Growth of Single Crystals of Pb(Zn<sub>1/3</sub>Nb<sub>2/3</sub>)O<sub>3</sub> and Its Properties

Abstract

Single crystals of perovskite-type Pb(Zn1/3Nb2/3)O3 were grown from PbO flux. Their thermal stability, ferroelectric property, and phase transition were studied.(1) Single crystals with a dimension of approximately 3×3×2mm were obtained from the 50 to 55 wt% PbO flux at a cooling rate of 25°C/hr after the 1150°C soaking. The crystal growth rate along the [100] direction was about 0.5mm/hr from 1100 to 900°C. Addition of SiO2, Al2O3, or B2O3 to the PbO flux prevented the formation of a perovskitetype Pb(Zn1/3Nb2/3)O3 crystal.(2) The single crystals prepared were confirmed to have a Nb rich composition deviating from a stoichiometric ratio of Zn/Nb and to have a perovskite-type structure with rhombohedral lattice parameters, a=4.063±0.003Å and α=89°55′±5′ at room temperature. The super-lattice due to an ordered arrangement of Zn and Nb ions was not observed.(3) The Pb(Zn1/3Nb2/3)O3 crystals showed a thermal decomposition only near the surface at 1000°C in air, resulting in conversion into Pb2Nb2O7ss, PbOss, and ZnO. On the other hand, the pulverized crystals completely decomposed into the above-mentioned three phases at the same conditions. Pb(Zn1/3Nb2/3)O3 is nstable in solid equilibrium at ordinary atmosphere, but becomes stable in liquid state, or molten solution with PbO.(4) The temperature of maximum dielectric constant increases with increasing the atomic ratio of Zn/Nb. The Single crystals with Zn/Nb ratio of 0.463, 0.481 and 0.485 showed temperatures of maximum dielectric constant of 135°C, 144°C, and 147°C, respectively, at the frequency of 103Hz. The temperature of high pressure-sintered specimens was 188°C at the same frequency.(5) The ferroelectric-paraelectric transition is presumed to be a higher order-transition, because of no domain structure, no hysteresis in thermal expansion, and gradual and uniform change of optical anisotropy throughout the crystal.