La content and size effects on crystal structure and phase transition of Bi4−xLaxTi3O12 nanocrystals

Crystal structure and phase transition of Bi4−xLaxTi3O12 nanocrystals with x=0−1.25 and grain sizes of 23, 42 and 53 nm were investigated in detail by X-ray diffraction and Raman scattering. The results showed that La atoms substitution for Bi atoms in Bi4Ti3O12 nanocrystal strengthens the short-range interaction between atoms and leads to a ferroelectric-paraelectric phase transition at a critical La content xc. The critical xc decreases as the grain size d decreases. The relationship between xc and 1/d can be described by a linear equation.