Showing papers in "Physics of the Solid State in 2010"
TL;DR: In this paper, a theoretical model has been proposed for calculating the surface energy of nanowhiskers in the nearest neighbor approximation for different faces of III-V semiconductor crystals with cubic and hexagonal structures.
Abstract: A theoretical model has been proposed for calculating the surface energy of nanowhiskers in the nearest neighbor approximation. The surface energy has been calculated for different faces of III–V semiconductor crystals with cubic and hexagonal structures. The effect of the formation of the hexagonal wurtzite phase in nanowhiskers of III–V semiconductor compounds has been considered using the obtained data. Estimates for the critical radius of the phase transition in III–V semiconductor nanowhiskers are presented.
91 citations
TL;DR: In this paper, the heat capacity, thermal conductivity, thermal diffusivity, and thermal expansion of Bi4Ge3O12 single crystals have been measured over a wide temperature range.
Abstract: The heat capacity, thermal conductivity, thermal diffusivity, and thermal expansion of Bi4Ge3O12 single crystals have been measured over a wide temperature range.
89 citations
TL;DR: In this paper, the authors used Raman and IR spectroscopy to examine polyvinyl alcohol (PVA) thermally treated in air or vacuum, and found that after several hours of treatment in air at 470 K bands in Raman spectrum, some bands in PVA became weaker and some became stronger.
Abstract: Raman and IR spectroscopy were used to examine polyvinyl alcohol (PVA) thermally treated in air or vacuum. It was found that after several hours of treatment in air at 470 K bands in Raman spectrum disappear. After vacuum treatment some bands disappear and other become stronger, and slightly change their positions. Such a phenomenon is attributed to the increase of molecular polarizability along polymer chain caused by conjugation.
85 citations
TL;DR: The main regularities of structural and phase transformations occurring in solids have been analyzed experimentally and theoretically within the framework of the concept of manifestation of additional channels providing the dissipation of an elastic energy introduced into a solid under megaplastic deformation.
Abstract: The main regularities of structural and phase transformations occurring in solids have been analyzed experimentally and theoretically within the framework of the concept of manifestation of additional channels providing the dissipation of an elastic energy introduced into a solid under megaplastic deformation. It has been demonstrated that an active participation of low-temperature dynamical recrystallization processes, phase transitions of the type crystal ai amorphous state, and thermal effects under the conditions of an insufficient efficiency of the dislocation and disclination relaxation modes can consistently explain almost all the experimental results obtained for very severe plastic deformations.
75 citations
TL;DR: In this article, a two-level approach has been proposed for describing the plastic deformation under high-rate loading of metals by using the molecular dynamics simulation, which has been used to study the evolution of the dislocation subsystem under shock-wave loading of an aluminum target.
Abstract: A two-level approach has been proposed for describing the plastic deformation under high-rate loading of metals. The characteristics of the motion of dislocations under shear stresses have been investigated at the atomistic level by using the molecular dynamics simulation. The macroscopic motion of a material has been described at the continuum level with the use of the model of continuum mechanics with dislocations, which uses information obtained at the atomistic level on the dislocation dynamics. The proposed approach has been used to study the evolution of the dislocation subsystem under shock-wave loading of an aluminum target. The behavior of the dynamic yield stress with an increase in the temperature has been analyzed. The results of the calculations are in good agreement with experimental data.
66 citations
TL;DR: In this article, the magnetoelectric effect in layered composites has been considered in the cases of a thin rectangular plate and a thin disk under the condition that the sizes of the sample are smaller than the electromagnetic wave length.
Abstract: The magnetoelectric effect in layered composites has been considered in the cases of a thin rectangular plate and a thin disk under the condition that the sizes of the sample are smaller than the electromagnetic wave length. The theoretical model is based on the exact solution to the equations of motion of a medium and employs the material parameters of the initial components of the structure.
46 citations
TL;DR: In this paper, the thermal expansion along the principal crystallographic axes of (NH4)2WO2F4 and (NH 4)2MoO 2F4 oxyfluorides has been studied and the anomalous behavior of αi(T) due to the phase transitions has been revealed.
