Abstract
Piezoelectric ceramics for acoustic applications have been prepared by mixing the piezoelectric phase Pb 1−1.5 x La x □ x/2 (Ti 1− y Zr y )O 3 (PLZT) with variable fractions of Al 2O 3. The samples are in form of pellets and polarized at high temperature. After thermal treatment, X-ray diffraction and scanning electron microscopy have been used to determine the phase and morphological modifications. The morphotropic PLZT initial phase disproportionates into modified PLZT and ZrO 2 phases. Using electrical impedance spectroscopy, the resonance frequencies of the composite system have been determined and analyzed. As the Al 2O 3 volume fractions increase, the resonance frequency and the amplitude of the electrical response both decrease. An interpretation of the role of Al 2O 3 additions is proposed in terms of phase and microstructure modifications. Using LRC electrical equivalent circuits, the impedance variations close to the resonance frequency are modeled: the increase of the resistance R (electrical losses) and of the capacitance C are respectively correlated to the change in microstructure and in nature of PLZT initial phase.
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