Flux growth of high-homogeneity PMN–PT single crystals and their property characterization

Abstract

The effects of B 2O 3 addition to the PbO flux for growing Pb(Mg 1/3Nb 2/3)O 3- yPbTiO 3 (PMN- yPT) single crystals, where y = 0.28 – 0.34 , have been investigated. The results show that the amount of B 2O 3 in the PbO flux is crucial in altering the chemistry of the high-temperature solution and determining the quality of the ensuing crystals. With optimum amounts of B 2O 3 in the PbO flux, inclusion-free high-uniformity PMN-PT single crystals have been successfully grown. The typical size of the crystals obtained is about 25–35 mm in edge length. Ferroelectric transition temperature, T c, distribution measurements reveal that the bottom half of the grown crystals, i.e., the portion adjacent to the nucleation site, shows good compositional uniformity, with Δ T c ≈ ± 3.0 ° C . The PT content of this uniform composition portion is typically 2 mol% smaller than that in the initial charge, indicating that the composition of the actual flux is PbO+ z(B 2O 3+ δPT), where δ depends on the amount of B 2O 3 in the flux. Electrical poling studies reveal that while crystals of PMN-(31–32)%PT ( T c = 140 - 145 ° C ) composition are susceptible to overpoling, both PMN-28%PT ( T c = 125 ° C ) and PMN-30%PT ( T c = 135 ° C ) crystals show good resistance to overpoling. Of the latter two, PMN-30%PT exhibits better dielectric and piezoelectric properties with K T = 7500 – 9000 , k 33=2200–2500 pC/N, d 31=1100–1400 pC/N. The various electromechanical coupling factors are relatively insensitive to poling conditions and crystal composition, with k 33=0.90–0.94, k 31=0.48–0.55 and k t=0.58–0.62 for PMN-(28–32)%PT. The results show that flux-grown PMN-PT single crystals exhibit superior dielectric and piezoelectric properties in comparison to their melt-grown counterparts, possibly due to a lower concentration of defects in flux-grown crystals.