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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.

The crystal structure of the novel compound Yb3Pt23Si11 has been determined from powder X-ray diffraction data to be isotypic with cubic Ce3Pt23Si11 (space group F m 3 ¯ m ; a = 1.68052(5) nm). Magnetic susceptibility, electrical resistivity and heat capacity measurements, performed down to 0.4 K, revealed that Yb3Pt23Si11 is a moderately enhanced paramagnetic compound with fairly unstable 4f electronic shell.

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.

The crystal structure, the distribution of electron density, and the energy, kinetic, and magnetic properties of the n-TiNiSn intermetallic semiconductor are investigated. It is shown that a priori doping of n-TiNiSn with donors originates from partial, up to 0.5 at %, redistribution of Ti and Ni atoms in crystallographic sites of Ti atoms. The correlation is established between the donor concentration, amplitude of modulation of the continuous energy bands, and degree of filling of low-scale fluctuation potential wells with charge carriers. The results obtained are discussed within the Shklovskii-Efros model of a heavily doped and compensated semiconductor.

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.

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.

In the Ag–Ba–Ge system the clathrate type-Ι solid solution, Ba8AgxGe46−x−y□y, extends at 800 °C from binary Ba8Ge43□3 (□ is a vacancy) to Ba8Ag5.3Ge40.7. For the clathrate phase (1 ⩽ x ⩽ 5.3) the cubic space group Pm 3 ¯ n was established by X-ray powder diffraction and confirmed by X-ray single-crystal analyses of the samples Ba8Ag2.3Ge41.9□1.8 and Ba8Ag4.4Ge41.3□0.3. Increasing the concentration of Ag causes the lattice parameters of the solid solution to increase linearly from a value of a = 1.0656 (x = 0, y = 3) to a = 1.0842 (x = 4.8, y = 0) nm. Site preference determination using X-ray refinement reveals that Ag atoms preferentially occupy the 6d site randomly mixed with Ge and vacancies, which become filled in the compound Ba8Ag4.8Ge41.2 when the Ag content increases. At 600 °C the phase region of the clathrate solution Ba8AgxGe46−x−y□y becomes separated from the Ba–Ge boundary and extends from 6.6 to 9.8 at.% Ag. The compound Ba6Ge25 (clathrate type-ΙX) dissolves at 800 °C a maximum of 1.5 at.% Ag. The homogeneity regions of the two ternary compounds BaAg2−xGe2+x (ThCr2Si2-type, 0.2 ⩽ x ⩽ 0.7) and Ba(Ag1-xGex)2 (AlB2-type, 0.65 ⩽ x ⩽ 0.75) were established at 800 °C. Studies of transport properties for the series of Ba8AgxGe46−x−y□y compounds evidenced that electrons are the predominant charge carriers with the Fermi energy close to a gap. Its position can be fine-tuned by the substitution of Ge by Ag atoms and by mechanical processing of the starting material, Ba8Ge43. The proximity of the electronic structure at Fermi energy of Ba8AgxGe46−x−y□y to a gap is also corroborated by density functional theory calculations. This gap near the Fermi energy gives rise to distinct features of the temperature-dependent electrical resistivity and the Seebeck effect is in very good agreement with the experiment findings.

The Ta-V system is an interesting system exhibiting the existence of Laves phases among elements of the same group in the periodic system, and with an unusual order of stability of Laves phase structures at 0 K. Whereas the hexagonal C14 Laves phase is stable at 0 K and at high temperatures, the C15 structure is the most stable Laves phase at intermediate temperatures. The ab initio calculations of the total energies of formation for both C14 and C15 Laves phases employed two- and three-sublattice models to revise the thermodynamic description of the system published recently. The remodeled Gibbs energies of Laves phases require less fitting parameters than those obtained in previous treatments and the corresponding phase diagrams provide an excellent agreement with the experimental data on the phase stability and phase boundaries found in the literature. The new fitting procedure proposed involves a temperature dependent heat capacity for the C15 structure and allows us to compare the optimized heat capacity differences between the Laves phase and Standard Element Reference structure with those determined experimentally and theoretically. (C) 2010 Elsevier Ltd. All rights reserved.

