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This paper reports on measurement of the heat capacity at constant pressure C p of silicon bio-carbide prepared within the 5–300 K temperature interval from beech tree wood (bio-SiC(BE)), and within 80–300 K, from tree wood of sapele (bio-SiC(SA)), as well as SiC/Si ecoceramics of beech, sapele, and white eucalyptus wood. It has been shown that in bio-SiC(BE) the measured heat capacity contains a significant contribution of surface heat capacity, whose magnitude decreases with increasing temperature. Of the ecoceramics, only SiC/Si(SA) characterized by a high enough porosity has revealed a small contribution to the heat capacity coming from its surface component. The experimental results obtained are discussed.

Samples of β-SiC/Si ecoceramics with a silicon concentration of ∼21 vol % have been prepared using a series of consecutive procedures (carbonization of sapele wood biocarbon, synthesis of high-porosity biocarbon with channel-type pores, infiltration of molten silicon into empty channels of the biocarbon, formation of β-SiC, and retention of residual silicon in channels of β-SiC). The electrical resistivity ρ and thermal conductivity κ of the β-SiC/Si ecoceramic samples have been measured in the temperature range 5–300 K. The values of ρ Si chan (T) and κ Si chan (T) have been determined for silicon Sichan located in β-SiC channels of the synthesized β-SiC/Si ecoceramics. Based on the performed analysis of the obtained results, the concentration of charge carriers (holes) in Sichan has been estimated as p ∼ 1019 cm−3. The factors that can be responsible for such a high value of p have been discussed. The prospects for practical application of β-SiC/Si ecoceramics have been considered.

The electrical resistivity and thermal conductivity of high-porosity (∼52 vol %, channel-type pores) bio-SiC samples prepared from sapele wood biocarbon templates have been measured in the temperature range 5–300 K. An analysis has been made of the obtained results in comparison with the data for bio-SiC samples based on beech and eucalyptus, as well as for polycrystalline β-SiC. The conclusion has been drawn that the electrical resistivity and thermal conductivity of bio-SiC samples based on natural wood are typical of heavily doped polycrystalline β-SiC.

This paper reports on measurements within the 5–300-K temperature interval of the thermal conductivity of Si3N4 and BN polycrystalline ceramic samples and Si3N4/BN fiber monoliths (FM) with different fiber arrangement architecture, [0], [90], and [0/90], with fibers arranged, accordingly, along and across the sample axis and the [0] and [90] layers stacked alternately. In the 3.5–300-K interval, the heat capacity at constant pressure, and at 77 K, the sound velocity have been measured in polycrystalline Si3N4 and BN samples and in Si3N4/BN [0] fiber monoliths. Our studies suggest that, with a high enough degree of confidence, but for some compositions—with minor assumptions, it can be maintained that, in the case of the Si3N4/BN fiber monoliths, one can use for calculation of their thermal conductivities and heat capacities within certain temperature intervals simple models considering mixtures of the Si3N4 and BN components with due account of their contributions to formation of the Si3N4/BN FM. It has been established that in the low-temperature domain (5–25 K), phonons in Si3N4/BN [0], [90], and [0/90] fiber monoliths scatter primarily from dislocations. This effect is not observed in ceramic Si3N4 and BN samples. The experimental data obtained on the thermal conductivity, heat capacity, and sound velocity have been used to calculate phonon mean free path lengths in polycrystalline Si3N4 and BN samples and the effective mean free path length in the Si3N4/BN [0] FM.

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 A 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.

This paper reports on the measurements of the thermal conductivity κ and electrical resistivity ρ in the temperature range 5–300 K and the heat capacity at constant pressure Cp in the range 80–300 K for the metallic nonmagnetic compound LuMgCu4. The experimental values of κ and Cp for the LuMgCu4 compound are compared with the corresponding data available in the literature for the light heavy-fermion compound YbMgCu4. It is shown that, in the low-temperature range (5–20 K), the phonon thermal conductivity κph of YbMgCu4 is lower than κph of LuMgCu4 as a result of phonon scattering from magnetic moment fluctuations of the Yb 4f electrons and, conversely, the heat capacity of LuMgCu4 in the range 80–300 K is lower than that of YbMgCu4 because the heat capacity of the latter compound has an additional magnetic component.

