Dielectric properties of Ba(Sn_xTi_1-x)O₃ thin films grown by a sol-gel process

Ferroelectric Ba(Sn_xTi_1-x)O₃ (BTS) thin films were deposited using a sol-gel process on LaNiO₃-coated silicon substrates. The films showed a (100) preferred orientation depending on composition. The grain size decreased and the microstructure became denser with increasing tin content The decreasing grain size with increasing tin may be attributable to lower grain-growth rates from the more slowly diffusing Sn ⁴⁺ ion, which has a larger ionic radius than Ti⁴⁺. The ferroelectric phase transition temperature of Ba(Sn_xTi _1-x)O₃ thin films with (a) x = 0, (b) x = 0.05, (c) x = 0.10, and (d) x = 0.15 occurs at about 150°, 45°, 28°, and 20°C, respectively. The highest K (figure of merit defined as K = tunability/tan δ = {[ε(0) - ε(E)]/ε(E)}/tan δ) was found for BTS thin films with x = 0.10, even though tunability was highest with x = 0.05. An increase of dielectric loss as compared with films with x = 0.10 produced a decrease in K value. The J-E characteristics were highly nonlinear and the electric field resulting in nonlinearity moved to lower electric fields with decreasing tin content.