Phase transition associated with the variation of oxygen vacancy/ion distribution in the oxide‐ion conductor La 2 Mo 2– x W x O 9

The effects of tungsten doping in La 2 Mo 2– x W x O 9 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 La 2 Mo 2 O 9 is suggested to be associated with a phase transition from the static disordered state to the dynamic disordered state of oxygen ion/vacancy distribution. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)