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Several measurement methods for the dielectric permittivity at constant strain ε33S of a piezoelectric ceramic have been proposed1-2. In this paper a comparison of these methods is made and an alternative and complementary method is proposed. This method requires a clear and well shaped thickness resonance and is based on the measurement of the electrical input impedance at the frequencies fs and fp of the fundamental resonance of the thickness extensional mode of vibration. Other parameters - kt and Qm - can also be obtained from these measurements1-3.Several samples of different piezoelectric ceramics have been measured and the results using the proposed and the above mentioned methods are compared.

In the preparation of piezoelectric composites from an inorganic glass and calcium modified lead titanate ceramics, the anomalous thermal expansion in the ceramic on cooling from the para-ferroelectric transition, may cause mechanical stresses in the phases and their fracture.A combination of the Knoop and Vickers indentation techniques is here applied to the mechanical characterization of the component phases, which is of primary interest for the piezoelectric composite preparation.Values of Knoop and Vickers hardness and Young's modulus are obtained for PTC ceramics with molar ratios Ca/Pb=24/76 and 35/65 and for boron glasses.The variation of the crack to indentation sizes ratio in the Vickers test with respect to the applied load has been studied. This leads to the conclusion that in ceramics there is a transitional regime of crack development, whereas in glasses a median regime prevails. These results allow us to select the method for the calculation of the toughness, Kic, and internal stresses of these materials.

Canmodified PbTiO3 ceramics were obtained from oxides and carbonates. By adding controlled quantities of NO3H during one of the process stages the reactivity in the synthesis and sintering is increased. Relations between microstructure and piezoelectric properties are established.

It has been developed a procedure to obtain extruded ceramic fibers of Ca-modified PbTiO3. The plasticity needed for the extrusion molding was provided to the crystalline precursor by an inorganic colloid of similar composition which was processed by a sol-gel method. Due to the presence of the gel phase, the acuous mixture of both components presents a high reactivity which enhances the sintering mechanisms and gives place to a particular microstructure of the sintered fibers that relates to its electromechanical properties.

New data of 90° domain reorientation on Ca-modified lead titanate ceramics obtained from XRD and thermal expansion measurements are reported. Results confirm that microstructure and poling treatment that favor a relatively high percentage of 90° domains reoriented (N(90°) = 10.9%) are needed to have ceramics with zero planar coupling factor (KP = 0).

A study is presented on the thermal behaviour of the thickness, Kt, and planar, Kp, electromechanical coupling factors of Ca-substituted PbTiO3 ceramics with Ca/Pb ratios of 24/76 and 35/65 and their composites. Glass was used as a matrix material so as to obtain composites able to work at higher temperatures than those with an organic matrix. In ceramics it is shown that the thermal behaviour of the electromechanical anisotropy (Kt/Kp) depends strongly on microtexture, due mainly to variations of Kp whereas Kt varies slightly. In PTC24/76 the planar electromechanical coupling coefficient vanishes between 100° and 200°C, for less dense ceramic; for higher densities Kp has values of 2 - 6 % in the same interval. In PTC35/65 composites Kp is very low, sometimes unmeasurable, and Kt/Kp is further enhanced. Permittivity is significantly lower than in the ceramic and there is also a moderate reduction in density. These properties make glass matrix composites potencially attractive in ultrasonic transducer applications.