摘要:

In the present paper, making the crusial assumption that the rheological state of the lower mantle silicate materials controlled by creep mechanism, we study: (i) the upper and lower limits in the depth (i.e. temperature and pressure) variation of the activation volume for creep and (ii) the lower permissible isoviscous temperature profile.

ISSN:1042-0150    

DOI:10.1080/10420159508222723

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Valuable information about minority point defects in binary oxides can be obtained by using fast temperature (T) and oxygen partial pressure (Po2) changes during high temperature creep deformation. A creep transient is established after a T or Po2change, which reflects the evolution of the point defect concentration responsible for the diffusion of the slowest species to the new equilibrium value, allowing us the determination of the chemical diffusion coefficient and the migration energy of these defects.

ISSN:1042-0150    

DOI:10.1080/10420159508222724

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Creep tests have been performed on 21 mole% yttria fully stabilized zirconia single crystals between 1400°C and 1800°C. The mechanical parameters measured have been adjusted to a conventional creep law. The temperature dependence of the strain rate has been fitted to a conventional Arrhenius plot. From the stress exponents and activation energies found, it is concluded that there is a remarkable transition in the mechanical behaviour of this solid solution at T≅1500°C. This behaviour is compared with one found for lower Yttria concentration single crystals, within the full stabilized field.

ISSN:1042-0150    

DOI:10.1080/10420159508222725

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The combination of scanning electron microscopy (SEM), cathodoluminescence (CL) and scanning optical microscopy (SOM) with a computer-controlled signal detection system is promising in the study of deformed ionic crystals. The present experiments were designed to unite many image processing methods in scanning microscopies and to clarify the structure of the deformed regions around the indentation.

ISSN:1042-0150    

DOI:10.1080/10420159508222726

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Atomic transport of oxygen in nonstoichiometric oxides is an extremely important topic that overlaps science and technology. In many cases, diffusion of oxygen controls sintering, grain growth, and creep. High oxygen diffusivity is critical for efficient operation of many fuel cells. Additionally, oxygen diffusivities are an essential ingredient in any point defect model. Secondary ion mass spectrometry (SIMS) is the most accurate modern technique for measuring oxygen tracer diffusion. This paper will briefly review the principles and applications of SIMS for the measurement of oxygen transport. Case studies will be taken from recent work on ZnO and selected high-temperature superconductors.

ISSN:1042-0150    

DOI:10.1080/10420159508222727

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

In this paper, we discuss the effects of the defect interactions on the thermodynamic properties and electronic transport of nonstoichiometric oxides. We first show that two limited thermodynamic behaviours can be distinguished depending on whether the oxide has a metallic type electronic conduction or a hopping electronic conduction. In the first case, the interactions are expected to be short ranged because of the screening of the conduction electrons, while they are Coulombic in the second case. This paper is limited to this last case, exemplified mainly by M1−xO(M=Co, Mn,…) cubic oxides.

ISSN:1042-0150    

DOI:10.1080/10420159508222728

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The ionic conductivity of well-annealed crystals of rubidium chloride and of RbCl doped with Sr2+or S2-ions has been measured, using an automated system, over a wide range of temperature, generally from 960 K until precipitation occurred. Conductivity data were analyzed using a multiparameter non-linear least squares fitting program. The defect model used allowed for the possibility of Frenkel defects on both cation and anion sub-lattices and the association of cation vacancies with divalent cations and of anion vacancies with divalent anions. Data for the individual crystals were analyzed separately and a consistent set of defect parameters were obtained.

ISSN:1042-0150    

DOI:10.1080/10420159508222729

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The effect of hydrostatic pressure on the ionic conductivities in β-PbF2β-Pb1−xMxmF2+(m−2)x(where Mm= Na+, Cd+2, Tb+3, U+4), LaF3and La1−xCaxF3-xhas been investigated in the temperature range between 300 K and 700 K for pressures up to 0.25 GPa (for β-PbF2) and 0.8 GPa (for LaF3). The activation volumes of defect formation and migration, impurity defect segregation and dissociation were determined from the effect of pressure on the conductivity. Keyes’ treatment based on the strain energy Zener model in Grüenisen approximation was used to estimate theoretical values of activation volumes.

ISSN:1042-0150    

DOI:10.1080/10420159508222730

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

We have investigated the enhancement effect on the transport phenomena in solid solutions relative to the pure end members. Only single crystals and measurements carried out in the middle of the intrinsic range have been considered. The enhancement effect for both the self and heterodiffusion coefficients reaches a factor of about 2 around the middle composition. The diffusion data are analysed in terms of vacancies. The correlation effects have been accounted for by making use of Manning's equations for vacancy diffusion in random alloys via unbound free vacancies. We conclude that the major part of the enhancement originates from an increase of the vacancy concentration relative to the pure end members.

ISSN:1042-0150    

DOI:10.1080/10420159508222731

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The chemical diffusion of oxygen and the structure of the electronic defects in undoped and transition metal doped YSZ single crystals have been investigated by a contactless relaxation technique and magneto-optical resonance (MCD(A))-studies. The local structure and the transport properties of YSZ (9.5 mol% Y2O3) are interrelated by the actual defect distribution of 7- and 6-fold coordinated Zr-defects with trigonal symmetry which mainly originate from Zr d- conduction band tail states and act as electron traps.

ISSN:1042-0150    

DOI:10.1080/10420159508222732

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor