The temperature dependence of dielectric and piezoelectric properties, electric-field-induced strains of 0.66 Pb(In1/2Nb1/2)O-3-0.34 PbTiO3 single crystals, which were grown directly from melt by using the modified Bridgman technique with the allomeric Pb(Mg2/3Nb1/3)O-3-PbTiO3 seed crystals, were determined as a function of crystallographic orientation with respect to the prototypic (cubic) axes. Ultrahigh piezoelectric response (d(33) similar to 2000 pC/N, k(33) similar to 94%) and strain levels up to 0.8%, comparable to rhombohedral (1-x)Pb(Mg2/3Nb1/3)O-3-xPbTiO(3) and (1-x)Pb(Zn2/3Nb1/3)O-3-xPbTiO(3) single crystals, were observed for the <0 0 1>-oriented crystals. Strain levels up to 0.47% and piezoelectric constant d(33) 1600 pC/N could be achieved being related to an electric-field-induced rhombohedral-orthorhombic phase transition for the <1 1 0>-oriented crystals. In addition, high electromechanical coefficients k(33) (similar to88%) can be achieved even heating to 110degreesC. High T-C (similar to200degreesC), large electromechanical coefficients k(33) (similar to94%) and low dielectric loss factor (similar to1%), along with large strain make the crystals promising candidates for a wide range of electromechanical transducers. (C) 2003 Elsevier Science Ltd. All rights reserved.