In the Au-Ba-Ge system the clathrate type I solid solution, Ba8Au x Ge46−x−y □ y , extends at 800 °C from binary Ba8Ge43□3 (□ is a vacancy) to Ba8Au6Ge40. For the clathrate phase (1 ≤ x ≤ 6) cubic primitive symmetry (space group $$ Pm{\bar{{3}}}n $$ ) was confirmed by x-ray powder diffraction assisted by x-ray single crystal analyses of Ba8Au4.6Ge40.3□1.1. The lattice parameters of the solid solution show an almost linear increase with increasing gold content. Site preference from x-ray refinement shows that gold atoms preferably occupy the 6d site in random mixture with Ge and vacancies, which vanish at the solubility limit. Clathrate type ΙX (Ba6Ge25 type) has a maximum solubility of 2.7 at.% gold at 800 °C. Phase equlilibria at 800 °C are characterized by four ternary phases in the investigated region up to 33.3 at.% barium. The homogeneity range of Ba(Au1−x Ge x )2 (AlB2-type) and BaAu1+x Ge3−x has been established: Ba(Au1−x Ge x )2 extends from BaAu0.5Ge1.5 to BaAu0.9Ge1.1 and BaAu1+x Ge3−x from BaAu1.1Ge2.9 (BaNiSn3-type) to BaAu2.7Ge1.3 (Ce(Ni,Sb)4-type). The crystal structures of two phases in the gold-rich part have been determined from single crystal x-ray data and were found to form new structure types: BaAu3Ge with BaAu3Ge-type (space group P4/nmm, a = 0.6459(2), c = 0.5487(2) nm) and BaAu5+x Ge2−x (x = 0, BaAu5Si2-type, space group Pnma, a = 0.8981(2), b = 0.7106(2) and c = 1.0363(2) nm), the latter revealing with increasing gold content a closely related derivative structure type (BaAu5.3Ge1.7, $$ a = a_{{{\text{BaAu}}_{5} {\text{Si}}_{2} }} ,\;b = b_{{{\text{BaAu}}_{5} {\text{Si}}_{2} }} ,\;c = 2c_{{{\text{BaAu}}_{5} {\text{Si}}{}_{2}}} $$ ). Transport properties and particularly the thermoelectric behavior were studied for Ba8Au6Ge40.

For thermoelectrics it is important to produce thermodynamically stable bulk nanostructured materials. Ball milling/hot pressing was shown to reduce the crystallite size by a factor of 100 and to reach about 100 nm with dislocation densities of 1012 – 1013m-2. Thereby thermoelectric properties of single, double and multifilled Sb-based skutterudites were improved significantly leading to figures of merit ZT, which in some cases are twice as high as those of their microstructured counterparts. With HPT treatment the crystallite size can be decreased to even 50 nm with dislocation densities as high as 1015m-2. The small grains as well as the high dislocation density result in a further lowering of thermal conductivity holding a high potential for future enhancement of ZT.

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.

Three series of vacancy-free quaternary clathrates of type I, Ba 8 Zn x Ge 46− x − y Si y , Ba 8 (Zn,Cu) x Ge 46− x , and Ba 8 (Zn,Pd) x Ge 46− x , have been prepared by reactions of elemental ingots in vacuum sealed quartz at 800 °C. In all cases cubic primitive symmetry (space group Pm 3 n , a ∼1.1 nm) was confirmed for the clathrate phase by X-ray powder diffraction and X-ray single crystal analyses. The lattice parameters show a linear increase with increase in Ge for Ba 8 Zn x Ge 46− x − y Si y . M atoms (Zn, Pd, Cu) preferably occupy the 6 d site in random mixtures. No defects were observed for the 6 d site. Site preference of Ge and Si in Ba 8 Zn x Ge 46− x − y Si y has been elucidated from X-ray refinement: Ge atoms linearly substitute Si in the 24 k site whilst a significant deviation from linearity is observed for occupation of the 16 i site. A connectivity scheme for the phase equilibria in the “Ba 8 Ge 46 ” corner at 800 °C has been derived and a three-dimensional isothermal section at 800 °C is presented for the Ba–Pd–Zn–Ge system. Studies of transport properties carried out for Ba 8 {Cu,Pd,Zn} x Ge 46− x and Ba 8 Zn x Si y Ge 46− x − y evidenced predominantly electrons as charge carriers and the closeness of the systems to a metal-to-insulator transition, fine-tuned by substitution and mechanical processing of starting material Ba 8 Ge 43 . A promising figure of merit, ZT ∼0.45 at 750 K, has been derived for Ba 8 Zn 7.4 Ge 19.8 Si 18.8 , where pricey germanium is exchanged by reasonably cheap silicon.