The thermal conductivity and electrical resistivity of a sample of YbMgCu4 belonging to “light” heavy-fermion compounds have been measured in the temperature range 5–300 K. The sample studied was in the region of homogeneity of this compound. It is shown that, throughout the temperature range studied, the phonon thermal conductivity of the sample has an amorphous-like character, which should be assigned to the homogeneous mixed valence of the Yb ion in YbMgCu4.

This paper reports on a measurement of the heat capacity at constant pressure (C p ) in the temperature range 3–320 K and the sound velocity (v) at 77 K for the “light” heavy-fermion compound YbMgCu4. The present experimental data on C p and v of YbMgCu4, combined with our earlier phonon thermal conductivity data for YbMgCu4 in the range 5–300 K, have been used to calculate the phonon mean free path l in this compound. The temperature dependence of l obtained is found to be characteristic of classical amorphous materials.

The thermal conductivity of bio-SiC, a heavily defected material with specific cellular pores (channels), was studied in the temperature range 5–300 K. The bio-SiC sample was prepared from the SiC/Si biomorphic composite through the chemical removal of silicon. The thermal conductivity of silicon embedded in cellular pores of the SiC/Si biomorphic composite was determined.

The specific heat at a constant pressure (C p) and the velocity of sound (v) are measured for a moderate heavy-fermion compound YbZnCu4 in the temperature range 3.5–250 K and at 77 K, respectively. The experimental values of C p and v obtained in this study and the phonon thermal conductivity previously measured in the temperature range 5–300 K are used to calculate the phonon mean free path l for this compound. The temperature dependence of the phonon mean free path l thus determined is characteristic of classical amorphous materials.

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.

The heat capacity Cp of a biocarbon template based on white eucalyptus wood is measured at a constant pressure in the temperature range T = 3.5–300 K. The phonon mean free path l for a white-eucalyptus biocarbon template is calculated from the measured dependence Cp(T) and data available in the literature on the phonon thermal conductivity and velocity of sound. It is established that, in the range 100–300 K, the phonon mean free path l is nearly constant and equal to ∼13 A. This value is close to the smallest size of graphite-like crystallites (∼12 A), which was derived earlier from x-ray diffraction data for a quasi-amorphous biocarbon template.

The thermal conductivity of ultrathin (∼5 nm in diameter) and long (10 mm) InSb semiconductor quantum nanowires embedded in nanochannels of a dielectric chrysotile asbestos matrix is measured in the temperature range 5–300 K. The possible manifestation of the spin-charge separation of current carriers in these nanowires is discussed, which would provide an additional argument for the InSb nanowires possessing properties of the Luttinger liquid.

The thermal conductivity κ and electrical resistivity ρ of a cast polycrystalline sample of YbIn0.2Ag0.8Cu4, which belongs to the class of moderate heavy-fermion compounds, are measured in the temperature range 5–300 K. It is shown that the phonon thermal conductivity of the sample follows an amorphous-like pattern throughout the temperature range covered, which should be assigned to the presence of Yb ions with a homogeneous mixed valence in this compound. The temperature dependence ρ(T) is divided into three portions: a high-temperature portion characteristic of conventional metals, a medium-temperature portion typical of Kondo compounds, and a low-temperature portion corresponding to a coherent Kondo lattice (the heavy-fermion regime). The Kondo temperature is estimated.

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.

The thermal conductivity κ tot b of the quasi-one-dimensional (S=1/2) Heisenberg antiferromagnet LiCuVO4 with uniform (-CuO6-) spin chains aligned parallel to the b axis in a crystal with an orthorhombically distorted inverse spinel structure is measured in the temperature range 10–300 K. The spinon component κ m chain of the thermal conductivity is separated out.

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.

