Compositional modification of ferroelectric BiScO3-PbTiO3 (BS-PT) ceramics was investigated by Zr-Sc center dot doping as a function of temperature and electric field. Zr doping decreased the Curie temperature; yet depoling temperature was higher as determined from the weak field measurements. Weight change measurements explain the difference in sintering behavior, emphasizing the effects of sacrificial powder on the defect structure. Possible mechanisms are discussed in collaboration with the crystal structure analysis. Pb'(Bi) replacement was shown as a possible charge balance mechanism. Pb'(Bi) is supported by the weight loss data, crystal structure analysis and the weak-field electrical and electromechanical measurements. However, high field measurements contradicted the postulated Pb'(Bi) mechanism. Unipolar and bipolar high field polarization, strain and dielectric constant measurements indicated that the donor doping creates A-site vacancies; a similar observation to Pb(Zr,Ti)O-3 (PZT)-based ceramics. At higher temperatures, the property dependence on the composition decreased suggesting that thermally assisted domain motion eliminated the dependence of the domain wall mobility on the extrinsic contributions (i.e., defect structure induced by doping). Effect of Zr-Sc center dot doping on electrical and electromechanical properties are reported and discussed as a function of temperature.