Enhancement of Dielectric Properties in Epitaxial Bismuth Ferrite–Bismuth Samarium Ferrite Superlattices

Abstract

Artificially layered bismuth ferrite (BiFeO 3 )/bismuth samarium ferrite (Bi 1– x Sm x )FeO 3 superlattices (SLs) are investigated for their dielectric properties. In short‐period (5–10 nm) SLs, the stabilization of an incommensurately modulated nanoscale mixture due to a strong interlayer coupling mechanism results in a large dielectric permittivity ( ε 33 ≈ 170 at 1 MHz), reduced loss tangent, and increased tunability ( τ ≈ 37%) for a samarium concentration range much larger than that for single‐layer (Bi 1– x Sm x )FeO 3 thin‐films. The enhanced dielectric tunability is observed across a large frequency and temperature range. Increasing the thickness of the SL layers reduces the strength of the interlayer coupling, which results in reductions in dielectric permittivity ( ε 33 ≈ 150), increases in dielectric loss tangent and decreased tunability ( τ ≈ 14%). A phenomenological model confirms that the enhanced dielectric properties, tunability and stabilization of the polar phase to higher Sm 3+ concentrations over a wide range of temperatures and frequencies in the short period SLs is due to electrostatic coupling. Thus, the epitaxial short‐period SLs have significant potential as a highly tunable lead (Pb)‐free materials system in low‐to‐medium frequency applications. Electrostatic coupling effect between polar/non‐polar layers in SL structures could thus be a universal method to achieve enhanced dielectric properties.