Role of an intermediate phase (Ba,Sr)_2Ti_2O_5CO_3 in doped (Ba_(0.7)Sr_(0.3))TiO_3 thin films

摘要

(Ba_(0.7)Sr_(0.3))TiO_3 (BST) thin films doped with La, Nb, and Mg ions were prepared by metal-organic deposition method (MOD) on Pt/Ti/SiO_2/Si substrates. An intermediate phase formed under an annealing temperature of 550―650 ℃, and disappeared at higher temperatures during the formation of BST. The intermediate phase was analyzed by X-ray diffraction (XRD) analysis, transmission electron microscopy (TEM), Fourier transform-infrared spectroscopy (FT-IR) and Raman spectra and found to be an oxycarbonate with a chemical formula of (Ba,Sr)_2Ti_2O_5CO_3. The stability of this intermediate phase increased with the addition of dopants, irrespective of doping types. It is proposed that distortion of crystal structure, physical constraint in the two-dimensions and small grain size favor the existence of poor crystallized (Ba,Sr)_2Ti_2O_5CO_3.