High performance of advanced composites based on relaxor-ferroelectric single crystals

The outstanding electromechanical properties of single crystals of relaxor-ferroelectric solid solutions near the morphotropic phase boundary suggest that these materials can be regarded as potential components of high-performance piezo-active composites. In this chapter we discuss the advantages of using the relaxor-ferroelectric single crystals of solid solutions of (1-x)Pb(Mg_1/3 Nb_2/3)O₃-xPbTiO₃ and (1-y)Pb(Zn_1/3Nb_2/3)O₃-yPbTiO₃ as components of single crystal/polymer and single crystal/porous polymer composites of the 2-2 and 1-3 types. Examples of the high piezoelectric activity and sensitivity and large hydrostatic parameters of the aforementioned composites are analysed in connection with the electromechanical properties of the single-crystal component. The influence of the polarisation orientation on the effective electromechanical properties and related parameters of the single crystal/polymer composite are discussed for different connectivity patterns. Comparisons are made between the effective parameters of 2-2 connectivity composites based on polydomain single crystals and single-domain single crystals of the same chemical composition (for instance, 0.67Pb(Mg_1/3Nb_2/3)O₃-0.33PbTiO₃). Specific effective parameters of single crystal/polymer composites are compared to those of piezo-active composites based on the conventional ferroelectric ceramic and having the same connectivity pattern (either 2-2 or 1-3). In general, data presented in the chapter show how the relaxor-ferroelectric single-crystal component improves the effective parameters of the novel composites and promotes the formation of non-monotonic volume-fraction dependences of the effective parameters which are of particular interest for a variety of piezotechnical applications, such as active elements of sensors, actuators, transducers, hydrophones, etc.