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The thermal conductivity k and resistivity ρ of biocarbon matrices, prepared by carbonizing medium-density fiberboard at Tcarb = 850 and 1500°C in the presence of a Ni-based catalyst (samples MDFC( Ni)) and without a catalyst (samples MDF-C), have been measured for the first time in the temperature range of 5–300 K. X-ray diffraction analysis has revealed that the bulk graphite phase arises only at Tcarb = 1500°C. It has been shown that the temperature dependences of the thermal conductivity of samples MDFC- 850 and MDF-C-850(Ni) in the range of 80–300 K are to each other and follow the law of k(T) ~ T1.65, but the use of the Ni-catalyst leads to an increase in the thermal conductivity by a factor of approximately 1.5, due to the formation of a greater fraction of the nanocrystalline phase in the presence of the Ni-catalyst at Tcarb = 850°C. In biocarbon MDF-C-1500 prepared without a catalyst, the dependence is k(T) ~ T1.65, and it is controlled by the nanocrystalline phase. In MDF-C-1500(Ni), the bulk graphite phase formed increases the thermal conductivity by a factor of 1.5–2 compared to the thermal conductivity of MDF-C-1500 in the entire temperature range of 5–300 K; k(T = 300 K) reaches the values of ~10 W m–1 K–1, characteristic of biocarbon obtained without a catalyst only at high temperatures of Tcarb = 2400°C. It has been shown that MDF-C-1500(Ni) in the temperature range of 40‒300 K is characterized by the dependence, k(T) ~ T1.3, which can be described in terms of the model of partially graphitized biocarbon as a composite of an amorphous matrix with spherical inclusions of the graphite phase

Natural composites (biocarbons) obtained by carbonization of beech wood at different carbonization temperatures Tcarb in the range of 800–2400°C have been studied using X-ray diffraction. The composites consist of an amorphous matrix and nanocrystallites of graphite and graphene. The volume fractions of the amorphous and nanocrystalline phases as functions of Tcarb have been determined. Temperature dependences of the phonon thermal conductivity κ(T) of the biocarbons with different temperatures Tcarb (1000 and 2400°C) have been analyzed in the range of 5–300 K. It has been shown that the behavior of κ(T) of the biocarbon with Tcarb = 1000°C is controlled by the amorphous phase in the range of 5–50 K and by the nanocrystalline phase in the range of 100–300 K. The character of κ(T) of the biocarbon with Tcarb = 2400°C is determined by the heat transfer (scattering) in the nanocrystalline phase over the entire temperature range of 5–300 K.

High-porosity samples of beech wood biocarbon (BE-C) were prepared by pyrolysis at carbonization temperatures T carb = 650, 1300, and 1600°C, and their resistivity ρ and thermal conductivity κ were studied in the 5–300 and 80–300 K temperature intervals. The experimental results obtained were evaluated by invoking X-ray diffraction data and information on the temperature dependences ρ(T) and κ(T) for BE-C samples prepared at T carb = 800, 1000, and 2400°C, which were collected by the authors earlier. An analysis of the κ(T carb) behavior led to the conclusion that the samples under study undergo an amorphous-nanocrystalline phase transition in the interval 800°C < T carb < 1000°C. Evaluation of the electronic component of the thermal conductivity revealed that the Lorentz number of the sample prepared at T carb = 2400°C exceeds by far the classical Sommerfeld value, which is characteristic of metals and highly degenerate semiconductors.

A “porous glass + indium” nanocomposite has been prepared. The thermal conductivity κ(T) and electrical resistivity ρ(T) of the nanocomposite have been measured in the temperature range 5–300 K, and their fractions accounted for by nanoindium embedded in 7-nm channels of the porous glass have been determined. For comparison, κ and ρ of the bulk polycrystalline indium sample have been measured in the same temperature range. The electronic and phonon components of the thermal conductivity have been calculated for the nanoindium and bulk indium. It has been demonstrated that, as the result of the emergence of boundary electron and phonon scattering in the nanoindium, the electrical resistivity of this material becomes larger, and the phonon thermal conductivity, smaller than those of the bulk indium.

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.

The Neel temperature T N(n) of the Co3O4 antiferromagnet nanostructured in channels of porous borosilicate glass with channel cross sections of ∼7 nm has been determined from thermal conductivity measurements. It has been shown that the Neel temperature T N(n) of this nanomaterial is approximately equal to 20 K, which is considerably lower than T N = (30–40) K for the bulk Co3O4 sample.

