Effect of hot pressing on processing and properties of BBN ceramics

BBN (BaBi 2 Nb 2 O 9 ) is very interesting and promising lead free material with relaxor properties in capacitors, sensors and actuators. Results of investigations of fine-grained, weakly porous, BBN-type ceramics using hot-pressing method are presented. Based on a thermal deformation curve (i.e. a shrinkage curve) of a sample the method for optimisation of the hot-pressing sintering conditions has been proposed. Some advantages of hot-pressing method over the classical ceramic method used for BBN ceramics fabrication is shown. It has been found that the deficiency in bismuth causes a change of the space group of the perovskite phase crystalline structure of BBN and unit cell parameters. The influence of bismuth deficiency on dielectric properties materials and relaxor features is presented. The measurements of pyroelectric and thermally stimulated depolarization currents (TSDC) were carried out in order to better display unusual behaviour of dielectric characteristics.