Publications (96)124.12 Total impact
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Article: Diffusion-Controlled Formation of Ti2O3 during Spark-Plasma Synthesis.
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ABSTRACT: The spark-plasma-sintering (SPS) technique has successfully been applied for the single-step direct synthesis of Ti2O3 from a mixture of powders of rutile/anatase with titanium. The components react by diffusion through the grain boundaries, forming several intermediate phases locally. A single-phase material of titanium(III) oxide is obtained in compact bulk form after 180 min of SPS treatment at 1473 K. The electrical and thermal transport properties of such a SPS-prepared material measured in the temperature range between 300 and 800 K reflect the known semiconductor-to-metal transition above 400 K. The observed metallic-like electrical and thermal conductivity above this temperature is in good agreement with previously reported results. A maximum of the thermoelectric figure-of-merit ZT = 0.04 is achieved at 350 K.Inorganic Chemistry 03/2013; · 4.60 Impact Factor -
Article: Charge-Doping-Driven Evolution of Magnetism and Non-Fermi-Liquid Behavior in the Filled Skutterudite CePt_{4}Ge_{12-x}Sb_{x}
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ABSTRACT: The filled skutterudite compound CePt_{4}Ge_{12} is situated close to the border between the intermediate valence of Ce and heavy-fermion behavior. Substitution of Ge by Sb drives the system into a strongly correlated and, ultimately, upon further increasing the Sb concentration, an antiferromagnetically ordered state. Our experiments evidence a delicate interplay of emerging Kondo physics and the formation of a local 4f moment. An extended non-Fermi-liquid region, which can be understood in the framework of a Kondo-disorder model, is observed. Band-structure calculations support the conclusion that the physical properties are governed by the interplay of electron supply via Sb substitution and the concomitant volume effects.Physical Review Letters 12/2012; 109(23):236405. · 7.37 Impact Factor -
Article: Charge-Doping driven Evolution of Magnetism and non-Fermi-Liquid Behavior in the Filled Skutterudite CePt4Ge12-xSbx
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ABSTRACT: The filled-skutterudite compound CePt4Ge12 is situated close to the border between intermediate-valence of Ce and heavy-fermion behavior. Substitution of Ge by Sb drives the system into a strongly correlated and ultimately upon further increasing the Sb concentration into an antiferromagnetically ordered state. Our experiments evidence a delicate interplay of emerging Kondo physics and the formation of a local 4f moment. An extended non-Fermi-liquid region, which can be understood in the framework of a Kondo-disorder model, is observed. Band-structure calculations support the conclusion that the physical properties are governed by the interplay of electron supply via Sb substitution and the concomitant volume effects.09/2012; -
Article: Physical properties and crystal chemistry of Ce2Ga12Pt.
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ABSTRACT: Single crystals of the new ternary compound Ce(2)Ga(12)Pt were prepared by the self-flux technique. The crystal structure with the space group P4/nbm was established from single crystal x-ray diffraction data and presents a derivative of the LaGa(6)Ni(0.6) prototype. Magnetic susceptibility measurements show Curie-Weiss behaviour due to local Ce(3+) moments. At high temperatures, the magnetic anisotropy is dominated by the crystal-electric-field (CEF) effect with the easy axis along the crystallographic c direction. Ce(2)Ga(12)Pt undergoes two antiferromagnetic phase transitions at T(N,1) = 7.3 K and T(N,2) = 5.5 K and presents several metamagnetic transitions for the magnetic field along c. Specific-heat measurements prove the bulk nature of these magnetic transitions and reveal a doublet CEF ground state. The 4f contribution to the resistivity shows a broad maximum at T(max) ≈ 85 K due to Kondo scattering off the CEF ground state and excited levels.Journal of Physics Condensed Matter 05/2012; 24(25):256006. · 2.55 Impact Factor -
Article: New scandium rhodium boride Sc4Rh17B12 with a framework structure: synthesis, crystal structure, and properties
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ABSTRACT: The new scandium rhodium boride Sc4Rh17B12 was synthesized by arc-melting of the elements followed by annealing in inert atmosphere. The crystal structure of Sc4Rh17B12 was solved using single crystal X-ray diffraction data. The structure can be described as a three-dimensional frame-work formed by trigonal prisms [BRh6] and [BRh5Sc] with isolated boron atoms inside the prisms and trigonal prisms [BRh5B] representing the coordination polyhedra of paired boron atoms. The temperature dependences of the magnetic susceptibility and specific resistance of Sc4Rh17B12 revealed that the compound is a Pauli paramagnet and shows metal-like specific resistance.Russian Chemical Bulletin 05/2012; 57(3):532-540. · 0.38 Impact Factor -
