Study On The Preparation Of Barium Titanate-based Ceramics And Its Electrical Card Performance

With the rapid development of industrial technology,both the preservation of fruits and vegetables,and the cooling of large equipment,from production to life,modern people are increasingly inseparable from refrigeration technology.There are many advanced refrigeration technologies,such as caloric effect refrigeration?including magnetocaloric,electrocaloric,elastocaloric,etc.?,semiconductor refrigeration,thermoelectric refrigeration,micro-vapor compression refrigeration,etc.Now the electrocaloric effect?ECE?refrigeration has drawn a wide attention because it has some advantages,such as high efficiency,environmental protection,fast response speed,and no mechanical moving parts,etc.BaTiO₃?BTO?is one of strong dielectric compound materials with large dielectric constant,low dielectric loss,and large pyroelectric coefficient.Therefore,in this thesis,BTO ceramics were chosen as the basic object,and the effects of sintering temperature and Sr-/Zr-doping on phase constitute,microstructures and ECE were investigated.The Sr-doping?BST?and Zr-doping?BZT?powders were synthesized by the conventional solid-state reaction method at air atmosphere.The mechanism of ECE of the studied systems has been explored.The main work and results of this thesis are listed as follows:1.The effect of Sr-doping on the ECE of BTO.The average particle size increases with the increase of sintering temperature.The density of BST ceramic reaches the highest at a sintering temperature of 1250 ^oC.It is interesting to note that a good ECE was achievedin the studied BST ceramics.The maximum adiabatic temperature change?T_ECE is as highas 0.99 K under an electric field of 5 kV/mm at 100 ^oC,moreover,a wide working temperature range of nearly 30 ^oC is present in this system.2.The effect of Zr-doping on the ECE of BTO.It is revealed that a small amount of Zr⁴⁺-doping can improve the ECE of the BZT ceramics.The Zr⁴⁺-doping results in a decrease of Curie temperatureof the ferroelectric ceramics.When the Zr⁴⁺-doping amount is 10%,the ECE performance of ceramics reaches the maximum with the maximum?T_ECE of 0.272 K under an electric field of 3 kV/mm at room temperature.Moreover,the ECE response speed of BZT is very fast with a response time about 3 s,which indicates that BZT ceramics may provide a relatively strong refrigeration capacity although the?T_ECE is not so large.