Effect of Li and Li-RE co-doping on structure, stability, optical and electrical properties of bismuth magnesium niobate pyrochlore

New Bi1.5Mg0.9-xLixNb1.5O7-delta (x = 0.25; 0.40) and Bi1.4RE0.1Mg0.5Li0.4Nb1.5O7-delta (RE - Eu, Ho, Yb) compounds with the pyrochlore structure were synthesized. The displacements of the A-site atoms (96g) and O' ones (32e) as well as the Li and RE atoms distribution in the A-sites were determined. The dopant distribution was proven by ab initio calculations. The most preferable (Bi1.5Li0.5)(Nb1.5Mg0.5)O-7 model was predicted with a direct band gap of 3.18 eV corresponding to the experimental E-g for Bi1.5Mg0.5Li0.4Nb1.5O7-delta. The thermal stability of the compounds in air up to 1100-1220 degrees C and the reducing atmosphere up to 400 degrees C was determined. The charge disbalance in the A(2)O' sublattice and the oxygen vacancies predetermine the dielectric behavior of the ceramics up to 200 degrees C, the mixed conductivity at high temperatures (T > 200 degrees C), and the proton transport up to 400 degrees C.

Automated summary

New pyrochlore-structured compounds Bi1.5Mg0.9-xLixNb1.5O7-delta (x = 0.25; 0.40) and Bi1.4RE0.1Mg0.5Li0.4Nb1.5O7-delta (RE - Eu, Ho, Yb) were synthesized and their atomic displacements and dopant distribution were studied. The preferred model with a direct band gap of 3.18 eV was predicted, and the thermal stability of the compounds was determined. Charge disbalance and oxygen vacancies were found to affect the dielectric behavior and conductivity of the ceramics.