Single-phase perovskite 0.9Pb(Mg 1/3 Nb 2/3 )O 3 -0.1PbTiO 3 The solid solution 0.9Pb(Mg 1/3 Nb 2/3 )O 3 -0.1PbTiO 3 (0.9PMN-(0.9PMN-0.1 PT) from a stoichiometric mixture of starting 0.1 PT) is one of the most widely investigated relaxor ferromaterials was synthesized by applying a mechanochemical electrics, because of its high dielectric constant and outstanding technique to the stage of a precursor. A stoichiometric mixelectrostriction near room temperature. 16 Preparation of ture of PbO, TiO 2 , Mg(OH) 2 , and Nb 2 O 5 was milled for 60 0.9PMN-0.1 PT solid solution, as well as PMN, is difficult, min and heated at temperatures as low as 850؇C for 4 h to however, because of the persistence of the second phase, pyroobtain a single phase. The maximum dielectric constant of chlore, which severely degrades the dielectric properties. Sevthe samples from the milled mixture increased as the sintereral attempts have been made to avoid the formation of ing temperature increased, with the remarkable grain pyrochlore phase. 17-20 Complete elimination of pyrochlore is growth, and attained 24600 at 1200؇C. In contrast, poor very difficult, however, mainly because of the evaporation of densification and coexistence of the pyrochlore phase werePbO. An addition of excess PbO 21,22 or MgO 23 reduces pyroobserved on the samples from the nonmilled mixture. Furchlore formation, but the resulting perovskite PMN is often ther observation suggested that the pyrochlore phase connonstoichiometric, with poor dielectric properties. 24,25 centrated near the surface during sintering and then A columbite precursor method, 26 by reacting a slight excess migrated into the PbZrO 3 packing powder, leading to a of MgO with Nb 2 O 5 and then with PbO, results in better repropyrochlore-free phase at 1250؇C. The dielectric constant of ducibility of PMN formation with a very low pyrochlore conthe latter ceramics was explained by the series mixing rule tent. However, it requires a series of complex reaction steps. for the dielectric constant of a diphasic solid.One of the nonconventional mixed-oxide processes, as an alternative, i.e., the KCl molten salt method, 27 forms single-phase PMN as well as PMN-PT powder. However, the removal of I. IntroductionKCl is not very easy. Another attempt was made, with a careful A MECHANOCHEMICAL technique serves the formation of pre-choice of the starting raw materials and wet attrition milling. 28 cursors of complex oxides for advanced ceramics. 1 The Pyrochlore-free PMN was formed from a mixture of PbO method has a wide application to synthesize complex oxides (massicot), Mg(CO) 3 , and monoclinic Nb 2 O 5 by heating at a from metallic, covalent, or ionic compounds. 2 Based on a simitemperature of 800ЊC for 5 h. In contrast, the pyrochlore phase lar concept, mechanical alloying technology is applied for remained in the case of a mixture from MgO instead of producing composite metal powders with a controlled fine Mg(CO) 3 at the same heating condition. The difference is microstructure. 3,4 explained by the higher ...

Phase-pure perovskite Pb(Zn x Mg 1-x ) 1/3 Nb 2/3 O 3 solid solution (PZ x M 1-x N) is obtained for x Ϲ 0.7 by heating a milled stoichiometric mixture of PbO, Mg(OH) 2 , Nb 2 O 5 , and 2ZnCO 3 ⅐3Zn(OH) 2 ⅐H 2 O at 1100°C for 1 h. Percent perovskite (f P ) with respect to total crystalline phase decreases with increasing temperature of subsequent heating then increases to 900°C for the mixtures where x Ϲ 0.8 and milled for 3 h. For mixtures with x ‫؍‬ 0.9 and x ‫؍‬ 1, f P decreases monotonically. Curie temperature increases almost linearly with increasing x up to x ‫؍‬ 0.7. The maximum dielectric constant at 1 kHz is 2؋10 4 and 1.7؋10 4 for the mixture with x ‫؍‬ 0.4 and x ‫؍‬ 0.7, respectively. The stabilization mechanism of strained perovskite is discussed.

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Synthesis of Pyrochlore-Free 0.9Pb(Mg1/3Nb2/3)O3-0.1PbTiO3 Ceramics via a Soft Mechanochemical Route. -Single-phase perovskite is prepared by milling a stoichiometric mixture of PbO, TiO2, Mg(OH)2, and Nb2O5 for 60 min and heating at 850 • C for 4 h. The increase of the dielectric constant of the samples from the milled mixture with sintering temp. correlates with the increase of the grain size. It reaches a maximum value Kmax of 29000 at 1 kHz after sintering at 1250 • C, a Tmax of 42 • C and a grain size of 9.23 µm as compared to a Kmax = 19000, a grain size of 20 µm, and Tmax = 53 • C for samples from nonmilled mixtures which show the coexistence of the pyrochlore phase. -(BAEK, J.-G.; ISOBE, T.; SENNA, M.; J. Am. Ceram.

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