A combined diffraction and dielectric properties investigation of Ba ₃MnNb₂O₉ complex perovskites

A combined synthesis, diffraction and dielectric properties investigation of the dependence (and effect) of Mn²⁺/Nb⁵⁺ ordering in Ba₃MnNb₂O₉ (BMN) upon annealing atmosphere and processing conditions has been carried out. Annealing in different atmospheres was not found to significantly alter either nominal stoichiometry or structure type. The obtained structure type (disordered metrically cubic or ordered trigonal) as well as the measured electrical properties (in particular, the dielectric loss) were, however, found to be sensitive to the synthesis route. Samples obtained via solid-state reaction were found to be predominantly of 1:2 Mn²⁺/Nb⁵⁺ ordered, P3̄m1 trigonal structure type whereas samples obtained via an aqueous solution route were found to be of a Mn²⁺/Nb⁵⁺ 'disordered', metrically cubic structure type. All solid-state synthesized samples showed reasonable dielectric properties. The microwave dielectric constant and dielectric quality factor, Q, at 8 GHz of an as-synthesized BMN sample were 38 and 100, respectively. By contrast, the dielectric loss of the metrically cubic, Mn²⁺/Nb⁵⁺ 'disordered' samples obtained via an aqueous solution synthesis process were significantly worse.