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Electrical resistivity (4.2–800 K), Seebeck coefficient (300–800 K), specific heat (2–110 K), Vickers hardness, elastic moduli (RT) were defined for single-phase nonstoichiometric compounds: Ti2.13Ni2Sn0.87, Zr2.025Ni2Sn0.975, and Hf2.055Ni2Sn0.945.

Several n- and p-type Half-Heusler (HH) thermoelectric materials (Ti0.5Zr0.5NiSn-based and NbFeSb-based) have been processed by high-pressure torsion (HPT) to improve their thermoelectric performance via a drastic reduction towards ultra-low thermal conductivity. This reduction occurs due to grain refinement and a high concentration of deformation-induced defects, i.e. vacancies and dislocations as inferred by this severe plastic deformation and documented via SEM and TEM investigations. In most cases the figure of merit, ZT, and the thermo-electric conversion efficiency were enhanced up to η ∼ 10% for the thermally stable HPT-processed sample. Raman spectroscopy, backed by DFT calculations, proves that HPT induces a stiffening of the lattice and as a consequence, a blue-shift of the lattice vibrations occurs. Furthermore for all investigated specimens Vickers hardness values after HPT were significantly higher, whereas the change in the elastic moduli was less than 5% in comparison to the HP reference sample.

As various branches of industry are interested in good thermoelectric generators, there is a serious demand for an easy, fast, cheap and sustainable production route of excellent thermoelectric materials. In this paper we demonstrate how we could achieve a high-ZT (ZT ∼ 1.45 at 823 K) n-type bulk skutterudite, (Mm,Sm)yCo4Sb12, by processing the industrially produced raw powder using a modified high-pressure torsion (HPT) equipment at elevated temperature under inert gas. For this HPT processed sample as well as for the annealed one, structural properties, especially focused on grain size and dislocation density (backed up by electron probe microanalysis, transmission electron microscopy investigations as well as XPD profile analysis), physical properties (from 300 to 823 K and for the electrical resistivity in addition from 4.2 to 300 K) and mechanical properties (elastic moduli, hardness, fracture resistance) were measured and evaluated and compared with the values of a traditionally prepared bulk material, using hot pressing (HP). As a consequence of severe plastic deformation, we found a change from metallic to semiconducting behavior during measurement induced annealing of the HPT processed skutterudite, which could be explained via the change of lattice distortion and its influence on the band gap. A positive ZT net effect occurred because although the electrical resistivity was enhanced the thermal conductivity was decreased. It turned out that the elastic moduli of the HPT samples were not much different from those of the HP skutterudite, however, that the hardness was significantly increased.

The influence of shear strain on the microstructural, physical, and mechanical properties was studied on large bulk samples (diameter: 30 mm, thickness: 1 or 8 mm), which were consolidated by high-pressure torsion (HPT) from a commercial powder DD0.7Fe3CoSb12. Particularly, the thick sample (mass similar to 53 g) allowed measuring the thermoelectric (TE) properties with respect to various orientations of the specimen in the sample. All data were compared with those of a hot-pressed (HP) reference sample, prepared with the same powder. Transmission electron microscopy, as well as X-ray powder diffraction profile analyses, Hall measurements, and positron annihilation spectroscopy, supported these investigations. Furthermore, synchrotron data for the temperature range from 300 to 825 K were used to evaluate the changes in the grain size and dislocation density as well as the thermal expansion coefficient via the change in the lattice parameter during heating. In addition, hardness and direct thermal expansion measurements of the HPT samples were performed and compared with the HP reference sample's values. With the increase of the shear strain from the center to the rim of the sample, the electrical resistivity becomes higher, whereas the thermal conductivity becomes lower, but the Seebeck coefficient remained almost unchanged. For the thin as well as thick samples, the enhanced electrical resistivity was balanced out by a decreased thermal conductivity such that the maximum ZT values (ZT = 1.3-1.35 at 856 K) do not vary much as a function of the shear strain throughout the sample, however, all ZTs are higher than that of the HP sample. The thermal-electric conversion efficiencies are in the range of 14-15% (for 423-823 K). With similar high ZT values for the n-type skutterudites, fabricated in the same fast and sustainable way, these p- and n-type skutterudites may serve as legs for TE generators, directly cut from the big HPT bulks.

The crystal structure of the novel Al-rich intermetallic phase Ce4Pt9Al13 was determined from single-crystal X-ray diffraction data and confirmed by powder X-ray diffraction. The compound crystallizes with its own structure type, which is a “site exchange” variant of the Ho4Ir13Ge9-type (Pearson symbol oP52, space group Pmmn, No. 59, Z = 2, lattice parameters: a = 4.1826(1) A, b = 11.4424(3) A, c = 19.8475(5) A, V = 949.88(7) A3). The magnetic properties of Ce4Pt9Al13 were determined in the temperature range 1.72–400 K. Down to the lowest temperatures studied, the compound shows a Curie-Weiss paramagnetic behavior with strong crystalline electric field contribution observed below about 200 K. The electrical conductivity in Ce4Pt9Al13 has metallic character, and at low temperatures it is governed by an interplay of strong crystal field and Kondo interactions.

