Ultrahigh anharmonicity low-permittivity tunable nanocrystalline thin-film BaTi2O5

Electrically tunable dielectric thin films in active circuits and systems are challenged by capacitance-induced delays and impedance matching requiring a lower dielectric constant. Here an approach to increasing the intrinsic tunability of compounds containing TiO6 octahedra by considering the influence of different connectivity among these octahedra is presented. Such connectivity variants in nanocrystalline monoclinic BaTi2O5 thin films enable a two orders of magnitude enhancement in Ti anharmonic interaction, thereby permitting a approximate to 65% decrease in dielectric constant to 70 at room temperature without sacrificing tunability. Edge-sharing TiO6 octahedra possess a much shorter Ti-Ti distance of only 2.91 angstrom as compared to the perovskite structure (similar to 4 angstrom), permitting large field-induced structural re-arrangement and intrinsic tunability. (C) 2021 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.