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[hide abstract]
ABSTRACT: The crystal structure of Ti(8)(Ti(x)Mn(1-x))(6)Mn(39), x = 0.187, was obtained from x-ray single-crystal diffraction data, confirming it to have rhombohedral symmetry (space group [Formula: see text]; a(hex) = 1.100 70(2) nm, c(hex) = 1.944 11(4) nm; R(F) = 0.0293) and isotypism with the prototype Mo(0.38)Cr(0.16)Co(0.46) (the so-called R-phase). On the basis of electron probe micro-analyser results and structure determination, the homogeneity region of the phase TiMn(∼4) was determined for temperatures in the range 800 °C < T < 1200 °C and is in between 16.0 at.% Ti and 20 at.% Ti. Various physical properties, determined in the temperature range from ∼2 K to room temperature, characterize the compound with composition TiMn(4.26) as a metallic spin fluctuation system, evidenced from a T(3)lnT dependence of the heat capacity in combination with large values of the electronic Sommerfeld constant of the order of 140 mJ mol(-1) K(-2). The occurrence of a small anomaly in the heat capacity and magnetization data around 10 K is attributed to a scenario involving spin freezing phenomena, since a fraction of the order of 10% of all Mn-Mn distances within the unit cell are above a critical distance, where Mn atoms carry a spontaneous magnetic moment.
Journal of Physics Condensed Matter 02/2013; 25(10):106002. · 2.55 Impact Factor
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Journal of Alloys and Compounds. 02/2013; 550:302-307.
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[show abstract]
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ABSTRACT: Phase relations and solidification behavior in the Ge-rich part of the phase diagram have been determined in two isothermal sections at 700 and 750 °C and in a liquidus projection. A reaction scheme has been derived in the form of a Schulz-Scheil diagram. Phase equilibria are characterized by three ternary compounds: τ(1)-BaRhGe(3) (BaNiSn(3)-type) and two novel phases, τ(2)-Ba(3)Rh(4)Ge(16) and τ(3)-Ba(5)Rh(15)Ge(36-x), both forming in peritectic reactions. The crystal structures of τ(2) and τ(3) have been elucidated from single-crystal X-ray intensity data and were found to crystallize in unique structure types: Ba(3)Rh(4)Ge(16) is tetragonal (I4/mmm, a = 0.65643(2) nm, c = 2.20367(8) nm, and R(F) = 0.0273), whereas atoms in Ba(5)Rh(15)Ge(36-x) (x = 0.25) arrange in a large orthorhombic unit cell (Fddd, a = 0.84570(2) nm, b = 1.4725(2) nm, c = 6.644(3) nm, and R(F) = 0.034). The body-centered-cubic superstructure of binary Ba(8)Ge(43)□(3) was observed to extend at 800 °C to Ba(8)Rh(0.6)Ge(43)□(2.4), while the clathrate type I phase, κ(I)-Ba(8)Rh(x)Ge(46-x-y)□(y), reveals a maximum solubility of x = 1.2 Rh atoms in the structure at a vacancy level of y = 2.0. The cubic lattice parameter increases with increasing Rh content. Clathrate I decomposes eutectoidally at 740 °C: κ(I) ⇔ (Ge) + κ(IX) + τ(2). A very small solubility range is observed at 750 °C for the clathrate IX, κ(IX)-Ba(6)Rh(x)Ge(25-x) (x ∼ 0.16). Density functional theory calculations have been performed to derive the enthalpies of formation and densities of states for various compositions Ba(8)Rh(x)Ge(46-x) (x = 0-6). The physical properties have been investigated for the phases κ(I), τ(1), τ(2), and τ(3), documenting a change from thermoelectric (κ(I)) to superconducting behavior (τ(2)). The electrical resistivity of κ(I)-Ba(8)Rh(1.2)Ge(42.8)□(2.0) increases almost linearly with the temperature from room temperature to 730 K, and the Seebeck coefficient is negative throughout the same temperature range. τ(1)-BaRhGe(3) has a typical metallic electrical resistivity. A superconducting transition at T(C) = 6.5 K was observed for τ(2)-Ba(3)Rh(4)Ge(16), whereas τ(3)-Ba(5)Rh(15)Ge(35.75) showed metallic-like behavior down to 4 K.