Skutterudites are known as excellent thermoelectric p- and n-type materials and have already achieved good efficiencies for the conversion of heat to electricity, but nevertheless researchers try to further enhance the figure of merit, ZT. In the present work the aim was to mix p- and n-type skutterudite powders with additives in order to produce an evenly dispersed distribution of sub micron grains, preferable small nano-particles, which enhance the scattering of the heat carrying phonons of different wavelengths and reduce thermal conductivity without changing electrical resistivity and Seebeck coefficient. Various quantities of three groups of materials (a) nonmetallic oxides (Al 2 O 3 ), (b) metallic oxides (Cu 2 O and La 1.85 Sr 0.15 CuO 4 ) and (c) metallic borides (Fe 2.25 Co 0.75 B and Ta 0.8 Zr 0.2 B) were added to industrially produced p-type (DD y Fe 3 CoSb 12 ) and n-type ((Mm,Sm) y Co 4 Sb 12 ) skutterudite powders. First the influence of pre-sieving and various ball milling conditions before hot pressing were studied, using Al 2 O 3 as additive. As a consequence of these studies pre-sieved powders and high-energy ball milling were used for all following experiments. The goal, to enhance ZT was not reached with Al 2 O 3 and Cu 2 O. La 1.85 Sr 0.15 CuO 4 was successful for the n-type, Fe 2.25 Co 0.75 B for the p-type skutterudites, although ZT-enhancement was small, but with Fe 2.25 Co 0.75 B the maximum ZT could be shifted to lower temperatures, a valuable information for device production. Much better results in respect to ZT values were gained with adding 0.5, 1.0 and 1.5 wt.% Ta 0.8 Zr 0.2 B to p-type DD y Fe 3 CoSb 12 . In this series it was possible to enhance ZT (from ZT ∼ 1.2 to ZT ∼ 1.3) as well as to significantly increase the thermal-electrical conversion efficiency η. In addition, we found that all boride additives enhanced the hardness, elastic moduli and fracture resistance.

More than hundred diffusion couples between p- and n-type skutterudites and various materials were prepared and interaction zones were investigated after heat treatment at 600 °C for 1100 h. The constitution of reaction/diffusion zones was discussed in terms of: (a) atom site preference in the skutterudite lattice, (b) phase equilibria in multicomponent systems and (c) particularities of the crystal structure of intermediate phases. It could be shown that phase composition and thermo-mechanical properties of bonding can be engineered by chemical substitution. The results obtained allowed the determination of several necessary criteria for the development of chemically and mechanically stable diffusion barriers/couples for skutterudite based thermoelectric (TE) modules.

The temperature and phase stability of p-type skutterudites, DD

The constitution of the two phase diagrams Nb-Mn and Ta-Mn has been determined from light optical and transmission and scanning electron microscopy (LOM, TEM and SEM) with energy dispersive (EDX) as well as wavelength dispersive (WDX) X-ray spectroscopy, X-ray powder (XPD) and single crystal diffraction (XSCD), differential thermal analysis (DTA) and/or differential scanning calorimetry (DSC). The Laves phases NbMn2 and TaMn2 are the only binary compounds in these systems. High-temperature differential thermal analyses revealed congruent melting for NbMn2 with T,(NbMn2) = 1515 +/- 15 degrees C, whereas TaMn2 melts incongruently with T-m(TaMn2)= 1797 +/- 40 degrees C close to a depleted peritectic reaction. Both Laves phases engage in eutectic reactions l (Mn) + Nb(Ta)Mn-2 (T-eut = 1220 +/- 10 degrees C at 4.9 at% Nb and T-eut = 1234 +/- 10 degrees C at 0.7 at% Ta, respectively). NbMn2 also forms a eutectic with (Nb): l (Nb) + NbMn2 at T-eut = 1493 +/- 15 degrees C and 53.2 at% Nb. Mn shows remarkably large maximum solid solubilities of 19.4 at% Mn in (Nb) as well as of 21.3 at% Mn in (Ta). Detailed atom site distribution has been established for the Laves phases by means of temperature dependent X-ray single crystal data (both C14 - MgZn2-type). Combined data from XPD, EDX/WDX and SEM microstructure indicate that for both Laves phases extended homogeneity regions exist: Nb1+xMn2+x (62.5-73.0 at% Mn at 950 degrees C: -0.19

After our successful new and energy-saving production route to prepare bulk skutterudites with high ZTs from commercial powders via cold pressing (CP) and high-pressure torsion (HPT), we present in this paper a detailed study of the influence of shear strain and the preparation parameters, especially the temperature, on the micro-structural, thermoelectric and mechanical properties by analyzing specimens cut from various positions of the HPT disks of (Sm,Mm)0.15Co4Sb12. Across these large discs (30 mm in diameter and about 1 mm thickness) the shear strain γ rises linearly from the center of the sample to the rim reaching γ ∼ 450 (for 5 revolutions), a value first time realized for skutterudites. HPT-straining is essential for the introduction of high densities of crystal lattice defects, particularly dislocations, which result in a significant refining of the grains. Whereas the processing temperature mainly influences the density of the HPT consolidated samples and as a consequence, physical and mechanical properties, the applied shear strain rules the thermoelectric parameters. As an important feature, the Seebeck coefficient remained roughly unchanged under strain. Although the increasing shear strain caused the thermal conductivity to significantly decrease, this beneficial effect is accompanied by a concomitant significant increase of the electrical resistivity. Consequently, the interplay of the two controversial influences results in a maximum and record high thermoelectric figure of merit ZT ∼2.1.

This paper documents that consolidation and subsequent severe plastic deformation of commercial skutterudite powders via high pressure torsion (HPT) serves for an easy, fast, cheap and sustainable production method for excellent n-type skutterudite bulks, (Sm,Mm)0.15Co4Sb12, with high ZT values. Large cylindrical samples with 30 mm in diameter and 8 mm thickness (∼55 g) were successfully prepared in one step. These large samples enabled for the first time to (i) study the influence of shear strain on the micro-structural, thermoelectric and mechanical properties by analysing specimens cut from various positions of the HPT disks and (ii) to evaluate these properties orientation sensitive. These investigations were supported by electron probe microanalyses, transmission electron microscopy as well as XPD full profile analyses, XPS, Raman and Hall measurements. Whilst the orientation dependence on the electrical and thermal conductivity is found to be rather weak, the applied shear strain has a pronounced influence, as with increasing strains the thermal conductivity was reduced to the targeted levels. This beneficial effect, however, is accompanied by a massive increase of the electrical resistivity. ZT values turned out to be rather homogeneous over the entire sample with ZT∼1.3 at 850 K.

