Microwave dielectric properties of Ba<Subscript>4</Subscript>LaTiNb<Subscript>3−<Emphasis Type="Italic">x</Emphasis></Subscript>Ta<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>15</Subscript> ceramics

High dielectric constant and low loss ceramics in the system Ba₄LaTiNb_3−x Ta _x O₁₅ (x = 0–3) have been prepared by conventional solid-state ceramic route. Ba₄LaTiNb_3−x Ta _x O₁₅ solid solutions adopted A₅B₄O₁₅ cation-deficient hexagonal perovskite structure for all compositions. The materials were characterized at microwave frequencies. They show a linear variation of dielectric properties with the value of x. Their dielectric constant varies from 53.1 to 42.3, quality factor Q_u × f from 18,790 to 28,070 GHz and temperature variation of resonant frequency from +94.3 to +33.1 ppm/°C as the value of x increases.     

Thermal conductivity of Er<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Sn<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Se (<Emphasis Type="Italic">x</Emphasis> ≤ 0.025) solid solutions

The thermal conductivity of Er _x Sn_{1 ? x} Se solid solutions has been measured at temperatures from 80 to 360 K. The results have been used to evaluate the electronic and lattice components of thermal conductivity for elastic carrier scattering, parabolic bands, and arbitrary degeneracy. With increasing erbium content and temperature, both the electronic and lattice components decrease considerably. Long-term annealing increases both components. It follows from the present experimental data that heat conduction in Er _x Sn_{1 ? x} Se is mainly due to phonons and that the observed rise in thermal resistance with Er content is due to phonon-phonon and paramagnetic-ion scattering.     

Phase transformation of <Emphasis Type="Italic">p</Emphasis>-Cd<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Mn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>GeAs<Subscript>2</Subscript> single crystals at 5.5 GPa

The electrical resistivity and Hall coefficient of oriented single-crystal p-Cd_{1 − x} Mn _x GeAs₂ samples have been measured at high pressures. The results indicate that the crystals undergo a reversible structural transformation at 5.5 GPa, which is independent on the sample orientation.     

Enhanced Superconductivity in Double-Doping Cu<Subscript>0.15</Subscript>TaSe<Subscript>2−<Emphasis Type="Italic">x</Emphasis></Subscript><Emphasis Type="Italic">S</Emphasis><Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>

Superconducting Cu _x TaSe₂(x=0.05, 0.15) and Cu_0.15TaSe_2?x S _x (x=0, 0.5, 1, 1.5) single crystals have been systematically fabricated by a chemical vapor transport method. It is found that the double doping in TaSe₂, i.e., the simultaneous intercalation of Cu and substitution of Se by S, can substantially enhance the superconducting transition temperature. Transport property measurements give evidence of the coexistence and competition of charge density wave state and superconductivity in Cu _x TaSe₂ which provide meaningful information to understand the complex electronic states in this system. The parallel shift and the fan-shape broadening behaviors are observed in the superconducting transition curves under magnetic fields of Cu_0.15TaSeS and TaSeS, respectively, indicating an increase of coherence length and suppression of superconducting fluctuation induced by copper intercalation.     

Electrical conductivity and thermoelectric power of LaCo<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Ga<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>3</Subscript> solid solutions

Increasing the degree of Ga³⁺ substitution for Co³⁺ ions in LaCo_{1 − x} Ga _x O₃ solid solutions (x = 0–1) considerably reduces their electrical conductivity: at T= 850 K, from 190.5 S/cm in LaCoO₃ to 1.32 × 10⁻⁵ S/cm in the x = 0.95 solid solution. The anomaly in the temperature-dependent conductivity of the solid solutions, due to the broad semiconductor-metal transition, decreases with increasing x. For x ≥ 0.8, there is a very weak or no anomaly. The activation energies for conduction in the samples with x = 0.90 and 0.95 are 0.89 and 0.92 eV, respectively. At room temperature, the materials with 0 ≤ x ≤ 0.3 have a negative thermoelectric power. With increasing temperature, it increases, crosses zero between 435 and 530 K, reaches a maximum in the range 500–650 K, and decreases at higher temperatures.     

