Effect of grain size on dielectric and piezoelectric properties of bismuth layer structure CaBi₂Nb₂O₉ ceramics

Micro- and nano-sized bismuth layer-structured CaBi₂Nb₂O₉ (CBNO) powder were synthesized by traditional and hydrothermal synthesis, respectively. These CBNO powders were used as raw materials to prepare CBNO ceramics by ordinary sintering and dynamic-control temperature sintering. The microstructures of the samples were characterized by XRD and SEM. The piezoelectric properties and dielectric performance of the samples were measured. The effects of grain size on the phase structure, density, dielectric and piezoelectric properties were investigated. It was found that the pure, fine-grained CBNO ceramics with grain size of ~0.75 μm could be prepared by hydrothermal method combining with dynamic-control temperature sintering. Such preparation method could effectively control the length–diameter ratio of the grain of the bismuth layer-structured ceramics. Grain size reduction, which is beneficial to improve the density and the dielectric properties of the material, made the ceramics easier to be polarized with the decreased length–diameter ratio. The piezoelectric coefficient, d ₃₃, of the fine-grained 0.75-μm CBNO ceramics was nearly three times compared with that of the 10-μm ceramics. Such size effect is attributed mainly to the grain size of the ceramics.