The temperature and phase stability of p-type skutterudites, DD0.7Fe3CoSb12, manufactured via various preparation techniques, all exhibiting a high ZT-level, have been studied by means of thermal analysis and Knudsen effusion mass spectrometry. The results from phase transformation measurements and characteristics of evaporation of antimony, as the volatile element, supported by microstructure observations and by diffusion profiles are summarized and discussed in view of a full understanding of the degradation processes and knowledge on long term operation stability of the bulk and nano-structured thermoelectrics studied. It was found out that the antimony evaporation is a complex diffusion kinetic process resulting in a stable Sb level dependent on the preparation route. The studied p-type skutterudites, DD0.7Fe3CoSb12, have proven their long term stability in thermoelectric devices at maximum operation temperature of 600°C. Complementary data on structural, physical and mechanical properties of the materials are presented as well. Pomocí termické analýzy a Knudsenovy efuzní hmotnostní spektrometrie byla studována teplotní a fázová stabilita skutteruditů DD0.7Fe3CoSb12 typu p, vyrobených různými technikami přípravy, všechny vykazující vysokou úroveň ZT. Jsou shrnuty a diskutovány výsledky z měření fázových přeměn a charakteristiky odpařování antimonu, jako těkavého prvku, za podpory pozorování mikrostruktury a difúzních profilů, s ohledem na úplné pochopení procesů degradace a znalostí o dlouhodobé provozní stabilitě studovaných objemových a nanostrukturovaných termoelektrických materiálů. Bylo zjištěno, že odpařování antimonu je komplexní difúzí řízený kinetický proces vedoucí k stabilní hladině Sb, závislé na způsobu přípravy. Studované skutterudity typu p, DD0.7Fe3CoSb12, prokázaly svou dlouhodobou stabilitu v termoelektrických zařízeních při maximální provozní teplotě 600 °C. Jsou také prezentovány doplňkové údaje o strukturních, fyzikálních a mechanických vlastnostech materiálů. The temperature and phase stability of p-type skutterudites, DD0.7Fe3CoSb12, manufactured via various preparation techniques, all exhibiting a high ZT-level, have been studied by means of thermal analysis and Knudsen effusion mass spectrometry. The results from phase transformation measurements and characteristics of evaporation of antimony, as the volatile element, supported by microstructure observations and by diffusion profiles are summarized and discussed in view of a full understanding of the degradation processes and knowledge on long term operation stability of the bulk and nano-structured thermoelectrics studied. It was found out that the antimony evaporation is a complex diffusion kinetic process resulting in a stable Sb level dependent on the preparation route. The studied p-type skutterudites, DD0.7Fe3CoSb12, have proven their long term stability in thermoelectric devices at maximum operation temperature of 600°C. Complementary data on structural, physical and mechanical properties of the materials are presented as well.

The best p-type skutterudites with ZT > 1.1 so far are didymium (DD) filled, Fe/Co substituted, Sb-based skutterudites. DD0.68Fe3CoSb12 was prepared using an annealing-reacting-melting-quenching technique followed by ball milling and hot pressing. After severe plastic deformation via high-pressure torsion (HPT), no phase changes but particular structural variations were achieved, leading to modified transport properties with higher ZT values. Although after measurement-induced heating some of the HPT induced defects were annealed out, a still attractive ZT-value was preserved. In this paper we focus on explanations for these changes via TEM investigations, Raman spectroscopy and texture measurements. The grain sizes and dislocation densities, evaluated from TEM images, showed that (i) the majority of cracks generated during high-pressure torsion are healed during annealing, leaving only small pores, that (ii) the grains have grown, and that (iii) the dislocation density is decreased. While Raman spectra indicate that after HPT processing and annealing the vibration modes related to the shorter Sb-Sb bonds in the Sb4 rings are more affected than those related to the longer Sb-Sb bonds, almost no visible changes were observed in the pole intensity and/or orientation.

Phase relations have been established by electron probe microanalysis (EPMA) and X-ray powder diffraction (XPD) for the Sr-poor part of four ternary systems: Sr–{Pd,Pt}–Si at 900 °C and Sr–{Pd,Pt}–Ge at 700 °C. In the Sr–Pd–Si system the formation of the silicide SrPdSi 3 (BaNiSn 3 -type) was confirmed and a small homogeneity region was found. Furthermore, two novel compounds were detected and their crystal structure was refined from X-ray powder patterns: SrPd 0.3 Si 1.7 (AlB 2 -type) and SrPd 5.9 Si 6.1 (own-type). In the Sr–Pt–Si ternary system a novel compound with AlB 2 -type was discovered (SrPt 0.3 Si 1.7 ), whereas SrPtSi 3 with the BaNiSn 3 -type was confirmed. Two more compounds were detected by EPMA, but their crystal structure remains unknown. In the Sr–{Pd,Pt}–Ge systems no new compounds were observed, but the existence of SrPdGe 3 and SrPtGe 3 (both adopt the BaNiSn 3 structure type), and SrPt 4 Ge 12 , crystallizing in the LaFe 4 Sb 12 structure type, was corroborated. For selected ternary silicides the electronic structure was evaluated by DFT calculations.

