Grain growth control and solid-state crystal growth in the $Pb(Mg_{1/3}Nb_{2/3})O_3-PbTiO_3$ system

Abstract

Polycrystalline ceramics in the $Pb(MG_{1/3}Nb_{2/3})O_3$ - $PbTiO_3(PMN-PT)$ system have been the subject of considerable research due to their excellent dielectric and piezoelectric properties. Recently, single crystals of PMN-35PT (mol%) have been found to possess superior properties to those of polycrystalline ceramics of the same composition. In the present investigation the effect of dopants and atmosphere on abnormal grain growth in polycrystalline PMN-35PT ceramics has been studied and Solid-State Crystal Growth (SSCG) experiments have been carried out. The effect of dislocations on single crystal growth has also been studied. For polycrystals, improvement of mechanical properties has been attempted using diffusion-induced interface migration (DIIM) technique. The equilibrium shape of $SrTiO_3$ crystals in a melt has been determined from the shape of grains on a planar section using the recently developed Saylor and Rohrer’s technique. In chapter III, abnormal grain growth in $Pb(MG_{1/3}Nb_{2/3})O_3$ - 35 mol % $PbTiO_3$ (PMN-35PT) ceramics doped with $Li_2O$ and PbO has been investigated. Replacing PbO dopant with up to 1 mol % $Li_2O$ caused an increase in the number of abnormal grains. For the composition containing 2 mol % $Li_2O$ and 6 mol % PbO, the amount of abnormal grain growth decreased with increasing sintering temperature. Single crystals approximately $6 mm \times 6 mm \times 2 mm$ thickness were grown from the $2 mol % Li_2O$ 6 mol % PbO-containing composition via the SSCG method. Grain growth behavior with temperature is explained in terms of the effect of $Li_2O$ on interface reaction-controlled grain growth and the critical driving force. In chapter IV, we studied the effect of dislocation density in seed crystals on single crystal growth in $Li_2O$ doped $Pb(MG_{1/3}Nb_{2/3})O_3$ - $PbTiO_3-PbO$ samples. Addition of $Li_2O$ dopant first enhances and then reduces abnormal grain growth behaviors. Increasing the dislocation ...