Epitaxial strain can unlock enhanced properties in oxide materials, but restricts substrate choice and maximum film thickness, above which lattice relaxation and property degradation occur. Here we employ a chemical alternative to epitaxial strain by providing targeted chemical pressure, distinct from random doping, to induce a ferroelectric instability with the strategic introduction of barium into today’s best millimetre-wave tuneable dielectric, the epitaxially strained 50-nm-thick n = 6 (SrTiO3)nSrO Ruddlesden–Popper dielectric grown on (110) DyScO3. The defect mitigating nature of (SrTiO3)nSrO results in unprecedented low loss at frequencies up to 125 GHz. No barium-containing Ruddlesden–Popper titanates are known, but the resulting atomically engineered superlattice material, (SrTiO3)n−m(BaTiO3)mSrO, enables low-loss, tuneable dielectric properties to be achieved with lower epitaxial strain and a 200% improvement in the figure of merit at commercially relevant millimetre-wave frequencies. As tuneable dielectrics are key constituents of emerging millimetre-wave high-frequency devices in telecommunications, our findings could lead to higher performance adaptive and reconfigurable electronics at these frequencies.
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Figure data, DFT files and additional information can be accessed on the NIST Public Data Repository via the following link: https://doi.org/10.18434/M31968.
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The synthesis, characterization and theoretical work at Cornell was supported by the US Department of Energy, Office of Basic Sciences, Division of Materials Sciences and Engineering (Award no. DE-SC0002334). Sample preparation was in part facilitated by the Cornell NanoScale Facility, a member of the National Nanotechnology Coordinated Infrastructure (NNCI), which is supported by the National Science Foundation (grant no. NNCI-1542081). Ferroelectric and dielectric measurements with temperature were conducted at the Center for Nanophase Materials Sciences, which is a DOE Office of Science User Facility. Infrared and terahertz studies were supported by the Czech Science Foundation (project no. 18–09265S) and by the MŠMT (project no. SOLID21-CZ.02.1.01/0.0/0.0/16 019/0000760). This work made use of Cornell Center for Materials Research Shared Facilities, which are supported through the NSF MRSEC program (no. DMR-1719875). Certain commercial equipment, instruments or materials are identified in this article to specify the experimental procedure adequately. Usage of commercial products herein is for information only; it does not imply recommendation or endorsement by NIST, and it is not intended to imply that the materials or equipment identified are necessarily the best available for the purpose.
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Dawley, N.M., Marksz, E.J., Hagerstrom, A.M. et al. Targeted chemical pressure yields tuneable millimetre-wave dielectric. Nat. Mater. 19, 176–181 (2020). https://doi.org/10.1038/s41563-019-0564-4