Inorganic Chemistry 01/2013; · 4.60 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: The phase relations, crystal structure and thermoelectric properties of the type-I solid solution Ba(8)Ni(x)Si(46-x) were investigated. Based on X-ray diffraction, differential thermal analysis and electron probe microanalysis data, a partial phase diagram was constructed for the Si-rich part of ternary system Ba-Ni-Si at 800 °C. The solubility range of Ni in the clathrate-I phase at 800 °C was determined (2.9 ≤x≤ 3.8) and thermoelectric properties, namely electrical resistivity, Seebeck-coefficient and thermal conductivity, were measured in the temperature range from 300 to 850 K. A shift of the thermoelectric properties from a predominantly metallic to a more semiconducting behavior was observed for an increasing Ni-content. Density functional calculations revealed a significant decrease of the gap width in the density of states induced by the incorporation of Ni. Electrical resistivity and Seebeck coefficients for Ba(8)Ni(x)Si(46-x) with 3.3 ≤x≤ 3.8 have been modeled within the rigid band approximation.
Dalton Transactions 06/2012; 41(29):8839-49. · 3.84 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: TypeI clathrates have been considered as promising thermoelectric materials due to their special structural characteristics:
the “rattling” guest atoms in the larger of the two cages of the clathrateI structure are frequently held responsible for
the low lattice thermal conductivity. By single-crystal x-ray diffraction, we investigated the quaternary clathrates Ba8Cu5Si
x
Ge41−x
(x=6, 18, 41). Rietveld refinements confirmed that the clathrates in this system crystallize with cubic primitive symmetry,
in the typeI clathrate structure, and that no phase transitions occur in the temperature range investigated (100K to 300K).
We derive the concentration dependencies of the Debye temperature, the Einstein temperatures, the static disorder parameters,
and the size of the two cages and argue that these dependencies underpin the previously assumed different bonding character
of the Ba guest atoms in the larger and smaller cages. The linear thermal expansion coefficients for the samples are derived.
KeywordsClathrate–single-crystal x-ray diffraction–cage size–thermal expansion coefficient
Journal of Electronic Materials 04/2012; 40(5):589-596. · 1.47 Impact Factor
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ABSTRACT: 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.
KeywordsSkutterudites-thermoelectrical generator unit-automotive application
Journal of Electronic Materials 04/2012; 39(9):2074-2078. · 1.47 Impact Factor
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ABSTRACT: Phase relations in the ternary system Al-Ru-Ti were studied on arc-melted alloys and specimens annealed at 1100 °C, 950 °C,
and 800 °C employing optical and electron microscopy, x-ray diffraction, and electron probe microanalysis. The results, in
combination with an assessment of all literature data available, were used to construct liquidus and solidus surfaces, a series
of isothermal sections, and a Schulz-Scheil diagram monitoring solidification (crystallization) in thermodynamic equilibrium.
The crystal structure of the ternary G-phase was determined by x-ray single crystal diffraction to be a filled variant of
the Th6Mn23-type (space group Fm3m). Furthermore, a new ternary compound with AuCu3-type structure was detected.
Journal of Phase Equilibria 04/2012; 24(6):511-527.
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ABSTRACT: 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[`3]n 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 2.7at.% gold at 800°C. Phase equlilibria at 800°C are characterized by four ternary
phases in the investigated region up to 33.3at.% 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\textBaAu5 \textSi2 ,b = b\textBaAu5 \textSi2 ,c = 2c\textBaAu5 \textSi2 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.