Article: BaxPd4SnySb12−y: A New Palladium-Containing Skutterudite
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ABSTRACT: A new compound with the filled-skutterudite structure, Ba x Pd4Sn y Sb12−y , was prepared by the flux growth and spark plasma sintering (SPS) techniques. The crystal structure was determined from single crystal and powder x-ray diffraction data. The structure is electronically stabilized by the Sn:Sb ratio, and the lattice parameters depend on this ratio. For magnetic, electrical conductivity, Hall coefficient, Seebeck coefficient and thermal conductivity measurements, single crystal and/or SPS-densified specimens were utilized. Ba1.0Pd4Sn7.1Sb5.2 exhibits diamagnetic behavior. The Hall coefficient is negative and increases with temperature. The lattice thermal conductivity of Ba0.97Pd4Sn6.90Sb4.97 (SPS-densified) is smaller than for CoSb3, but the thermoelectric figure of merit (ZT) is comparatively low due to the low Seebeck coefficient. Key wordsFilled skutterudite-crystal structure-magnetic susceptibility-Hall coefficient-electrical conductivity-Seebeck coefficient-thermal conductivityJournal of Electronic Materials 04/2012; 39(9):1837-1841. · 1.47 Impact Factor -
Article: Electron localizability indicator for correlated wavefunctions. III: singlet and triplet pairs
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ABSTRACT: The electron pair density can be decomposed into the symmetric and antisymmetric parts. The antisymmetric component is connected with the probability that two electrons are coupled to a triplet. On the basis of triplet-coupled electrons the electron localizability indicator is defined, describing the correlation of motion of electrons forming a triplet pair. In case of spin-polarized systems the electron localizability indicator for triplet pairs combines the two spin channels together into a single functional.Theoretical Chemistry Accounts 04/2012; 119(5):413-420. · 2.16 Impact Factor -
Article: Spin dynamics of S-state ions in the filled skutterudites La1-xRx$Pt4Ge12 (R= Gd, Eu)
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ABSTRACT: A detailed study of the spin dynamics of the S-state ions Gd3+ and Eu2+ in the filled skutterudites La1-xRxPt4Ge12 (R= Gd, Eu) is reported. The spin dynamics is investigated directly by means of Gd3+ and Eu2+ electron spin resonance (ESR), performed at X-band (~ 9.4 GHz) and Q-band (~ 34 GHz) frequencies in the temperature intervals 8<T<300 K and 1.5<T<300 K respectively. The ESR parameters provide direct evidence for the vibrational behavior of the Gd3+ ions but not for the Eu2+ ions. These results are interpreted in the light of recent discussions about the spin relaxation in cage systems. In particular, the Gd3+ spin relaxation in La0.9Gd0.1Pt4Ge12 provide evidence for the existence of an extra phonon mode with an Einstein temperature (thetaE) ~ 24 K in this system. The work suggests that the so-called "rattling" modes have a general and important role that should be taken into account in the study of spin dynamics in cage systems.04/2012; -
Article: Structural transformation with "negative volume expansion": chemical bonding and physical behavior of TiGePt.
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ABSTRACT: The synthesis and a joint experimental and theoretical study of the crystal structure and physical properties of the new ternary intermetallic compound TiGePt are presented. Upon heating, TiGePt exhibits an unusual structural phase transition with a huge volume contraction of about 10 %. The transformation is characterized by a strong change in the physical properties, in particular, by an insulator-metal transition. At temperatures below 885 °C TiGePt crystallizes in the cubic MgAgAs (half-Heusler) type (LT phase, space group F43m, a = 5.9349(2) Å). At elevated temperatures, the crystal structure of TiGePt transforms into the TiNiSi structure type (HT phase, space group Pnma, a = 6.38134(9) Å, b = 3.89081(5) Å, c = 7.5034(1) Å). The reversible, temperature-dependent structural transition was investigated by in-situ neutron powder diffraction and dilatometry measurements. The insulator-metal transition, indicated by resistivity measurements, is in accord with band structure calculations yielding a gap of about 0.9 eV for the LT phase and a metallic HT phase. Detailed analysis of the chemical bonding in both modifications revealed an essential change of the Ti-Pt and Ti-Ge interactions as the origin of the dramatic changes in the physical properties.Chemistry 03/2012; 18(20):6272-83. · 5.93 Impact Factor -
Article: Synthesis, crystal structure, and physical properties of the type-I clathrate Ba(8-δ)Ni(x)□(y)Si(46-x-y).