Phase equilibria in the system Si–U–V were established at 1100 °C by optical microscopy, EMPA and X-ray diffraction. Two ternary compounds were observed, U 2 V 3 Si 4 and (U 1− x V x ) 5 Si 3 , for which the crystal structures were elucidated by X-ray powder data refinement and found to be isotypic with the monoclinic U 2 Mo 3 Si 4 -type (space group P 2 1 / c ; a = 0.6821(3), b = 0.6820(4), c = 0.6735(3) nm, β = 109.77(1)°) and the tetragonal W 5 Si 3 -type (space group I 4/ mcm , a = 1.06825(2), c = 0.52764(2) nm), respectively. (U 1− x V x ) 5 Si 3 appears at 1100 °C without any significant homogeneity region at x ∼ 0.2 resulting in a formula U 4 VSi 3 which corresponds to a fully ordered atom arrangement. DTA experiments clearly show decomposition of this phase above 1206 °C revealing a two-phase region U 3 Si 2 + V 3 Si. At 1100 °C U 4 VSi 3 is in equilibrium with V 3 Si, V 5 Si 3 , U 3 Si 2 and U(V). At 800 °C U 4 VSi 3 forms one vertex of the tie-triangle to U 3 Si and V 3 Si. Due to the rather high thermodynamic stability of V 3 Si and the corresponding tie-lines V 3 Si + liquid at 1100 °C and V 3 Si + U(V) below 925 °C, no compatibility exists between U 3 Si or U 3 Si 2 and vanadium metal.

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.

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.

Since severe plastic deformation (SPD) has demonstrated its capability of producing bulk nanomaterials with highly advanced mechanical properties, research is increasingly focusing on the question as to whether functional nanomaterials can be achieved by SPD and in bulk shape, too. This paper presents promising results of reaching functional properties in SPD-processed bulk nanocrystalline magnetic alloys, bulk shape memory nanoalloys, as well as nanometals and alloys for hydrogen storage, and also reports on problems with other functional properties, like those of thermoelectricity, occurring in non-metallic nanomaterials.

The influence of multi-filling on the thermoelectric properties was investigated for skutterudites (Ca,Sr,Ba,Mm) y Co 4 Sb 12 , where Mm is Mischmetal, a naturally mixed rare earth (Ce,La,Nd,Pr), which throughout this work was treated for convenience as one filler element. Regardless of the filling elements, triple filling shows lower electrical resistivity as well as lattice thermal conductivity and consequently a higher figure of merit ZT than single and double filling, indicating the positive influence of multi-filling on thermoelectric performance. Investigations of triple-filled alloys (Sr,Ba) A Yb R Co 4 Sb 12 point out that Yb-filling in multi-filled skutterudites entails better thermoelectric properties than Mm-filling. Also the ratio A:R is a critical parameter to achieve high ZT. Moreover, for (Sr,Ba,Yb) y Co 4 Sb 12 , a larger filling level y leads to lower electrical resistivity. Although Ni substitutions for Co in double-filled Ca y Mm y (Co 1− x Ni x ) 4 Sb 12 result in complicated compositional dependences for the electrical resistivity and the Seebeck coefficient, they exert almost no influence on the thermal conductivity, and the Ni-free sample shows the highest ZT in Ca y Mm y (Co 1− x Ni x ) 4 Sb 12 , indicating a different impact of Ni with respect to unfilled (Co 1− x Ni x ) 4 Sb 12 .