In the ternary system Sr-Cu-Ge, a clathrate type-I phase, Sr8Cu5.3Ge40.7 (a = 1.06311(3), exists close to the Zintl limit in a small temperature interval. Sr8Cu5.3Ge40.7 decomposes eutectoidally on cooling at 730��C into (Ge), SrGe2 and tau1-SrCu2-xGe2+x. Phase equilibria at 700��C have been established for the Ge rich part and are characterized by the appearance of only one ternary compound, tau1-SrCu2-xGe2+x, which crystallizes with the ThCr2Si2 structure type and forms a homogeneity range up to x=0.4 (a = 0.42850(4), c = 1.0370(1) nm). Additionally, the extent of the clathrate type-I solid solution Ba8-xSrxCuyGe46-y (5.2 < y < 5.4) has been studied at various temperatures. The clathrate type-I crystal structure (space group ) has been proven by X-ray single crystal diffraction on two single crystals with composition Sr8Cu5.3Ge40.7 (a = 1.06368(2) nm) and Ba4.9Sr3.1Cu5.3Ge40.7 (a = 1.06748(2) nm) measured at 300, 200 and 100 K. From the temperature dependency of the lattice parameters and the atomic displacement parameters, the thermal expansion coefficients, the Debye- and Einstein-temperatures and the speed of sound have been determined. From heat capacity measurements of Sr8Cu5.3Ge40.7 at low temperatures, the Sommerfeld coefficient and the Debye temperature have been extracted, whereas from a detailed analysis of these data at higher temperatures, Einstein branches of the phonon dispersion relation have been derived and compared with those obtained from the atomic displacement parameters. Electrical resistivity measurements of Sr8Cu5.3Ge40.7 reveal a rather metallic behaviour in the low temperature range (< 300 K)., 22 pages, 7 figures

Phase relations for the Ba-poor part of the ternary system Ba–Zn–Sn at 500 °C were established by electron probe microanalysis (EPMA) and X-ray powder diffraction (XPD). Besides the already known compounds BaZnSn (ZrBeSi type) and BaZn 2 Sn 2 (CaBe 2 Ge 2 type), a novel ternary compound BaZnSn 2 was found to crystallize with the CeNiSi 2 -type. The precise determination (EPMA) of the homogeneity region at 500 °C for the compound BaZn 1− x Sn 1+ x with the ZrBeSi type (0.22 ⩽ x ⩽ 0.35) excludes the stoichiometric composition. The stannide BaZn 2− x Sn 2+ x ( x = 0.05) is characterized by mixed occupancy of Zn and Sn atoms in the 2 c site; accordingly the composition is slightly shifted from stoichiometry 1:2:2. Structural effects in the Ba–Zn–Sn compounds were explained on the basis of crystal chemistry analyses and electronic structure calculations employing the electron localization function ELF. The solubility of Sn in the clathrate phase Ba 8 Zn 7 Si 39 was found to be insignificant (around 1 at.%; 800 °C).

High-pressure torsion (HPT), a severe plastic deformation technique, can effectively improve the thermoelectric performance of skutterudites, resulting in ZT values higher than for ball-milled and hot-pressed (BMHP) samples. In this paper the influence of the HPT parameters, i.e. the number of revolutions (equivalent to the applied strain), the processing temperature and the hydrostatic pressure on the microstructural and thermoelectric properties of the skutterudite DD 0.60 Fe 3 CoSb 12 are evaluated and compared with the BMHP samples before HPT processing. Whilst the three parameters have specific effects on (i) the crystallite size, (ii) the density of lattice defects and (ii) the density of cracks, a suitable combination thereof allows for an increase of the figure of merit by at least 20%.

The crystal structure of the novel intermetallic Yb ∼3 Pt ∼4 Si 6− x was determined by single crystal X-ray diffraction: space group P 2 1 / m (No. 11); a = 8.4560(3) A, b = 4.2109(2) A, c = 12.7864(5) A, β = 99.537(2)°, R F = 0.046, wR2 = 0.132. The title compound is a disordered variant of the Y 3 Pt 4 Ge 6 type. It is characterized by the intergrowth of slabs cut from the ThCr 2 Si 2 and YIrGe 2 types of structures.

A systematic investigation is presented on the influence of Sn-substitution in the clathrate-I compound Ba(8)Zn(x)Ge(46-x-y)Sn(y), particularly for the crystal structure and thermoelectric properties including electrical resistivity, Seebeck coefficient, and thermal conductivity. Two series of samples were prepared to explore the changes for different Sn-contents, (y), and to define the optimum Zn-content, (x), for Ba(8)Zn(x)Ge(46-x-y)Sn(y). Sn-incorporation leads to a linear expansion of the unit cell parameters. Sn-atoms occupy the 6d and 24k positions of the clathrate type-I structure (SG Pm3n, standardized setting). Whereas the electrical resistivity and the Seebeck coefficient modify only slightly compared to Ba(8)Zn(x)Ge(46-x), the thermal conductivity is significantly decreased by the Sn-atoms incorporated into the clathrate-I framework. Furthermore the charge carrier mobility is larger and the effective mass (m* = 1.7 m(e)) is much smaller than those of the ternary compound Ba(8)Zn(x)Ge(46-x). The maximum thermoelectric figure of merit is improved by 80% and reaches ZT = 0.82 at 850 K for Ba(8)Zn(7.66)Ge(36.55)Sn(1.79).

