Single-calcination synthesis of pyrochlore-free Pb(Ni1/3Nb2/3)O3–PbTiO3 using a coating method

Pyrochlore-free 0.64Pb(Ni1/3Nb2/3)O3–0.36PbTiO3 (0.64PNN–0.36PT) powder has been successfully synthesized by only one calcination step using a coating method. The formation of pyrochlore phase is prevented by coating NiCO3·2Ni(OH)2·2H2O on Nb2O5 particles. NiCO3·2Ni(OH)2·2H2O-coated Nb2O5 powder is prepared by heterogeneous precipitation method. The coating structure is confirmed by transmission electron microscope (TEM) with energy dispersive spectroscope (EDS). Single calcination treatment of the coating powder mixed with appropriate amounts of Pb3O4 and TiO2 powders at 900 °C for 2 h produces the pure-perovskite 0.64PNN–0.36PT powder. The elimination of the pyrochlore phase can be explained in terms of the separating of Pb3O4 and Nb2O5 by the NiCO3·2Ni(OH)2·2H2O coating layer.