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).

Time-of-flight and resonant ultrasound spectroscopy techniques were employed for elastic moduli measurements on a set of various Fe 4 Sb 12 - and Co 4 Sb 12 -based skutterudites filled by mischmetal, didymium, or alkaline earths (Ca, Sr, Ba). A weak temperature influence on the longitudinal modulus C 11 indicates weak degradation of elastic properties within the thermoelectric working temperature range. Elastic moduli for Co 4 Sb 12 -based skutterudites are only slightly higher than for Fe 4 Sb 12 -based skutterudites, and the influence of various filler atoms or filling fractions on the elastic moduli is even smaller. Ball milled and hot pressed samples (grain size ∼250 nm) illustrate an obvious improvement of elastic properties in relation to those hot pressed from hand milled powders (grain size ∼50 μm). Debye temperatures calculated from sound velocity measurements are comparable to the values obtained from the parameters fitted to thermal expansion, which indicate that Co 4 Sb 12 -based skutterudites having slightly higher values than Fe 4 Sb 12 -based skutterudites. Vickers hardness is increased by Co or Ni substitution and demonstrates a linear dependence on density, Young's modulus, and shear modulus.

The formation and crystal chemistry of ternary clathrates in the Ba-Cu-Si system were investigated on a series of compounds Ba8Cu x Si46−x (3 ≤ x ≤ 8). The phase diagram around the clathrate phase was constructed at 800°C, revealing a homogeneity range from Ba8Cu3.4Si42.6 to Ba8Cu4.8Si41.2. Structural investigations confirmed that the clathrates in this system crystallize with cubic primitive symmetry, in the type I clathrate structure (space group Pm $$ \bar{3} $$ n). Single-crystal x-ray diffraction indicates that the Cu atoms partially substitute for Si atoms on the 6d site; no vacancies are observed.

Phase equilibria and crystal structures of ternary compounds were determined in the systems Ce–Pd–B and Yb–Pd–B at 850 °C in the concentration ranges up to 45 and 33 at% of Ce and Yb, respectively, employing X-ray single crystal and powder diffraction. Phase relations in the Ce–Pd–B system at 850 °C are governed by formation of extended homogeneity fields, τ2-CePd8B2−x (0.10 The Yb–Pd–B system is characterized by one ternary compound, τ1-Yb2Pd14B5, forming equilibria with extended solution YbPd3Bx, YbB6, Pd5B2 and Pd3B. The crystal structures of both Yb2Pd14B5 and isotypic Lu2Pd14B5 were determined from X-ray Rietveld refinements and found to be closely related to the Y2Pd14B5-type (I41/amd). The crystal structure of binary Yb5Pd2−x (Mn5C2-type) was confirmed from X-ray single crystal data and a slight defect on the Pd site (x=0.06) was established. The three structures τ1-Ce6Pd47−xB6, τ2-CePd8B2−x and τ3-Ce3Pd25−xB8−y are related and can be considered as the packings of fragments observed in Nd2Fe14B structure with different stacking of common structural blocks. Physical properties for Yb2Pd13.6B5 (temperature dependent specific heat, electrical resistivity and magnetization) yielded a predominantly Yb-4f13 electronic configuration, presumably related with a magnetic instability below 2 K. Kondo interaction and crystalline electric field effects control the paramagnetic temperature domain.

In the present work we focus on cubic type I Ba-Ge-based clathrates, where Ge in \(\rm Ba_8Ge_{43} \square_3\) (where □ is a vacancy) is substituted by Cu, Zn, Pd, and Si. Structural investigations in all cases confirm cubic primitive symmetry consistent with the space group type \(Pm\bar{3}n\) of a typical type I clathrate structure with lattice parameter a ≈ 1.06 nm. Electronic transport has been studied in a broad temperature range from 4.2 K to about 800 K, demonstrating that substitution allows fine-tuning of the charge carrier density, shifting the materials into the proximity of a metal-to-insulator transition. This is evidenced from giant thermopower reaching values of 400 μV/K in the case of Ba8Cu5.2Zn0.8Ge40.0 at temperatures well below room temperature (TmaxS ≈ 150 K).

