Tunable phase transitions in NaNbO ceramics through bismuth/vacancy modification

Sodium niobate, NaNbO 3 , which exhibits a perovskite structure, has recently stimulated interest in the field of energy storage capacitors, with derived solid solutions shown to have promising energy storage densities. Here A-site Bi/vacancy doping in NaNbO 3 in the system Na 1−3 x Bi x V 2 x NbO 3 (where V = vacancy and x = 0.015, 0.05, 0.10, 0.15 and 0.20) is investigated. Phase evolution was systematically examined through X-ray powder diffraction, Raman spectroscopy and thermal analysis, and is found to correlate with changes in electrical behaviour. It is shown that through tuning the Bi/vacancy content, different high temperature phases (above 550 °C) of NaNbO 3 , including the tetragonal P 4/ mbm and cubic Pm 3&cmb.macr; m phases are stabilised at room temperature. The phase evolution from Pbcm ( x = 0.015 and 0.05) to P 4/ mbm ( x = 0.10 and 0.15) to Pm 3&cmb.macr; m ( x = 0.20) with increased Bi/vacancy content is accompanied by lattice expansion, which is explained in terms of the accommodation of increased disorder resulting from the mixed arrangement of species ( x Bi 3+ , (1 − x )Na + and 2 xV Na ) on the A-site. Bismuth/vacancy modification of NaNbO 3 is seen to induce relaxor-like behaviour, significantly increasing both the recoverable energy storage density and energy storage efficiency. Bi/vacancy incorporation in sodium niobate, NaNbO 3 , induces relaxor-like behaviour leading to higher recoverable energy storage density and efficiency, with potential use in energy storage capacitors.