Ultrafine niobate ceramic powders in the system RE_xLi_1-xNbO₃ (RE: La, Pr, Sm, Er) synthesized by polymerizable complex method

Nanopowders of lithium niobate LiNbO₃ and rare earth (RE) substituted LiNbO₃-RE_xLi_1-xNbO₃, x = 0.05 (RE: La, Pr, Sm, Er) were synthesized using a simple technique as the polymerizable complex method, based on the Pechini-type reaction route. A mixed solution of citric acid and ethylene glycol with Li, Nb and RE ions was polymerized. The formation mechanism, the homogeneity and the structure of the obtained powders have been investigated by thermogravimetry, X-ray diffraction, Raman spectroscopy and scanning electron microscopy measurements. The X-ray diffraction analysis indicated the formation of perovskite-type oxides, which crystallize in rhombohedral system when the Li-Nb and Li-Nb-RE polymeric precursors were treated at temperatures as low as 500°C for 2 h. No additional crystalline phases formed during calcinations, but shifting of the XRD peaks with the RE ion substitution for Li suggested that structural modification inside the LN is the same. The Raman spectroscopy data of LiNbO₃ substituted by RE were compared to the results of the unsubstituted system. The substitution dependence of frequency and damping in the A₁(TO₂), A₁(TO₃) and E(TO₂) modes were employed to deduce the incorporation site of RE ions in LiNbO₃.