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.

Both p- and n-type skutterudites (Pr 0.67 Fe 3 CoSb 12 , Pr 0.71 Fe 3.5 Ni 0.5 Sb 12 and Ba 0.06 Co 4 Sb 12 ) have been deformed by high pressure torsion (HPT) with 2 GPa resulting in a lamellar shaped nanograined structure. The crystallite size distribution and dislocation density are evaluated using X-ray powder diffraction data, revealing a crystallite size of 47 nm and a dislocation density of 7 × 10 14 m −2 for Ba 0.06 Co 4 Sb 12 . Whilst at T 0.67 Fe 3 CoSb 12 and Pr 0.71 Fe 3.5 Ni 0.5 Sb 12 do not indicate long-range magnetic order, the temperature dependent susceptibility elucidates antiferromagnetic ordering after HPT although the anomaly at the phase transition becomes washed out. The effective magnetic moments are 4.18 μ B and 4.07 μ B for Pr 0.67 Fe 3 CoSb 12 before and after HPT, revealing a non-zero effective moment on the Fe 3 CoSb 12 framework. Metamagnetic transitions at μ 0 H = 0.9 (before HPT) and 0.8 (after HPT) are clearly seen in isothermal magnetization curves. In comparison with the microstructures of milled and hot pressed samples, those after HPT exhibit markedly smaller although lamellar grains, and also amorphous aggregates. The thermal conductivity of HPT samples is smaller, but the electrical resistivity is markedly higher than that of milled material, which in sum results in a lower figure of merit ZT. The increase of resistivity is caused by the high density of microcracks observed in the HPT samples, which may be avoided by suitable modification of the HPT processing parameters.

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.

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.

The figure of merit (zT) of a thermoelectric material can be enhanced by incorporation of nanoinclusions into bulk material. The presence of bismuth telluride (Bi2Te3) nanoinclusions in Co4Sb12 leads to lower phonon thermal conductivity by introducing interfaces and defects; it enhances the average zT between 300-700 K. In the current study, Bi2Te3 nanoparticles were dispersed into bulk Co4Sb12 by ball-milling. The bulk was fabricated by spark plasma sintering. The presence of Bi2Te3 dispersion in Co4Sb12 was confirmed by x-ray diffraction, scanning electron microscopy, transmission electron microscopy and electron back scattered diffraction technique. Energy dispersive spectroscopy showed antimony (Sb) as an impurity phase for higher contents of Bi2Te3 in the sample. The Seebeck coefficient (S) and electrical conductivity (sigma) were measured in the temperature range of 350-673 K. The negative value of S indicates that most of the charge carriers were electrons. A decrease in S and increase in.. with Bi2Te3 content are due to the increased carrier concentration, as confirmed by Hall measurement. The thermal conductivity, measured between 423-673 K, decreased due to the increased phonon scattering at interfaces. A maximum zT of 0.17 was achieved at 523 K and it did not vary much throughout the temperature range. The experimental results of composites were compared by using effective medium theories.

Thermoelectric behaviour was studied for Mm y Fe 4− x Co x Sb 12 with x = 0 and 1 (Mm is mischmetal) within the temperature range from 300 K to 800 K and was compared with data for corresponding Ce y Fe 4− x Co x Sb 12 . No decrease of thermal conductivity at high temperatures was observed changing from a single atom filler (Ce) to a multi-element filler (Mm). The electrical resistivity of Mm y Fe 4− x Co x Sb 12 was found to be lower than or similar to that of Ce y Fe 4− x Co x Sb 12 . Accordingly the figure of merit for MmFe 3 CoSb 12 exceeds 1 at temperatures above 600 K. The influence of several parameters such as impurity phases and grain size on the thermoelectric performance of Mm y Fe 4− x Co x Sb 12 was investigated. FeSb 2 and Sb have little effect on the figure of merit whilst the presence of MmSb 2 and oxides reduces the thermoelectric performance, when these phases are segregated at the grain boundaries. The decrease of the crystallite size from micro scale (20–100 μm) to nano-scale (100–300 nm) in all cases improves the figure of merit by about 20%. Dislocations have no influence on ZT since the dislocation density after hot pressing is as low as 10 12 m −2 .

