Thermal conductivity of superconducting MgB 2 was studied in both the superconducting and the normal state region. The latter is almost equally determined by the electronic-and the lattice contribution to the total thermal conductivity. In the superconducting state, however, the lattice contribution is larger. The electronic thermal conductivity below T c was derived from the experimental data considering the Bardeen-Rickayzen-Tewordt theory together with the model of Geilikman. The analysis shows that electron scattering on static imperfections dominates.

Purpose Cathepsin X is a recently identified member of the papain-like cysteine protease family that is expressed by many cell types. The in vivo functions of Cathepsin X are unknown. Hence, the aims of this study are to localize cathepsin X expression in the mouse retina and to compare the retinal morphology and ERG function of cathepsin X knock-out mice (Ctsx-/-) to congenic wild type C57Bl/6 mice (Ctsx+/+). Methods Left eyes of adult mice were prepared for paraffin- and right eyes for cryo-sections. Histology was accomplished by Hämalaun-Eosin and PAS staining after depigmentation. Expression of cathepsin X and the proliferation marker Ki67 were investigated by immunohistochemistry. Retinal function was tested by ERG. Results Cathepsin X expression in WT mice accumulates along the external limiting membrane. Additionally, a netlike pattern of cathepsin X was found around the neuronal cells in the inner nuclear and ganglion cell layer. There is no significant difference between cathepsin X knock-out and WT mice in retinal morphology, cell proliferation or ERG readings. Conclusion We found prominent expression of cathepsin X in WT mice retina. Normal retinal morphology and ERG function in cathepsin X knock-out mice, however, suggest that other cathepsins might compensate for the loss of retinal cathepsin X.

Pr0.73Fe4Sb12 orders magnetically below about 5.5K. Magnetic order disappears upon Fe substitution by Ni or Co. The Seebeck coefficients is strongly influenced by the Fe/(Ni,Co) substitution and reaches values of up to 230μV/K at about 450K. Thus this series of compounds represents an attractive candidate for future thermoelectric applications.

Filled skutterudites RETM4X12 with RE = rare earth, TM = transition metal and X = pnictogen represent a class of complex materials exhibiting a broad variety of ground state properties. These model systems also allow to tailor the charge carrier density in order to optimise the thermoelectric performance with respect to its applicability in both, energy conversion and cooling processes. The present review focuses mainly on strong electron correlations in such compounds and their effect on thermoelectric properties.

Based on an analysis of the geometric crystallographic relations a general classification scheme is presented for intermetallides with four-coordinated networks isomorphous with hydrate clathrates. We prepared novel europium substituted clathrates, Eu2−x(Sr,Ba)6−xMySi46−y (M=Al, Ga), consistent with the standardized clathrate I—Ba8Al16Ge30 type structure (space group Pm3̄n). Europium atoms in Ba compounds preferentially occupy the 2a position and thus form a new quaternary version of the Ba8Al16Ge30 structure type. All clathrates studied are metals with low electrical conductivity. The negative Seebeck coefficients indicate transport processes dominated by electrons as carriers. Eu2Ba6Al8Si36 and Eu2Ba6Ga8Si36 exhibit long-range magnetic order below 32 and 38K of presumably ferromagnetic type. Magnetic susceptibilities indicate an Eu2+ ground state, in fine agreement with LIII absorption edge spectra.

A novel ternary structure type has been determined from single crystals of Ce2Zn6Ge3 grown from indium-zinc flux solvent. The Ce2Zn6Ge3 type is hexagonal (a = 0.767 69(2) nm; c = 0.41159(2) nm) with space group P62m, Z = 1. Isotypic compounds with La, Pr, Nd, Sm and Gd were synthesized by reaction sintering, and their isotypic crystal. structures were confirmed from Rietveld refinements. These novel temaries show metallic behaviour and their ground state depends on the particular rare earth ion. Long-range magnetic order was deduced for the compounds from Ce to Gd, with a maximum transition temperature T-N similar to 29 K for Gd2Zn6Ge3. While the compounds with Ce and Pr exhibit a spontaneous magnetic type of order, those with Nd, Sm and Gd are antiferromagnetic. The magnetic structures of Pr2Zn6Ge3 and Nd2Zn6Ge3 were resolved on the basis of neutron powder diffraction performed at 1.5 K.

