Temperature Dependence of Energy Conversion Efficiency in Piezoelectric Ceramics

Energy conversion efficiency of PZT energy harvesters depends on that of the PZT materials. The electromechanical coupling factor of piezoelectric materials represents the energy conversion efficiency between electrical energy and mechanical energy. Temperature dependence of the energy conversion efficiency of harvesters using PZT materials may depend on the electromechanical coupling factor of the PZT materials. In this paper, the effects of poling strength and thermal aging on temperature dependence of electromechanical coupling factor, k31 of PZT ceramics were investigated. The PZT ceramic specimens with rhombohedral phase, morphotropic phase boundary (MPB) and tetragonal phase were fabricated. And the specimens were poled at the poling strengths, 1.5, 2.5, 3.5 [kV/mm] respectively. Electromechanical coupling factor of the specimens were successively measured after poling, after first thermal aging and after second thermal aging. Thermal aging decreased electromechanical coupling factor k31 due to depoling. The degree for the factor to decrease was significant in the specimens with the composition of MPB and was the least in the specimens with the composition of tetragonal phase. When measurement temperature increased from -20[℃] to 80[℃], electro-mechanical coupling factor k31 of PZT ceramics decreased only a little. PZT energy harvesters need not worry about decrease of energy conversion efficiency due to change of measurement temperature. And forced thermal aging in fabrication process improved the thermal resisting property of the energy conversion efficiency of PZT energy harvesters.