Relaxation peaks associated with the oxygen-ion diffusion in La2−xBixMo2O9 oxide-ion conductors

The effects of bismuth doping on the oxygen-ion diffusion in oxide-ion conductors La2−xBixMo2O9 (x=0.05, 0.1, and 0.15) have been studied by both internal friction and dielectric relaxation techniques. Two internal friction peaks of relaxation type (P1 and P2 peak) were observed at a measurement frequency of 4 Hz around 380 and 430 K, respectively. As for the dielectric measurement, a prominent dielectric relaxation peak (Pd) was found in all the Bi-doped samples around 700 K at a measurement frequency of 50 kHz, which actually consists of two sub-peaks (denoted as Pd1 and Pd2 peak). With increasing Bi-doping content, two peaks shift to higher temperature and decrease in height, while the activation energy of both peaks increases. The main reason was interpreted as the introduction of the lone-pair electrons of bismuth, which tends to block the diffusion of oxygen ion.