Keywordscrystal structure–isothermal section–phase transition–ternary system–x-ray analysis
Journal of Phase Equilibria and Diffusion 04/2012; 32(2):115-127. · 0.62 Impact Factor
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ABSTRACT: The homogeneity ranges of the Laves phases and phase relations concerning the Laves phases in the quaternary system Ti-Fe-Ni-Al
at 900 °C were defined by x-ray powder diffraction (XPD) data and electron probe microanalysis (EPMA). Although at higher
temperatures the Laves phase forms a continuous solid solution, two separate homogeneity fields of TiFe2-based (denoted by λFe) and Ti(TiNiAl)2-based (denoted by λNi) Laves phases appear at 900 °C. The relative locations of Laves phases, G phase, Heusler phase, and CsCl-type phase as well
as the associated tie-tetrahedra were experimentally established in the quaternary for 900 °C and presented in three-dimensional
(3D) view. Furthermore, a partial isothermal section TiFe2-TiAl2-TiNi2 was constructed, and a connectivity scheme, derived for equilibria involving Laves phases in the Ti-Fe-Ni-Al quaternary system
at 900 °C was derived. As a characteristic feature of the quaternary phase diagram, the solid solubility of fourth elements
in both the TiFe2-based and Ti(NiAl)2-based Laves phases is limited at 900 °C and is dependent on the ternary Laves phase composition. A maximum solubility of
about 8 at.% Ni is reached for composition Ti33.3Fe33.3Al33.4. Structural details have been evaluated from powder x-ray and neutron diffraction data for (i) the Ti-Fe-Ni ternary and the
Ti-Fe-Ni-Al quaternary Laves phases (MgZn2-type, space group: P63/mmc) and (ii) the quaternary G phase. Atom site occupation behavior for all phases from the quaternary system corresponds to
that of the ternary systems. For the quaternary Laves phase, Ti occupies the 4f site and additional Ti (for compositions higher than 33.3 at.%Ti) preferably enters the 6h site. Aluminum and (Fe,Ni) share the 6h and the 2a sites. The compositional dependence of unit cell dimensions, atomic coordinates, and interatomic distances for the Laves
phases from the quaternary system is discussed. For the quaternary cubic G phase, a centrosymmetric as well as a noncentrosymmetric
variety was observed depending on the composition: from combined x-ray and neutron powder diffraction measurements Ti33.33Fe13.33Ni10.67Al42.67 was found to adopt the lower symmetry with space group
F[`4]3m F\bar 43m .
Journal of Phase Equilibria and Diffusion 04/2012; 29(5):414-428. · 0.62 Impact Factor
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[show abstract]
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ABSTRACT: Alloys with composition Ti25(Fe50−x
Ni
x
)Al25 (0≤x≤50) were investigated employing electron probe microanalysis (EPMA) and X-ray powder diffraction (XPD). For TiFe2Al, insitu neutron powder diffraction (ND) was used for the inspection of phase constitution covering the temperature range
from 27°C (300K) to 1277°C (1550K). Combined Rietveld refinement of ND and XPD data for TiFe2Al revealed that Fe atoms occupy the 8c site in space group Fm[`3]m , Fm\bar{3}m , Ti with a small amount of Al sharing the 4a site, and the remaining Ti and Al atoms adopting the 4b site. This structural model was successfully applied in the refinement of all alloys Ti25(Fe50−x
Ni
x
)Al25 (0≤x≤50). Partial atom order exists on the Fe-rich side while complete order is observed for the Ni-rich side. Profiles recorded
by insitu neutron powder diffraction for TiFe2Al in the range of investigated temperatures show two phases, namely Heusler phase and MgZn2-type Laves phase. Diffraction peaks from the Heusler phase dominate the profiles at lower temperatures but at higher temperatures
the MgZn2-type Laves phase is the main phase. No CsCl-type phase was found in the alloy in the investigated temperature range. The
thermal expansion coefficient of TiFe2Al is 1.4552×10−5K−1.
Journal of Phase Equilibria and Diffusion 04/2012; 29(6):500-508. · 0.62 Impact Factor
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[show abstract]
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ABSTRACT: In the present work we focus on cubic typeI Ba-Ge-based clathrates, where Ge in
Ba8Ge43 \square3\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[`3]nPm\bar{3}n of a typical typeI clathrate structure with lattice parameter a≈1.06nm. Electronic transport has been studied in a broad temperature range from 4.2K to about 800K, 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 400μV/K in the case of Ba8Cu5.2Zn0.8Ge40.0 at temperatures well below room temperature (T
max
S
≈150K).
KeywordsTypeI clathrates-Ba8Ge46−x
-transport properties-figure of merit-metal-to-insulator transition
Journal of Electronic Materials 04/2012; 39(9):1687-1691. · 1.47 Impact Factor
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[show abstract]
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ABSTRACT: High temperature thermoelectric (TE) properties for triple-filled skutterudites (Sr(x)Ba(x)Yb₁₋₂x)(y)Co₄Sb₁₂ were investigated for alloy compositions in two sections of the system: (a) for x = 0.25 with a filling fraction y ranging from 0.1 to 0.25 and (b) for 0 < x < 0.5 and y = 0.11 + 0.259x. The representation of the figure of merit, ZT, as a function of skutterudite composition, defined the compositional range (0.25 < x < 0.4; 0.18 < y < 0.24) with ZT over 1.4 at 800 K. It was shown that an enhanced TE performance for these triple-filled skutterudites is caused by low electrical resistivities and low lattice thermal conductivities, as well as by a fine tuning of the chemical composition. Low temperature measurements for the samples with the highest ZT values showed that even a small change of the filler ratios changes the contribution of scattering effects, the carrier concentration and the mobility.