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.

The power output of a thermoelectric generator (TEG) was investigated under engine partial-load operation based on measured exhaust gas temperatures and mass flow rates. Materials with properties required for highend temperature TE couples (>500°C) were evaluated. Various possible material combinations for p- and n-legs of these couples as well as the conflicting targets of high efficiency and low cost as required for automotive mass production are discussed. New skutterudite materials for both p- and n-legs as identified during a joint research project are presented, which can help to overcome this conflict. Efficiencies >10% were achieved with these new materials, which have potentially twofold lower production costs than telluride-based materials due to the price of their elements. Some potential for improvement in efficiency and costs has been identified by developing highly integrated TEG units, specifically designed for automotive applications. These initial results of the material development and the evaluation of different integration concepts will be applied in a subsequent step for the fabrication of a pilot number of TEG modules/units.

The phase diagram of the Dy–Ni–Sn ternary system was constructed at 870 K (0–50 at.% Sn) and 770 K (more than 50 at.% Sn) using X-ray analysis and scanning electron microscopy. The interaction of the elements results the formation of 11 ternary compounds—Dy6Ni2Sn (Ho6Co2Ga-type), DyNi5Sn (CeCu4.38In1.62-type), DyNiSn2 (LuNiSn2-type), DyNiSn (TiNiSi-type), Dy2Ni2Sn (W2CoB2-type), DyNiSn4 (LuNiSn4-type), DyNi3Sn2 (HoGa2.4Ni2.6-type), Dy2Ni7Sn3 (own structure type), DyNi2−xSn (YbNi2−xSn-type), Dy3Ni4Sn6 (Ce3Pd4Sn6-type), and Dy4Ni12Sn25 (Ce4Pt12Sn25-type). The formation of Dy2NiSn6 compound with Lu2NiSn6 type structure was found at 670 K. The crystal chemistry analysis of ternary compounds formed in the Dy–Ni–Sn system was done.

The crystal structure, density of electron states, and charge-transport characteristics of an intermetallic semiconductor ZrNiSn heavily doped with acceptor impurity Y (N A Y ≈ 3.8 × 1020−4.8 × 1021 cm−3) have been studied in the temperature range T = 80–380 K. Relation between the impurity concentration and the amplitude of a large-scale fluctuation and also the degree of occupation of the potential well of small-scale fluctuation by charge carriers (fine structure) is established. The results are discussed in the context of the Shklovskii-Efros model for a heavily doped and compensated semiconductor.

Temperature dependences of resistivity, thermoelectric coefficient, and structural characteristics of the n-TiNiSn intermetallic semiconductor heavily doped with Co impurity (the Co concentration NCo ≈ 9.5 × 1019−1.9 × 1021 cm−3) have been studied in the temperature range 80–380 K; the distribution of the electron density of states is also calculated. It is shown that, in TiNi1 − xCoxSn with x < 0.03, the impurity atoms occupy crystallographic sites of atoms Ti and Ni simultaneously and in various proportions and generate the donor and acceptor defects, respectively. It is established that there is a relation between the impurity concentration, the amplitude of a large-scale fluctuation, and also the degree of filling of the potential well of a small-scale fluctuation (fine structure). The results are discussed in the context of the Shklovskiĭ-Efros model of a heavily doped and compensated semiconductor.

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.

