Different effect of Li+, Na+, K+ -doping on crystal structure and electrical property of Sr0.6Ba0.4Nb2O6

Ferroelectric Sr0.6Ba0.4Nb2O6 (SBN) shows typical unfilled tetragonal tungsten bronze structure where 1/6 A sites and all C sites are unoccupied. The presence of such structural vacancy provides the possibility to further modulate the crystal structure and electrical properties. In this work, alkali ions (Li+, Na+, K+) doped SBN ceramics have been fabricated via solid-solution reaction method. In general, each doping promotes the crystal structure evolves from unfilled toward filled tungsten bronze. However, the different doping ion radius causes the differences in occupying initial structural vacancies, resulting in significantly different electrical properties, Li+ doping enhances relaxor characteristic whereas Na+ and K+ doping lead to normal ferroelectric behavior, accompanying an increase in Curie temperature (Tc) from 36 °C of SBN to 40, 212, 148 °C of Li+, Na+ and K+ doping, respectively. Benefiting from improved relaxor degree and high density, the Li+ doped SBN displays a good energy storage performance. Since the ratio of Sr/Ba and (Sr + Ba)/Nb has not been changed, this work presents direct evidence for the effect of structural vacancy on crystal structure and properties, as well as inspiration for further work on unfilled tungsten bronze.