High, purely electrostrictive strain in lead-free dielectrics

Co-doping of bismuth (Bi) and sodium (Na) in SrTiO3 helps to enhance the solubility of Bi in SrTiO3, shifting the permittivity-maximum temperature of the ferroelectric relaxor to higher temperatures. When the dopant Bi ions are occupied at off-center positions in SrTiO3, Bi ions act as independent dipoles and the system shows dielectric-relaxor behavior. But increase in the Bi concentration leads to introduction of more vacancies, making the crystalline structure distorted, hence limiting solubility. When the Bi concentration exceeds a certain threshold, the whole system is expected to change into a normal ferroelectric.