H. Misiorek

Transition and rare earth element dodecaborides

Abstract Original results on the technology of melting and single-crystal growth of Sc and rare earth element (from Dy) dodecaborides by the floating zone method are presented. Investigations of electrical resistance and thermal conductivity for all received materials between 4.2 and 300 K were conducted. A joint analysis of the obtained results was performed. The magnetic ordering temperatures of dodecaborides were refined.

Thermal and electrical properties of a white-eucalyptus carbon preform for SiC/Si ecoceramics

The thermal conductivity κ and electrical resistivity ρ of a white-eucalyptus cellular carbon preform used to fabricate silicon-carbide-based (SiC/Si) biomorphic ceramics have been measured in the 5-to 300-K temperature interval. The carbon preform was obtained by pyrolysis (carbonization) of white-eucalyptus wood at 1000°C in an argon ambient. The κ(T) and ρ(T) relations were measured on samples cut along the tree growth direction. The experimental data obtained were processed.

Thermal conductivity of the SiC/Si biomorphic composite, a new cellular ecoceramic

The thermal conductivity κ and electrical resistivity ρ of a SiC/Si biomorphic composite were measured at temperatures T = 5–300 K. The composite is a cellular ecoceramic fabricated by infiltrating molten Si into the channels of a cellular carbon matrix prepared via pyrolysis of wood (white eucalyptus) in an argon ambient. The κ(T) and ρ(T) relations were measured on a sample cut along the direction of tree growth. The experimental results obtained are analyzed.

Lattice parameters, magnetic susceptibility and thermal conductivity of ScFe4Al8 and YFe4Al8

Abstract ScFe 4 Al 8 and YFe 4 Al 8 crystallise in a tetragonal structure of the ThMn 12 -type. Although antiferromagnetic ordering in the Fe sublattice exists below about 100 K in these compounds, they can be considered as the reference materials for the RFe 4 Al 8 ternaries where R is a magnetic lanthanide, U or Np. The present magnetic measurements in a low magnetic field of 50 Oe have revealed another pronounced anomaly in the temperature dependence of magnetic susceptibility at temperatures lower than the Neel point. Low temperature (LT) X-ray diffraction (XRD) examination has confirmed the stability of the crystal structure in the whole investigated temperature range. Therefore the lattice distortion as a reason for the LT magnetic anomalies has been excluded. Also heat conductivity measurements have not given any explanation for the LT anomalies. Based on a thermal conductivity investigation it was possible to separate the electron and phonon components from the total thermal conductivity. Thus a deviation from stoichiometry, spin-reorientation transition (SRT) and spin-glass (SG) state are discussed as reasons for the LT anomalies.

Thermal conductivity of high-porosity cellular-pore biocarbon prepared from sapele wood

This paper reports on measurements (in the temperature range T = 5–300 K) of the thermal conductivity κ(T) and electrical conductivity σ(T) of the high-porosity (∼63 vol %) amorphous biocarbon preform with cellular pores, prepared by pyrolysis of sapele wood at the carbonization temperature 1000°C. The preform at 300 K was characterized using X-ray diffraction analysis. Nanocrystallites 11–30 Å in ize were shown to participate in the formation of the carbon network of sapele wood preforms. The dependences κ(T) and σ(T) were measured for the samples cut across and along empty cellular pore channels, which are aligned with the tree growth direction. Thermal conductivity measurements performed on the biocarbon sapele wood preform revealed a temperature dependence of the phonon thermal conductivity that is not typical of amorphous (and X-ray amorphous) materials. The electrical conductivity σ was found to increase with the temperature increasing from 5 to 300 K. The results obtained were analyzed.