This paper reports on measurements of the thermal conductivity κ and the electrical resistivity ρ in the temperature range 5–300 K, and, at 300 K, on X-ray diffraction studies of high-porosity (with a channel pore volume fraction of ∼47 vol %) of the beech wood biocarbon prepared by pyrolysis (carbonization) of tree wood in an argon flow at the carbonization temperature T carb = 800°C. It has been shown that the biocarbon template of the samples studied represents essentially a nanocomposite made up of amorphous carbon and nanocrystallites—“graphite fragments” and graphene layers. The sizes of the nanocrystallites forming these nanocomposites have been determined. The dependences ρ(T) and κ(T) have been measured for the samples cut along and perpendicular to the tree growth direction, thus permitting determination of the magnitude of the anisotropy of these parameters. The dependences ρ(T) and κ(T), which have been obtained for beech biocarbon samples prepared at T carb = 800°C, are compared with the data amassed by us earlier for samples fabricated at T carb = 1000 and 2400°C. The magnitude and temperature dependence of the phonon thermal conductivity of the nanocomposite making up the beech biocarbon template at T carb = 800°C have been found.

The heat capacity at constant pressure C p of the biocarbon matrix prepared at a beech wood carbonization temperature of 1000°C has been measured in the temperature range 80–300 K. It has been shown that, in the temperature range 90–180 K, the heat capacity is C ∼ T 0.8 and, at T = 190–300 K, it is C p ∼ T 1.2. The phonon mean free path l(T) in the biocarbon matrix has been calculated using the obtained dependences C p (T), our previous results on the phonon thermal conductivity of the carbon framework of this biocarbon matrix, and data available in the literature on the sound velocity in the matrix. It has been demonstrated that, in the temperature range 200–300 K, the mean value of l is ∼ 15 A, which is close to the sizes of nanocrystallites (“carbon fragments”) of ∼ 12A, obtained earlier from X-ray diffraction data for the carbon matrix under consideration. These nanocrystallites participate in the formation of the carbon framework of the beech wood biocarbon matrix.

A nanocomposite chrysotile-KDP (KH2PO4) was prepared. KDP was introduced into empty nanochannels of chrysotile asbestos with diameters of ∼5 nm. Thermal conductivity κ and heat capacity at a constant pressure C p of the samples of chrysotile asbestos and nanocomposite chrysotile asbestos-KDP were measured in a temperature range of 80–300 K. Based on the analysis of the behavior of temperature dependences κ(T) and C p (T) of the composite, temperatures of the ferroelectric transition T F for KDP in nanochannels of chrysotile asbestos were determined. It turned out to be equal to ∼250 K at T F ∼ 122 K for massive KDP samples.

The thermal conductivity of composites of a new type prepared by infiltration under vacuum of melted copper into empty sap channels (aligned with the sample length) of high-porosity biocarbon preforms of white pine tree wood has been studied in the temperature range 5–300 K. The biocarbon preforms have been prepared by pyrolysis of tree wood in an argon flow at two carbonization temperatures of 1000 and 2400°C. From the experimental values of the composite thermal conductivities, the fraction due to the thermal conductivity of the embedded copper is isolated and found to be substantially lower than that of the original copper used in preparation of the composites. The decrease in the thermal conductivity of copper in the composite is assigned to defects in its structure, namely, breaks in the copper filling the sap channels, as well as the radial ones, also filled by copper. A possibility of decreasing the thermal conductivity of copper in a composite due to its doping by the impurities present in the carbon preform is discussed.

This paper reports on measurements performed in the temperature range 5–300 K for the thermal conductivity κ and electrical resistivity ρ of high-porosity (cellular pores) biocarbon preforms prepared by pyrolysis (carbonization) of beech wood in an argon flow at carbonization temperatures of 1000 and 2400°C. X-ray structure analysis of the samples has been performed at 300 K. The samples have revealed the presence of nanocrystallites making up the carbon matrices of these biocarbon preforms. Their size has been determined. For samples prepared at T carb = 1000 and 2400°C, the nanocrystallite sizes are found to be in the ranges 12–25 and 28–60 κ(T) are determined for the samples cut along and across the tree growth direction. The thermal conductivity κ increases with increasing carbonization temperature and nanocrystallite size in the carbon matrix of the sample. Thermal conductivity measurements conducted on samples of both types have revealed an unusual temperature dependence of the phonon thermal conductivity for amorphous materials. As the temperature increases from 5 to 300 K, it first increases in proportion to T, to transfer subsequently to ∼T 1.5 scaling. The results obtained are analyzed.

This paper reports on measurements of the heat capacity at constant pressure Cp in the 80–300-K temperature interval and the thermopower coefficient S at 5–300 K of the carbon preform of sapele wood, which was prepared at the carbonization temperature of 1000°C. Measurements of Cp(T), our previous data on the phonon thermal conductivity, and literature information on the sound velocity have been used to calculate the phonon mean free path l(T) for this material. It has been shown that within the temperature interval 200–300 K, l is constant and equal to 11 A, a figure matching the size of the nanocrystallites (“graphite fragments”) making up the carbon framework of the sapele carbon preform. The high-temperature parts of S(T) have been found to follow a linear course characteristic of diffusive thermopower for the degenerate state of charge carriers, with only one type of charge carriers present. The anisotropy of the thermopower coefficient has been estimated.

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 measurements of the thermal conductivity κ and the electrical conductivity σ of high-porosity (cellular pores) biocarbon precursors of white pine tree wood in the temperature range 5–300 K, which were prepared by pyrolysis of the wood at carbonization temperatures (T_(carb)) of 1000 and 2400°C. The x-ray structural analysis has permitted the determination of the sizes of the nanocrystallites contained in the carbon framework of the biocarbon precursors. The sizes of the nanocrystallites revealed in the samples prepared at T_(carb) = 1000 and 2400°C are within the ranges 12–35 and 25–70 A, respectively. The dependences κ(T) and σ(T) are obtained for samples cut along the tree growth direction. As follows from σ(T) measurements, the biocarbon precursors studied are semiconducting. The values of κ and σ increase with increasing carbonization temperature of the samples. Thermal conductivity measurements have revealed that samples of both types exhibit a temperature dependence of the phonon thermal conductivity κ_(ph), which is not typical of amorphous (and amorphous to x-rays) materials. As the temperature increases, κ_(ph) first varies proportional to T, to scale subsequently as ∼T ^(1.7). The results obtained are 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 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.

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 effective thermal conductivity κeff of seven opal + epoxy resin nanocomposite samples with 100% filling of first-order pores by epoxy resin was measured in the 100-to 300-K temperature interval. In the nanocomposite studied, the thermal conductivity of the matrix (amorphous SiO2 spheres) is larger than that of the filler material (epoxy resin). κeff(T) of the opal + epoxy resin nanocomposite at intermediate temperatures (100–300 K) is shown to behave similar to pure opal. An explanation of the observed effect is proposed.

Samples of the opal + HgSe nanocomposite with 100% filling of the first-order opal pores by mercury selenide were prepared. The effective thermal conductivity κeff and electrical resistivity ρeff were measured in the temperature range T=5–200 K, and the thermopower coefficient α was measured in the interval 80–300 K. The coefficient α of HgSe in opal was shown to remain the same as that in bulk mercury selenide samples with similar carrier concentrations. The mechanism of carrier scattering in the HgSe loaded in opal also did not change. The total thermal conductivity κ tot 0 and electrical resistivity ρ0 were isolated from κeff and ρeff, and the electronic (κ e 0 ) and lattice (κ ph 0 ) components of thermal conductivity of HgSe in opal were determined. The magnitude of κ ph 0 was found to be considerably smaller than κph of bulk HgSe with the same carrier concentration throughout the temperature interval studied (5–200 K). For T>20 K, this behavior of κ ph 0 (T) is accounted for by the presence of specific impurities and defects forming in HgSe, and for T

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.

Thermal conductivity of the opal-epoxy resin nanocomposite is measured in the range 4.2–250 K, and the material is studied by electron microscopy at 300 K. An analysis of the electron microscope images permits a conclusion on the character of opal void filling by the epoxy resin. It is shown that the thermal conductivity of the nanocomposite within the range 40–160 K can be fitted fairly well by the corresponding standard expressions for composites. For T 160 K, the experimental values of the nanocomposite thermal conductivity deviate strongly from the calculated figures.

The thermal conductivity κ of photonic crystals differing in degree of optical homogeneity (single crystals of synthetic opals) was measured in the 4.2–300 K temperature range. The thermal conductivity revealed, in addition to the conventional decrease in comparison with solid amorphous SiO2 characteristic of porous solids, a noticeable decrease for T

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 heat capacity at constant pressure (in the range 3–50 K) and the lattice heat conductivity (from 5 to 75 K) of a single-crystal synthetic opal are measured. It is shown that the heat capacity of the opal behaves at these temperatures in a way similar to porous amorphous materials. The data on the heat conductivity suggest that single-crystal opals can be related to a class of semicrystalline (partially crystallized amorphous) materials. However, because of specific features of their crystal structure, the opals form a nonstandard type of semicrystalline material which we termed semiamorphous.

The lattice heat conductivity κph of PrTe1.46 and LaTe1.46 has been measured within the 2-to 100-K interval. The quantity −Δκres(T), the decrease in the heat conductivity caused by resonant phonon scattering due to crystal-field-split paramagnetic levels of Pr, was derived from experimental data using the relation \( - \Delta \kappa _{res} (T) = \kappa _{ph(PrTe_{1.46} )} (T) - \kappa _{ph(LaTe_{1.46} )} (T)\). The energy of the first split paramagnetic level of Pr, Δ1 was calculated from the Δκres(T) relation for T Tres.

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.

The electrical conductivity σa and permittivities ɛa, ɛb, and ɛc of a LiCuVO4 single crystal have been measured along the a, b, and c crystallographic axes, respectively, in the temperature range 300–390 K at a frequency of 103 Hz. The temperature dependences σ(T) and ɛ(T) were found to be typical for superionics.

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.