ELECTROMECHANICAL STRENGTH AND FATIGUE OF FERROELECTRIC CERAMICS

As is well known, ferroelectric ceramics are widely used for electro-mechanical transducers because of their strong piezoelectric effects. For practical applications, the electrical fatigue and aging are very important and have been investigated since 1957. On the other hand, the mechanical strength and fatigue should also be important; however, very few paper have been reported till now. In this report, static mechanical compressive strength and repeated fatigue test were carried out for ferroelectric ceramics such as Pb(Zr, Ti)O3, BaTiO3 ceramics and others. It is revealed that the mechanical strength of ferroelectric ceramics are greatly affected by the electrical conditions such as poling conditions, aging conditions and electrical conditions during compressive tests. Fracture patterns, intergranular and/or transgranular, are also systematically changed by the residual internal stress induced above conditions. In order to estimate the internal stress, microindentation technology was applied to transparent pore free (Pb, La)(Zr, Ti)O3 ceramics with various crystal structures. Based on these results, theoretical model for residual strength degradation is proposed and the electrical and mechanical interaction phenomena are discussed.