Reducing leakage current and enhancing dielectric properties of isovalent-substituted lead-free NBT perovskite

The influence of isovalent substitution at B-site by Ge4+ on the dielectric constant and dielectric losses of (Na0.5Bi0.5)TiO3 has been experimentally investigated. The compositions (Na0.5Bi0.5)(Ti1-xGex)O3 (x (mol) = 0.00, 0.01, 0.03, and 0.05) were fabricated using the solid-state reaction (SSR) method, with a sintering temperature of 1150 °C for 3 hours in air. Rietveld refinement revealed that the phases had a rhombohedral structure and belong to the R3c space group. Ge4+ substitution inhibits grain growth and improves dielectric properties, with optimized permittivity. Simultaneously, dielectric losses are reduced at both room temperature and elevated temperatures. At room temperature and 1 kHz, it is approximately (tan(δ) ≈ 0.17) for x = 0.03, which is significantly lower than that of NBT (tan(δ) ≈ 0.61), reaching a minimum of 0.02 at 310 °C and 1 MHz. Leakage current is also optimized after Ge4+ modification. Modelling of Nyquist diagrams using an electrical model indicated two contributions: grains and grain boundaries. These results suggest that Ge4+ substitution in the NBT compound could open new possibilities for its application in the manufacturing of capacitors with improved properties.