Group　VIII　metal　oxides,　that　is,　Fe2O3,　Co2O3,　and　NiO　have　been　introduced　to　0.2Pb(Zn1/3Nb2/3)O-3-0.8Pb(Zr0.50Ti0.50)O-3　(PZN-PZT)　to　deterministically　identify　the　substitution　mechanism　and　meantime　to　tailor　mechanical　and　piezoelectric　properties　in　obtaining　energy　harvesting　materials.　On　the　basis　of　the　X-ray　diffraction　and　Raman　analysis,　it　is　clear　that　the　group　VIII　metal　oxides　induce　a　phase　transformation　from　the　morphotropic　phase　boundary　to　the　tetragonal　phase　side,　and　the　corresponding　grain　size　increases　accordingly.　It　is　reasonable　to　deduce　that　two　types　of　substitution　behaviors　coexist　in　the　group　VIII　metal　oxides　added　PZN-PZT　system.　Due　to　the　mixed　valence　of　+2　and　+3,　the　foreign　doping　ions　prefer　to　enter　the　B　site　in　the　perovskite　structure,　not　only　substituting　for　Ti4+,　Zr4+,　and　Nb5+　ions　in　the　inequivalence　replacement　but　also　substituting　for　Zn2+　ions　in　the　equivalence　replacement.　The　proposed　complex　substitution　mechanisms　can　give　the　full　explanation　about　the　grain　growth　phenomena　and　the　variation　in　mechanical　and　electric　properties　in　the　modified　PZN-PZT　system.　At　the　same　doping　level　of　0.3mol%,　the　maximum　transduction　coefficient　(d(33)g(33)=13120x10(-15)m(2)/N)　and　good　fracture　toughness　(K-IC=1.32MPam(1/2))　are　obtained　in　Co2O3　added　0.2PZN-0.8PZT　ceramics,　which　shows　great　promise　as　practical　materials　for　energy　harvesting　device　applications.