Structural–Property Relations in a Reduced and Internally Biased Oxide Wafer (RAINBOW) Actuator Material

Reduced and internally biased oxide wafer (RAINBOW) actuators are fabricated by a controlled reduction of Pb(Zr, Ti)O₃-based piezoelectric material. The reduction process results in a conductive layer composed of an interconnected metallic lead phase and refractory oxides (ZrTiO₄, ZrO₂, La₂O₃, etc.). The nature of the reduction is discovered to be the result of a complex volume change leading to a nanoscale interconnected metallic structure. The distribution of phases within the cermet vary within the thickness of the wafer. Within the piezoelectric ceramic phase, the reduction process modifies the grain-boundary structure to give two distinct types of fracture: transgranular and intergranular. The complexed microstructures of the RAINBOW actuator materials are discussed in relation to their dielectric and piezoelectric properties.