Structural distortion of ferroelectric thin films caused by film strain has a strong impact on the microwave dielectric properties. thin films epitaxially grown on substrates using molecular beam epitaxy are extremely strained (i.e., in-plane tensional strain) from of bulk . The room-temperature in-plane dielectric constant and its tuning of the films at are observed to be 6000 and 75% with an electric field of , respectively. The control of strain in provides a basis for room-temperature tunable microwave applications by elevating its phase-transition peak to room temperature.
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It is worth to note that the Gibb’s energy expression to derive the relationship took positive signs (i.e., +) for all electrostriction-related terms like the Devonshire expression (see Ref. 23) so that the relevant electrostriction coefficients had the opposite signs (i.e., and ) to the case of a Gibb’s energy expression containing negatively signed electrostriction-related terms.
