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

Abstract

Using a tolerance factor approach, it was predicted that x Bi Sc O 3 – ( 1 − x ) Ba Ti O 3 will have a morphotropic phase boundary that should enhance both the polarizability and permittivity, relative to the Bi Sc O 3 end member, near a composition of x = 0.4 . To verify this prediction, pulsed laser deposition was used to grow x Bi Sc O 3 – ( 1 − x ) Ba Ti O 3 thin films on (100) Sr Ru O 3 ∕ La Al O 3 and Pt-coated Si substrates. Typical growth conditions were 700 ° C and 100 mTorr O 2 ∕ O 3 . 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 Bi Sc O 3 is added to Ba Ti O 3 , and increasingly relaxorlike behavior is observed with increasing Bi Sc O 3 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 . 0.4 Bi Sc O 3 – 0.6 Ba Ti O 3 showed a broad permittivity maximum near 800 from 150 – 275 ° C . Films with x = 0.4 show a coercive field of about 200 kV ∕ cm with a modest room temperature remanent polarization near 8 μ C ∕ cm 2 . The films exhibit a dielectric tunability of greater than 25% at fields of ∼ 500 kV ∕ cm . 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.