Two-step Bridgman growth of 0.91Pb(Zn 1/3Nb 2/3)O 3–0.09PbTiO 3 single crystals

Abstract

A two-step growth process has been developed for the Bridgman growth of relaxor ferroelectric single crystal 0.91Pb(Zn 1/3Nb 2/3)O 3−0.09PbTiO 3 (PZNT91/9) using 50 mol% PbO as a flux. PZNT crystals were grown in a home-made vertical Bridgman furnace with a gas-cooling system assembled at the bottom of the platinum crucible. In the early stage, the nucleation was induced by the gas flow and a large temperature gradient was formed near the solid–liquid interface. After the crystal had been grown about 20 mm in length, the gas flow was closed and the lowering mechanism stopped working for several hours. Subsequently, self-seeded growth of PZNT crystal was carried out when the previous grown crystal was partially melted and a stable solid–liquid interface was re-established. The growth parameters were optimized and PZNT91/9 crystal up to 30 mm in diameter and 15 mm in length were obtained. Compared with the samples grown by the flux-Bridgman method, the inclusions were reduced considerably. The piezoelectric constants d 33 of several wafers were measured and it showed that the homogeneity of PZNT wafers was greatly improved.