Strain-induced band gap tuning in flexible ferroelectric/mica thin films

Precise control of the band gap is crucial for lead-free ferroelectrics in the application of high-performance optical devices. In this work, we demonstrate that continuous and reversible tuning of optical band gap can be realized through mechanical strain in flexible Ba_0.9Ca_0.1Ti_0.975Fe_0.025O₃ (BCTF)/mica films. Through bending the flexible films, a large mechanical strain of 0.85% could be introduced into the ferroelectric active layer, leading to a reduction in the band gap of 0.38 eV. The strong dependence of the optical band gap on mechanical bending mainly arisen from the strain-induced modification of Fe-O bond. Because of the superior mechanical property of mica, the flexible BCTF/mica film also exhibits excellent anti-fatigue characteristics over 10³ bending cycles. Thus, this work provides an alternate perspective for the design and fabrication of ferroelectric optical devices that cover the entire visible light region.