Journal of Physics Condensed Matter 07/2011; 23(27):275601. · 2.55 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: High temperature thermoelectric (TE) properties for triple-filled skutterudites (SrxBaxYb1 − 2x)yCo4Sb12 were investigated for alloy compositions in two sections of the system: (a) for x = 0.25 with a filling fraction y ranging from 0.1 to 0.25 and (b) for 0 < x < 0.5 and y = 0.11 + 0.259x. The representation of the figure of merit, ZT, as a function of skutterudite composition, defined the compositional range (0.25 < x < 0.4; 0.18 < y < 0.24) with ZT over 1.4 at 800 K. It was shown that an enhanced TE performance for these triple-filled skutterudites is caused by low electrical resistivities and low lattice thermal conductivities, as well as by a fine tuning of the chemical composition. Low temperature measurements for the samples with the highest ZT values showed that even a small change of the filler ratios changes the contribution of scattering effects, the carrier concentration and the mobility.
Journal of Physics Condensed Matter 06/2011; 23(27):275601. · 2.55 Impact Factor
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[show abstract]
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ABSTRACT: Ti(2)(Ti(0.16)Ni(0.43)Al(0.41))(3) is a novel compound (labeled as τ(6)) in the Ti-rich region of the Ti-Ni-Al system in a limited temperature range 870 < T < 980 °C. The structure of τ(6)-Ti(2)(Ti,Ni,Al)(3) was solved from a combined analysis of X-ray single crystal and neutron powder diffracton data (space group C2/m, a = 1.85383(7) nm, b = 0.49970(2) nm, c = 0.81511(3) nm, and β = 99.597(3)°). τ(6)-Ti(2)(Ti,Ni,Al)(3) as a variant of the V(2)(Co(0.57)Si(0.43))(3)-type is a combination of slabs of the MgZn(2)-Laves type and slabs of the Zr(4)Al(3)-type forming a tetrahedrally close-packed Frank-Kasper structure with pentagon-triangle main layers. Titanium atoms occupy the vanadium sites, but Ti/Ni/Al atoms randomly share the (Co/Si) sites of V(2)(Co(0.57)Si(0.43))(3). Although τ(6) shows a random replacement on 6 of the 11 atom sites, it has no significant homogeneity range (~1 at. %). The composition of τ(6) changes slightly with temperature. DSC/DTA runs (1 K/min) were not sufficient to define proper reaction temperatures due to slow reaction kinetics. Therefore, phase equilibria related to τ(6) were derived from X-ray powder diffraction in combination with EPMA on alloys, which were annealed at carefully set temperatures and quenched. τ(6) forms from a peritectoid reaction η-(Ti,Al)(2)Ni + τ(3) + α(2) ↔ τ(6) at 980 °C and decomposes in a eutectoid reaction τ(6) ↔ η + τ(4) + α(2) at 870 °C. Both reactions involve the η-(Ti,Al)(2)Ni phase, for which the atom distribution was derived from X-ray single crystal intensity data, revealing Ti/Al randomly sharing the 48f- and 16c-positions in space group Fd3̅m (Ti(2)Ni-type, a = 1.12543(3) nm). There was no residual electron density at the octahedral centers of the crystal structure ruling out impurity stabilization. Phase equilibria involving the τ(6) phase have been established for various temperatures (T = 865, 900, 925, 950, 975 °C, and subsolidus). The reaction isotherms concerning the τ(6) phase have been established and are summarized in a Schultz-Scheil diagram.
