摘要:

This paper reports the behaviour of electrical conductivity of a Chromium doped α-LiIO3crystal perpendicular to c-axis from room temperature up to the melting point. Our results indicate that the sample does not break out through the sequence of phase transitions, contrary to a pure crystal. Indeed, it has been possible to measure the electrical conductivity in the α, γ and β phases. A phase-sequence scheme is then proposed and compared with other published results.

ISSN:1042-0150    

DOI:10.1080/10420159508222743

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

A novel approach is proposed to describe hopping conductivity in a band of uniformly distributed localized levels. The basic equations are taken in full forms and their respective involvements are discussed. Ultimately, a first step approach of conductivity is derived, with hopping distance expressed by a plausible empirical function.

ISSN:1042-0150    

DOI:10.1080/10420159508222744

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

We discuss novel electrochemical data on Bi2Sr2CaCu2O8+δ(BSCCO) at high temperature, where equilibrium with the oxygen containing neighboring phase is established. Measurements of the electronic conductivity as a function of oxygen partial pressure and temperature convey information about the defect chemistry. Careful investigation of the electrochemical polarization on glass-sealed cells allows the determination of the ionic conductivity. The investigation of the instationary response of the electrochemical polarization measurements enables us to determine the chemical diffusion coefficients.

ISSN:1042-0150    

DOI:10.1080/10420159508222745

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The influence of temperature and pump power on phonon modes in YBa2Cu3Ox, was investigated. The Raman spectra of the YBa2Cu3O6.4single crystal measured after laser-heating (488 nm, P ≤ 2.5 mWt/μm2) show a decrease of linewidth and frequency of A, apex oxygen mode. The experimental results can be explained as an ordering of chain-oxygen vacancies.

ISSN:1042-0150    

DOI:10.1080/10420159508222746

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Determinations of the T-O and OI-OII phase boundaries by electrical transport property measurements are reported. These results are coherent with those of a preliminary neutron diffraction experiment and an electron diffraction study.

ISSN:1042-0150    

DOI:10.1080/10420159508222747

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The electron structure of the semi infinite CuO2layer has been calculated to understand peculiarities of the layered oxides surfaces. All computations have been performed by means of the Green function method along with the simple tight-binding model. Fourier transforms of the Green functions were derived analytically. The potential at the atoms nearest to the boundary was directed to infinity. This formal maneuver led to dividing the ideal CuO2layer into two semi infinite layers. The density of states near the surface has been obtained by integrating the imaginary part of the diagonal element of the Green function over the wave vector. It has been shown that the charge on the surface Cu atoms is greater than on the bulk one. Changes of the density of states via the energy and the distance from the surface have been obtained.

ISSN:1042-0150    

DOI:10.1080/10420159508222748

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

X-ray powder diffraction of the new high-Tc superconducting phase (Hg1−xCux) Ba2CuO4+∞, where × = 0.17 with the onset superconducting transition at 125 K was used to define coordinates, isotropic thermal parameters of the atoms and for interatomic distances calculation. For the first time in the Hg-based cuprate superconductors was observed the occurrence of the optical second harmonic generation (SHG) of YAG-Nd laser, which gives evidence for the appearance the asymmetric electronic density, correlated with an increase of superconducting transition temperature. It is assumed that the increase of Tcassociated with the formation of two (CuO2) layers in the average unit cell at the substitution of the part atoms Cu for Hg and the partial occupancy of the (1/2 0 0) sites by oxygen atoms.

ISSN:1042-0150    

DOI:10.1080/10420159508222749

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Substituting metallic or rare-earth atoms or removing O in the superconductor YBa2Cu3O7usually has a strong effect on the superconducting properties. We have made extensive XAFS studies on Co, Fe, Ni, Zn, Gd, and Pr substituted materials including some thin film samples. In nearly all cases, significant distortions are found. Although the lattice constant change is small (< 0.05 Å) the local distortions can be significant larger (∼ 0.1 to 0.3 Å). The observed large local distortions of the lattice together with a change in the charge distribution at a site indicate that the interior of the unit cell is easily distorted. The correlation of a strong T<sb>c suppression with large local distortions suggests that distortions of the nearby layers must play a significant role in models for superconductivity in high Tc materials.

ISSN:1042-0150    

DOI:10.1080/10420159508222750

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor