performed electronic structure calculations are in good agreement with electrical and magnetic behaviors and allowed to explain limited solubility in these phases.

The crystal structures of a series of compounds have been solved from X-ray single crystal diffractometry: Mo(CuxAl1−x)6Al4 (x = 0.416), MoNi2−xAl8+x (x = 0.165), WNi2−x−y□yAl8+x−z□z, (x = 0.162, y = 0.015, z = 0.010) and ReNi2Al8−x (x = 0.033). Mo(CuxAl1−x)6Al4 crystallizes with hexagonal symmetry and lattice parameters, a = 0.50030(1) and c = 0.76279(3) nm; space group P6/mmm, No. 191, as an unfilled structure variant of the MgFe6Ge6-type with a vacant 2c site. This structure is made up of alternate blocks of (unfilled) CaCu5 and Zr4Al3 in a ratio of 1:1. A superstructure of this compound (a = a0√3, c = 2c0) was solved with a Rietveld refinement of X-ray powder diffraction data as a fully ordered structure with formula MoCu2Al8−x. It adopts space group P6, No. 168 with lattice parameters a = 0.86769(1), c = 1.52149(2) nm. A Barnighausen tree was derived reflecting the close relation among these two structure types. The compounds {Mo,W,Re}Ni2−xAl8+x crystallize in a novel structure type (ReNi2Al8−x–type; space group Pbam, No. 55). Whereas ReNi2Al8−x is a fully ordered structure with some defects in the two 4g sites occupied by Al, Ni + Al atoms randomly share one crystallographic site in isotypic {Mo,W}Ni2−xAl8+x, which causes splitting of three neighboring Al-sites. Lattice parameters and residual values of the refinements were: a = 1.00320(2), b = 1.51258(3), c = 0.83890(2) nm; RF2 = 0.017 for the Re-compound, a = 1.00664(2), b = 1.53108(2), c = 0.85205(2) nm, RF2 = 0.035 for the Mo-compound and a = 1.00683(2), b = 1.53236(3), c = 0.85232(2) nm; RF2 = 0.024 for the W-compound. As the ReNi2Al8−x-type structure is another superstructure of the hexagonal Mo(CuxAl1−x)6Al4 type, a Barnighausen tree was derived, which documents the close relation among these two structure types. Phase equilibria in the Al-rich corner of W–Ni–Al at 930 °C is also reported showing the presence of a WNi2Al8 phase. Precise atom positions have been derived from X-ray single crystal data for binary Ni2Al3 confirming the space group P 3 ¯ m1 (No. 164). Atom positions and lattice parameters (a = 0.40533(2), c = 0.49038(3) nm) are very close to the parameters hitherto reported in the literature from X-ray powder diffraction data. Vicker’s hardness was measured for all isotypic compounds {Mo,W,Re}Ni2Al8−x revealing a hardness of HV = 965 ± 25 MPa for the Re-containing material, which is higher by about 100 MPa in comparison to the Mo and W containing phases.

The crystal structure of the compound in the Al-rich region of the Ti–Ni–Al system, τ5–TiNi2−xAl5, x = 0.48, has been derived from X-ray powder and single crystal, neutron powder and electron diffraction (space group I4/mmm, a = 0.3984(2) nm, c = 1.4073(3) nm, RF2 = 0.0133). Titanium atoms were unambiguously located from neutron powder data. τ5 is isotypic with the crystal structure of ZrNi2Al5. Detailed transmission electron microscopy (TEM) in several crystallographic directions confirmed the lattice parameters and crystal symmetry. Although occupancy of Ni in the 4e site revealed a defect (occ. = 0.76), no significant homogeneity region was observed for this phase at 1020°C. Rietveld analyses of X-ray powder diffraction data for the Zr- and Hf-homologues confirmed for both compounds isotypism and revealed defects in the Ni sites and to a lesser extent also in the Al sites: ZrNi2−xAl5−y, x = 0.4, y = 0.4 and HfNi2−xAl5−y, x = 0.5, y = 0.2. The crystallographic relations among the structure types of Cu, TiAl3, ZrNi2Al5 and Zr(Ni,Ga)7 have been defined in terms of a Barnighausen scheme.