Inorganic Chemistry 05/2011; 50(10):4537-47. · 4.60 Impact Factor
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[show abstract]
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ABSTRACT: We report powder inelastic neutron-scattering experiments on the type-I clathrates Ba8ZnxGe46−x−y◻y with x=0,2,4,6,8, y=3−3x/8, and ◻ characterizing a vacancy. The focus of this study is set on the modulation of the eigenfrequency distribution of the clathrate compounds by the progressive substitution of germanium by zinc and its response to temperature variation between 2 and 300 K. A shift of a number of peaks toward higher energies by about 1–2 meV can be confirmed as a result of the substitution. An identification of the partial contribution of the barium cations to the eigenmode spectrum has been determined by ab initio lattice-dynamics calculation of the compounds Ba8Zn6Ge40 and Ba8Ge43◻3. The Ba-weighted eigenmodes are located predominantly at energies lower than 14 meV. Within the resolution of the experiment the density of vibrational states associated with the Ba2 site, e.g., modes at about 4.8 meV, are not affected by the substitution. The entire suite of our temperature-dependent data on Ba8ZnxGe46−x−y◻y is in agreement with a softening of the mode at 4.5–4.8 meV upon cooling by at most 5%. No clear temperature effect on the Ba-weighted modes can be confirmed in the binary Ba8Ge43◻3 and Ba8Zn2Ge41.2◻2.8 compounds. Higher-frequency Ge and Zn weighted modes display a redshift upon heating.
Phys. Rev. B. 12/2010; 82(21).
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G. Rogl,
L. Zhang,
P. Rogl, A. Grytsiv,
M. Falmbigl,
D. Rajs,
M. Kriegisch,
H. Muller,
E. Bauer,
J. Koppensteiner,
W. Schranz,
M. Zehetbauer,
Z. Henkie,
M. B. Maple
[show abstract]
[hide abstract]
ABSTRACT: The current paper gives an overview of the newly obtained thermal expansion coefficients of skutterudites as well as those so far available in literature. Thermal expansion was determined for CoSb <sub>3</sub> , Pt <sub>4</sub> Sn <sub>4.4</sub> Sb <sub>7.6</sub> , for As- and Ge-based skutterudites as well as for various high-ZT skutterudites (micro- and nanostructured) with didymium (DD) and mischmetal (Mm) as filler atoms in frameworks of ( Fe <sub>1- x </sub> Co <sub> x </sub>)<sub>4</sub> Sb <sub>12</sub> and ( Fe <sub>1- x </sub> Ni <sub> x </sub>)<sub>4</sub> Sb <sub>12</sub> , and for double and triple-filled skutterudites such as Ca <sub>0.07</sub> Ba <sub>0.23</sub> Co <sub>3.95</sub> Ni <sub>0.05</sub> Sb <sub>12</sub> and Sr <sub>0.025</sub> Ba <sub>0.075</sub> Yb <sub>0.1</sub> Co <sub>4</sub> Sb <sub>12</sub> . For low temperatures, a capacitance dilatometer was used (4–300 K), whereas for temperatures 300≪ T ≪750 K , a dynamic mechanical analyzer was employed. For a set of Ge-, P-, and Sb-based skutterudites, lattice parameters of single crystals, measured at three different temperatures, were used to derive the thermal expansion coefficient. The semiclassical model of Mukherjee [Phys. Rev. Lett. 76, 1876 (1996)] has been successfully used to quantitatively describe the thermal expansion coefficient in terms of Einstein and Debye temperatures, which compare well with the corresponding results from specific heat, electrical resistivity, or temperature depend-
ent x-ray measurements.
Journal of Applied Physics 03/2010; · 2.17 Impact Factor
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[show abstract]
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ABSTRACT: The influences of single, double and triple filling of Yb, Ba and Sr in CoSb3 on thermoelectric performance were evaluated. A significant suppression of lattice thermal conductivity κl is achieved by the increase in the number of filler elements. The highest power factor appears in triple-filled (Ba0.1Yb0.1)0.25(Sr0.1Yb0.1)0.75Co4Sb12, whereas single-filled Ba0.23Co4Sb12 has higher S2/ρ than double-filled (Ba,Yb)0.2Co4Sb12 forming a sequence S2/ρ(triple filling) > S2/ρ(single filling) > S2/ρ(double filling). However, the respective figures of merit follow a sequence ZT(triple filling) > ZT(double filling) > ZT(single filling) proving a strong correlation with κl that appears to be a predominant factor in the efficiency of filled skutterudites. Thus, κ and ZT increase with increasing lattice thermal resistivity (1/κl) and maximum efficiencies may be obtained for 1/κl > 0.2 cm K mW−1.