Phase relations have been established for the system Ce–Ni–Zn in the isothermal section at 800 °C using electron microprobe analysis and X-ray powder diffraction. Phase equilibria at 800 °C are characterized by a large region for the liquid phase covering most of the Ce-rich part of the diagram, whereas a Zn-rich liquid is confined to a small region near the Zn-corner of the Gibbs triangle. Whereas solubility of Ce in the binary Ni-Zn phases is negligible, mutual solubilities of Ni and Zn at a constant Ce content are large at 800 °C for most Ce–Zn and Ce–Ni compounds. The solid solution Ce(Ni1−xZnx)5 with the CaCu5-type is continuous throughout the entire section and for the full temperature region from 400 to 800 °C. Substitution of Zn by Ni is found to stabilize the structure of CeZn11 to higher temperatures. At 800 °C Ce(NixZn1−x)11 (0.03≤x≤0.22) appears as a ternary solution phase. Similarly, a rather extended solution forms for Ce2(NixZn1−x)17 (0≤x≤0.53). Detailed data on atom site occupation and atom parameters were derived from X-ray structure analyses for single crystals of Ce2+y(NixZn1−x)17, y=0.02, x=0.49 (a=0.87541(3), c=1.25410(4) nm; Th2Zn17 type with space group R 3 ¯ m , R F 2 = 0.018 ) and Ce(Ni0.18Zn0.82)11 (a=1.04302(2), c=0.67624(3)nm, BaCd11 type with space group I41/amd, R F 2 = 0.049 ).

Phase relations have been evaluated for the Ta-V-Si system at 1500 and 1200 degrees C. Three ternary phases were found: tau(1)-(Ta,V)(5)Si-3 (Mn5Si3-type), tau(2)-Ta(Ta,V,Si)(2) (MgZn2-type) and tau(3)-Ta(Ta,V,Si)(2) (MgCu2-type). The crystal structure of tau(2)-Ta(Ta,V,Si)(2) was solved by X-ray single crystal diffraction (space group P6(3)/mmc). Atom order in the crystal structures of tau(1)-(Ta,V)(5)Si-3 (Mn5Si3 type) and tau(3)-Ta(Ta,V,Si)(2) was derived from X-ray powder diffraction data. A large homogeneity range was found for tau(1)-(TaxV1-x)(5)Si-3 revealing random exchange of Ta and V at a constant Si content. At 1500 degrees C, the end points of the tau(1)-phase solution (0.082

The crystal structures of three ternary Ni-Zn borides have been elucidated by means of X-ray single-crystal diffraction (XSC) and X-ray powder diffraction techniques (XPD) in combination with electron microprobe analyses (EMPA) defining the Ni/Zn ratio. Ni(21)Zn(2)B(24) crystallizes in a unique structure type (space group I4/mmm; a = 0.72103(1) nm and c = 1.42842(5) nm; R(F)(2) = 0.017), which contains characteristic isolated cages of B(20) units composed of two corrugated octogonal boron rings, which are linked at four positions via boron atoms. The B(20) units appear to have eight-membered rings on all six faces like the faces of a cube. Each face is centered by a nickel atom. The six nickel atoms are arranged in the form of an octahedron nested within the B(20) unit. Such a boron aggregation is unique and has never been encountered before in metal-boron chemistry. The crystal structure of Ni(12)ZnB(8-x) (x = 0.43; space group Cmca, a = 1.05270(2) nm, b = 1.45236(3) nm, c = 1.45537(3) nm; R(F)(2) = 0.028) adopts the structure type of Ni(12)AlB(8) with finite zigzag chains of five boron atoms. The compound Ni(3)ZnB(2) crystallizes in a unique structure type (space group C2/m, a = 0.95101(4) nm, b = 0.28921(4) nm, c = 0.84366(3) nm, β = 101.097(3)°, and R(F)(2) = 0.020) characterized by B(4) zigzag chain fragments with B-B bond lengths of 0.183-0.185 nm. The Ni(3)ZnB(2) structure is related to the Dy(3)Ni(2) type.

Thermoelectric (TE) properties of skutterudites DDy(Fe1-xCox)4Sb12 for 0.2  x 0.3 were studied in the temperature range from 300 K to 800 K and compared with values for x = 0. Didymium (DD, 4.76 mass % Pr and 95.24 mass % Nd) was used as natural double filler. At Co-concentrations 0.225  x  0.25 maximum TE-performance was obtained with impressive power-factors (4.5 mW/mK2) and ZTs (ZT1.2 at 700 K). Furthermore these skutterudites maintain the high ZT over a broad temperature range providing an excellent p-leg for high-efficiency thermoelectric power generation.

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.

X-ray powder data for YbCu 2 Ge 2 , YbAg 2 Si 2 and YbAg 2 Ge 2 confirmed the atom order of the ThCr 2 Si 2 type (ordered BaAl 4 type) as reported earlier. YbCu 2 Ge 2 is an intermediate valence system with the Yb ions valence close to +2 at low temperatures, whereas the other two compounds are weakly temperature-dependent paramagnets. All these ternaries show metallic character of their electrical conductivity. The structure of Yb(Cu 1− x Zn x ) 2 Si 2 ( x = 0.65, 0.77) was found to correspond to the BaAl 4 type, assuming a random distribution of Cu and Zn atoms over the positions 4d (0, 1/2, 1/4). The Si atoms were found in the sites 4e (0, 0, z ). These two pseudoternary compounds are diamagnetic. A novel phase with the composition Yb(Ag 0.18 Si 0.82 ) 2 crystallizes in the ThSi 2 -type on the verge to a symmetry reduction towards orthorhombic GdSi 2 -type. This phase is a Pauli paramagnet and exhibits metallic behavior of the resistivity.

