The effects of acceptor doping with manganese as either MnO(2)or MnNb2O6(MnN) with CuO on the dielectric, ferroelectric, and piezoelectric properties of PIN-PMN-PT ceramics were investigated. The 2% MnNb2O6-doped PIN-PMN-PT (6Pb(Mn1/3Nb2/3)O-3-25Pb(In1/2Nb1/2)O-3-34Pb(Mg1/3Nb2/3)O-3-35PbTiO(3)) ceramics possessed hard properties such as high coercive field (E-C) of 11.7 kV/cm, low dielectric loss (tan delta) of 0.7%, and high electromechanical quality factor (Q(M)) of 1011. These properties were diminished in MnO2-doped ceramics because of lower oxygen vacancy defect concentration, and exaggerated grain growth resulted in >20 mu m grain size. Co-doping with 2 mol% MnNb(2)O(6)and 0.5 mol% CuO retained hardened properties such as highE(C)of 9.6 kV/cm, low tan delta of 0.6%, and highQ(M)of 1029. MnNb2O6-doped and MnNb2O6 + Cu co-doped ceramics display excellent figures of merit for resonance and off-resonance applications as well as high energy conversion efficiencies which make them promising candidates for high-power transducer elements.