Phase diagrams of bismuth ferrite barium titanate thin films with misfit strains and their improved electrical properties

Phase diagrams of BiFeO3-BaTiO3 (BF-BT) thin films were constructed via thermodynamic model calculation, as well as their electrical properties. The calculated morphotropic phase boundary (MPB) of BF-BT thin films without strain is located near the composition of 0.663BF-0.337BT, which agrees well with the experimental results of reported BF-BT ceramics (between 0.66BF-0.34BT and 0.71BF-0.29BT). The permittivity, tunability and d33of BF-BT thin films on Si substrates are higher than those on SrTiO3(ST) plates, which are also in accordance with the measured data in the literature. Further calculation indicates that 0.7BF-0.3BT and 0.6BF-0.4BT thin films can achieve enormous piezoelectric coefficient d33 ( similar to 1200 and similar to 1000 pm/V, respectively) by selecting the substrates with the TEC respectively of 0.3 and 3.1 x 10-6/circle C, because of the phase transition from aa phase to rhombohedral phase. Such results help to clarify the phase diagrams of BF-BT thin films, implying that huge d33can be achieved by choosing the composition near MPB on the substrates with small TEC.