Phase transformations during the synthesis and sintering of Y<Subscript>2 − <Emphasis Type="Italic">x</Emphasis></Subscript>Yb<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>3</Subscript> nanopowders

The formation of an Y₂O₃-Yb₂O₃ solid solution (8 mol % Yb₂O₃) during the thermal decomposition of (Y,Yb)₂(CO₃)₃ · 2H₂O mixed carbonates obtained by coprecipitation from a nitrate solution has been studied by X-ray diffraction, thermal analysis, and optical microscopy. The results demonstrate that the formation of a cubic yttria-based solid solution begins in the range 470–500°C and reaches completion at temperatures above 1100°C. The unit-cell parameter a of the cubic solid solution and the X-ray density of the corresponding ceramic are 10.5910 Å and 5.349 g/cm³, which corresponds to the intended chemical composition of the isovalent substitutional solid solution: Y_1.84Yb_0.16O₃.     

Magnetic Phase Diagram of CuCr<Subscript>2–<Emphasis Type="Italic">x</Emphasis></Subscript>Sb<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>S<Subscript>4</Subscript> Solid Solutions

The magnetization of CuCr_2–xSb _x S₄ solid solutions has been measured as a function of temperature between 300 and 5 K in a weak (3980 A/m) and a strong (7960 A/m) magnetic field. We have identified the type and character of the magnetic transformations observed in the system and determined the temperature and composition limits of the stability regions of the magnetically active phases involved and the cation and valence distributions in them. A magnetic phase diagram of the synthesized materials has been mapped out, where the largest area (0 < x < 0.23) after the paramagnetic region is occupied by solid solutions based on the CuCr₂S₄ ferromagnet. In the composition range (0.23 < x < 0.40) adjacent to the infinite clusters—CuCr₂S₄ ferromagnet and CuCr_1.5Sb_0.5S₄ antiferromagnet—the phase diagram contains medium and small finite ferro- and antiferromagnetic clusters forming a short-range magnetic order or spin glass. The compositions based on the CuCr_1.5Sb_0.5S₄ antiferromagnet lie in the composition range 0.4 < x < 0.5.     

Fluorine doping in dilute magnetic semiconductor Sn<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Fe<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>2</Subscript>

Recent studies have reported room-temperature ferromagnetism (FM) in Fe doped SnO₂. The FM in semiconductors due to transition metal doping has been argued to be carrier mediated. Fluorine (F) doping in pure SnO₂ has been reported to significantly increase the carrier concentration. In this work, we investigated the role of F doping in the range from 0% to 0.79% on the FM of chemically synthesized single phase Sn_1?x Fe _x O₂ using X-ray diffraction, UV–Vis spectrophotometry, particle-induced X-ray emission, particle-induced gamma ray emission and magnetometry. The saturation magnetization M _s (0.03 emu/g) increased by a factor of 2.5 and the lattice volume and band gap energy decreased by 0.35 Å³ and 0.2 eV, respectively, with 0.67% F doping (F/Sn atom %) compared to the sample without any fluorine.     

Low-temperature heat capacity of Li<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Ni<Subscript>2 − <Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>2</Subscript> solid solutions

The heat capacity of Li _x Ni_{2 − x} O₂ (x = 0.40–0.76) oxides has been measured using an adiabatic calorimeter, and their thermodynamic functions have been determined. The results indicate that the lithium nickelate solid-solution series contains a two-phase region and that near-stoichiometric LiNiO₂ has a layered structure, in accordance with earlier results.     

Thermal conductivity of TlIn<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Dy<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Te<Subscript>2</Subscript> solid solutions

The thermal conductivity of TlIn_{1 ? x} Dy _x Te₂ solid solutions, based on the compound semiconductor TlInTe₂, has been measured as a function of temperature (80–350 K). The results have been used to assess the effects of phonon-phonon and impurity scattering on the thermal conductivity of the solid solutions. Phonon scattering by the isovalent impurity Dy is shown to be significant above the Debye characteristic temperature of the materials.     

