The dielectric and electrically induced strain characteristics of Fe-substituted Pb(Zn1/3Nb2/3)O-3-PbTiO3 single crystals have been investigated. These investigations have shown that Fe substitution results in: (i) a lowering of the field level required to obtain large strains, (ii) an increased squareness in the epsilon-E response indicative of "hard" piezoelectric properties, and (iii) enhanced linearity in the region where saturation is approached at high field levels. Interestingly, the hard characteristics occur along with an enhanced stability of an intermediate ferroelectric orthorhombic state. (C) 2002 American Institute of Physics.