Anelastic relaxation from hydrogen and other defects in La-doped BaTiO3

We present anelastic spectroscopy measurements between 2 and 500 K in Ba1-xLaxTiO3 (0.10 <= x <= 0.20). The phase transitions of pure BaTiO3 are shifted to lower temperature by increasing the La doping and are completely suppressed starting from x = 0.15. The samples are expected to contain H impurities since sintering was performed in flowing H-2 to ensure electronic rather than cation vacancy compensation, and indeed at least three relaxation processes of the complex anelastic spectrum are strongly influenced by annealing the samples in CO or H-2 at 1450 K. A thermally activated anelastic peak around 250 K (f similar to 2 kHz) is ascribable to H hopping between different O atoms, while a possible indication of fast reorientation around a same O atom comes from a broad peak around 100 K. At least other three relaxation processes are present between 30 and 150 K, but the present data do not allow their nature to be ascertained; possible mechanisms involve polarons and hopping of Ti and possibly 12 among off-centre positions. (C) 2009 Elsevier B.V. All rights reserved.