Abnormal temperature dependence of dielectric constant in (Ba0.7Sr0.3)TiO3 thin films

Pt∕(Ba0.7Sr0.3)TiO3∕YBa2Cu3O7−x capacitors were fabricated on LaAlO3 substrates. Dielectric and ferroelectric properties were measured in the temperature range from 20 to 250K. It was found that the dielectric constant decreased with decreasing temperature from 250 to ∼150K but then increased as the temperature continued to decrease to 20K. Considering this phenomenon along with the irregular temperature dependence of spontaneous polarization, it is indicated that such abnormal behavior originates in a second-order structural phase transition in the (Ba1−xSrx)TiO3 thin film in the vicinity of 150K.