Dielectric properties and microstructure of Sr_0.8(K,Na)_0.2Bi₂Nb₂O₉ ferroelectric ceramics

The influence of the microstructure on dielectric properties of Sr_0.8(K,Na)_0.2Bi₂Nb₂O₉ (SKNBNO) prepared by the solid-state route is reported. The formation of Bi-layer structure was obviously restrained owing to the K and Na ions substituting Sr ions by the X-ray diffraction analysis (XRD) and scanning electron micrograph (SEM). At the same time, some slight secondary phase of bismuth oxide was detected but the structure was not changed. The dielectric constant was restrained by K and Na ions substituting Sr ions, which is mainly attributed to the slight change of lattice constants resulting in a decreased "rattling space" for the cations inside the distorted Nb(V)O₆ oxygen octahedron of the perovskite block. A clear enhancement in the stability of frequency and temperature was noticed for SKNBNO sample compared to Sr₂Bi₂Nb₂O₉ (SBN) samples.