Abstract: The thermal expansion along the principal crystallographic axes of the (NH4)2WO2F4 and (NH4)2MoO2F4 oxyfluorides has been studied. The anomalous behavior of αi(T) due to the phase transitions has been revealed at T1 = 271.4 K and T2 ≈ 180 K for the molybdate and at T1 = 201.5 K and T2 ≈ 161 K for the tungstate. The quantities dT/dp and dT/dσi, which characterize the dependence of the phase transition temperatures on the hydrostatic and uniaxial pressures, have been determined from analyzing the results of studies of the thermal expansion and heat capacity with the use of the Pippard relations. The p-T and αi-T phase diagrams reflect different characters of the influence of the pressure on the stability of the initial and distorted phases of the oxyfluorides. The magnitudes of the extensive and intensive barocaloric effects determined in the vicinity of the structural phase transitions are as follows: ΔSBCE varies from approximately −10 to −17 J/mol K and ΔTAD ≈ 8−17 K for the molybdate and ΔSBCE varies from approximately −10 to −17 J/mol K and ΔTAD ≈ 8−13 K for the tungstate.
41 citations
TL;DR: In this paper, the infrared spectra of BiFeO3 ceramic samples have been measured using submillimeter spectroscopy (on a backward-wave tube spectrometer) and Fourier-transform infrared spectrographs in the frequency range from 5 to 1000 cm−1 at temperatures in the range from 10 to 500 K.
Abstract: Reflection and transmission infrared spectra of BiFeO3 ceramic samples have been measured using submillimeter spectroscopy (on a backward-wave tube spectrometer) and Fourier-transform infrared spectroscopy in the frequency range from 5 to 1000 cm−1 at temperatures in the range from 10 to 500 K. New resonant modes (probably, magnetic in nature) with the eigenfrequencies decreasing with an increase in the temperature have been recorded in the range 10–30 cm−1 by IR spectroscopy for the first time. An additional absorption with a fairly large dielectric contribution has been revealed in the range 30–60 cm−1. It has been demonstrated that the corresponding oscillators couple with both the lowest frequency phonon mode and the magnetic subsystem.
41 citations
TL;DR: In this article, a study of crystallization of thin lead zirconate-titanate films deposited on Si/SiO2/Pt substrates by RF magnetron sputtering at a low temperature and annealed at 540-580°C is presented.
Abstract: This paper reports on a study of crystallization of thin lead zirconate-titanate films deposited on Si/SiO2/Pt substrates by RF magnetron sputtering at a low temperature and annealed at 540–580°C. In this temperature interval, one observes successively two first-order phase transitions: the low-temperature pyrochlore phase—perovskite-I phase and perovskite-I phase-perovskite-II phase transitions, which are accompanied by film volume shrinkage. The phase transformations have been studied by atomic force microscopy, scanning electron microscopy, X-ray diffraction and visual (optical) observation of the growth of islands of a new phase. It has been found that the dielectric parameters undergo substantial changes upon the transition from phase I to phase II. The origin of the observed effects has been discussed.
41 citations
TL;DR: In this article, the behavior of the electrical and thermal conductivities of a nanostructured material based on BixSb2 − xTe3 solid solutions is investigated and the effect of boundary scattering has been taken into account by introducing the scattering mechanism with a constant mean free path equal to the nanoparticle size.
Abstract: This paper reports on a theoretical and experimental investigation of the behavior of the electrical and thermal conductivities of a nanostructured material based on BixSb2 − xTe3 solid solutions. The effect of boundary scattering has been taken into account by introducing the scattering mechanism with a constant mean free path equal to the nanoparticle size. A comparison with the results of the measurements has demonstrated that one can describe satisfactorily the experimental dependences of the electrical and thermal conductivities on the nanoparticle size by using only the parameters of the initial solid solution and its pure constituents. The estimates have revealed that the lattice thermal conductivity of nanostructured materials can be reduced by 20–30% as compared to the initial solid solution with nanoparticle sizes of the order of 20 nm, which should produce a favorable effect on the magnitude of the thermoelectric figure-of-merit.
38 citations
TL;DR: In this article, the structures of several aqueous magnetic fluids stabilized by different combinations of surfactants have been compared using small-angle neutron scattering, and the degree of clustering of magnetic nanoparticles has been obtained from comparison with electron microscopy data.
Abstract: The structures of several aqueous magnetic fluids stabilized by different combinations of surfactants have been compared using small-angle neutron scattering. The size distribution functions of colloidal particles in water have been determined. The degree of clustering of magnetic nanoparticles has been obtained from comparison with electron microscopy data. The combinations of surfactants that lead to a minimum clustering have been revealed.
TL;DR: In this article, the results obtained from measurements of the magnetic properties of the ferrihydrite produced by Klebsiella oxytoca in its two main crystalline modifications are reported, and the data obtained are analyzed theoretically.
Abstract: Ferrihydrite nanoparticles (2–5 nm in size) produced by bacteria Klebsiella oxytoca in the course of biomineralization of iron salt solutions from a natural medium exhibit unique magnetic properties: they are characterized by both the antiferromagnetic order inherent in a bulk ferrihydrite and the spontaneous magnetic moment due to the decompensation of spins in sublattices of a nanoparticle. The magnetic susceptibility enhanced by the superantiferromagnetism effect and the magnetic moment independent of the magnetic field provide the possibility of magnetically controlling these natural objects. This has opened up the possibilities for their use in nanomedicine and bioengineering. The results obtained from measurements of the magnetic properties of the ferrihydrite produced by Klebsiella oxytoca in its two main crystalline modifications are reported, and the data obtained are analyzed theoretically. This has made it possible to determine numerical values of the magnetic parameters of real biomineral nanoparticles.
TL;DR: In this article, the barocaloric effect in the oxyfluoride Rb2KTiOF5 has been studied in the vicinity of the structural phase transition at a temperature of 215 K in the pressure range 0.6 GPa.
Abstract: The barocaloric effect (BCE) in the oxyfluoride Rb2KTiOF5 has been studied in the vicinity of the structural phase transition at a temperature of 215 K in the pressure range 0—0.6 GPa. It has been established that the extensive and intensive barocaloric effects are ΔSBCE ∼ −46 J/kg K and ΔT
AD ∼ 18 K, respectively, over a wide temperature range 215—280 K. The studies performed have shown that the external hydrostatic pressure is a very effective tool for changing the entropy and temperature of the crystals which undergo structural phase transitions accompanied by a large change in the entropy.
TL;DR: In this paper, regular domain structures on the Y cuts of the LiNbO3 substrates and Ti:LiNb O3 waveguide structures based on these substrates have been fabricated under electron-beam irradiation.
Abstract: Regular domain structures on the Y cuts of the LiNbO3 substrates and Ti:LiNbO3 waveguide structures based on these substrates have been fabricated under electron-beam irradiation. It has been revealed that the domains in undoped and titanium-doped LiNbO3 crystals are formed as a result of different processes. It has been demonstrated using chemical etching and waveguide second-harmonic generation that regular domain structures in the Ti:LiNbO3 waveguides are formed at a depth of approximately 8 μm from the surface, where the titanium concentration does not exceed 2 mol %. The quasi-synchronous waveguide optical second harmonic generation with an efficiency of 8.8% has been obtained using the fabricated structures.
TL;DR: The ground state of ten free-standing ferroelectric superlattices based on crystals with the perovskite structure was calculated from first principles within the density functional theory taking into account criteria for stability of the structures with respect to acoustic and optical distortions as discussed by the authors.
Abstract: The crystal structure of the ground state of ten free-standing ferroelectric superlattices based on crystals with the perovskite structure (BaTiO3/SrTiO3, PbTiO3/SrTiO3, PbTiO3/PbZrO3, SrZrO3/SrTiO3, PbZrO3/BaZrO3, BaTiO3/BaZrO3, PbTiO3/BaTiO3, BaTiO3/CaTiO3, KNbO3/KTaO3, and KNbO3/NaNbO3) was calculated from first principles within the density functional theory taking into account criteria for stability of the structures with respect to acoustic and optical distortions. It was shown that the ground state in all the considered superlattices corresponds to the ferroelectric phase. It was found that the polarization vector has a tendency toward a tilt to the plane of the superlattice layers, which makes it possible to decrease the electrostatic and elastic energy in the superlattices consisting of materials with different ferroelectric properties. The importance of the inclusion of structural distortions due to unstable phonons at the Brillouin zone boundary, which, in a number of cases, lead to significant changes in ferroelectric and dielectric properties of the superlattices, was demonstrated.
TL;DR: In this paper, the volume fraction of crystalline and amorphous phases of partially crystalline alloys from X-ray diffraction data has been discussed, and the angular range has been determined and the calibration graph has been constructed, which can be used to determine the volume fractions of the amorphus and crystalline components in amorphized-crystalline samples.
Abstract: The possibility of determining volume fractions of crystalline and amorphous phases of partially crystalline alloys from X-ray diffraction data has been discussed. The crystallization of an amorphous microwire of the Fe73.9B13.2Si10.9C2 composition has been investigated. The crystallization leads to the formation of α-Fe and Fe(Si). An analysis has been made of the X-ray diffraction patterns recorded for a series of samples with different contents of the crystalline and amorphous phases. The angular range has been determined and the calibration graph has been constructed, which can be used to determine the volume fractions of the amorphous and crystalline components in amorphous-crystalline samples.
TL;DR: In this article, it has been experimentally demonstrated that electron irradiation of photochromic glasses containing ions of univalent copper gives rise to the formation of metallic copper nanocrystals in near-surface layers of the glass.
Abstract: It has been experimentally demonstrated that electron irradiation of photochromic glasses containing ions of univalent copper gives rise to the formation of metallic copper nanocrystals in near-surface layers of the glass. The glass composition and conditions for electron irradiation and heat treatment have been shown to affect the amplitude and spectral position of the plasmon resonance of copper nanoparticles. A model has been proposed for explaining the spectral shift in the plasmon resonance.
TL;DR: In this paper, the results of measurements of the dynamic elastic limit and spall strength under shock-wave loading of aluminum samples AD1 of thicknesses between 0.5 and 10.0 mm at room temperature and at temperature increased up to 600°C are presented.
Abstract: The results of measurements of the dynamic elastic limit and spall strength under shock-wave loading of aluminum samples AD1 of thicknesses between 0.5 and 10.0 mm at room temperature and at temperature increased up to 600°C are presented. The anomalous thermal hardening of aluminum under high strain rate has been confirmed. An analysis of the decay of precursors at temperatures of 20 and 600°C has shown that the change in the main mechanism of drag of dislocations occurs at a strain rate equal approximately to 5 × 103 s−1, which agrees with the results of measurements by the Hopkinson split bar method. The results of measurements of the spall strength in a wide range of strain rates add the previously obtained data and agree with them.
TL;DR: In this paper, the contributions of different mechanisms of self-diffusion in face-centered cubic metals Ni, Cu, and Al at thermodynamic equilibrium have been analyzed using the molecular dynamics method.
Abstract: The contributions of different mechanisms of self-diffusion in face-centered cubic metals Ni, Cu, and Al at thermodynamic equilibrium have been analyzed using the molecular dynamics method. The vacancy, divacancy, and cyclic mechanisms of self-diffusion, as well as the mechanisms involving the vacancy migration to the second coordination sphere and the formation and recombination of Frenkel pairs, have been considered. It has been shown that the second in contribution to the self-diffusion after the vacancy mechanism in the metals under consideration is the migration of divacancies. The third is the mechanism involving the formation and recombination of dynamic Frenkel pairs. The cyclic mechanisms (with simultaneous atomic displacements) and the vacancy migration directly to the second coordination sphere in face-centered cubic metals are unlikely.
TL;DR: In this article, the electronic structures of undoped anatase and anatase doped with carbon and vanadium have been calculated using the ab initio tight-binding linear muffin-tin orbital (TB-LMTO) method in the LSDA + U approximation.
Abstract: The electronic structures of undoped anatase and anatase doped with carbon and vanadium have been calculated using the ab initio tight-binding linear muffin-tin orbital (TB-LMTO) method in the LSDA + U approximation. It has been shown that the doping of TiO2 leads to the formation of narrow bands of the C and Vimpurity states in the band gap. The calculations of the imaginary part of the dielectric function have made it possible to estimate the intensity of the optical absorption. It has been established that the doping with vanadium and carbon leads to optical absorption in the visible range and to an increase in the absorption in the ultraviolet range up to 4 eV. This should result in an increase in the photocatalytic activity on the surface of the doped anatase. The experimental determination of the photocatalytic activity of whiskers of the anatase doped with carbon and vanadium in the reaction of hydroquinone oxidation has confirmed the increase in the activity of the doped materials under exposure to ultraviolet, visible, and blue light. The phenomenon of dark catalysis in the anatase doped with carbon and vanadium has been interpreted within the concept of low-energy electronic excitatio ns between the impurity levels of carbon.
