Mechanisms of multi-component perovskite synthesis from stoichiometric mixtures by a soft-mechanochemical route

Mechanism of complex formation by milling a mixture comprising PbO, TiO2, Nb2O5 and Mg(OH)(2) was examined. Due to the strong acidity of Nb2O5 and basicity of Mg(OH)(2), a typical acid-base reaction takes place during milling with simultaneous partial reduction of Nb5+ to Nb2+, as evidenced by XPS. This mechanochemical reaction, together with further interaction with PbO and TiO,, brings about precursors of the perovskite solid solution, (1-x)Pb(Mg(1/3)Nbu(2/3))O-3-xPbTiO(3) with x ranging from 0 to 0.2. The mixture after milling is more homogeneous and contains even a small amount of crystalline perovskite. On subsequent heating, growth of perovskite takes place parallel with a solid state reaction via pyrochlore, resulting in a pure perovskite phase at temperatures as low as 850 degrees C. A mixture without mechanical stressing brings about a pyrochlore as a main phase by heating under the same condition.