Zone leveling of lead magnesium niobate-lead titanate crystals using RF heating

The zone melting method was used to grow lead magnesium niobate-lead titanate (or PMNT) crystals of composition (1−x)PbMg1/3Nb2/3O3-xPbTiO3 using cylindrical Pt crucibles and RF heating. Axial variations in Ti concentration that had been observed during Bridgman growth of the material were reduced using this technique. Growth runs were performed using an initial charge composition of x=0.32 and a temperature gradient at the solid-liquid interface of ∼30 °C/cm. Under these conditions, crucible translation rates ⩽3 mm/h produced good-quality crystals, while those >3 mm/h produced evidence of growth interface breakdown, i.e. inclusions. In all cases, composition profiles showed an almost constant Ti concentration after an initial transient region. Boules produced by this method appeared blue-gray rather than the orange-yellow typical of PMNT crystals. Annealing the samples in oxygen restored the crystal color. The dielectric constant at room temperature was measured to be ∼3400 and d33 was measured to be ∼2100 pC/N for annealed (0 0 1)-oriented single-crystal samples having a composition of x=0.32. The equilibrium segregation coefficient for Ti in this system was estimated to be 0.83 near x=0.32. Calculations were also performed to predict the onset of constitutional supercooling as a function of the growth rate and temperature gradient at the growth interface.