Experiments of mechanical alloying/milling of filled and unfilled skutterudites have been performed under various ball milling conditions in order to (a) optimise the preparation of nano-sized skutterudites and (b) to elucidate formation and/or decomposition of unfilled (CoSb 3 ) and filled skutterudites Mm y Fe 4 Sb 12 (Mm means ‘mischmetal’). State-of-the-art X-ray techniques have been used to evaluate the size distribution of the smallest crystallographically undisturbed regions (coherent-scattering-domains), which in many cases are significantly smaller than the physical size of grains. The influence of oxides in in situ precipitations on the stability of the nanostructures at 600 °C was investigated and compared with oxide-free nano-sized skutterudites. It was shown that at 600 °C the crystallites of nano-sized CoSb 3 grow rapidly reaching micro-size after 90 h, whilst in situ oxide stabilized nanostructures MmFe 4 Sb 12 with crystallite size below 200 nm do not show coagulation even after 600 h of heat treatment at 600 °C. The nano-sized oxide composite has a significantly lower lattice thermal conductivity resulting in an improvement of the thermoelectric figure of merit ZT 740 K = 0.52 being about 20% higher than for oxide-free macro-crystalline Mm y Fe 4 Sb 12 as reference. The composition of nano-composite was optimised for large-scale production in oxidizing atmosphere. Attempts to evaluate the dislocation density for ball-milled samples indicate that it is only slightly above the lower limit of resolution of the method of about 10 12 m −2 .

Phase relations at 700 deg. C, 800 deg. C and solidus temperatures have been derived for the clathrate system Ba{sub 8}Cu{sub x}Ge{sub 46-x-y}square{sub y} via X-ray single crystal and powder diffractometry combined with electron probe micro analysis and differential thermal analysis. The ternary clathrate phase derives from binary Ba{sub 8}Ge{sub 43}square{sub 3} and extends up to x=6. Structure investigations define cubic primitive symmetry with the space group type Pm3-barn consistent with a clathrate type I structure throughout the entire homogeneity region 0 =5.5. - Graphical Abstract: Cages and atom thermal displacement parameters in clathrate Ba{sub 8}Cu{sub x}Ge{sub 46-x-y}square{sub y} for Ba{sub 8}Cu{sub 2}Ge{sub 42}square{sub 2} and Ba{sub 8}Cu{sub 6}Ge{sub 40}.

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 ).

Phase relations in the ternary systems Ce–M–Sb (M=Si, Ge, Sn) in composition regions CeSb2–Sb–M were studied by optical and electron microscopy, X-ray diffraction, and electron probe microanalysis on arc-melted alloys and specimens annealed in the temperature region from 850 to 200 °C. The results, in combination with an assessment of all literature data available, were used to construct solidus surfaces and a series of isothermal sections. No ternary compounds were found to form in the Ce–Si–Sb system whilst Ce12Ge9−xSb23+x (3.3

A new series of rare earth compounds with stoichiometry R MgSi 2 ( R =La, Ce, Pr, Nd) is reported. The single crystal X-ray diffraction showed that CeMgSi 2 , which melts congruently at 1200 °C, crystallizes in a new tetragonal structure type ( I 4 1 / amd , tI 32, a =4.2652(4) A, c =36.830(4) A, Z =8; w R 2 =0.042 (19 parameters, 393 F 0 2 ), R 1 =0.018 (297 F 0 >4 σF 0 ). The crystal structure of CeMgSi 2 can be formally built up by alternating along the z direction four CeMg 2 Si 2 -type CeMg 2 Si 2 slabs with four AlB 2 -type CeSi 2 slabs, one after the other. The structural model obtained from a CeMgSi 2 single crystal has been confirmed for the La, Pr and Nd homologous compounds by means of Rietveld refinement. The trend of the unit-cell parameters, plotted versus the R 3+ ionic radius, shows a linear behaviour, which strongly suggests a trivalent state for the Ce atoms. An analysis of the features of this new structure is reported, in comparison with the other known CeMg 2 Si 2 /AlB 2 -type linear intergrowth compounds.

