Structural effects of Li and K additives on the columbite precursor and 0.9PMN–0.1PT powders

Single-phase perovskite 0.9Pb(Mg1/3Nb2/3)O3–0.1PbTiO3 (PMN–PT) powders were prepared by using a Ti-modified columbite precursor (MNT) obtained by the polymeric precursor method. The innovation consists in the preparation of Ti-modified columbite in order to react directly with a stoichiometric amount of PbO to obtain pyrochlore-free PMN–PT powders. It has been shown that titanium oxide forms a solid solution with columbite (MN) and does not affect the obtaining of a single-phase columbite precursor. Thus, a high amount of perovskite phase can be obtained by reaction with PbO at 800 °C for 2 h. Effects of K and Li additives on the structure of MNT and PMN–PT were studied. X-ray diffraction studies were carried out to verify the phase formation at each processing step and these data were used for structural refinement by the Rietveld method. Both K and Li additives increase the crystallinity of MNT powders, being this effect more intense for the Li-doped samples. For PMN–PT samples the additives cause an insignificant decrease in the amount of perovskite phase. The morphology of the PMN–PT powder depends on the type of the additive.