Ordering effect on the electrical properties of stoichiometric Ba${}_3$CaNb${}_2$O${}_9$-based perovskite ceramics

Abstract

Cation ordering is most common process detected in A${}_3$B'B"${}_2$O${}_9$-based complex perovskites. Some important physical features of this system are due to the B-site ordering at long and short range. For microwave applications as filters and resonators, the 1:2 order is more appropriate. Otherwise, the oxygen vacancies and 1:1 order are considered the main factors behind the good performance of nonstoichiometric A${}_3$B'${}_{1+x}$B"${}_{2-x}$O${}_{9-\delta }$-based ceramics as proton conductors. Until now, however, there are no available reports regarding the isolated effects of B-site order at long range on the electrical properties of stoichiometric systems. This work reports the preparation of 1:1 and 1:2 fully-ordered Ba${}_3$CaNb${}_2$O${}_9$ ceramics. Here, we combine the Raman scattering and group-theory calculations to distinguish the fingerprints of the 1:1 and 1:2 orders. The electric properties of the ordered Ba${}_3$CaNb${}_2$O${}_9$ are analyzed in terms of a phenomenological model based on a parallel combination of a resistor, constant phase element, and capacitor. In particular, the conductivity relaxation ascribed to the grain is due to the oxygen vacancies. Besides, we found that the 1:1 order increases the dc conductivity, but not enough to account the good performance reported for the non-stoichiometric Ba${}_3$Ca${}_{1+x}$Nb${}_{2-x}$O${}_{9-\delta }$-based proton conductors.

33 pages, 8 figures, 3 tables