A-site and B-site order in (Na1/2La1/2) (Mg1/3Nb2/3)O3 perovskite

(Na1/2La1/2)(Mg1/3Nb2/3)O-3 undergoes a series of phase transitions that involve cation order on the A- and B-sites of the parent perovskite structure. At high temperatures both sites contain a random distribution of cations; below 1275degreesC a I 11 layering of Mg and Nb leads to the formation of a 1:2 ordered structure with a monoclinic supercell. A second transition was observed at 925degreesC, where the Na and La cations order onto alternate A-site positions along the 001 direction of the parent subcell. By quenching samples from above 1275degreesC to preserve the disorder on the B-site, a fourth variant of this compound was obtained by inducing A-site order through a subsequent anneal at 900degreesC. Although the changes in structure do not produce significant alterations in the relative permittivity (epsilon(r) similar to 35), they do have a significant effect on the value of the temperature coefficient of the capacitance.