Material properties of La0.8Sr0.2Ga0.9+xMg0.1O3- as a function of Ga content

The crystalline phases, sintering behavior, microstructure and conductivity of the compound La0.8Sr0.2Ga0.9-xMg0.1O3-delta (-0.02<x<0.04) were characterized as a function of Ga content. Depending on thermal treatment and Ga content, the compounds LaSrGa3O7, LaSrGaO4 and La2O3 were identified in addition to the perovskite phase. Dilatometric measurements have shown that a volume expansion occurs in the range from 1300 degreesC to 1500 degreesC, which decreases from x=-0.02 towards x=0.04. This seems to be due to the amount of the second phase LaSrGaO4 present. The ionic conductivity decreases with increasing Ga content, which is attributed to both the reduction of the oxygen vacancy concentration and the formation of the insulating LaSrGa3O7 phase. (C) 2000 Elsevier Science B.V. All rights reserved

Vacuum plasma spraying of NiTi protection layers

A promising application for NiTi intermetallics is as a protection layer against corrosion or wear. In the present investigation, NiTi layers were produced by vacuum plasma spraying (VPS) using elemental powder mixtures as the starting material with a composition of 50.8 at.% Ni. This paper reports on studies of the microstructure and the phase formation of samples produced by different spraying parameters. (C) 2002 Elsevier Science B.V. All rights reserved

Correlation between thermal expansion and oxide ion transport in mixed conducting perovskite-type oxides for SOFC cathodes

Oxygen deficiency, electrical conductivity, ionic transport and thermal expansion of alternative cathode materials of the A(1-a)A(a)'BO3 perovskite-type oxides (A = La, Pr, Ce; A' = Sr: B = Mn, Fe, Co, Ni, Ga. Mg) were measured as a function of temperature and oxygen partial pressure. Additionally, lanthanum strontium gallates were investigated as electrolyte materials. On the basis of the results a general picture of the A- and B-site influences on the thermal and electrical properties of the perovskite-type oxides is discussed. From lanthanum manganite to strontium ferrite and from lanthanum ferrite to strontium cobaltite the thermodynamic stabilities decrease and thermal expansion coefficients increase. The increase of the ionic conductivity is more influenced by Sr concentration on the A-site, and the increase of the electronic conductivity more by Fe and Co concentration on the B-site, respectively. The ionic conductivities at 800 degreesC calculated from permeation measurements are correlated with the thermal expansion coefficients in the form of log sigma (O) = - 7.08 + 2.9 X 10(5) X TEC (sigma (O) in S cm(-1), TEC in 10(-6) K-1). The correlation is discussed on the basis of the dependence of both quantities on oxygen vacancy concentration. (C) 2000 Elsevier Science B.V. All rights reserved