Pleiades Publishing Ltd

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.

The heat capacity of multiferroics Bi1–x Pr x FeO3 (0 ≤ x ≤ 0.20) has been studied in the temperature range 130–800 K. An insignificant substitution of praseodymium for bismuth is found to lead to a noticeable shift of the antiferromagnetic phase transition temperature and to an increase in the heat capacity in the temperature range 240–780 K. The temperature dependence of the excess heat capacity is shown to be due to the Schottky effect for three-level states. The temperature dependences of the heat capacity of the compositions with x = 0.10 and x = 0.15 and 0.20 exhibit additional anomalies characteristic of the phase transitions at T ≈ 755 K and ≈710 K, respectively. The results are discussed in combination with the data of structural studies.

Nanophosphors in the amorphous state are first obtained via pulsed electron beam evaporation of targets made of polycrystalline phosphors with the compositions Ca2M8(SiO4)6O2:Eu (M = Y and Gd) and Ca2La8(GeO4)6O2:Eu with the structure of oxyapatite. Reduction of ions Eu3+ → Eu2+ in the electron beam is found. Modification of the Raman scattering (RS) spectra of the samples in the case of a decrease in the size of the particles from bulk to a nanosized state is found. The change in the forbidden band width Eg of the samples in the case of transition from a bulk powder to an NP is considered. The spectral and luminescence characteristics of the samples in the polycrystalline and nanoamorphous states are studied. It is shown that, in the case of transition to nanosamples, the ligand field around Eu2+ changes. This may be due to the violation of the translational symmetry in the NP. The bond between the 4f and 5d electrons weakens. Degeneracy of the 2eg level appears. Presumably, the reduction of ions Eu3+ → Eu2+ in the electron beam due to the breaking of the Si(Ge)–O bond in the process of evaporation of the samples and capture of the released electron by the Eu3+ ions is found.

Các phổ phát quang (T=5 K) và hấp thụ (T=295 K) cũng như các đường cong phát quang bị kích thích nhiệt (T=5–300 K) của phim poly(methylphenyl)silane (PMPS) được nghiên cứu dựa trên độ dày của phim, nhiệt độ ủ và hàm lượng oxy trong không khí. Kết quả cho thấy rằng các phổ quang học và đường cong phát quang bị kích thích nhiệt của các phim PMPS được chế tạo trong không khí ở nhiệt độ phòng có sự thay đổi sau khi ủ ở T=370–450 K. Giả thuyết được đưa ra rằng các sự thay đổi quan sát được liên quan tới việc hình thành các đoạn chuỗi polymer dài với sự sắp xếp chặt chẽ hơn. Điều này dẫn đến việc tăng mật độ các trạng thái năng lượng thấp của exciton và các mang điện tích. Kết quả cho thấy oxy trong khí quyển có ảnh hưởng đáng kể đến các quá trình hình thành và sự rối loạn năng lượng trong các phim đã được chế tạo. Các phim PMPS bị suy giảm sau khi được đun nóng đến T≥500 K.

The electronic structure and specific features of the structure of nonstoichiometric cobaltite Li x Na y CoO2 (x = 0.42, y = 0.36) have been studied comprehensively. The calculated multiplet for the lowspin state of the Co3+ ion agrees with the experimental spectra. It has been established using X-ray absorption spectra measured in the total photoelectric effect yield and total fluorescence yield modes that the Li x Na y CoO2 cobaltite is stoichiometric with respect to the alkali metal near its surface and is defective inside. It has been demonstrated that the charge compensation in the case of an alkali metal deficit in LixNayCoO2 is due to holes in O 2p states.

The characteristics of Li+-ion conductivity σdc of structural γ modifications of Li3R2(PO4)3 compounds (R = Fe, Sc) existing in the superionic state have been investigated by impedance spectroscopy. The type of structural framework [R2P3O12]∞3- affects the σdc value and the σdc activation enthalpy in these compounds. The ion transport activation enthalpy in γ-Li3R2(PO4)3 (ΔHσ = 0.31 ± 0.03 eV) is lower than in γ-Li3Fe2(PO4)3 (ΔHσ = 0.36 ± 0.03 eV). The conductivity of γ-Li3Fe2(PO4)3 (σdc = 0.02 S/cm at 573 K) is twice as high as that of γ-Li3R2(PO4)3. A decrease in temperature causes a structural transformation of Li3R2(PO4)3 from the superionic γ modification (space group Pcan) through the intermediate metastable β modification (space group P21/n) into the “dielectric” α modification (space group P21/n). Upon cooling, σdc for both phosphates decreases by a factor of about 100 at the superionic TSIC transition. In Li3Fe2(PO4)3 σdc gradually decreases in the temperature range TSIC = 430–540 K, whereas in Li3R2(PO4)3 σdc undergoes a jump at TSIC = 540 ± 25 K. Possible crystallochemical factors responsible for the difference in the σdc and ΔHσ values and the thermodynamics and kinetics of the superionic transition for Li3R2(PO4)3 are discussed.

During crystallization, the LiF-YF3-LuF3 compounds form a continuous series of solid solutions having a scheelite structure at any proportion of the YF3 and LuF3 components. It is established that the crystals conform to the Vegard law and the Rutgers rule. The spectral characteristics of the 5d–4f transitions of Ce3+ ions and color centers induced by ultraviolet radiation in these crystals were studied as a function of the Lu3+ concentration. It is shown that the active media based on LiF-YF3-LuF3: Ce3+ solid solutions are more efficient as compared to LiYF4: Ce3+ and LiLuF4: Ce3+ crystals in possible directional changes in the spectral-kinetic characteristics of impurity ions and the parameters of the losses induced by pumping radiation and in enhancement of energetic and spectral characteristics of lasers on their basis.

The electron transport in hydrogenated amorphous carbon films a-C: H with copper nanocluster inclusions has been investigated. The conditions of cluster formation are derived. It is theoretically demonstrated that the energy band structure of the matrix substantially affects the conditions of cluster formation. The electron transport depends on the cluster structure. It is found that, below the percolation threshold (the case of isolated clusters), the transport current is governed by two components depending on the electric field strength. At low field strengths, the current is caused by electrons in the conduction band of amorphous carbon, which are thermally excited from copper clusters. At high field strengths, the transport current is provided by tunneling electrons from the Fermi level of copper clusters to the conduction band of a-C: H. The difference between the mobility edge of the conduction band of amorphous carbon and the Fermi level in copper clusters is determined from the temperature dependence of the resistance and proves to be equal to 0.48 eV. The temperature dependences of the resistance at low field strengths exhibit a fine structure. It is revealed that, above the percolation threshold, the electrical resistance of clusters is considerably contributed by the residual resistance, which is supposedly associated with the electron scattering by cluster surfaces. The temperature effect on the electron transport is examined using the spin-wave scattering technique at a frequency of 4.0 GHz. It is found that the spin wave in the yttrium iron garnet (YIG) film is predominantly affected by thermally excited electrons located above the mobility edge in the conduction band of a-C: H.