Phase transition associated with the variation of oxygen vacancy/ion distribution in the oxide-ion conductor La2Mo2-x,Wx,O9

The effects of tungsten doping in La2Mo2-xWxO9 Samples (x = 0, 0. 1, 0.25, 0.5, 0.75, 1.0, 1.2, 1.4) were studied using dielectric relaxation measurements. Additional to the low-temperature relaxation peak P-d associated with oxygen ion diffusion, a new dielectric loss peak P-h was observed around 740 K. With increasing tungsten concentration, the activation energy of peak P-d increases and saturates at a value of about 1.45 eV, and the height of peak P-h increases at first and then decreases after passing a maximum at 25% tungsten doping. With increasing measurement frequency, the height of peak P-h decreases monotonically but its position shifts very little. Peak P-h in pure and tungsten-doped La2Mo2O9 is suggested to be associated with a phase transition from the static disordered state to the dynamic disordered state of oxygen ion/vacancy distribution. (C) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.