Electric-Field Tunability of Dielectric in Polycrystalline Sr_1?xMn_xTiO₃ Thin Films

The electric-field tunability of dielectric constant (ϵ–E) in Sr_1?xMn_xTiO₃ films (x=0, 0.005, 0.010, 0.020 and 0.030) prepared by the metal organic decomposition method on Pt/Ti/SiO₂/Si substrates is studied in the frequency range from 100 Hz to 1 MHz with different Mn contents at different temperatures. The frequency-independent tunability increases strongly with decreasing the temperature from 300 K to 150 K. The tunability (～31%) in thin films (x=0.005) at 150 K is obtained and the temperature for the same tunability in ceramics is about 60 K lower than the present one. This tunability is comparable with that in one of ferroelectric Sr_1?1.5xBi_xTiO₃ thin films. Similarly, the well-defined P(E) hysteresis loop and 2P_r (1.2 μC/cm²) can be obtained at 300 K in Sr_1?xMn_xTiO₃ films with x=0.005. Both the existence of electric dipole or poled micro domain introduced by the doped Mn²⁺ located in the off-center position at Sr sites and the strain between the thin film and the substrate are the origins of the tunable and polar behavior in Sr_1?xMn_xTiO₃ films.