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ABSTRACT: Type-I clathrate phase Ba(8)Ni(x)□(y)Si(46-x-y) (□ = vacancy) was obtained from the elements at 1000 °C with the homogeneity range 2.4 ≤ x ≤ 3.8 and 0 ≤ y ≤ 0.9. In addition, samples with low Ni content (x = 1.4 and 1.6; y = 0) and small Ba deficiency were prepared from the melt by steel-quenching. Compositions were established by microprobe analysis and crystal structure determination. Ba(8-δ)Ni(x)□(y)Si(46-x-y) crystallizes in the space group Pm ̅3n (No. 223) with lattice parameter ranging from a = 10.3088(1) Å for Ba(7.9(1))Ni(1.4(1))Si(44.6(1)) to a = 10.2896(1) Å for Ba(8.00(3))Ni(3.82(4))Si(41.33(6)). Single-crystal X-ray diffraction data together with microprobe analysis indicate an increasing number of framework vacancies toward compositions with higher Ni content. For all compositions investigated, Ni K-edge X-ray absorption spectroscopy measurements showed an electronic state close to that of elemental Ni. All samples exhibit metallic-like behavior with moderate thermopower and low thermal conductivity in the temperature range 300-773 K. Samples with compositions Ba(7.9(1))Ni(1.4(1))Si(44.6(1)) and Ba(7.9(1))Ni(1.6(1))Si(44.4(1)) are superconducting with T(c) values of 6.0 and 5.5 K, respectively.Inorganic Chemistry 03/2012; 51(8):4730-41. · 4.60 Impact Factor -
Article: Insulator-Metal Transition in TiGePt: a combined photoelectron spectroscopy, x-ray absorption spectroscopy, and band structure study
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ABSTRACT: We present a combined experimental and theoretical study of the electronic structure of the intermetallic compound TiGePt by means of photoelectron spectroscopy, x-ray absorption spectroscopy and fullpotential band structure calculations. It was recently shown that TiGePt undergoes a structural phase transition by heating which is accompanied by a large volume contraction and a drastic change of physical properties, in particular a large decrease of the electrical resistivity. The present study revealed substantial differences in the electronic structure for the two TiGePt modifications, although they have the same nominal composition and show similar electron counts for particular valence band states. Our photoemission experiments and band structure calculations establish that an insulator-to-metal transition occurs with an appreciable band broadening and closing of the band gap03/2012; -
Article: Physical properties and valence state of cerium in the filled skutterudite CePt4Ge12
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ABSTRACT: Electronic, magnetic, and transport properties of the filled platinum–germanium skutterudite CePt4Ge12 are investigated. High resolution x-ray absorption spectroscopy measurements at the cerium LIII edge demonstrate that Ce in this compound has a temperature-independent valence close to three. However, magnetic susceptibility, thermopower, Hall effect, and electronic specific heat reveal a broad maximum at Tmax = 65–80 K, suggesting the presence of valence fluctuations. The Sommerfeld coefficient γ = 105 mJ mol−1 K−2, deduced from specific heat, indicates moderately enhanced band masses for CePt4Ge12. We discuss these findings and conclude that CePt4Ge12 represents a system at the border between intermediate valence (IV) and Kondo lattice behavior. In addition, the lattice specific heat and the thermal conductivity are discussed with respect to the vibrational dynamics of Ce in the [Pt4Ge12] framework.Journal of Physics Condensed Matter 11/2011; 23(46):465601. · 2.55 Impact Factor -
Article: Transport properties of the clathrate BaGe5
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ABSTRACT: We report on the synthesis, crystallographic and transport properties of the Zintl phase BaGe5, which crystallizes in a new clathrate-type structure. This compound was synthesized by the decomposition of the type-I clathrate Ba8Ge43□3 subjected to annealing treatment at 623, 673 and 793 K. Electrical resistivity, thermopower and thermal conductivity measurements were performed in the temperature range 2 – 773 K and complemented by magnetization, specific heat and Hall experiments below room temperature. Additional information on the chemical bonding and electronic band structure in BaGe5 was obtained through the electron localizability indicator (ELI) and the total density of states, all calculated within the all-electron full-potential local orbital method (FLPO). In agreement with the chemical bonding and electronic band structure calculations, electrical resistivity and specific heat data show that BaGe5 is a semiconductor. The complex crystal structure of BaGe5 contributes to the low thermal conductivity which displays a conventional crystalline-like behavior. Further measurements were carried out on samples annealed at 623, 673 and 793 K for four up to 30 days to probe possible variations of the crystal structure and electronic properties as a function of the annealing temperature and time. Even though the annealing temperature does not alter the semiconducting nature of this material, differences in the absolute values of the transport properties were unveiled in samples annealed for short-time periods. These differences are significantly reduced in samples which underwent long-time annealing treatment even though the measured curves do not merge completely.Journal of Applied Physics 08/2011; 110(4):043715-043715-12. · 2.17 Impact Factor -