This work evaluates the influence of single, double and triple filling of didymium, Ca and Ba in Fe 4 Sb 12 as well as in Fe 3 CoSb 12 on the thermoelectric performance. Various filling levels, as well as various preparation methods and nanostructuring were used to improve the thermoelectric performance. It is shown that samples prepared via ball milling have a higher ZT (ZT = 1.1) than their hand milled counterparts (ZT ≈ 0.8). Co/Fe-substituted samples have ZT > 1.2 i.e. 25% higher than samples without Co, an average ZT up to 0.93 and an efficiency up to 14% for the temperature gradient of 300–800 K. With this good thermoelectric performance in such a wide temperature range these materials are hitherto the best p-type skutterudites for thermoelectric devices.

Phase equilibria within the isothermal section of the ternary system Nd–Fe–Sb were derived at 800 °C by using X-ray powder diffraction, light optical microscopy and electron probe microanalysis. Crystal structures of the ternary compounds Nd2Fe7−xSb6−y (τ2-orthorhombic), Nd2Fe5−xSb10−y (τ2-tetragonal) Nd3Fe3Sb7 (τ3) and NdFeSb3 (τ4) were determined by single crystal X-ray diffraction and by Rietveld X-ray powder data refinement. The phase τ2 was found to exhibit two modifications, orthorhombic (Nd2Fe7−xSb6−y-type, S.G. Immm, a = 0.42632(6) nm, b = 0.43098(7) nm, c = 2.5823(3) nm) and tetragonal (La2Fe5−xSb10−y-type, S.G. I4/mmm, a = 0.42897(2) nm, c = 2.5693(4) nm). Tetragonal and orthorhombic modifications form a crystallographic group–subgroup relation and are closely related to the Zr3Cu4Si6-type. Nd3Fe3Sb7 (τ3) crystallizes with a unique structure type (S.G. P63/m, a = 1.31808(3) nm, c = 0.41819(3) nm), which is isopointal to the Cu10Sb3-type. NdFeSb3 (τ4) adopts the LaPdSb3-type. Physical properties comprising magnetization, resistivity and specific heat were measured for RE2Fe5−xSb10−y (RE = Ce, Nd), NdFeSb3 and Nd3Fe3Sb7. NdFeSb3 orders antiferromagnetically below 3.0 K due to the presence of magnetic moments on Nd sites. For the other compounds a more complex magnetic behaviour is observed at low temperatures that may be related to the contributions coming from both the rare earth and iron sublattices.

The influence of double, triple and multi-filling of didymium, Ca, Ba, Sr and Yb in Fe 3 CoSb 12 on the thermoelectric performance was investigated. Ball-milling followed by hot pressing was used for sample preparation to gain dense and nanostructured samples. Almost all of the samples studied in this work have a ZT higher than 1, some even reach ZT > 1.2 at 700 K or at 800 K and an average ZT up to 1.0 in the temperature range from 300 K to 800 K. Thermal expansion, hardness and the elastic moduli were investigated exemplarily for two alloys with ZT > 1.2. With these results we can claim to have very promising p-type skutterudites for thermoelectric devices.

Phase relations in the system Ce–Zn–Si have been determined for the isothermal section at 800 °C using electron microprobe analysis and X-ray powder diffraction. Phase equilibria are characterized by extended solid solutions along the section CeSi 2 –CeZn 2 , which form a structurally related sequence of structure types: Ce(Zn x Si 1− x ) 2 (αThSi 2 -type, 0 ≤ x ≤ 0.32), τ 2 -Ce(Zn x Si 1− x ) 2 (AlΒ 2 -type, 0.36 ≤ x ≤ 0.76) and Ce(Zn 1− x Si x ) 2 (CeCu 2 -type, 0 ≤ x ≤ 0.18). Silicon stabilizes the ternary compound τ 1 -Ce 7 Zn 21 (Zn 1− x Si x ) 2 , (0.28 ≤ x ≤ 0.98) for which the crystal structure was derived from X-ray diffraction data for a single crystal of Ce 7 Zn 21 (Zn 1− x Si x ) 2 ( x = 0.28; unique structure type, Pbam ; a = 1.55722(3) nm, b = 1.71942(3) nm, c = 0.44772(1) nm; R F = 0.029). The structure of Ce 7 Zn 21 (Zn 1− x Si x ) 2 can be considered as an arrangement of slightly distorted building blocks of Cu 3 Au-type (Zn[Ce 4 Zn 8 ]) and BaAl 4 -type (Ce[Ce 2 Zn 10 M 4 ] and Ce[Ce 2 Zn 13 M 2 ]), arranged in form of a zig-zag string of face-sharing units…Cu 3 Au–BaAl 4 –BaAl 4 –BaAl 4 –Cu 3 Au… running parallel to the b -axis. Structural analyses proved isotypism for homologous La 7 Zn 21 (Zn 1− x Si x ) 2 ( x = 0.27), Ce 7 Zn 21 (Zn 1− x Si x ) 2 -type, Pbam ; a = 1.56817(2) nm, b = 1.72923(3) nm, 0.450887(7) nm; X-ray single crystal data and La(Zn x Si 1− x ) 2 , ( x = 0.56, AlΒ 2 -type, P6/ mmm , a = 0.42775(4) nm, c = 0.42832(4) nm; X-ray powder data). The structure types of the ternary compounds τ 3 -Ce(Zn x Si 1− x ), 0.17 ≤ x ≤ 0.23, and τ 4 -Ce 40 Zn 37 Si 23 (in at.%) are still unknown.