Synthesis and properties of SrFe<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>M<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>3 − <Emphasis Type="Italic">z</Emphasis></Subscript> (M = Mo,W) perovskites

We have synthesized SrFe_{1 ? x} M _x O_{3 ? z} (M = Mo, W; 0 < x ≤ 0.5) solid solutions. Our results indicate that the introduction of stable MO₆ octahedra narrows the range of oxygen stoichiometries of the material and suppresses the perovskite-brownmillerite structural phase transition at low temperatures and oxygen partial pressures. We have studied the thermal stability of the synthesized materials in a reducing atmosphere and the effect of oxygen stoichiometry on their electronic and oxygen-ionic conductivity and phase transformations.     

Heat capacity of Li<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Ni<Subscript>2 − <Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>2</Subscript> solid solutions

We have synthesized Li _x Ni_{2 − x} O₂ oxides in the range x = 0.1–0.84 and showed that the solid-solution system contains a two-phase region. The heat capacity of Li _x Ni_{2 − x} O₂ has been determined by differential scanning calorimetry.     

Anisotropic ferromagnetism in Fe<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Sn<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>2</Subscript> nanostructure arrays

Periodic arrays of Fe _x Sn_1?x O₂ nanostructures were fabricated by glancing angle sputter deposition onto self-assembled close-packed arrays of 200-nm-diameter polystyrene microspheres. After annealing at 873 K for 3 h, all the films were crystallized to rutile SnO₂ and maintained good thermal stability in the morphology. Compared with Fe _x Sn_1?x O₂ flat films, arrays of Fe _x Sn_1?x O₂ nanostructures possessed larger saturation magnetic moment and exhibited both perpendicular and in-plane magnetic anisotropy, resulting from the anisotropic morphology of Fe _x Sn_1?x O₂ nanostructures. The EPR signal originating from the oxygen vacancies significantly varied with the Fe concentration and reached the strongest at x = 0.059, which is consistent with the saturation magnetization. It demonstrates that the oxygen vacancies are an important factor for the ferromagnetism of Fe _x Sn_1?x O₂ films.     

Visible photoluminescence of hydrothermal synthesized Sn<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Ni<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>2</Subscript> nanostructures

Sn_1−x Ni _x O₂ nanostructures such as nanocubes, nanospheres and hollow spheres were synthesized by a simple hydrothermal method. Room temperature photoluminescence spectra of the as-synthesized samples display a strong yellow emission at about 600 nm and a weak blue emission at about 430 nm. The as-prepared and annealed Sn_1−x Ni _x O₂ (x = 0, 0.01, 0.02, 0.04) were characterized by X-ray diffraction, field emission scanning electron microscopy, Raman spectrum, UV–Vis absorption spectra, and room temperature photoluminescence spectra. By investigating the relationship between the Raman band centered at 560 cm⁻¹ and the photoluminescence of the samples, we suggest that the broad yellow emission and weak blue emission primarily originate from singly ionized oxygen vacancies and tin interstitials, respectively.     

Thermal conductivity of Sn<Subscript>1–<Emphasis Type="Italic">x</Emphasis> </Subscript>Mn<Subscript> <Emphasis Type="Italic">x</Emphasis> </Subscript>Te single crystals

The thermal conductivity of homogeneous crystalline Sn_1–xMn_xTe samples has been measured in the temperature range 90–305 K. We have determined their electron and lattice thermal conductivities and their thermal resistivity due to structural defects. The results demonstrate that the electron thermal conductivity reaches ~50% of the total thermal conductivity in some of the samples and that structural defects make an appreciable contribution to the thermal resistivity of the crystals.     

Thermal conductivity of Sn<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Nd<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>S single crystals

The thermal conductivity of Sn_{1 − x} Nd _x S (x = 0, 0.001, 0.002) single crystals has been measured in the temperature range 80–840 K. The results have been used to evaluate the electronic and lattice components of the thermal conductivity. Both the electronic and lattice components are shown to decrease with increasing temperature and to increase with neodymium content.     