Two series of intermetallic alloys, RT2Si and RTSi2, have been synthesized from stoichiometric compositions. The crystal structures of EuPt1+xSi2−x (CeNiSi2-type), CeIr2Si (new structure type), YbPd2Si and YbPt2Si (both YPd2Si-type) have been elucidated from X-ray single crystal CCD data, which were confirmed by XPD experiments. The crystal structures of LaRh2Si and LaIr2Si (CeIr2Si-type), {La,Ce,Pr,Nd}AgSi2 (all TbFeSi2-type), and EuPt2Si (inverse CeNiSi2-type) were characterized by XPD data. RT2Si/RTSi2 compounds were neither detected in as-cast alloys Sc25Pt50Si25, Eu25Os25Si50 and Eu25Rh25Si50 nor after annealing at 900 °C. Instead, X-ray single crystal data prompted Eu2Os3Si5 (Sc2Fe3Si5-type) and EuRh2+xSi2−x (x=0.04, ThCr2Si2-type) as well as a new structure type for Sc2Pt3Si2 (own type).

Pt 4 Sn 4.4 Sb 7.6 ( a = 9.3304(2) Å, space group [Formula: see text] ) is an unfilled skutterudite member of the solid solution Sn x Pt 4 Sn y Sb 12- x . In contrast to Sn x Ni 4 Sn y Sb 12- y and Sn x Pt 4 Sn y Sb 12- x no Sn could be found in the 2 a sites of the Sn / Sb framework. Physical properties have been data for Ni 4 Sn 3 Sb 9 and Ni 4 Sn 3.5 Sb 8.5. Resistivity measurements for Pt 4 Sn 4.4 Sb 7.6 reveal a temperature dependent crossover from metallic to semiconducting behaviour connected with a corresponding change from negative to positive thermopower at 30 K. Vicker's hardness, thermal expansion and elastic moduli compare well with values of other Sb - investigated in the temperature range from 4.2 K to 800 K and have been compared with based skutterudites.

Phase relations in the ternary system Ce–Pd–Si have been established for the isothermal section at 8001C based on X-ray powder diffraction and EMPA techniques on about 130 alloys, which were prepared by arc-melting under argon or powder reaction sintering. Eighteen ternary compounds have been observed to participate in the phase equilibria at 8001C. Atom order was determined by direct methods from X-ray single-crystal counter data for the crystal structures of t8—Ce3Pd4Si4 (U3Ni4Si4type, Immm; a ¼ 0.41618(1), b ¼ 0.42640(1), c ¼ 2.45744(7) nm), t16—Ce2Pd14Si (own structure type, P4/nmm; a ¼ 0.88832(2), c ¼ 0.69600(2) nm) and also for t18—CePd1� xSix (x ¼ 0.07; FeB-type, Pnma; a ¼ 0.74422(5), b ¼ 0.45548(3), c ¼ 0.58569(4) nm). Rietveld refinements established the atom arrangement in the structures of t5—Ce3PdSi3 (Ba3Al2Ge2-type, Immm; a ¼ 0.41207(1), b ¼ 0.43026(1), c ¼ 1.84069(4) nm) and t13—Ce3� xPd20+xSi6 (0rxr1, Co 20Al3B6-type, Fm3 ¯ m; a ¼ 1.21527(2) nm). The ternary compound Ce2Pd3Si3 (structure-type Ce2Rh1.35Ge4.65, Pmmn; a ¼ 0.42040(1), b ¼ 0.42247(1), c ¼ 1.72444(3) nm) was detected as a high-temperature compound, however, does not participate in the equilibria at 8001C. Phase equilibria in Ce–Pd–Si are characterized by the absence of cerium solubility in palladium silicides. Mutual solubility among cerium silicides and cerium–palladium compounds are significant whereby random substitution of the almost equally sized atom species palladium and silicon is reflected in extended homogeneous regions at constant Cecontent such as for t2—Ce(PdxSi1� x)2 (AlB2-derivative type), t6—Ce(PdxSi1� x)2 (ThSi2-type) and t7—CePd2� xSi2+x. The crystal structures of compounds t4—Ce� 8Pd� 46Si� 46, t12—Ce� 29Pd� 49Si� 22, t15—Ce� 22Pd� 67Si� 11, t17—Ce� 5Pd� 77Si� 18 and t18—CePd1� xSix (x� 0.1) are still unknown.

The crystal structures of ternary compounds RPt3−xSi1−y(R=Y, Tb, Dy, Ho, Er, Tm, Yb) have been elucidated from X-ray single crystal CCD data. All compounds are isotypic and crystallize in the tetragonal space group P4/mbm. The general formula RPt3−xSi1−y arises from defects: x≈0.20, y≈0.14. The crystal structure of RPt3−xSi1−y can be considered as a packing of four types of building blocks which derive from the CePt3B-type unit cell by various degrees of distortion and Pt, Si-defects.

The crystal structure of Mn6Ni16Si7 was reinvestigated by X-ray powder, single crystal and neutron powder diffraction data in form of a combined refinement. In contrast to the various structure variants observed for titanium aluminium-based G-phases Ti6({Fe,Co,Ni}1−xAlx)23+1 as well as for Ti6Ni16+xSi7, Mn6Ni16Si7 was confirmed to crystallize as a simple ordered variant of the Th6Mn23 structure type (a = 1.11674(6) nm, Mg6Cu16Si7-type; space group F m 3 ¯ m ): Ni atoms adopt two 32f sites, Si atoms occupy 4a and 24d sites and Mn-atoms are located at 24e sites. A Fourier difference map proved the absence of atoms in the 4b site (1/2, 1/2, 1/2). Thus the crystal structure of Mn6Ni16Si7 is a true representative of the Mg6Cu16Si7-type.