Two tau-borides, τ-(Fe0.54Ir0.46)20Fe3B6 and τ-(Co0.64Ir0.36)21Co0.16B4B6 were studied by X-ray powder and single crystal diffraction with respect to precise atom site distribution and metal atom ordering. X-ray structure determination for a single crystal of τ-(Fe0.54Ir0.46)20Fe3B6 revealed isotypism with a partially ordered Cr23C6-type (space group Fm 3 ¯ m, a = 1.11020 nm) but with a high degree of random replacement of Fe/Ir atoms in sites 48h and 32f. X-ray single crystal data for τ-(Co0.64Ir0.36)21Co0.16B4B6 showed a novel low-symmetry structure variant of tau-borides characterized by a noncentrosymmetric distribution of boron tetrahedra and a defect Co-site (space group F 4 ¯ 3m as a translationengleiche, nonisomorphic maximal subgroup of index 2 of Fm 3 ¯ m, a = 1.09359 nm). The crystal structures of both τ-phases are described with nested polyhedra geometrically related to the α-Mn structure. Stability ranges and various structural arrangements of (MM')23B6 phases are discussed. The crystal structures of (Fe1−xIrx)3B (x = 0.24; X-ray single crystal data; Fe3C-type, space group Pnma, a = 0.5430(2), b = 0.6958(2) nm, c = 0.4654(2) nm), and of isotypic (Fe1−xRhx)3B (XPD Rietveld refinement, x = 0.25, space group Pnma, a = 0.54560(1) nm, b = 0.69552(1) nm, c = 0.46169(1) nm) show both a high degree of randomness in the metal sites.

Calcium and Barium were combined as fillers in the ternary skutterudite Co 4− x Ni x Sb 12 in order to improve the thermoelectric properties. In addition cobalt by nickel substitution was used to enhance the electrical conductivity. The chemical composition has been determined from combined data of X-ray powder diffraction and electron microprobe analysis (EMPA). Thermoelectric properties have been characterized by measurements of electrical resistivity, thermopower and thermal conductivity in the temperature range from 4.3 to 800 K. Measurements of the charge carrier density n and Hall coefficient indicate n -type transport with n = 2.5 × 10 19 cm −3 . This results in a strongly enhanced Seebeck coefficient of S = −200 μV/K as well as in a figure of merit ZT = 1.2 at 775 K. Thermal conductivity and electrical resistivity have been analysed for their relevant transport mechanics. Density and micro-hardness have been measured.

In order to improve the thermoelectric properties via efficient phonon scattering Didymium (DD), a mixture of Pr and Nd, was used as a new filler in ternary skutterudites (Fe 1− x Co x ) 4 Sb 12 and (Fe 1− x Ni x ) 4 Sb 12 . DD-filling levels have been determined from combined data of X-ray powder diffraction and electron microprobe analyses (EMPA). Thermoelectric properties have been characterized by measurements of electrical resistivity, thermopower and thermal conductivity in the temperature range from 4.3 to 800 K. The effect of nanostructuring in DD 0.4 Fe 2 Co 2 Sb 12 was elucidated from a comparison of both micro-powder (ground in a WC-mortar, ∼10 μm) and nano-powder (ball-milled, ∼150 nm), both hot pressed under identical conditions. The figure of merit ZT depends on the Fe/Co and Ni/Co-contents, respectively, reaching ZT > 1. At low temperatures the nanostructured material exhibits a higher thermoelectric figure of merit. The Vickers hardness was measured for all samples being higher for the nanostructured material.

