The effects of B2O3 addition to the PbO flux for growing Pb(Mg1/3Nb2/3)O-3-yPbTiO(3) (PMN-yPT) single crystals, where y = 0.28-0.34, have been investigated. The results show that the amount of B2O3 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 B2O3 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 Delta T-c approximate to +/- 3.0 degrees C. The PT content of this uniform composition portion is typically 2mol% smaller than that in the initial charge, indicating that the composition of the actual flux is PbO + z(B2O3 + delta PT), where 6 depends on the amount of B2O3 in the flux. Electrical poling studies reveal that while crystals of PMN-(31-32)%PT (T-c = 140 - 145 degrees C) composition are susceptible to overpoling, both PMN28%PT (T-c = 125 degrees C) and PMN-30%PT (T-c = 135 degrees 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. (c) 2005 Elsevier B.V. All rights reserved.