In order to define the ability of magnetic elements M = Mn, Fe, Co to stabilise clathrate structures, alloys of the Ba – M – Ge system were investigated in the as-cast state and after annealing at 700°C and 800°C by means of X-ray powder diffraction, light optical and electron-probe microanalysis. Temperatures of phase transformations were derived from differential thermal analysis. Results are summarised in (i) isothermal sections at 700°C and 800°C, (ii) solidus and liquidus surfaces covering the region of existence for both clathrate phases in these systems. Invariant reactions during crystallisation are presented in form of Schultz – Scheil diagrams. In all three cases only limited solubility of the M element was found for clathrate IX (Ba6Ge25) i. e. the Ge-framework in the crystal structure of Ba6M x Ge25 – x dissolves 0.6 atom of Mn, and about 1 atom of Fe and Co per unit cell. The maximum solubility of iron in clathrate type I (Ba8Ge46 – x ) was found to be less than 0.5 Fe atom per unit cell, and clathrates with Mn and Co contain up to 1.0 and 2.5 atoms in the unit cell, respectively. Whilst Fe does not decrease the formation temperature of the clathrate phase, Mn and Co decrease it from 770°C (for binary Ba8Ge43) to 766°C and 749°C, respectively.

X-ray powder data for Ba 0.8 Ca 0.2 Pt 4 Ge 12 and X-ray single crystal data for EuPt 4 Ge 12 define cubic body-centered symmetry consistent with novel Ge-based skutterudites SrPt 4 Ge 12 and BaPt 4 Ge 12 (space group Im 3 ). Structural and electron microprobe analysis investigations evidence a complete filling of the icosahedral cages without large atomic displacement parameters. Ba 0.8 Ca 0.2 Pt 4 Ge 12 exhibits phonon-mediated superconductivity at T c = 5.2 K. Density functional theory (DFT) calculations (LDA+U) carried out for EuPt 4 Ge 12 proved that Eu guest atoms strongly stabilize the compound in which the calculated density of states around the Fermi energy essentially consists of hybridized Ge 4 p -like and Pt 5 d -like states. Low temperature resistivity studies evidence magnetic ordering at T m ≈1.7 K. Susceptibility measurements reveal a divalent state for europium, in excellent agreement with the DFT calculations.

Phase relations and crystal structures have been evaluated within the sections LaNi2Si2-LaZn2Si2 and CeNi2Si2-CeZn2Si2 at 800 °C using electron microprobe analysis and X-ray powder and single crystal structure analyses. Although the systems La-Zn-Si and Ce-Zn-Si at 800 °C do not reveal compounds such as "LaZn2Si2" or "CeZn2Si2", solid solutions {La,Ce}(Ni1-xZnx)2Si2 exist with the Ni/Zn substitution starting from {La,Ce}Ni2Si2 (ThCr2Si2-type; I4/mmm) up to x = 0.18 for Ce(Ni1-xZnx)2Si2 and x = 0.125 for La(Ni1-xZnx)2Si2. For higher Zn-contents 0.25 ≤ x ≤ 0.55 the solutions adopt the CaBe2Ge2-type (P4/nmm). The investigations are backed by single crystal X-ray diffraction data for Ce(Ni0.61Zn0.39)2Si2 (P4/nmm; a = 0.41022(1) nm, c = 0.98146(4) nm; RF = 0.012) and by Rietveld refinement for La(Ni0.56Zn0.44)2Si2 (P4/nmm; a = 0.41680(6) nm, c = 0.99364(4) nm; RF = 0.043). Interestingly, the Ce-Zn-Si system contains a ternary phase CeZn2(Si1-xZnx)2 of the ThCr2Si2 structure type (0.25 ≤ x ≤ 0.30 at 600 °C), which forms peritectically at T = 695 °C but does not include the composition "CeZn2Si2". The primitive high temperature tetragonal phase with the CaBe2Ge2-type has also been observed for the first time in the Ce-Ni-Si system at CeNi2+xSi2-x, x = 0.33 (single crystal data, P4/nmm; a = 0.40150(2) nm, c = 0.95210(2) nm; RF = 0.0163). Physical properties (from 400 mK to 300 K) including specific heat, electrical resistivity and magnetic susceptibility have been elucidated for Ce(Ni0.61Zn0.39)2Si2 and La(Ni0.56Zn0.44)2Si2. Ce(Ni0.61Zn0.39)2Si2 exhibits a Kondo-type ground state. Low temperature specific heat data of La(Ni0.56Zn0.44)2Si2 suggest a spin fluctuation scenario with an enhanced value of the Sommerfeld constant.

The ternary intermetallic Ce 16 Ru 8 In 37 was synthesized by arc-melting from elemental Ce, Ru, and In under an argon atmosphere. The crystal structure of Ce 16 Ru 8 In 37 was determined from the single-crystal X-ray diffraction data: a = 4.7451(1) A, b = 9.3518(2) A, c = 32.6162(7) A; space group Immm , Z = 1. The architecture of the crystal structure of Ce 16 Ru 8 In 37 is based on CeIn 3 units with cubic Cu 3 Au-type and can be presented as consisting of two different slabs: CeIn 3 -like slab of composition Ce 4 In 14.5 and a slab of composition Ce 4 Ru 4 In 4 .