We have studied the crystal chemistry, thermodynamic and transport properties of ternary compounds RNi9Si4 with R=La and Ce. The Rietveld refinement of the X-ray diffraction pattern revealed a tetragonal crystal structure (space group I4/mcm) that is derived from the cubic NaZn13 structure type. In the case of CeNi9Si4 resistivity, magnetic susceptibility and specific heat measurements reveal Kondo-lattice behaviour with a T2 temperature dependence of the electrical resistivity, an enhanced Pauli susceptibility χ0=5×10−3emu/mol and a Sommerfeld value γ=155(5)mJ/molK2. The magnetic susceptibility and specific heat contribution is well described by the Coqblin–Schrieffer model with a fully degenerate J=5/2 ground state and a characteristic temperature T0≃180K. LaNi9Si4 exhibits simple Pauli paramagnetic, metallic behaviour with a Sommerfeld value γ=33mJ/molK2.

SnyNi4Sb12−xSnx (2.4⩽x⩽5.6; 0⩽y⩽0.31 at 250°C) belongs to a new class of skutterudites in which the 8c site is fully occupied by Ni atoms. Sn atoms occupy two inequivalent sites (24g and 2a) and have a large thermal displacement parameter in 2a. Within the homogeneity range, electronic transport is primarily governed by the number of charge carriers, revealing a crossover from metallic- to a semiconducting behaviour with increase in x.

We have investigated the electrical resistivity of the intermediate valence narrow-gap semiconductor SmB6 at temperatures below 80 K and under pressure in the range between 1 bar and 70 kbar. We report on a continuous suppression of the gap under pressure, and on the observation of a critical point at p(cr)approximate to40 kbar, characterizing the pressure induced transition from a Kondo insulator below p(cr) to a metallic heavy fermion liquid well above p(cr). In the metallic phase close to p(cr) strong indications for a non-Fermi-liquid region, in which the electrical resistivity can be described by a power law rho(T)=rho(0)+AT(n) with 1less than or equal tonless than or equal to2, were observed.

We report on sample preparation and electron microprobe analysis in the series Ce1-pYbpFe4Sb12 that shows that a solid solution exists for all compositions in the series. As shown from X-ray absorption spectroscopy, Ce is trivalent throughout the series, whereas Yb valence linearly changes from 2.16 for Yb0.93Fe4Sb12.08 to 2.71 for Ce0.85Yb0.05Fe4Sb12.06. The Seebeck coefficient is enhanced by more than 20% at room temperature in Ce-Yb mixed compounds as compared to CeFe4Sb12 or YbFe4Sb12.

Electron correlations and intermediate valence distinctly influence electronic transport in skutterudites and hence modify the thermoelectric performance. Kondo interaction remarkably enhances thermopower, and electrons provided, e.g., by intermediate valent Yb may compensate holes of the transition metal–pnictogen units, which then can show thermopower values well above 100μV/K.

A novel ternary phase, SnyNi4Sb12−xSnx, has been characterized and found to exhibit a wide range of homogeneity (at 250 °C, 2.4 ≤ x ≤ 5.6, 0 ≤ y ≤ 0.31; at 350 °C, 2.7 ≤ x ≤ 5.0, 0 ≤ y ≤ 0.27). SnyNi4Sb12−xSnx crystallizes in a skutterudite-based structure in which Sn atoms are found to occupy two crystallographically inequivalent sites: (a) Sn and Sb atoms randomly share the 24g site; and (b) a small fraction of Sn atoms occupy the 2a (0, 0, 0) position, with an anomalously large isotropic atomic displacement parameter. Eu0.8Ni4Sb5.8Sn6.2, Yb0.6Ni4Sb6.7Sn5.3 and Ni4As9.1Ge2.9 are isotypic skutterudites. Depending on the particular composition, metallic as well as semiconducting states appear. The crossover from semiconducting to metallic behaviour is discussed in terms of a temperature-dependent carrier concentration employing a simple model density of states with the Fermi energy slightly below a narrow energy gap. This model accounts for the peculiar temperature-dependent electrical resistivity. These skutterudites are characterized by a number of lattice vibrations, which were elucidated by Raman measurements and compared to the specific heat data. The Eu-containing compound exhibits long-range magnetic order at Tmag ≈ 6 K, arising from the Eu2+ ground state.