Article: RuIn3-xSnx, RuIn3-xZnx, and Ru1-yIn3—new thermoelectrics based on the semiconductor RuIn3
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ABSTRACT: A systematic investigation of the intermetallic phase Ru1-yIn3 (0 ≤ y ≤ 0.025) and its substitution derivatives RuIn3-xSnx and RuIn3-xZnx (x = 0.01, 0.025, 0.05, and 0.1) is performed. The samples were prepared from a liquid–solid reaction of components with subsequent spark plasma sintering treatment. Ru1-yIn3 exhibits n- and p-type behavior crossing over from low to high temperatures. Substitution of indium by tin or zinc up to 2.5 at.% leads to an increase of the charge carrier concentration, with negative (Sn) or positive (Zn) Seebeck values, respectively. The electrical resistivity was P changed from semiconductor- to metal-like properties by substitution, whereas the thermal conductivity was reduced down to 50% of that of RuIn3. Higher values of the thermoelectric figure of merit were achieved by chemical substitution (RuIn3-xSnx, RuIn3-xZnx), opening up a possibility for tuning the thermoelectric properties in this class of materials.Journal of Materials Research. 08/2011; 26(15):1886 - 1893. -
Article: Magnetic and transport properties of rare-earth-based half-Heusler phases RPdBi: prospective systems for topological quantum phenomena
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ABSTRACT: RPdBi (R = Er, Ho, Gd, Dy, Y, Nd) compounds were studied by means of x-ray diffraction, magnetic susceptibility, electrical resistivity, magnetoresistivity, thermoelectric power and Hall effect measurements, performed in the temperature range 1.5-300 K and in magnetic fields up to 12 T. These ternaries, except diamagnetic YPdBi, exhibit localized magnetism of $R^{3+}$ ions, and order antiferromagnetically at low temperatures ($T_{N}$ = 2-13 K). The transport measurements revealed behavior characteristic of semimetals or narrow-band semiconductors. Both, electrons and holes contribute to the conductivity with dominant role of p-type carriers. The Hall effect of ErPdBi is strongly temperature and magnetic field dependent, reflecting complex character of the underlying electronic structures with multiple electron and hole bands. RPdBi, and especially DyPdBi, exhibit very good thermoelectric properties with a power factor coefficient $PF$ ranging from 6 to 20 $\mu$Wcm$^{-1}$K$^{-2}$.06/2011; -
Article: Evidence for time-reversal symmetry breaking in superconducting PrPt4Ge12
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ABSTRACT: Zero and longitudinal field muon spin rotation (muSR) experiments were performed on the superconductors PrPt4Ge12 and LaPt4Ge12. In PrPt4Ge12 below Tc a spontaneous magnetization with a temperature variation resembling that of the superfluid density appears. This observation implies time-reversal symmetry (TRS) breaking in PrPt4Ge12 below Tc = 7.9 K. This remarkably high Tc for an anomalous superconductor and the weak and gradual change of Tc and of the related specific heat anomaly upon La substitution in La_(1-x)Pr_xPt_4Ge_(12) suggests that the TRS breaking is due to orbital degrees of freedom of the Cooper pairs. Comment: To appear in Phys. Rev. B. 5 pages, 3 figures07/2010; -
Article: Magnetic order in the filled skutterudites RPt4Ge12 (R = Nd, Eu)
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ABSTRACT: Rare-earth metal filled skutterudites RPt4Ge12 with R=La-Nd, and Eu exhibit a variety of different ground states, e.g., conventional and unconventional superconductivity in LaPt4Ge12 and PrPt4Ge12, respectively, and intermediate valence behavior in CePt4Ge12. In this work we investigate the magnetic state of NdPt4Ge12 and EuPt4Ge12 by specific heat, dc-susceptibility and magnetization. NdPt4Ge12 shows two magnetic phase transitions at T_N1=0.67 K and T_N2=0.58 K, while EuPt4Ge12 displays a complex magnetic phase diagram below the magnetic ordering temperature of 1.78 K. The specific heat indicates that in NdPt4Ge12 the crystalline electric field (CEF) ground state of the Nd3+ is a quartet and that, as expected, in EuPt4Ge12 the Eu2+ state is fully degenerate.07/2010; -
Article: Magnetic properties and electronic structures of intermediate valence systems CeRhSi2 and Ce2Rh3Si5.
