The impact of annealing temperature and dopant concentration on the crystal structure and conductivity of single doped (Bi2O3)1–x(Tb4O7)x solid electrolyte systems

Abstract

In this paper, the binary systems (Bi2O3)1–x (Tb4O7)x (x % = 10, 15, 17, 20, 22, 25) were successfully synthesized by solid–state reactions and characterized by XRD, TG & DTA, FPPT, and SEM technique. With the exception of (Bi2O3)0.90(Tb4O7)0.10, which exhibited a combination of β2 and δ phases, the XRD patterns confirmed that all samples were stabilized with the high–ion conducting δ–phase. This mixed phase, however, changed into a single δ–phase after repeated heat treatments. The Arrhenius plots revealed that conductivity dropped as the Tb4O7 ratio increased. The highest conductivity was measured for the (Bi2O3)0.90(Tb4O7)0.10 system with 0.17 S cm−1 at 750 °C, exhibiting the lowest activation energy of 0.727 eV. Additionally, an annealing operation at 800 °C was successful in increasing electrical conductivity in the (Bi2O3)0.83(Tb4O7)0.17 system. The SEM images of (Bi2O3)0.85 (Tb4O7)0.15 and (Bi2O3)0.80(Tb4O7)0.20 indicated that grain size was not uniform and decreased with increasing Tb4O7 content.