Reduction of sintering energy and evaporation for PZN-based ceramics using microwave process

Abstract
To reduce environmental contamination of lead containing materials, new processing methods need to be considered. Effectiveness of microwave sintering process was evaluated through investigations of microstructural characteristics and electrical properties of (1-x)(0.94PbZn_{1 / 3}Nb_{2 / 3}O₃  + 0.06BaTiO₃) + xPbZr_yTi_{1 - y}O₃ (PBZNZT) ceramics with x = 0.6 and y = 0.52 sintered by conventional (CS) and microwave (MW) methods. Experimental results imply that the relative density of specimens reaches 95% for microwave-sintered samples with sintering temperature at 850C for 2 h. However, the relative density of CS samples at the same sintering condition is only 84%. The piezoelectric properties of MW samples sintered below 900C exhibit similar magnitudes to those of CS samples with the same working temperature and periods, but the piezoelectric properties were improved markedly by the MW process at higher sintering temperatures. The piezoelectric coupling coefficient, K_p, is 68% for specimens sintered at 1050C for 2 h using the MW process, but the maximum value of K_p is only 58% for all CS samples. The microstructural investigations show that the grain size of MW samples were larger than that of CS samples at sintering temperature higher than 900C for 2 h in this material system. The grain growth mechanism after densification was investigated in terms of the phenomenological kinetics expression: G - G  = K₀texp(-Q/RT). The mean exponent n was determined to be 1.4 and 1 and the apparent activation energy was 132 kJ/mol and 238 kJ/mol for MW and CS samples respectively. The results indicate that MW process can reduce sintering energy and temperature, and therefore the MW process reduces PbO pollution in the working environment. In addition, excellent electrical properties can be obtained using a microwave process.