Structural, optical, and electric properties of BNT–BT_0.08 thin films processed by sol–gel technique

Thin films with the composition [(Bi_0.5Na_0.5)TiO₃]_0.92–[BaTiO₃]_0.08 (hereafter BNT–BT_0.08) were deposited on Pt–Si by spin-coating from a stable sol precursor. The BNT–BT_0.08 film, crystallized on the Bi_0.5Na_0.5TiO₃ rhombohedral lattice, was obtained after annealing the film-gel at 700 °C. The films have a smooth surface (Rms = 2.76 nm) and grains with ferroelectric domains. The film showed a bandgap of 3.25 eV and a refractive index of 2.20 at a wavelength of 630 nm. The dielectric characteristics of BNT–BT_0.08 thin films were measured at room temperature and 10 kHz the dielectric constant (ε _r) was 243 and the loss tangent (tanδ) was 0.38. The remnant polarization (P _r) was 0.87 μC/cm² and the coercive field (E _c) was 220 kV/cm at 10 kHz and room temperature. The current density was approximately 2.7 × 10⁻⁵ A/cm² at low electric fields (100 kV/cm). BNT–BT_0.08 thin films shown piezoelectric properties (d _33eff = 100 pm/V) comparable to those of PZT thin films.