Effect of bismuth doping on the properties of strontium titanate thin films


Strontium titanate-based materials with ferroelectric or relaxor-like properties have drawn vast attention for research and wide range of applications in different areas. This chapter summarises firstly the electrical behaviour of Bi-doped strontium titanate ceramics, where three relaxation modes, related to individual hopping of off-centre Bi ions with and without oxygen vacancies nearby, as well as to their collective polar cluster reversal, are induced by Bi doping. Then, the structural and microstructural properties of sol-gel derived Sr1-1.5xBixTiO3 films are reported, revealing enlarged lattice parameter and film roughness with increasing Bi content. Dielectric response of these films as a function of frequency demonstrates that, besides the oxygen vacancy related mode, only two polar relaxation modes exist in the temperature range of 10-300 K. Polarisation versus ac electric field hysteresis response of Sr1-1.5xBixTiO3 films confirms the low-temperature polar state induced by Bi doping in strontium titanate (STO) films. Results on the dielectric permittivity versus dc electric field indicate that moderately Bi-doped STO films can be considered as a promising material for tunable device applications, due to their high values of relative tunability (up to ~ 40%) and communication quality factor (up to ~ 10 000) under 125 kV/cm.


Okhay, O; Tkach, A; Vilarinho, PM

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