TL;DR: In this paper, the variations with temperature of the lattice parameters a(T) and c(T), and the thermal expansion coefficients of rare-earth diborides RB2(R=Tb, Dy, Ho, Er, Tm, Lu) have been investigated in the temperature range 4.2-300 K.
Abstract: The variations with temperature of the lattice parameters a(T) and c(T) and the thermal expansion coefficients of rare-earth diborides RB2(R=Tb, Dy, Ho, Er, Tm, Lu) have been investigated in the temperature range 4.2—300 K. It has been revealed that the dependences a(T) and c(T) exhibit an anomalous behavior in the vicinity of the ferromagnetic transformation temperatures Tc which correlates with the temperature dependences of the heat capacity. It has been established that the magnetic contributions to the thermal expansion of the diborides Δam(T) increase with increasing temperature and tend to constant values at T≫Tc and that the magnetic components Δcm(T) decrease for all the diborides studied, also tending to constant values at elevated temperatures. The exchange integrals Ya and Yc for the paramagnetic metal ions in the rare-earth diborides are determined from the dependences Δam(T) and Δcm(T).
TL;DR: In this article, the electro-optical properties of PMN-xPT single-crystal relaxor solid solutions with different PT contents (x = 6, 10, 13%) and the PLMN-25PT transparent ceramic with a La content of 3% have been studied at room temperature.
Abstract: The electro-optical properties of the PMN-xPT single-crystal relaxor solid solutions with different PT contents (x = 6, 10, 13%) and the PLMN-25PT transparent ceramic with a La content of 3%, which has been synthesized for the first time, have been studied at room temperature. It has been shown that the dependence of the quadratic electro-optical coefficients on the PT concentration in single crystals passes through a maximum at x ∼ 13%. It has been revealed that, although the PT concentration in the PLMN-25PT ceramic is above 13%, this material exhibits the largest quadratic electro-optical coefficients and the lowest half-wave voltage among all the known relaxor systems. Possible origins of the above phenomena have been discussed.
TL;DR: In this paper, a comprehensive study of depolarization field bulk screening in lithium niobate and lithium tantalate single crystals with various stoichiometry was carried out, and three used complementary methods are based on: dependence of coercive field on delay time; decrease of optical contrast of domain wall trace; and relaxation of light diffraction intensity on domain walls.
Abstract: Comprehensive study of depolarization field bulk screening was carried out in lithium niobate and lithium tantalate single crystals with various stoichiometry. Three used complementary methods are based on: 1) dependence of coercive field on delay time; 2) decrease of optical contrast of domain wall trace; 3) relaxation of light diffraction intensity on domain walls. The following parameters of bulk screening process were obtained: relaxation time constants, type of relaxation law, maximal value of bias field and “true” value of coercive field. Advantages and disadvantages of used experimental methods were analyzed.
TL;DR: In this paper, it was observed that doping with Fe3O4 nanoparticles and applying a magnetic field during the polymerization process led to a significant change in the local structure of the elastomer.
Abstract: Stomaflex elastomers filled with two types of magnetic particles (nano- and micro-sized) were investigated. It was observed that doping with Fe3O4 nanoparticles and applying a magnetic field during the polymerisation process led to a significant change in the local structure of the elastomer. Decreases in the quasi-crystalline phase concentration, in the average size of the crystalline blocks, and in the ordering distance were observed after doping the elastomer with magnetite nanoparticles. After filling the polymer with Fe3O4 nanoparticles, yet the elastomer fractal dimension changes. For the elastomer filled with a large amount of Fe microparticles (75% particle concentration) a texture effect is observed, and this effect is larger for the samples polymerised in a magnetic field. At all microparticle concentrations, these elastomers exhibit surface fractal structure.
