Two-step Bridgman growth of 0.91Pb(Zn1/3Nb2/3)O3-0.09PbTiO3 single crystals

A two-step growth process has been developed for the Bridgman growth of relaxor ferroelectric single crystal 0.91Pb(Zn1/3Nb2/3)O3−0.09PbTiO3 (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 d33 of several wafers were measured and it showed that the homogeneity of PZNT wafers was greatly improved.