Properties of YBaCuFe<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Ni<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>5</Subscript> (0 < <Emphasis Type="Italic">x</Emphasis> ≤ 0.3) solid solutions

YBaCuFe_{1 – x}Ni_xO₅ solid solutions are shown to exist for x 0.3. Data are presented on the lattice parameters, thermal stability, thermal expansion, electrical conductivity, thermoelectric power, magnetic susceptibility, and dielectric properties of the solid solutions. Ni substitution for Fe notably increases the electrical conductivity of the solid solutions, reduces their thermoelectric power and thermal expansion, and shifts the antiferromagnetic—paramagnetic phase transition and dielectric anomalies in YBaCuFe_{1 – x}Ni_xO₅ to lower temperatures.Translated from Neorganicheskie Materialy, Vol. 40, No. 12, 2004, pp. 1515–1519.Original Russian Text Copyright © 2004 by Chizhova, Klyndyuk, Bashkirov, Petrov, Makhnach.     

Raman spectroscopy determination of carrier concentration in <Emphasis Type="Italic">n</Emphasis>-In<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Ga<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>As epitaxial films

We have studied in detail the coupled phonon-plasmon mode Raman spectra of n-In _x Ga_{1 − x} As with n in the range 10¹⁷ to 10¹⁹ cm⁻³. The results indicate that the behavior of the high-frequency mode L ₊ can be described in terms of coupled modes in the Drude approximation. The proposed theory and experimental data are used to estimate the carrier concentration in the solid solution and its composition.     

Electrical conduction in La<Subscript>0.9</Subscript>Ba<Subscript>0.1</Subscript>Er<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Mg<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>3−α</Subscript> ceramics

Doubly doped LaErO₃ ceramics, La_0.9Ba_0.1Er_1−x Mg _x O_3−α (x = 0.05, 0.10, 0.15, 0.20), were synthesized by solid-state reaction method and characterized by X-ray diffraction (XRD). The samples have a single orthorhombic perovskite-type structure. The conduction behavior was investigated using various electrochemical methods including AC impedance spectroscopy, gas concentration cell, isotope effect of hydrogen, and hydrogen electrochemical permeation (pumping) in the temperature range of 500–1000 °C. The results indicated that specimens were pure ionic conductors under low oxygen partial pressure (about 10⁻⁷–10⁻²⁰ atm) and mixed conductors of proton, oxide ion, and electron hole under high oxygen partial pressure (about 10⁻⁵–1 atm). The pure ion conduction of the ceramics in hydrogen atmosphere was confirmed by electromotive force method of hydrogen concentration cell, and the observed emf values coincided well with the theoretical ones. The conductivity in H₂O–Ar atmosphere was higher than that in D₂O–Ar atmosphere, exhibiting an obvious isotope effect and proton conduction in water vapor containing atmosphere. It has been confirmed by electrochemical hydrogen permeation (hydrogen pumping) experiment that the ceramics were mainly proton conductors in hydrogen containing atmosphere. Whereas in dry oxygen-containing atmosphere, observed emf values of the oxygen concentration cell were far lower than the theoretical ones, indicating that the ceramics were mixed conductors of electron hole and oxide ion.     

Homogeneity of high-resistivity <Emphasis Type="Italic">p</Emphasis>-Si<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Ge<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>〈Au〉 crystals

p-Si_{1 ? x} Ge _x crystals have been diffusion-doped with gold. Gold diffusion in the p-Si_{1 ? x} Ge _x 〈Au〉 samples and their electrical properties have been studied. The results demonstrate that the highest gold concentration in the crystals can be achieved in the temperature range 1000–1050°C. An expression has been derived which indicates that, all other factors being the same, compensation with Au, an amphoteric impurity, insures better homogeneity compared to codoping with acceptor and donor impurities. The hole concentration homogeneity in gold-compensated samples is at the same level as or even better than that in the uncompensated material.