The thermal conductivity of porous glass with randomly distributed connecting pores ∼70 A in size (glass porosity ∼25%), as well as of a porous glass + NaCl composite, was measured in the temperature range 5–300 K. NaCl filled one fourth of the pores in the composite. The experimental results on the composite thermal conductivity can be accounted for only by assuming that phonons scatter from the boundaries of NaCl nanocrystals embedded in channels of the porous glass.

The thermal conductivity of crystalline chrysotile asbestos made up of hollow tubular Mg3Si2O5(OH)4 filaments is measured in the range 5–300 K. The paper discusses the possibility of using this material in studies of the thermal conductivity of thin filaments of metals and semiconductors incorporated into the channels of crystalline chrysotile asbestos tubes.

Samples of various compositions were obtained in the homogeneity range of the Yb-In-Cu system (YbIn1−xCu4+x), from stoichiometric (YbInCu4) to YbIn0.905Cu4.095. Their lattice constant (at 300 K and in the range 20–100 K), total thermal conductivity, and electrical resistivity (from 4 to 300 K) were measured. All the compositions studied exhibited an isostructural phase transition at Tv⋍40–80 K driven by a change in the Yb ion valence state. It was shown that within the YbIn1−xCu4+x homogeneity range, the lattice thermal conductivity κph decreases with increasing x; at T>Tv, κph grows with temperature and the Lorenz number (which enters the Wiedemann-Franz law for the electronic component of thermal conductivity) of the light heavy-fermion system, to which YbIn1−xCu4+x belongs for T

The electrical resistivity and thermal conductivity of two polycrystalline YbInCu4 samples prepared by different techniques at the Ioffe Physicotechnical Institute, RAS (St. Petersburg, Russia), and the Goethe University (Frankfurt-am-Main, Germany) are studied within the temperature range 4.2–300 K. At Tv∼75–78 K, these samples exhibited an isostructural phase transition from a state with an integer valence (at T>Tv) to a state with an intermediate valence (at T Tv, where YbInCu4 is a semimetal, the Lorenz number has a value characteristic of standard metals.

The thermal conductivity κ (within the range 4–300 K) and electrical conductivity σ (from 80 to 300 K) of polycrystalline Sm3S4 with the lattice parameter a=8.505 A (with a slight off-stoichiometry toward Sm2S3) are measured. For T>95 K, charge transfer is shown to occur, as in stoichiometric Sm3S4 samples, by the hopping mechanism (σ ∼ exp(−ΔE/kT) with ΔE ∼ 0.13 eV). At low temperatures [up to the maximum in the lattice thermal conductivity κph(T)], κph ∼ T2.6; in the range 20–50 K, κph ∼ T−1.2; and for T>95 K, where the hopping charge-transfer mechanism sets in, κph ∼ T−0.3 and a noticeable residual thermal resistivity is observed. It is concluded that in compounds with inhomogeneous intermediate rare-earthion valence, to which Sm3S4 belongs, electron hopping from Sm2+ (ion with a larger radius) to Sm3+ (ion with a smaller radius) and back generates local stresses in the crystal lattice which bring about a change in the thermal conductivity scaling of κph from T−1.2 to T−0.3 and the formation of an appreciable residual thermal resistivity.

This paper reports on the electrical resistivity and thermal conductivity of polycrystalline YbIn0.7Ag0.3Cu4 at temperatures from 4.2 to 300 K, which exhibits, at T v , a continuous isostructural first-order phase transition from a Curie-Weiss paramagnet with localized magnetic moments (for T>T v ) to a Pauli paramagnet in a nonmagnetic Fermi liquid state with the Yb ion in a mixed valence state (for TT v , it acquires the value typical of standard metals.

The heat conductivity and electrical resistivity of a polycrystalline YbAgCu4 sample were measured in the 4.2–300-K temperature range. It is shown that at low temperatures (in the region corresponding to the coherent Kondo lattice) the Lorenz number behaves in accordance with a theoretical model developed for heavy-fermion materials.

