Non-stoichiometry and electrical conductivity of strontium niobates with perovskite structure

The conductivity of compounds with perovskite structure characterized by the simultaneous occupancy of the twelvefold sites and a great part of the sixfold sites by the large cation is studied in terms of oxygen partial pressure at high temperatures (900 to 1450 °C) it concerns the family: Sr(Sr(1/3)+xNb(2/3)−x)O3−(3/2)x (0≦×≦ 1/6). For the x= 0.00 compound and for PO2, ≦ 10−9 atm, the lg conductivity exhibits a linear relationship with lg Poe, lg PO2 = −1/4 lg PO2 + C. For 10−9 < PO2 < 1 atm, the conductivity is partly ionic due to a great amount of oxygen vacancies created by a predominant Schottky disorder. Contrary to other perovskite compounds (BaTiO3, etc.) the importance of the Schottky disorder is enhanced by the fact that Sr2+ is located on both, A and B sites of the perovskite. For the x = 0.03 compound, the conductivity is oxygen partial pressure independent for a wide range and it is then quite entirely ionic. An order- disorder transition occurs for both the chemical compositions between 1050 and 1200 °C which affects the ionic conductivity. Below the transition temperature, it seems that the mobility of the oxygen vacancies decreases.