Abstract: The regularities of the influence of the number of passes under equal-channel angular pressing on the mechanical properties and defect structure of an aluminum alloy have been elucidated. It has been established that the degradation of the mechanical properties (a decrease in the durability) is associated with the formation of nanoregions of an excess free volume in the course of severe plastic deformation under equalchannel angular pressing. A correlation between the nucleation of excess free volume regions and the formation of high-angle grain boundaries under equal-channel angular pressing has been revealed. The nature of the influence of severe plastic deformation on the elastic modulus, the vibration decrement, and the microplastic flow stress has been analyzed.
TL;DR: In this paper, the authors investigated the mechanisms of phase relaxation of excitons in GaAs single quantum wells using resonant reflection spectroscopy and found that an increase in the excitation level by five orders of magnitude above the linear limit leads to an insignificant change in the oscillator strength of the exciton transition and a multiple broadening of the spectral line profile.
Abstract: A technique that makes it possible to investigate the mechanisms of phase relaxation of excitons in GaAs single quantum wells has been developed using resonant reflection spectroscopy. The dependence of the oscillator strength of the exciton transition on the quantum well thickness has been measured in the thickness range 9.1–30.0 nm. It has been demonstrated that the oscillator strength with a high accuracy does not depend on the temperature in the range 8–90 K. The temperature dependence of the homogeneous broadening has been measured, and the inhomogeneous broadening of the resonance exciton line has been determined. A nonmonotonic dependence of the spectral broadening of the exciton line on the intensity of the resonant excitation at a temperature of 8 K has been revealed for the sample with a high-quality quantum well. It has been established that an increase in the excitation level by five orders of magnitude above the linear limit leads to an insignificant change in the oscillator strength of the exciton transition and to a multiple broadening of the spectral line profile.
TL;DR: In this article, a dielectric study of nanoparticles of the Rochelle salt embedded in pores of porous alumina has been performed in the temperature range from 80 K to the decomposition temperature of the bulk Rochelle Salt.
Abstract: Dielectric studies of nanoparticles of the Rochelle salt embedded in pores of porous alumina have been performed in the temperature range from 80 K to the decomposition temperature of the bulk Rochelle salt. It has been revealed that the permittivity exhibits an anomaly corresponding to the lower structural transition to the paraelectric phase, whereas the upper ferroelectric transition is shifted above the decomposition temperature in agreement with the recently published data. The temperature of the lower transition for nanoparticles in pores is found to decrease by 10 K. Possible physical factors that can be responsible for the broadening of the region of existence of the ferroelectric phase have been discussed.
TL;DR: In this paper, the mechanisms of plastic deformation under compression in a shock wave and under tension in rarefaction waves have been investigated, and the influence of the defect structure formed in the compression wave on the spall strength and the fracture mechanism has been analyzed.
Abstract: The plastic deformation and the onset of fracture of single-crystal metals under shock-wave loading have been studied using aluminum as an example by the molecular dynamics method. The mechanisms of plastic deformation under compression in a shock wave and under tension in rarefaction waves have been investigated. The influence of the defect structure formed in the compression wave on the spall strength and the fracture mechanism has been analyzed. The dependence of the spall strength on the strain rate has been obtained.
TL;DR: A detailed review of theories describing the current-phase relations in Josephson junctions based on heterostructures with ferromagnetic layers is presented in this article, where the possibilities of making the so-called ϕ-junctions in which the ground state in the absence of the current is realized when the Josephson phase ϕ is nonzero.
Abstract: A detailed review of theories describing the current-phase relations in Josephson junctions based on heterostructures with ferromagnetic layers is presented. The particular attention has been focused on the possibilities of making the so-called ϕ-junctions in which the ground state in the absence of the current is realized when the Josephson phase ϕ is nonzero. The recently popular speculations concerning the possibility of applying the Josephson π- and ϕ-junctions, which are made on the basis of heterostructures with ferromagnetic layers, to the formation of quantum bits (qubits) have been illustrated. An attempt to formulate the requirements for the characteristics of the Josephson heterostructures based on the first principles of the quantum-mechanical description of superconducting interferometers with a low inductance has been made.
TL;DR: In this paper, the thermal conductivity and electrical resistivity 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 were analyzed.
Abstract: 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.