Alloys with nominal composition Nb(Ni1−xAlx)2 (xAl=0.15, 0.23, 0.30, 0.38, 0.46, 0.54, 0.62, 0.69, 0.77, 0.85) were investigated by means of X-ray powder and single crystal diffraction, optical microscopy, electron probe microanalysis (EPMA) concentrating on structural details of the C14 MgZn2-type Laves phase. Rietveld refinements of X-ray powder data ( 0.23 x Al 0.77 ) revealed that Nb atoms fully occupy the 4f sites, whereas Ni and Al atoms share 6h and 2a sites in a random fashion. Single crystal refinement for Nb(Ni0.54Al0.46)2 confirmed structure type and atom order in line with results from powder diffraction. The characteristic site preferences throughout the series of alloys serve as a basis for the interpretation of the non-linear dependence of unit cell parameters with Al content.

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.

Phase relations in the ternary system Ce–Pt–Si have been established for the isothermal section at 800 °C based on X-ray powder diffraction, metallography, scanning electron microscopy (SEM) and electron probe microanalysis (EPMA) techniques on about 120 alloys, which were prepared by various methods employing arc-melting under argon or powder reaction sintering. Nineteen ternary compounds were observed. Atom order in the crystal structures of τ18-Ce5(Pt,Si)4 (Pnma; a=0.77223(3) nm, b=1.53279(8) nm c=0.80054(5) nm), τ3-Ce2Pt7Si4 (Pnma; a=1.96335(8) nm, b=0.40361(4) nm, c=1.12240(6) nm) and τ10-CePtSi2 (Cmcm; a=0.42943(2) nm, b=1.67357(5) nm, c=0.42372(2) nm) was determined by direct methods from X-ray single-crystal CCD data and found to be isotypic with the Sm5Ge4-type, the Ce2Pt7Ge4-type and the CeNiSi2-type, respectively. Rietveld refinements established the atom arrangement in the structures of Pt3Si (Pt3Ge-type, C2/m, a=0.7724(2) nm, b=0.7767(2) nm, c=0.5390(2) nm, β=133.86(2)°), τ16-Ce3Pt5Si (Ce3Pd5Si-type, Imma, a=0.74025(8) nm, b=1.2951(2) nm, c=0.7508(1) nm) and τ17-Ce3PtSi3 (Ba3Al2Ge2-type, Immm, a=0.41065(5) nm, b=0.43221(5) nm, c=1.8375(3) nm). Phase equilibria in Ce–Pt–Si are characterised by the absence of cerium solubility in platinum silicides. Cerium silicides and cerium platinides, however, dissolve significant amounts of the third component, whereby random substitution of the almost equally sized atom species platinum and silicon is reflected in extended homogeneous regions at constant Ce content such as for τ13-Ce(PtxSi1−x)2, τ6-Ce2Pt3+xSi5−x or τ7-CePt2−xSi2+x.

A series of isotypic RE 1.9 Cu 9.2 Sn 2.8 compounds, where RE are Y, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, was synthesized by arc-melting and the crystal structure was determined by X-ray powder diffraction. The structure is a partly disordered substitution variant of the CeNi 5 Sn structure type (space group P 6 3 / mmc ), which consists of CaCu 5 -type fragments of composition RE 0.9 Cu 4.2 Sn 0.8 and fragments of a hypothetical structure of composition RECu 5 Sn 2 . All the RE 1.9 Cu 9.2 Sn 2.8 compounds obtained here are paramagnets and characterized by metal-like conductivity.

Structural and electron transport characteristics of a TiCoSb intermetallic semiconductor heavily doped with the V donor impurity (dopant concentration ∼9.5 × 1019 − 1.9 × 1021 cm−3, temperatures 80–380 K) have been investigated and the distribution of the electron density of states in this material has been calculated. Different occupancies have been established for Co and (Ti, V) atomic positions in the Ti1 − xVxCoSb lattice; this difference is equivalent to introduction of two types of acceptors into the semiconductor. Suppression of the metallic conductivity in the n-type semiconductor with an increase in the donor concentration has been found, which is explained by simultaneous generation of acceptors. It is shown that the methods of numerical calculation adequately describe the physical processes if the occupancy of unit-cell positions is taken into account in construction of the Wigner-Seitz lattice. The results obtained are discussed within the model of a heavily doped and compensated Shklovskii-Efros semiconductor.