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ABSTRACT: The crystal structures and the physical (magnetic, electrical transport and thermodynamic) properties of the ternary compounds CeRhSi(2) and Ce(2)Rh(3)Si(5) (orthorhombic CeNiSi(2)- and U(2)Co(3)Si(5)-type structures, respectively) were studied over wide ranges of temperature and magnetic field strength. The results revealed that both materials are valence fluctuating systems, in line with previous literature reports. Direct evidence for valence fluctuations was obtained by means of Ce L(III)-edge x-ray absorption spectroscopy and Ce 3d core-level x-ray photoelectron spectroscopy. The experimental data were confronted with the results of ab initio calculations of the electronic band structures in both compounds.Journal of Physics Condensed Matter 06/2010; 22(21):215601. · 2.55 Impact Factor -
Article: Physical properties of β-TmAlB4; an AlB2-type analogous “tiling” compound
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ABSTRACT: β -TmAlB <sub>4</sub> was synthesized, and the magnetic properties and specific heat investigated in comparison with those of the α -type structure. Recent developments in rare earth aluminoboride compounds with two-dimensional boron layers have attracted interest due to the heavy fermion superconductivity in β -YbAlB <sub>4</sub> , multiple anomalies manifesting below the Néel temperatures in α -TmAlB <sub>4</sub> attributed to intrinsic building defects, and field stable state in Tm <sub>2</sub> AlB <sub>6</sub> . Strikingly, despite similarities in the metal-metal nearest neighbor distances and structural motifs, the strength of the magnetic interactions (temperature scale) in β -TmAlB <sub>4</sub> was discovered to be approximately 60% stronger that of the alpha phase (i.e., T<sub> N </sub>=9.2 versus 5.8 K). An anomaly in the specific heat with extreme field stability was also found with a temperature scale significantly higher compared to that of the α -type structure. This anomaly is conjectured to be a precursor to the antiferromagnetic transition and may be a particular feature of these “tiling” compounds with analogy to AlB <sub>2</sub> -type structure.Journal of Applied Physics 06/2010; · 2.17 Impact Factor -
Article: Anisotropic physical properties of the Al13Fe4 complex intermetallic and its ternary derivative Al13(Fe,Ni)4
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ABSTRACT: We have investigated the magnetic susceptibility, the electrical resistivity, the specific heat, the thermoelectric power, the Hall coefficient, and the thermal conductivity of the Al13Fe4 and Al13(Fe,Ni)4 monoclinic approximants to the decagonal quasicrystal. While the Al13Fe4 crystals are structurally well ordered, the ternary derivative Al13(Fe,Ni)4 contains substitutional disorder and is considered as a disordered version of the Al13Fe4 . The crystallographic-direction-dependent measurements were performed along the a∗ , b , and c directions of the monoclinic unit cell, where the (a∗,c) atomic planes are stacked along the b direction. The electronic transport and the magnetic properties exhibit significant anisotropy. The stacking b direction is the most conducting direction for the electricity and heat. The effect of substitutional disorder in Al13(Fe,Ni)4 is manifested in the large residual resistivity ρ(T→0) and significantly reduced thermal conductivity of this compound, as compared to the ordered Al13Fe4 . Specific-heat measurements reveal that the electronic density of states at the Fermi level of both compounds is high. The anisotropic Hall coefficient RH reflects complex structure of the anisotropic Fermi surface that contains electronlike and holelike contributions. Depending on the combination of directions of the current and the magnetic field, electronlike (RH<0) or holelike (RH>0) contributions may dominate, or the two contributions compensate each other (RH≈0) . Similar complicated anisotropic behavior was observed also in the thermopower. The anisotropic Fermi surface was calculated ab initio using the atomic parameters of the refined Al13Fe4 structural model that is also presented in this work.Physical review. B, Condensed matter 04/2010; 81(18):184203.
Top co-authors
Top Journals
Institutions
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2001–2013
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Max-Planck-Institut für chemische Physik fester Stoffe
Dresden, Saxony, Germany
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2005–2010
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Polish Academy of Sciences
Warsaw, Masovian Voivodeship, Poland -
Kazan State Medical University
Kazan’, Respublika Tatarstan, Russia
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2009
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Uniwersytet Śląski w Katowicach
- Institute of Physics
Katowice, Silesian Voivodeship, Poland
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2007
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University of Geneva
Carouge, GE, Switzerland
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1998
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Max-Planck-Institut für Festkörperforschung
Stuttgart, Baden-Wuerttemberg, Germany
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