In this letter, the shear-mode piezoelectric and electromechanical properties of 0.55Pb(Yb1/2Nb1/2)O3-0. 45PbTiO3 (PYNT45) single crystals are reported. The piezoelectric coefficients d15 and g15 were found to be 2100 pC/N and 0.064 Vm/N, respectively, with an electromechanical coupling coefficient k 15 of 91% at room temperature. With increasing temperature, the values decreased dramatically above 168��C, corresponding to the ferroelectric-ferroelectric phase transition temperature. In contrast to 0.955Pb(Zn1/3Nb2/3)O3-0.045PbTiO3 single crystals, PYNT45 crystals exhibit a larger g15 and the useful temperature range is significantly expanded. High-temperature aging experiments showed that PYNT45 single crystals exhibit good domain stability. �� 2002 American Institute of Physics.