Studies on the densification and grain growth mechanisms of Polycrystalline ceramic based on LaYO₃

Abstract

LaYO₃ is a polycrystalline ceramic with the perovskite type oxide structure. LaYO₃ was prepared using solid state synthesis method. Initially, the sample was heated between 1200 °C to 1500 °C for 10 hours and slowly cooled in air. The existence of secondary phases that belongs to orthorhombic shows the polymorphism properties of LaYO₃. Pure phase monoclinic structure was successfully synthesized after heated at 1500 °C for 10 hours and rapidly cooled in liquid nitrogen. Then, the pure monoclinic LaYO₃ powder was pelletized using cold isostatic pressing and been fabricated by two-step sintering method. For the first-step sintering (T1), pellets were heated at 1300 °C for 1 minute and then quenched into liquid nitrogen. The pellets were then reheated at the relatively lower temperature between 1000 °C to 1250 °C and denoted as T2 for 15 hours holding time. By increasing T2, the relative density increased from ~87 % to ~95 %. Percentage of shrinkage also linearly increased within error. Microstructural analysis shows homogenous microstructure. The grain size was directly proportional to the relative density. Cole-cole plot from complex impedance of sintered LaYO₃ shows one semicircle contribute to the bulk phenomenon responsible. The conductivity for samples sintered between 1000 °C to 1200 °C were in the range of 2 to 3 × 10-5 S/cm and the activation energy is about ~0.4 eV. Meanwhile, sample sintered at 1250 °C shows high conductivity that is 8.41 × 10-3 S/cm with 1.4 eV because phenomenon responsible in the sample have grain boundary effect. Therefore, increasing T2 temperature shows high ionic conductor with electrically insulative behaviour that contribute by larger formation of grain growth.