Unprecedented rock-salt ordering of A and B cations in the double perovskite Nd2-xCaxMgTiO6-δ and defect association

Abstract

The partial substitution of up to 5% Nd+3 by Ca+2 results in the oxide Nd1.90Ca0.10MgTiO5.94 that presents some remarkable structural features with noticeable influence on its properties. In this oxide with monoclinic perovskite-like structure and octahedral tilting scheme (a-a-b+), both A- and B-ions are arranged in a rock-salt like manner and represents thereby the first example of a type of perovskite theoretically predicted. Besides this unprecedented arrangement of A- and B-ions, the oxygen vacancies created through doping with acceptor ions are trapped by association with the acceptor defects (𝑉𝑂••-𝐶𝑎𝑁𝑑´) and hence the mobility of these vacancies is strongly limited. The oxygen conductivity of the substituted material is lower and the activation energy for oxygen motion higher than those of the parent oxide, in which the concentration of anions vacancies is only due to intrinsic defects.