Structural and electrical behaviour of the pyrochlores:: Sm2-xMxTi2O7-x/2 (M = Mg, Co, Ni)

Solid solutions in the binary system Sm2Ti2O7-MTiO3 (M = Mg, Co and Ni) with pyrochlore and ilmenite structure types, respectively, were synthesized using a conventional ceramic method. X-ray powder diffraction results showed that the resulting phases of formula Sm2-xMxTi2O7-x/2 crystallize with the pyrochlore type structure, cubic Fd3m space group, in the compositional range 0 less than or equal to x less than or equal to 0.4. The evolution of the degree of substitution, x, versus the cell parameters, a, displays a linear decrease as x increases. The study of electrical properties, carried out by the impedance method, shows that these materials behave as anionic conductors. It was also observed that the best conductivity properties are obtained in the more substituted phases, i.e., for higher x values in the system. This behaviour was interpreted as a result of migration of extrinsic oxygen vacancies into the conduction pathways. (C) 2003 Elsevier SAS. All rights reserved.