Two four-phase reactions of transition type in the Ti–Ni–Al system were studied on several alloys, which were annealed at carefully set temperatures and quenched. The phase constitution was established by XRD and EPMA analyses. Due to sluggish reaction kinetics, the transition temperatures were defined by annealing and quenching techniques as no DTA signals could be received. For the reaction NiAl + TiNiAl ⇔ TiNiAl 2 + TiNi 2 Al, the transition temperature was found to be 925 °C ± 15 °C and for the reaction TiNiAl + Ti 3 NiAl 8 ⇔ TiAl 2 + TiNiAl 2 , the transition temperature was found to be 990 °C ± 15 °C. Furthermore we confirmed the three-phase field TiNi 2 Al + Ti 3 Al + Laves phase (TiNiAl), as reported at 900 °C by Huneau et al. in 1999.

BaCo 4.7 Ge 9 (BaCo 5− x Ge 9 , x = 0.29) is a novel ternary compound which forms incongruently from the melt and crystallizes in a unique structure type (space group Pnma ; a = 1.39910(2), b = 0.40218(2), c = 1.69882(2) nm, Z = 4). Isotypic compounds were found with SrCo 4.7 Ge 9 ( a = 1.39389(8), b = 0.39665(1), c = 1.67860(9) nm) and EuCo 4.7 Ge 9 ( a = 1.3910(1), b = 0.39425(2), c = 1.6741(2) nm). Physical properties (electrical resistivity, specific heat, magnetic susceptibility) were studied for BaCo 4.7 Ge 9 and EuCo 4.7 Ge 9 . BaCo 4.7 Ge 9 shows metallic behaviour but neither a superconducting nor a magnetic phase transition was observed for temperatures as low as T = 2 K. Magnetic susceptibility and specific heat data of EuCo 4.7 Ge 9 , evidence the onset of antiferromagnetic order at 18.5 K. Both magnetic ordering and the effective magnetic moment derived verify the Eu 2+ state with a total angular momentum j = 7/2.

Formation and crystal structure of Laves phases in the systems Ti–{Pd,Pt}–Al were investigated employing XPD (X-ray powder diffraction), XSCD (X-ray single crystal diffraction) and EPMA (electron probe microanalysis) techniques. Laves phases with MgZn 2 type (space group: P 6 3 / mmc ) and its variant with the Nb(Ir,Al) 2 -type ( a √3 × a √3 × c supercell of MgZn 2 -type, space group: P 6 3 / mcm ) were found in both systems. Formation of a particular structure type is dependent on temperature and composition. Laves phases with the Nb(Ir,Al) 2 -type form around 25 at.% of Pd,Pt at 950 °C. The MgZn 2 -type Laves phase Ti(Pt,Al) 2 was not observed at 950 °C, but it forms in as-cast alloys at a slightly lower Pt content, Ti 37.8 Pt 19.0 Al 43.2 . In the Ti–Pd–Al system at 950 °C the MgZn 2 -type phase exists at the Pd-poor side of the homogeneity region whilst the Nb(Ir,Al) 2 -type phase is slightly richer in Pd. Phase relations associated with the Ti–Pt–Al Laves phase were established at 950 °C and reveal a new compound TiPtAl that derives from hexagonal ZrBeSi-type (ordered Ni 2 In-type, a = 0.43925(4) nm, c = 0.54844(5); space group P 6 3 / mmc ; R F2 = 0.015 from single crystal data). Atom distribution in the compound shows a slight deviation from full atom order Ti(Pt 0.97 Al 0.03 )(Al 0.98 Pt 0.02 ).

The crystal structure of the ternary Laves phase ZrTiCu 2 with unusual stoichiometry has been determined from combined refinement of X-ray powder, X-ray single crystal and neutron powder intensity data. The derived structure is of type MgZn 2 (space group P 6 3 / mmc ) with lattice parameters a = 0.51491(3) nm, c = 0.82421(8) nm. Crystal symmetry and composition reveal a high degree of atomic disorder, because Ti and Zr atoms share the 4f sites, whereas Ti and Cu atoms are found at the 6h sites. The 2a sites, however, are exclusively occupied by Cu. Lattice parameters for alloys Zr 1− x Ti 1− x Cu 2+2 x (annealed at 800 °C) as a function of the concentration of Cu for a constant ratio of Zr/Ti = 1 vary in a nonlinear way, which is consistent with the described complex atomic substitution mechanism. At a load of 2 N the micro-hardness was measured to be 7.5 ± 0.3 GPa, which is significantly larger than for most of the binary Ti–Cu or Zr–Cu phases. By a density functional theory ab initio approach the site preferences of Zr, Ti and Cu were calculated indicating that a random mixture of Ti and Cu atoms at the 6h lattice sites is a key factor to stabilize the proposed structure, which is unique for a Laves phase. Lattice parameters, elastic constants and shear moduli for polycrystalline ZrTiCu 2 were also derived. The Vickers hardness of 6.2 GPa was estimated by applying a correlation between shear modulus and hardness. Data as calculated by the ab initio approach are in good agreement with the experimental findings.

Alloys with composition Ti(Mn1−xAlx)2 (xAl = 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.55, 0.6, and 0.67) were studied by X-ray powder diffraction (XPD), optical microscopy, electron probe microanalysis (EPMA) and electronic density functional theory. EPMA and XPD defined an extensive solid solution of up to xAl = 0.64 at 900 °C. Structure determination from Rietveld refinements of X-ray powder diffraction data for Ti(Mn1−xAlx)2 (0 ≤ xAl ≤ 0.60) and from single crystal X-ray counter data for xAl = 0.2 revealed a C14-MgZn2-type Laves phase, where Ti atoms fully occupy the 4f sites, whereas Mn and Al atoms share the 6h and 2a sites in various ratios. By means of density functional theory, the structural stabilities and site preferences of nine ternary compositions, Ti(Mn1−xAlx)2 (xAl = 0, 0.125, 0.25, 0.375, 0.500, 0.625, 0.750, 0.875, 1.00), were further calculated for a large number of structural models. The derived Al content dependent structural stabilities, lattice parameters, and site occupations as well as enthalpies of formations are in nice agreement with experimental results. Based on the calculated data, we analyzed the occupation behaviour of Al atoms substituting for Mn atoms at the 2a and 6h sites: up to concentrations xAl

The binary phase diagrams {V,Nb,Ta}-Sb below 1450 °C were studied by means of XRPD, EPMA, and DTA measurements. In the V-Sb system, five stable binary phases were observed in this investigation: V3+xSb1−x, lT-V3Sb2, hT-V2−xSb, V7.46Sb9, V1−xSb2. The V-Sb phase diagram is characterized by two degenerate eutectic reactions: L↔V3+xSb1−x+(V) (T > 1450 °C at 18.1 at.% Sb) and L↔V1−xSb2+(Sb) (T=(621 ± 5)°C at ∼99 at.% Sb), three peritectic reactions: L + V3+xSb1−x↔hT-V2−xSb (T=(1230 ± 10)°C at ∼42 at.% Sb), L + hT-V2−xSb↔V7.46Sb9 (T=(920 ± 10)°C at ∼87 at.% Sb), and L + V7.46Sb9↔V1−xSb2 (T=(869 ± 5)°C at ∼88 at.% Sb), a peritectoid reaction: V3+xSb1−x + hT-V2−xSb↔lT-V3Sb2 at (875 ± 25)°C, a eutectoid reaction: hT-V2−xSb↔lT-V3Sb2+V7.46Sb9 at (815 ± 15)°C and congruent melting of V3+xSb1−x (T > 1450 °C). An X-ray single crystal study of V5Sb4C1−x proved the existence of interstitial elements in the octahedral voids of a partially filled Ti5Te4-type structure (x∼0.5; RF2 = 0.0101), therefore this phase (earlier labeled “V5Sb4”) was excluded from the binary equilibrium phase diagram. V5Sb4C1−x is the first representative of a filled Ti5Te4-type structure. A re-investigation of the Nb-Sb system removed the contradiction between the hitherto reported phase diagrams and confirmed the version derived by Melnyk et al. (see ref. [1]). Three binary phases exist in the Ta-Sb system: Ta3+xSb1−x, Ta5Sb4, TaSb2. Due to instrumental limits (≤1450 °C), only the peritectic reaction of TaSb2: L + Ta5Sb4 ↔ TaSb2 ((1080 ± 10)°C at ∼92 at.% Sb) and a degenerate Sb-rich eutectic reaction (L↔TaSb2+(Sb); (622 ± 5)°C; ∼99 at.% Sb) have been determined. Physical properties (mechanical and transport properties) of binary di-antimonides were investigated with respect to a potential use of these metals either as diffusion barriers or electrodes for thermoelectric devices based on skutterudites. All group-V metal di-antimonides have low metallic-type resistivity and relatively high thermal conductivity. Magnetic field has little influence on the resistivity of V1−xSb2 at low temperature, while on {Nb,Ta}Sb2 it increases the resistivity, especially on NbSb2. The coefficient of thermal expansion (CTE) decreases from V1−xSb2 to TaSb2, particularly the CTE value of NbSb2 is in the range of average n-type filled skutterudites. In contrast to the CTE value, elastic moduli increase from V1−xSb2 to TaSb2. The value for V1−xSb2 is in the range of Sb-based skutterudites, whereas the values for {Nb,Ta}Sb2 are significantly higher.

