Development of a Templated Grain Growth System for Texturing Piezoelectric Ceramics

Abstract

Abstract High strain actuation can be obtained by engineering the crystallographic texture of piezoelectric ceramics. Single crystal piezoelectrics have significantly improved strain performance because crystal orientation can be controlled during use — their highly perfect lattice greatly simplifies the crystal orientation. Single crystals have properties significantly better than those of randomly oriented ceramics, but they are expensive and difficult to produce. Highly textured ceramics offer an alternative means of producing easily aligned crystals, as the majority of the crystallites in the ceramic share a common crystallographic orientation. Textured piezoelectric ceramics are expected to provide improved properties compared to untextured ceramics, with lower processing costs than single crystals. NexTech Materials is developing textured piezoelectrics in PMN-PT system via Templated Grain Growth (TGG). In the TGG process, anisotropic template particles are oriented in a fine particle matrix in the green state. During heat treatment, the crystals consume the surrounding matrix, resulting in a textured polycrystal. A TGG system requires both matrix and template particles. The matrix must provide significant driving force for densification and grain growth. Templates must be large, anisotropic, and crystallographically isostructural with the matrix material. Anisotropic template shape is difficult to achieve in perovskite-based piezoelectrics, which have highly symmetric (cubic) crystal structures at their processing temperature. In addition, the matrix environment often contains highly corrosive lead based liquid phases that make chemical stability difficult to achieve. Characterization of textured samples involves texture evaluation and phase analysis via XRD, and SEM analysis of template growth and chemical stability as well as piezoelectric performance measurement The development and characterization of the TGG components and their integration will be discussed.