Journal of Physics D Applied Physics 10/2009; 42(22):225405. · 2.54 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: Novel ternary type-I clathrate compounds Ba(8){Zn,Cd}(x)Si(46-x), x∼7 have been synthesized from the elements by melting and reacting in quartz ampoules. Structural investigations for both compounds, i.e. x-ray single-crystal data at 300, 200 and 100 K for Ba(8)Zn(7)Si(39) and Rietveld data for Ba(8)Cd(7)Si(39), confirm cubic primitive symmetry consistent with the space group type [Formula: see text] (a(Ba(8)Zn(7)Si(39)) = 1.043 72(1) nm; a(Ba(8)Cd(7)Si(39)) = 1.058 66(3) nm). Whereas for Ba(8)Zn(7)Si(39) site 16i is completely occupied by Si atoms, a random atom distribution with different Zn/Si ratio exists for the two sites, 6d (0.77Zn+0.23Si) and 24k (0.91Si+0.09Zn). No vacancies are encountered and all atom sites are fully occupied. This atom distribution is independent of temperature. Rietveld refinements for Ba(8)Cd(7)Si(39) show that the 6d site is fully occupied by Cd atoms, leaving only the 24k site for a random occupation (0.96Si+0.04Cd) consistent with the chemical formula Ba(8)Cd(7)Si(39). The temperature-dependent x-ray spectra for Ba(8)Zn(7)Si(39) define an Einstein mode, Θ(E,U33) = 80 K. Studies of transport properties show electrons as the majority charge carriers in the system. Although the Cd- and Zn-based samples are isoelectronic, a significantly different electronic transport points towards substantial differences in the electronic density of states in both cases.
Journal of Physics Condensed Matter 09/2009; 21(38):385404. · 2.55 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: Novel ternary type-I clathrate compounds Ba8{Zn,Cd}xSi46−x, x~7 have been synthesized from the elements by melting and reacting in quartz ampoules. Structural investigations for both compounds, i.e. x-ray single-crystal data at 300, 200 and 100 K for Ba8Zn7Si39 and Rietveld data for Ba8Cd7Si39, confirm cubic primitive symmetry consistent with the space group type (aBa8Zn7Si39 = 1.043 72(1) nm; aBa8Cd7Si39 = 1.058 66(3) nm). Whereas for Ba8Zn7Si39 site 16i is completely occupied by Si atoms, a random atom distribution with different Zn/Si ratio exists for the two sites, 6d (0.77Zn+0.23Si) and 24k (0.91Si+0.09Zn). No vacancies are encountered and all atom sites are fully occupied. This atom distribution is independent of temperature. Rietveld refinements for Ba8Cd7Si39 show that the 6d site is fully occupied by Cd atoms, leaving only the 24k site for a random occupation (0.96Si+0.04Cd) consistent with the chemical formula Ba8Cd7Si39. The temperature-dependent x-ray spectra for Ba8Zn7Si39 define an Einstein mode, ΘE,U33 = 80 K. Studies of transport properties show electrons as the majority charge carriers in the system. Although the Cd- and Zn-based samples are isoelectronic, a significantly different electronic transport points towards substantial differences in the electronic density of states in both cases.
Journal of Physics Condensed Matter 08/2009; 21(38):385404. · 2.55 Impact Factor
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H. Kaldarar,
E. Royanian,
H. Michor,
G. Hilscher,
E. Bauer,
A. Gribanov,
D. Shtepa,
P. Rogl, A. Grytsiv,
Y. Seropegin,
S. Nesterenko
[show abstract]
[hide abstract]
ABSTRACT: In this work, we report on the physical properties of orthorhombic CePd3In2 in comparison with isotypic LaPd3In2 (space group Pnma). X-ray powder diffraction Rietveld analysis revealed single-phase composition of both specimens CePd3In2 and LaPd3In2 confirming the CePd3In2 type with space group Pnma. The lattice parameters are a=1.02788(8), b=0.46237(4), and c=0.98765(9) nm for CePd3In2 and a=1.02986(14), b=0.46424(6), and c=0.99498(13) nm for LaPd3In2. Physical properties of CePd3In2 at low temperatures are dominated by a magnetic phase transition into an antiferromagnetic ground state below TN∼2.1 K. A mutual interplay of the Kondo effect and the Rudermann-Kittel-Kasuy-Yoshida interaction is responsible for a large Sommerfeld value γ∼500 mJ/mol K2 derived from a model which simultaneously describes the Kondo effect and long-range magnetic order.
Phys. Rev. B. 05/2009; 79(20).