The extended ternary solid solution for the G-phase in the Ti–Co–Al system, Ti6+xCo7+yAl17−x−y, has been investigated by neutron powder diffraction of the as-cast alloys in order to elucidate the precise atom-site distribution. A concentration-dependent structural transformation has been observed between two crystal structures. Whilst the aluminium-rich G-phase crystallizes with the centrosymmetric, filled variant of the Th6Mn23-type (SG F m 3 ¯ m ), Ti-rich alloys adopt a new non-centrosymmetric structure (SG F 4 ¯ 3 m ) for compositions with more than 34 at.% Ti. Three states of high atomic order were denoted for the G-phase. The unit cells containing 24Ti–28Co–68Al atoms (x=0, y=0, SG F m 3 ¯ m ) and 56Ti–32Co–32Al atoms (x=8, y=1, SG F 4 ¯ 3 m ) represent fully ordered structures. The unit cell containing 40Ti–30Co–50Al atoms (x=4, y=0.5, SG F 4 ¯ 3 m ) shows partial atom order with a statistical distribution of atoms in the 4b site, whilst all other atom sites are completely ordered. A corresponding transition from centrosymmetric SG F m 3 ¯ m to non-centrosymmetric SG F 4 ¯ 3 m was furthermore established in the Ti–Fe–Al ternary system. Al-rich compositions of the G-phase crystallise in the filled variant of the Th6Mn23-type (SG F m 3 ¯ m ). The crystal structure of the Ti-rich G-phase adopts the non-centrosymmetric structure (SG F 4 ¯ 3 m ).

In order to establish site preference in the G-phases with Ti/Al substitution, the extensive range of the ternary solid solution for the G-phase in the Ti–Co–Al system has been investigated by X-ray powder/single crystal and neutron powder diffraction. A filled variant of the Th6Mn23 type (space group F m 3 ¯ m ) was confirmed for the Al-rich single-phase region, whereas a novel structure variant with space group F 4 ¯ 3 m was established for the Ti-rich side of the G-phase region. Precise atom site occupation has been established for both structure types throughout the full extension of the G-phase homogeneity region.

Magnetic and electrical transport properties of cubic phases RE 9 Ni 24 Sn 49 (RE=Y, Ce, Pr, Sm and Tb) have been investigated by means of magnetic susceptibility, magnetisation, electrical resistivity and Seebeck effect measurements. The Ce-, Pr- and Tb-based compounds order antiferromagnetically at T N =3.1, 4.5 and 4.2 K, respectively, Sm 9 Ni 24 Sn 49 remains paramagnetic down to the lowest temperature studied, while Y 9 Ni 24 Sn 49 is a weak Pauli paramagnet. All the materials studied exhibit metallic character of their electrical conductivity and thermoelectric power.

Ternary compounds formed by Ti and Al with transition metals of the eighth group have been investigated by X-ray powder/single crystal and neutron powder diffraction. Two series of compounds have been identified crystallizing either with a new filled variant of the Th6Mn23-type (G-phase, space group Fm 3 m ) or with the AuCu3-type (space group Pm 3 m ). Structure refinements of the G-phases reveal for the chemical formula TiMAl∼2 (Ti32M22Al46; M=Ru, Os, Rh, Ir; and Ti25M25Al50; M=Pd, Pt,) a rather high degree of atom order with a random distribution of Ti/Al in only the 4b(M2), 24e(M4) and 32f(M6) sites: M-atoms are located in the 4a(M1) and 24d(M3) sites, whereas the 32f(M5) sites accept only Al-atoms. Ti-atoms prefer the 24e(M4) site. General details of site preference have been determined and are discussed. No hydrogen was absorbed by Ti32Ru22Al46, Ti32Rh22Al46 and Ti32Ir22Al46 at room temperature under an H2 pressure of 5 MPa. It was demonstrated that refinement of neutron powder diffraction data allows precise evaluation of symmetry and atom site occupation for the AuCu3-type phases, Ti25.5Ni8.5Al66 and Ti26Pt6Al68: titanium atoms were found to be located only in the 1a site whilst Ni- and Pt-atoms substitute for aluminium in the 3c sublattice. The Re-, Os-, and Pt-based compounds show an equal average number of electrons in both crystallographic sites, thus reflections with mixed indices are vanishing in the X-ray profiles masking the AuCu3-type by the appearance of simple Cu-type X-ray patterns. Phase equilibria have been derived at 950 °C for the Ti–Ir–Al partial system αTi3Al–TiAl3–G-phase.

