The subsolidus phase diagram of the system Y2O3-BaO-CuO at 950° C in air has been investigated. In the binary system BaO-CuO the compound Ba2CuO3+δ has been isolated and a new compound with composition in the vicinity of Ba3Cu5O8+δ has been found. In the binary system BaO-Y2O3 it is shown in that the compounds “Ba4Y2O7” and “Ba2Y2O5” are oxycarbonates with composition Ba4Y2O7·CO2 and Ba2Y2O5·2CO2. New compounds that have been identified in the ternary system Y2O3-BaO-CuO are YBa4Cu3O8.5+δ, Y3Ba8Cu5O17.5+δ and a compound with composition close to YBa5Cu Cu2O8.5+δ. The oxygen content and the oxidizing power of these compounds has been measured. The oxygen content depends on the preparation method. Lists of interplanar spacings, relative intensities and h k l indices of these oxygen deficient perovskites as determined from X-ray powder diffraction measurements are presented and possible structures of the unit cells are described. Phase equilibrium relations have been investigated and tie lines in the phase diagram are presented.

Compounds and phase compatibilities in the system Y2O3-BaO-CuO at 950°C

The electrical conductivity of Sr1−xLaxTiO3 ceramics (x≤0.4) and single crystals (x≤0.1) was investigated in the temperature range between 19 and 1673 K. The mobility was calculated from the carrier concentration, n, which was determined by Hall measurements as well as by a chemical Ti3+ titration. The mobility of the single crystals agrees well with a model originally developed for undoped strontium titanate. At low T and high n scattering by ionized donor centers predominates. Above room‐temperature phonon scattering becomes predominant. Sr1−xLaxTiO3 ceramics follow the same model, but only if they had been previously reduced in water‐free and oxygen‐free hydrogen atmospheres. The behavior during the reducing and cooling process can be explained by a defect chemical model, using a set of constants developed in a former work. However, reduced in water saturated hydrogen the conductivity at low T decreases by decades compared to single‐crystal data and cannot be explained anymore by the above‐mentioned models. In conjunction with impedance spectroscopy experiments it was found, that in this case the electrical behavior of the ceramics is completely governed by grain‐boundary phenomena. These high‐ohmic grain boundaries may be depletion layers, which are formed or annihilated depending on the conditions of the preceding high‐temperature process.

Electronic transport properties of sr1-xlaxtio3 ceramics

Raman and IR-measurements on the high- T c material series La 2 CuO 4 and YBa 2 Cu 3 O 7 are reviewed. This summary focuses on lattice vibrations in these superconducting systems, on impurity phases, the influence of oxygen stoichiometry and element substitution. The determination of the superconducting gap, the phonon renormalization in the superconducting state, and the isotope effect with its implications on the theory of superconductivity in these materials are discussed. In addition, the measured lattice vibrations are compared with the results of lattice dynamics calculations.

Lattice vibrations in high-Tc superconductors: Optical spectroscopy and lattice dynamics☆

By using extended bosonic coherent states, a technique to solve the Dicke model exactly is proposed in the numerical sense. The accessible system size is two orders of magnitude higher than that reported in the literature. Finite-size scaling for several observables, such as the ground-state energy, Berry phase, and concurrence, is analyzed. A scaling exponent for ground-state energy is found. An existing discrepancy in the scaling exponent of the concurrence is reconciled.

Numerically exact solution to the finite-size Dicke model

This letter presents a triple-band compact and efficient ultrathin metamaterial absorber with wide-angle and polarization stability. The compact single unit cell includes a metallic background plane, four groups of dipoles lying around a metallic ring connected by four groups of pins, and only 1-mm low-cost dielectric layer. In addition, the main parameters of the designed absorber are investigated and optimized to show that each of three absorption frequency points can be effectively separately adapted, respectively. The simulation results demonstrate that this absorber has good absorption rates and polarization-insensitive characteristic over wide angles of incident waves for both transverse electric (TE) and transverse magnetic (TM) in three frequency bands. The waveguide measurement method is utilized to test the simulated results of three good absorption peaks.

A Triple-Band Ultrathin Metamaterial Absorber With Wide-Angle and Polarization Stability

Hall effect in single phase Ba2YCu3O7−δ

Superconductivity and phases of leaded Bi-Ca-Sr-Cu-O system

By measuring the structure, superconductivity, magnetoresistance of polycrystalline single-phase YBa2Cu3O7-δ samples, the phenomena of negative magnetoresistance and the hysteresis of the magnetoresistance have been studied. An analysis of the origin of the influence of grain boundaries on the superconductivity and the electronic transport properties are given.

Zhang Qirui

Papers

Hall effect in single phase Ba2YCu3O7−δ

Superconductivity and phases of leaded Bi-Ca-Sr-Cu-O system

The Behaviour of Negative Magnetoresistance and Hysteresis in YBa2Cu3O7-δ

Two- and three-dimensional polarons with extended coherent states.

Preparation and superconductivity of the high-Tc phase of Pb-doped Bi-Sr-Ca-Cu-O superconductor