High temperature thermodynamic properties and pseudo-binary phase diagram of the Pb(Zn1/3Nb2/3)(0.91)Ti0.09O3-PbO system

The high temperature thermodynamic properties of the relaxor-based ferroele ctric Pb(Zn1/3Nb2/3)(0.91)Ti0.09O3 (PZNT91/9) and the related PZNT91/9-PbO system have been studied by means of micro-thermogravimetry and differentia l thermal analysis (TG/DTA), combined with optical microscopic examination. A pseudo-binary phase diagram for the system has been established, which e xhibits a typical eutectic behavior. The eutectic temperature of the pseudo -binary system is determined to be 828 +/- 2 degreesC with a eutectic compo sition of 25 wt%PZNT91/9-75 wt%PbO. PZNT91/9 crystals partially decompose i nto a pyrochlore phase above 1140 degreesC. Upon further heating, they inco ngruently melt at 1225 +/- 2 degreesC. The liquidus melting behavior of Ph( Zn1/3Nb2/3)(0.91)Ti0.09O3 in the PbO flux for less than 75 wt% PbO (x(Pbo) < 0.75) follows a liquidus curve that is represented by the equation: T-L ( degreesC) = -435.34x(PbO)(2) - 214.34x(PbO) + 1227.6. The established phase diagram and the thermodynamic data Ph provide a valuable guidance for the growth of large and high quality PZNT piezocrystals.