Ferroelectric domain wall relaxation in Ba0.25Sr0.75TiO3 films displaying Curie-Weiss behavior

Abstract

Ferroelectric films may be used in integrated circuits for high frequency and memory applications. Losses and interfaces between films and electrodes are problematic. This work concerns the temperature and electric field response of the complex dielectric permittivity and the relaxation of domain walls in a ferroelectric layer that is of sufficient quality to show a Curie-Weiss behavior. Laser ablation was used to deposit 1200 nm thick Ba0.25Sr0.75TiO3 layers between metallic oxide, (100 nm) SrRuO3 and (120 nm) La0.67Ca0.33MnO3, films in epitaxial heterostructures. The electric field response (E⩽80kV∕cm) of the real ϵ′ and imaginary ϵ″ parts of the complex permittivity of the intermediate Ba0.25Sr0.75TiO3 layer in these parallel plane film capacitors was studied at temperatures above and below the phase transition point TCurie. The latter was determined from the temperature dependence of the inverse dielectric permittivity and its value, TCurie=145K, agrees well with that of bulk single crystal. ϵ′ of the Ba0.25Sr0.75TiO3 layer could be suppressed about 80% by a field E=80kV∕cm at temperatures close to TCurieϵ′(T,E) and ϵ″(T,E) curves were used to gain insight into the relaxation dynamics of ferroelectric domain walls (DW) in the Ba0.25Sr0.75TiO3 layer. Their influence on ϵ′ was noticed up to T=230K, well above TCurie. The most probable relaxation time τ of the DW in Ba0.25Sr0.75TiO3 follows a relation τ=τ0exp[(ϕ−βE)∕kT], where τ0=1.2×10−10sϕ=75–105meV, and β=4.7×10−24Jm1∕2V−1∕2.