A　NiO-added　Pb((Zn1/3Nb2/3)(0.20)(Zr0.50Ti0.50)(0.80))O-3　system　is　prepared　and　investigated.　The　results　reveal　that　Ni　doping　induces　a　phase　transformation　from　the　morphotropic　phase　boundary　to　the　tetragonal　phase　side.　Above　the　solubility　limit　of　0.3　wt%　in　NiO　form,　excess　Ni　ions　segregate　at　the　grain　boundaries　and　triple　junctions,　which　facilitate　the　formation　of　a　liquid　phase　with　excess　PbO　and　lead　to　remarkable　grain　growth.　The　mechanical　behavior　(Vickers　hardness　(H-v)　and　fracture　toughness　(K-IC))　can　be　tailored　by　controlling　the　content　of　additive;　this　is　accompanied　by　a　transition　in　the　fracture　mode　changed　from　transgranular　without　NiO　additive　to　intergranular　with　1.0　wt%　NiO　additive.　Moreover,　the　NiO　addition　weakens　the　dielectric　relaxor　behavior　and　improves　the　piezoelectric　properties　simultaneously.　The　0.2PZN-0.8PZT　with　0.5　wt%　NiO　addition　shows　good　transduction　coefficient　(d(33.g33)　=　10,050　x　10(-15)　m(2)/N)　and　large　fracture　toughness　(K-IC　=　1.35　MPa　(m1/2)).　(C)　2013　Elsevier　Ltd.　All　rights　reserved.