Heat transport over nonmagnetic lithium chains in LiCuVO4, a new one-dimensional superionic conductor

The thermal conductivity of three single-crystal samples of the quasi-one-dimensional spin system of LiCuVO4 with different concentrations of defects (primarily, vacancies on the lithium sublattice) was measured along the crystallographic a axis (along the nonmagnetic lithium chains) in the temperature interval 5–300 K. An increase in thermal conductivity from that of the crystal lattice was revealed for T>150–200 K. This increase can be accounted for only by assuming LiCuVO4 to be a superionic conductor. This assumption was confirmed by measuring its electrical conductivity in the temperature interval 300–500 K. Li+ ions move over vacancies on the lithium sublattice (conducting channels) and act as charge carriers in LiCuVO4. It is shown that LiCuVO4 is a fairly good superionic conductor with application potential.

Thermal conductivity of REIn3 (RETb, Dy, Tm, Lu) single crystals

Abstract Some results of thermal conductivity measurements on REIn3 (RETb, Dy, Tm, Lu) single crystals over the temperature range 4–80 K are reported. On the basis of experimental data, an extraction of the magnetic contribution to the thermal conductivity was performed. In the antiferromagnetic state the thermal conductivities of TbIn3 and DyIn3 are dominated by magnons. In the paramagnetic state the thermal conductivities of both compounds increase nearly linearly with increasing temperature. Contrary to other analogous compounds the temperature dependence of the thermal conductivity of TmIn3 is more complex. To separate the contribution resulting from the 4f electrons scattering from the total thermal conductivity in the studied compounds, the thermal conductivity of isomorphous and non-magnetic LuIn3 was measured.

Anisotropy of the thermal conductivity and electrical resistivity of the SiC/Si biomorphic composite based on a white-eucalyptus biocarbon template

The thermal conductivity κ and electrical resistivity ρ of a cellular ecoceramic, namely, the SiC/Si biomorphic composite, are measured in the temperature range 5–300 K. The SiC/Si biomorphic composite is fabricated using a cellular biocarbon template prepared from white eucalyptus wood by pyrolysis in an argon atmosphere with subsequent infiltration of molten silicon into empty through cellular channels of the template. The temperature dependences κ(T) and ρ(T) of the 3C-SiC/Si biomorphic composite at a silicon content of ∼30 vol % are measured for samples cut out parallel and perpendicular to the direction of tree growth. Data on the anisotropy of the thermal conductivity κ are presented. The behavior of the dependences κ(T) and ρ(T) of the SiC/Si biomorphic composite at different silicon contents is discussed in terms of the results obtained and data available in the literature.

Thermomagnetic properties of the overdoped La1.7Sr0.3CuO4 superconductor

Abstract We have studied the normal-state transport phenomena of the La 1.7 Sr 0.3 CuO 4 overdoped high- T c superconductor. The Ettingshausen ( P E ), Hall ( R H ) and Seebeck ( S ) coefficients as well as the thermal ( κ ) and electrical ( σ ) conductivities have been measured. The temperature dependence of the isothermal Nernst ( Q i ) coefficient has been estimated on the basis of the Bridgman relation. The results have been interpreted in terms of a rigid, single-band model, with an assumption that both doping and temperature change the band filling resulting in the variation of the Fermi surface curvature. The latter quantity appeared to be a key feature driving the temperature dependences of P E and R H . In opposition to the usual interpretation, the temperature dependence of the R H for La 1.7 Sr 0.3 CuO 4 is dominated by variations of the Fermi surface shape, and not by the changes in the charge carrier concentration. The consistency of this physical picture was controlled by an estimation of P E using measured values of σ , R H , S and κ and comparison with measured value of the Ettingshausen coefficient.

Thermal conductivity of niobium hydrides in the temperature range 4.2–420 K

Abstract Measurements of thermal conductivity and electrical resistivity of two niobium hydrides having hydrogen concentrations (H:Nb) of 0.78 and 0.86 were conducted in the temperature range 4.2–420 K. Distinct changes in the temperature dependence of both the thermal conductivity and the electrical resistivity were encountered, obviously connected with phase transitions: λ → β at 200 K and β → α ′+ β and α ′+ β → α ′ at about 400 K. Moreover, at about 100 K our results corroborate the existence of a low temperature phase in these compounds. The analysis of the obtained results was conducted on the basis of the models of Wilson and Ziman.