Effect of Grain Sizes on Temperature Hysteresis of Ceramic Barium Titanate

Introduction. The growing power of modern electronic devices imposes stricter requirements on their cooling systems. One promising cooling method employs the electrocaloric effect as the most accessible and simple phenomenon among all caloric effects to implement. However, thermal hysteresis near the phase transition point negatively affects the magnitude of the electrocaloric response and the cooling efficiency. Another important factor is the requirement for environmental friendliness of the devices, which makes the use of lead-containing compounds undesirable despite their pronounced electrocaloric effect. A possible alternative to such materials comprises solid solutions based on barium titanate; however, their temperature hysteresis phenomena are poorly studied. Aim. Investigation of temperature hysteresis phenomena in ferroelectric ceramics. Materials and methods. The samples under study were placed in a liquid thermostat to undergo a heating and cooling cycle at a given rate. The value of temperature hysteresis was calculated from the temperature dependencies of dielectric permittivity. The average grain size was estimated using SEM images of the sample surface. Results. The influence of synthesis processes on the structure and grain size of ceramic barium titanate, as well as its dielectric properties, were studied. Temperature dependencies of the grain size of barium titanate and the porosity of sintered samples were studied experimentally. The temperature range of effective sintering above 1320 °C was determined. Dielectric characteristics of the samples at heating and cooling were studied. The parameters of temperature hysteresis and dielectric properties were determined. Changes in the value of temperature hysteresis were shown to be associated with changes in the grain size of barium titanate and the contact area between the grains. Conclusion. An assumption about the optimal temperature of sample sintering was made. At this temperature, the material exhibits sufficiently good dielectric properties at a low temperature hysteresis.