Dielectric properties of PZT aerogels

Due to their low sound velocity and high porosity PZT aerogels have an exceptional low acoustic impedance. Therefore they are promising materials for impedance-matched ultrasonic transducers that can be used for ranging and sonar systems or medical imaging devices. Monolithic, nanostructured and open porous PZT aerogels of morphotropic stoichiometry (Pb(1.05)Zr(0.53)Ti(0.47)O(3)) were prepared by sol-gel synthesis and subsequent supercritical drying. Porosities up to 70% could be adjusted by the sintering conditions. The resulting material can be described as an interpenetrating 3-3 composite of PZT and air. The porosity of the PZT aerogels decreases with increasing sintering time and temperature. The relative dielectric permittivity at 1 kHz depends non-linearly on porosity. The dielectric permittivity could be monitored over two decades by the sintering conditions. For samples with comparable porosity the dielectric permittivity increases with sintering time. This behavior can be simulated by Looyenga's formula using different Values for the dielectric permittivity of the PZT backbone as parameter. A comparison between the experimental and theoretical data suggests, that the dielectric permittivity of the PZT backbone material is mainly influenced by the sintering time. The porosity is adjustable both by sintering time and temperature. This offers the possibility to tailor the porosity and dielectric permittivity of the PZT backbone in a wide range for the given application.