A detailed investigation of the phase relations in the Ti–Si–B system involving as-cast and heat-treated samples that were characterized via X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and Wavelength Dispersive Spectroscopy (WDS) microprobe analysis has shown the existence of a new ternary phase of composition Ti6Si2B. Rietveld refinement of X-ray powder intensity data revealed a hexagonal crystal structure, with lattice parameters a=0.68015 nm and c=0.33377 nm and proved isotypism with the Ni6Si2B-phase (Fe2P-type structure, Zr6CoGa2 ternary variant). The Ti6Si2B-phase forms from the liquid through the peritectic reaction: L+TiB+Ti5Si3⇔Ti6Si2B. At 1200 °C it forms narrow two-phase fields with Tiss, Ti5Si3 and TiB.

In the paper of J.H. Zhu et al. it is concluded that Miedema's approach is capable of predicting enthalpies of formation of transition metal lanthanide Laves phase systems. However, a comparative analysis of these data with experimental data clearly shows that discrepancies of the order of 20–80 kJ/mol are common. As an alternative route, ab initio calculations based on density-functional theory are suggested to provide accurate enthalpies of formation for Laves phases. Further data on enthalpies of formation of some Laves phases are added.

Phase equilibria in the Ce–Pd–In system at 750 °C were investigated in the whole concentration range not including the Pd-rich region, employing optical microscopy, microprobe analysis and X-ray diffraction. Besides the known intermetallic compounds (CePdIn, CePdIn2, CePd2In, Ce8Pd24In and the double-branched solid solutions Ce1.95Pd2+2xIn1−x and Ce2+xPd1.85In1−x), eight novel ternary compounds were revealed in the system. Furthermore, Pd/In solubilities were found in some of the novel ternary compounds and in the equiatomic compound. The complex phase equilibria resulting from the large number of binary and ternary compounds were determined.

Phase equilibria in Tb–Pd–In and Ho–Pd–In systems at 750 °C were investigated in the region near the composition of 50 at.% Pd employing optical microscopy (LOM), scanning electron microscopy (SEM), electron probe microanalysis (EPMA) and X-ray diffraction (XRD). The phase equilibria of the systems exhibit strong similarities, showing, in addition to R 2 Pd 2 In-based solid solutions, large substitutional R/In solid solutions starting from the PdIn binary compound. Selected alloys of other R–Pd–In (R=Pr, …, Er) systems were also investigated. A comparison was made between these systems and Ce–Pd–In.

The ternary compounds Yb2T2In (T=Cu, Pd and Au) have been synthesized. The indides Yb2Au2In and Yb2Pd2In crystallize in the Mo2FeB2 structure type, while Yb2Cu2In proved to be isotypic with the W2CoB2 structure. Magnetic, resistivity and specific heat measurements revealed no magnetic order for any of the compounds but, while in Yb2Cu2In and Yb2Au2In the valence of Yb was observed to be ν=2, Yb2Pd2In exhibits intermediate valence behavior.

Phase relations in the ternary systems Ti–{Pd,Pt}–Al have been experimentally established for the partial isothermal sections at 950°C in the Pd/Pt-poor region (

International audience; Phase relations in the ternary system Al±Ni±Ti have been experimentally established for the isothermal section at 900°C for concentrations 0.1 4 x Al 4 0.7. The investigation is based on X-ray powder diffraction, metallography, SEM and EMPA-techniques on about 40 ternary alloys, prepared by argon-arc or vacuum-electron beam melting of proper elemental powder blends. The existence of four ternary compounds, t 1 to t 4 , is con®rmed, however, in contrast to earlier investigations at significantly different compositions and with different shape of the homogeneity regions. This is particularly true for the phase regions of t 3 -Al 3 NiTi 2 with the MgZn 2-type structure ranging from Al 30 Ni 28 Ti 42 (composition lowest in Al) to Al 50 Ni 16 Ti 34 (composition richest in Al) and for t 2 -Al 2 NiTi. The complex atom site substitution mechanism in t 3 changing from Ti/Al exchange at Al-poor compositions towards Ni/Al replacement for the Al-rich part was monitored in detail by quantitative X-ray powder diffraction techniques (Rietveld analyses). In contrast to earlier reports, claiming a two-phase region Ni{Al x Ti 1-x } 2 +t 3 , we observed two closely adjoining three-phase equilibria: a 2 -AlTi 3 +Ni{Al x Ti 1-x } 2 + t 4 -AlNi 2 Ti and a 2 -AlTi 3 +t 3 -Al 2 NiTi 2 +t 4 -AlNi 2 Ti. The earlier reported ``homogeneous phase at Al 23 Ni 26 Ti 51 0 '' was shown by high resolution microprobe and X-ray diffraction measurements to be an extremely fine-grained eutectic. The experimental results are in fine agreement with the thermodynamic calculation.

