Ultrasonic sensor is suitable as a next-generation autonomous driving assist device because its lower price compared to that of other sensors and its sensing stability in the external environment. Although Pb(Zr, Ti)O₃ (PZT)-relaxor ferroelectric system has excellent piezoelectric properties, the change in capacitance is large in the daily operating temperature range due to the low phase transition temperature. Recently, many studies have been conducted to improve the temperature stability of ferroelectric ceramics by controlling the grain size and crystal structure, so it is necessary to study the effect of the grain size on the piezoelectric properties and the temperature stability of PZT-relaxor ferroelectric system. In this study, the piezoelectric properties, phase transition temperature, and temperature coefficient of capacitance (TCC) of 0.9 Pb(Zr_1-xTi_x)O₃-0.1 Pb(Zn_1/3Nb_2/3)O₃ (PZT_x-PZN) ceramics with various grain sizes were investigated. PZT_x-PZN ceramics with larger grain size showed higher piezoelectric properties and temperature stability, and are expected to be suitable for ultrasonic devices in the future.

We investigated dielectric relaxation properties of 0.95(Na0.5K0.5)NbO3-0.05BaTiO3 ceramics byaddition (0∼0.3 wt%) of (Ba,Ca)SiO3 glass frit. All composition of 0.95(Na0.5K0.5)NbO3-0.05BaTiO3 added(Ba,Ca)SiO3 glass frit showed the same crystallographic properties, coexistence of orthorhombic andtetragonal phase. By increasing addition of (Ba,Ca)SiO3 glass frit, the Curie temperatures of0.95(Na0.5K0.5)NbO3-0.05BaTiO3 ceramics were decreased, whereas maximum dielectric constants of0.95(Na0.5K0.5)NbO3-0.05BaTiO3 ceramics were dramatically increased. Especially the deviations of Curietemperature 0.95(Na0.5K0.5)NbO3-0.05BaTiO3 ceramics were increased by increasing amount of(Ba,Ca)SiO3 glass frit, and it indicated that 0.95(Na0.5K0.5)NbO3-0.05BaTiO3 ceramics added (Ba,Ca)SiO3glass frit have relaxor characteristics.