Properties of A-site-deficient La0.6Sr0.4Co0.2Fe0.8O3-δ-based perovskite oxides

A-site-deficient La0.6Sr0.4Co0.2Fe0.8O3-delta-based oxides of the compositions La0.6-zSr0.4Co0.2Fe0.8O3-delta, La0.6Sr0.4-zCo0.2Fe0.8O3-delta and (La0.6Sr0.4)(1-z)Co0.2Fe0.8O3-delta (0 less than or equal to z less than or equal to 0.2) were prepared and characterized. The crystal structure, electrical conductivity and thermal expansion of these oxides were studied using X-ray diffraction, four-point DC and dilatometry, respectively. All oxides had a rhombohedral perovskite structure. The pseudo-cubic lattice parameter increased with increasing z. The electrical conductivity increased with temperature up to about 600 degrees C, and then decreased due to the loss of lattice oxygen. The charge compensation mechanism in these A-site-deficient perovskites was probably the formation of oxygen vacancies rather than the oxidation B3+ --> B4+. The conductivity decrease and the activation energy increase became more significant in the order La0.6Sr0.4-z > (La0.6Sr0.4)(1-z) > La0.6-zSr0.4. The TEC was generally lower in the A-site-deficient oxides. The lowest TEC values at 700 degrees C were 14.2, 14.1 and 13.8 X 10(-6) cm (cm degrees C)(-1) for La1-zSr0.4Co0.2Fe0.8O3-delta, with z = 0.05, and La0.6Sr0.4-zCo0.2Fe0.8O3-delta, with z = 0.1 and 0.2, respectively. (C) 1999 Elsevier Science B.V. All rights reserved.