Structural and phonon characteristics of PbxLa1−xTiO3 nanocrystals prepared by hydrothermal technique

Pb1−xLaxTiO3 (PLT) nanocrystals of various La concentrations were prepared by hydrothermal technique. Raman spectroscopy, X-ray diffraction (XRD) and thermal gravity analysis (TGA) were used to investigate the lattice structures, phonon properties and volatile behaviors. With increasing La concentration, most of Raman modes shift downward. A soft mode E(1TO) at 82 cm−1 shifts and disappears at 60 cm−1 when the La concentration reaches 14 mol.%. This weaker softening property of the soft mode is attributed to the decrease of the tetragonality by La doping. Grain sizes of the PLT nanocrystals from 12 to 28 nm were obtained at various annealing temperatures by X-ray measurement, via the Sherrer formula. The saturation for grain growing becomes more appreciable with increased La doping, owing to more ‘pinning centers’ inside. When the La concentration is over 12 mol.%, after 1000oC heat treatment a PbTi3O7 impurity phase appears in PLT nanocrystals due to PbO volatilization. The volatile temperature for PbO from PbTiO3 lattice decreases with increasing La concentration.