A substitution of Cu by Au in cubic YbCu5 yields YbCu4Au crystallizing in the fully ordered ternary MgCu4Sn structure, isostructural to YbCu5. The exchange of Cu by Au drives the system from a high TK to a low TK Kondo scenario, enabling long-range magnetic order to occur. Thereby, a critical concentration range is passed with the possibility of non-Fermi-liquid behavior.

Skutterudites Pr0.73Fe4Sb12 and Nd0.72Fe4Sb12 order magnetically below 5 and 16.5K, respectively. Pr0.73Fe4Sb12 exhibits an unusual high electronic contribution to the specific heat Cp/T of about 1000mJ/molK2; moreover, magnetic fields of the order of 3T are able to suppress long range magnetic order and at some critical field Cp/T behaves proportional to −lnT. Additionally, the low temperature resistivity changes from a T2 behaviour at μ0H=0T to an almost linear dependence for μ0H≈3–4T.

Magnetic, transport, and x-ray diffraction measurements on single-crystal CeRhAs, the so-called Kondo insulator, have revealed successive transitions at T-1=370, T-2=235, and T-3=165 K. Below T-1, the unit cell is doubled along the b and c axes. Thereby, the resistivity jumps upwards and magnetic susceptibility in all the directions drops. Superlattice reflections at (0,1/3,1/3) and (1/3,0,0) appear at T<T-2. The latter suddenly increases below T-3 where a transport gap is enhanced. These observations indicate that the gap formation is intimately related to lattice modulations.

A novel ternary phase, SnyNi4Sb12-xSnx, has been characterised exhibiting a wide range of homogeneity (at 250degreesC, 2.4 less than or equal to x less than or equal to 5.6; 0 less than or equal to y less than or equal to 0.31). SnyNi4Sb12-xSnx crystallises in a skutterudite based structure in which Sri atoms are found to occupy both the 24g site randomly sharing with Sb atoms and the 2a position, with an anomalously large isotropic atomic displacement parameter. Eu0.8Ni4Sb5.8Sn6.2, Yb0.6Ni4Sb6.7Sn5.3 and Ni4As9.1Ge2.9 are isotypic skutterudites. Depending on the particular composition, metallic as well as semiconducting behaviour was observed. Eu containing compounds exhibit long range magnetic order arising from the Eu2+ ground state.

We report the results of magnetic measurements for the solid solution Ce$_2$Au$_{1-x}$Co$_x$Si$_3$. The results reveal that this solid solution is characterized by a magnetic phase diagram (plot of magnetic transition temperature versus $x$) unusual for Kondo lattices. In particular, the spin-glass freezing induced by disorder is observed only for the compositions at the weak coupling limit; as one approaches the quantum critical point by a gradual replacement of Au by Co, this disorder effect is surprisingly suppressed in favor of long range antiferro-magnetic ordering in contrast to expectations. This unusual interplay between disorder, spin-glass freezing and the Kondo-effect calls for further refinement of theories on competition between magnetism and the Kondo effect.

The filled skutterudite compound PrOs 4 Sb 12 displays superconductivity with a critical temperature T c ≈ 1.85 K which appears to involve heavy fermion quasiparticles with an effective mass m * ~ 50 - 100 m e as inferred from the slope of the upper critical field curve near T c and the specific heat. New measurements of electrical resistivity ρ(T) in applied magnetic fields, thermoelectric power, and X-ray diffraction are presented. A peak appears in the dρ/dT data for magnetic fields above 4 T that suggests the occurrence of a phase transition in the normal state of PrOs 4 Sb 12 below ~ 1K.