Combined refinement of neutron powder, X-ray single crystal and powder diffraction data allows precise evaluation of symmetry and atom site occupation for the MgZn2-type Laves phase. For compositions Ti(Ni1–x,Alx)2 titanium atoms were found to fully occupy the 4f site, whilst Ni- and Al-atoms randomly share the 2a and 6h sub-lattice sites of space group P63/mmc. At higher Ti-concentrations, Ti-atoms tend to enter the 2a and 6h 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 Ti0.463Ni0.273Al0.264. Heat of formation data, derived from adiabatic drop calorimetry, were Δ298 H 0 = –57.9 ± 3.5 kJ/mol for Ti0.34Ni0.18Al0.48and –61.6 ± 3.3 kJ/mol for Ti0.36Ni0.24Al0.40. 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 2a sites, and then continues occupying 6h sites. In compounds with Ti concentration larger than 33.3 at% the 4f sites are fully occupied by Ti, and the excessive Ti prefers 6h sites. The Al concentration of the Al-rich end of the homogeneity region of the ternary Laves phase was predicted to be 57 at%.

The discovery of superconductivity below 40 K in MgB 2 has motivated new investigations on similar compounds, especially on binary diborides. The great majority of these compounds represent the AlB 2 -type structure ( P 6/ mmm space group, number 191) and comprise line compounds. However, among those, NbB 2 and TaB 2 are reported to present a significant homogeneity region, a value of 12 at.% being reported for the case of NbB 2 . In this work we have evaluated the homogeneity range of the NbB 2 -phase through detailed microstructural characterization of as-cast, as-cast + heat-treated and solid state sintered Nb–B alloys. Neutron diffraction experiments were performed to assess the defect mechanism responsible for accommodating the non-ideal NbB 2 stoichiometries (ideal = 66.7 at.% B). The results clearly showed that the width of the homogeneity range of this phase is nearly 5 at.%, extending from 65 at.% B (NbB 1.86 ) up to 70 at.% B (NbB 2.34 ). Rietveld refinement of the neutron intensity diffraction data indicated a random distribution of vacancies in the Nb-subnet for hyperstoichiometric NbB 2 . The occurrence of a possible Nb-vacancy ordered supercell was evaluated; however, a simple AlB 2 -type is observed throughout the entire homogeneity range. The superconducting properties of selected alloys were checked via magnetic measurements. The Nb-deficient samples were found to contain traces of a superconducting phase with T c ≈ 3.5 K.

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.

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.

Phase equilibria of the system Ce–Zn–Si have been determined for the isothermal section at 600 °C for

Phase relations in the entire ternary system Mo–Si–B were studied at subsolidus temperatures on alloys prepared by arc-melting and employing Pirani–Althertum melting point data, differential thermal analysis, light and electron microscopy, X-ray diffraction, and electron probe microanalysis including the light element boron. All isothermal reaction temperatures measured were used to construct two vertical sections and a Schulz–Scheil flow diagram monitoring solidification (crystallization) in thermodynamic equilibrium over the whole concentration range. The ternary compound Mo 5 SiB 2 exhibits a solubility range from 8 to 13 at.% Si at solidus temperatures. Stoichiometric Mo 5 SiB 2 forms from a pseudobinary peritectic reaction with a maximum tie line at 2130 °C. The phase diagram is presented as a melting diagram projection.

A novel clathrate type-I phase, Sr8CuxGe46-x (5.2 ≤ x < 5.4), is detected in arc melted ingots which exists close to the Zintl limit in a small temperature interval.

Rietveld analysis was performed for the intermetallics Yb3Co4.3Sn12.7 and Yb3Co4Ge13 crystallizing with the closely related structure types, Yb3Rh4Sn13 and Yb3Co4Ge13. Below Tc = 3.4 K Yb3Co4.3Sn12.7 crosses over into a type-II superconducting ground state with Hc2(0)~2.5 T. Yb3Co4Ge13 stays in the normal state down to 300 mK. The γ value of 2.3(2) mJ gat-1 K-2 and the Debye temperature ΘD = 207(5) K deduced from the specific heat as well as Tc correspond to that of elementary Sn, thus indicating conventional BCS superconductivity. Hydrostatic pressure applied to Yb3Co4.3Sn12.7 reveals both an overall decrease of the absolute resistivity values, as well as a decrease of Tc, which vanishes for a critical pressure below 10 kbar. The magnetoresistance of both Yb-based compounds is positive at low temperature but does not exceed 8% in fields of 12 T. The Seebeck coefficient has a maximum value of about 18 µV K-1 at T~250 K. LIII and magnetic susceptibility measurements reveal intermediate valence: 2.66(3) and 2.18(3) for Yb3Co4Ge13 and Yb3Co4.3Sn12.7, respectively.

Phase relations in the Ba-poor part of the ternary Ba—Zn—Sn system at 500 °C are established by arc melting of the elements with an excess of Ba of 3 wt% (1.

The title compound is unintentionally obtained by arc melting of the elements in a ratio pertaining to YbPtSi2 with 3 wt.% excess of Yb due to its high volatility.The crystal structure of the novel intermetallic is determined by single crystal XRD (space group P21/m, Z = 2) and found to be a disordered variant of the Y3Pt4Ge6 type characterized by the intergrowth of slabs cut from the ThCr2Si2 and YIrGe2 types of structures.

Phase relations in the title system are evaluated for the isothermal sections at 1500 and 1200 °C.

Ni21Zn2B24 (I), Ni12ZnB7.57 (II), and Ni3ZnB2 (III) are prepared from mixtures of arc-melted NiBx and Zn powders (800 °C, 7 d) and characterized by powder and single crystal XRD.

We present results of magnetisation, resistivity, thermopower and thermal conductivity measurements on the compound Eu 0.83 Fe 4 Sb 12 , which orders magnetically below 84 K. An interesting feature of this compound is the large positive magnetoresistance, reaching values of 130% at 2 K and 12 T, and still 30% at room temperature. Fe/Co substitution causes a drop in the magnetic ordering temperature T mag and an increase of the thermopower values, which is expected from a decrease of the charge carrier density.