Structural and electrical characterization of xBiScO₃-(1-x) BaTiO₃ thin films

Using a tolerance factor approach, it was predicted that xBiSc O3 - (1-x) BaTi O3 will have a morphotropic phase boundary that should enhance both the polarizability and permittivity, relative to the BiSc O3 end member, near a composition of x=0.4. To verify this prediction, pulsed laser deposition was used to grow xBiSc O3 - (1-x) BaTi O3 thin films on (100) SrRu O3 LaAl O3 and Pt-coated Si substrates. Typical growth conditions were 700 °C and 100 mTorr O2 O3. The perovskite structure was found to be stable for compositions of x=0.2-0.6 in epitaxial films, with reduced stability in polycrystalline films. The temperature where the maximum permittivity occurs rises as BiSc O3 is added to BaTi O3, and increasingly relaxorlike behavior is observed with increasing BiSc O3 content. Room temperature permittivity values ranged from 200 to 400, with loss tangents of ∼0.1 at 10 kHz. The experimental morphotropic phase boundary occurs near x=0.4. 0.4BiSc O3 -0.6BaTi O3 showed a broad permittivity maximum near 800 from 150-275 °C. Films with x=0.4 show a coercive field of about 200 kVcm with a modest room temperature remanent polarization near 8 μC cm2. The films exhibit a dielectric tunability of greater than 25% at fields of ∼500 kVcm. The combination of high polarizability and high transition temperature makes this family an interesting base composition for lead-free piezoelectrics, especially if the degree of relaxor character could be reduced.