Ordering‐Induced Microstructures and Microwave Dielectric Properties of the Ba(Mg1/3Nb2/3)O3–BaZrO3 System

The structures of compositions across the Ba(Mg 1/3 Nb 2/3 )‐O 3 ‐BaZrO 3 (BMN–BZ) system have been examined using X‐ray diffractometry and transmission electron microscopy, and their dielectric properties have been characterized in the microwave range. Although pure BMN adopts a 1:2 ordered structure, of space group Pm 1, additions of 5–15 mol% BZ stabilize a cubic ( Fm m ), 1:1 ordered phase with a doubled perovskite repeat. At higher levels of substitution (>25 mol% BZ), the B‐site cations are disordered. After normal sintering, the niobates in the 1:1 phase field are comprised of nanometer‐sized ordered domains that are dispersed in a disordered matrix. However, by reducing the cooling rate to 10°C/h, a fully ordered microstructure is formed with domain sizes >100 nm in size. The structure of the 1:1 phases has been interpreted using a “random‐layer” model, in which one site is occupied by niobium, and the second is occupied by a random distribution of the remaining cations. The addition of small concentrations of BZ produces a 100% improvement in the dielectric‐loss properties of BMN, and a Q · f value of 82000 is obtained for a 5 mol% substitution.