The effect of Nb, V, Cr and Mn on the lattice parameters of γ-TiAl and the site preference of these transition metals were studied based on first-principles supercell calculations of the electronic structure and total energy of ordered Ti n − 1 XAl n and Ti n XAl n − 1 compounds with X = Nb, V, Cr and Mn. For the calculation of optimized volumes by total energy minimization 4-, 8- and 32-atom cells were taken into account. Trends of c a changes in connection with the analysis of the electronic structure are derived from 4-atom supercell results in continuation of a previously published Part 1 of our investigations. We find that Mn has the strongest preference for Al sites because of strong stabilizing electronic structure effects. The substantial decreased value of the c a ratio found for the case of Mn substituting for Al is related to a bcc-like local arrangement of Ti around the Mn atom. This geometrical situation is accompanied by the formation of a deep pseudogap in the density of states. The Fermi energy falls precisely into this pseudogap which distinctly separates TiMn bonding and antibonding states. The site preference trend for the other substitutional compounds containing X = Nb, V, Cr are also discussed in combination with their corresponding density of states.

The alloying potential of nickel as a minor constituent has been investigated in TiAl-based intermetallics with respect to its constitutional ability to provide the necessary microstructures for higher ductility and low fracture toughness. Six alloys (Ti0.60Al0.40)1 − x1Nix1 and (Ti0.56Al0.44)1 − x2Nix2 with x1.2 = 0.01, 0.02 and 0.05 have been studied by means of X-ray diffraction, optical microscopy, EDS and WD-EMP analyses on alloys as-cast and annealed at 900 °C for 240 h under vacuum. The microstructures obtained confirm the phase triangulation at 900 °C near the TiAl boundary. The solubility limit of Ni in the α2-phase is at lower Al/Ni contents than hitherto shown. The Ti, Al-rich vertices of the three-phase equilibrium at 900 °C, α2-Ti3Al(Ni) + γ-TiAl(Ni) + τ2-TiNiAl2, were located at Ti51.5Ni0.7Al47.8 (in at.%) and at Ti62.0Ni0.9Al37.1 respectively. Thus TiAl-based alloys with nickel can only develop a lamellar α2 + γ structure for small amounts of Ni (less than 1 at.% Ni at 900 °C). To compare the effects of Mn and Ni additions on γ-TiAl, self-consistent FLAPW bandstructure calculations were performed for model compounds Ti2XAl and TiXAl2 (X = Mn, Ni). Lattice parameters were determined by minimizing the total energy. From the comparison of the formation energies of the compounds, we found that Ni prefers Ti sites whereas Mn preferably substitutes Al. Taking into account the site preference both ternary additions tend to reduce the c a ratio.

The Linear Muffin Tin Orbital Method was applied to calculate from first principles the electronic structure and total energies of L 1 0 ordered TiXAl 2 and Ti 2 XAl ( X = Nb , V , Cr , Mn ) compounds. Volumes and lattice parameters were determined by minimizing total energies. If X substitutes for Ti, the ratio c/a of the lattice parameters is always slightly larger than for the reference compound γ-TiAl. In the case of Al substitutions, c/a decreases substantially for all X. In general, the Ti-rich Ti 2 XAl compounds have larger unit cell volumes than the Al-rich counterparts. For any particular X, the interatomic distances between X and Ti appear to be rather constant, irrespective of the chosen substitution site. These two findings are sufficient to explain the substantial reduction of c/a for the Ti-rich (or Al-substituted) cases obtained by the calculations. From the formation energies, Δ E , the site preference was derived by E site = ΔE Al - rich − ΔE Ti - rich combining site preferences and c/a changes, we found that Nb and V prefer the Ti sites whereas Cr and Mn tend to substitute for Al. We conclude that X = Nb or V slightly increases c/a whereas X = Cr or Mn decreases this ratio. Although our calculations were made for 25.at% substitutions, many of our results are in agreement with experimental data for alloys with a small percentage of x.