SINGLE CRYSTAL GROWTH AND TEXTURING OF LEAD-BASED PIEZOELECTRIC CERAMICS VIA TEMPLATED GRAIN GROWTH PROCESS

Abstract

In the field of high-performance piezoelectric materials, PMN-PT single crystals and textured ceramics have been attracting increased research interest for several years. On the other hand, the growth of single crystals from melt for PZT-based compositions is impossible due to its incongruent melting behavior. In order to obtain the characteristics of pure single crystal PZT as closely as possible, the PZT must be textured by secondary recrystallization of introduced seeds in a fine-grained matrix. Zirconium was therefore added to a PMN-PT-ceramic with 32 mol% PT ( Pb ( Mg 1/3 Nb 2/3)0.68 Ti 0.32 O 3) in order to obtain a PMN-PZT-ceramic with 37 mol% PT and 21 mol% PZ ( Pb ( Mg 1/3 Nb 2/3)0.42( Ti 0.638 Zr 0.362)0.58 O 3). Initially, the growth mechanism of (001)-oriented BaTiO 3 (BT) single crystals in those matrices was investigated. The piezoelectric single crystals were produced via a process that starts with the hot pressing of a BT single crystal in cold isostatically pressed ceramics, followed by an additional sintering step in order to achieve a secondary recrystallization. The measured growth lengths in PMN-PT and PMN-PZT matrices were up to 140 μm and 65 μm, respectively. Having developed this understanding, both ceramics were textured via the templated grain growth (TGG) process by using (001)-oriented BT templates. Sintering of templated grain bodies resulted in template growth into the matrix to produce textured ceramics with Lotgering factors up to 0.99 for both compositions. In textured samples unipolar strain s33 was enhanced by a factor of up to 1.8 compared to randomly oriented ceramics. By contrast, BT single crystal growth in an alternative PZT matrix with NdMn doping was not successful. Hence, in the present work, growth experiments in this NdMn -doped PZT were first performed using PZT fibers of similar composition as seeds. Growth of the fiber diameter of up to 100 μm was observed in that matrix.