The electrical resistivity and heat conductivity of LuAgCu4 have been studied within the 4.2–300-K range. An additional contribution to heat conductivity, most probably due to the bipolar component, has been revealed at T≥100 K. The conclusion is drawn that LuAgCu4 is apparently a semimetal.

Electrical resistivity and heat conductivity of the LuInCu4 semimetal have been studied in the 4.2–300-K range. For T≳100 K, the bipolar heat-conductivity component (κbip) was found to contribute. Data on κbip have been used to estimate the electron and hole subband-overlap energy (ɛ0) as ∼0.1 eV.

The thermal conductivity and electrical resistivity are measured in the temperature range 160–300 K for two compositions of the “golden” phase of the Sm1−x GdxS system with x=0.14 and 0.3, in which a homogeneous variable valence of samarium ions is observed. It is found that, in this temperature range, the experimentally obtained Lorentz number L appearing in the electron component of thermal conductivity for these compositions exceeds the theoretical Sommerfeld value L 0=2.45×10−8 WΩ/K2 typical of metals and highly degenerate semiconductors. It is also proved that the value of L increases with temperature in the interval 160–300 K starting from 160 K. A theoretical model capable of explaining the obtained experimental results is discussed.

Samples of the nanocomposite opal + NaCl with 100% filling of first-order voids in the opal by NaCl have been obtained. The thermal conductivity of the nanocomposite has been measured in the temperature interval 4.2–300 K. It is shown that NaCl, introduced into opal, forms a regular “matrix quasilattice” of microcrystals, which leads to suppression of coherent effects and, as a consequence, of properties characteristic of massive crystals.

Opal-based nanocomposites with selenium pressure-injected from the melt into first-order opal voids have been prepared. Two types of nanocomposites, with crystalline and amorphous selenium incorporated in opal voids, were studied. Their thermal conductivities were measured in the temperature range 4.2–200 K. An analysis of these data suggests that a new type of physical media has been developed, namely, quasicrystals with a large lattice constant and heavy “atomic” masses, formed from first-order opal voids interconnected by channels and filled by crystalline or amorphous selenium.

Data on the thermal conductivity ϰ ph of the cluster lattice of synthetic opals are analyzed. All opals are divided into two groups according to the temperature dependence of their ϰ ph. These are opals-1, whose thermal conductivity behaves like ϰ ph(T) of quasi-crystalline materials, and opals-2, with a ϰ ph(T) dependence typical of classical amorphous solids. Possible reasons for this difference are considered. An attempt is made to explain the complex temperature hysteresis in ϰ ph(T) observed earlier in opals-2.

Measurement of the heat conductivity and electrical resistivity of two Sm1−xGdxS compositions with x=0.1 and 0.14 is reported within the 80–300 K interval. An analysis of experimental data on the electronic component of heat conductivity permits a conclusion that the d subband of “heavy” carriers in the conduction band of these materials lies above the s “light”-carrier subband.

An opal-based nanocomposite has been prepared with NaCl incorporated in its pores. The nanocomposite was produced by impregnating the opal with a NaCl solution at room temperature. Thermal conductivity of the nanocomposite has been measured in the temperature range 4.2–300 K. The effective heat conductivity of the nanocomposite was found to be equal to that of pure opal. The observed phenomenon can be explained by assuming that NaCl resides in opal pores in the form of noncontacting needles, thus precluding heat propagation through it.

Our earlier experimental data on the thermal conductivity of porous glass and of the porous glass + NaCl composite in the temperature interval 25–300 K are analyzed from a different standpoint. It is shown that the thermal conductivity of sodium chloride filling randomly arranged nanochannels in porous glass behaves exactly like that of a strongly disordered crystalline system and can be described in terms of Einstein’s model of the thermal conductivity of solids.

The thermal conductivity, specific heat, and sound velocity of crystalline chrysotile asbestos made up of hollow tubular fibrils of composition Mg3Si2O5(OH)4 have been measured at temperatures of 5–300, 3–65, and 77 K, respectively. An analysis is made of the experimental data obtained.