Grain growth kinetics for B2O3-doped ZnO ceramics

Grain growth kinetics in 0.1 to 2 mol % B₂O₃-added ZnO ceramics was studied by using a simplified phenomenological grain growth kinetics equation Gⁿ = K₀ · t · exp(-Q/RT) together with the physical properties of sintered samples. The samples, prepared by conventional ceramics processing techniques, were sintered at temperatures between 1050 to 1250 °C for 1, 2, 3, 5 and 10 hours in air. The kinetic grain growth exponent value (n) and the activation energy for the grain growth of the 0.1 mol % B₂O₃-doped ZnO ceramics were found to be 2.8 and 332 kJ/mol, respectively. By increasing B₂O₃ content to 1 mol %, the grain growth exponent value (n) and the activation energy decreased to 2 and 238 kJ/mol, respectively. The XRD study revealed the presence of a second phase, Zn₃B₂O₆ formed when the B₂O₃ content was > 1 mol %. The formation of Zn₃B₂O₆ phase gave rise to an increase of the grain growth kinetic exponent and the grain growth activation energy. The kinetic grain growth exponent value (n) and the activation energy for the grain growth of the 2 mol % B₂O₃-doped ZnO ceramics were found to be 3 and 307 kJ/mol, respectively. This can be attributed to the second particle drag (pinning) mechanism in the liquid phase sintering.