Uniaxial dielectric anisotropy in Ba0.5Sr0.5TiO3 films studied by evanescent-probe microscopy

The dielectric permittivity, tunability (Delta epsilon/epsilon), and loss tangent of Ba1-xSrxTiO3 (BST) films grown by pulsed-laser deposition are studied by near-held microwave microscopy. Based on theoretical simulations, a method is developed to measure the uniaxial dielectric anisotropy, epsilon (perpendicular to)/epsilon (parallel to), in BST films grown at different oxygen pressures. The measured epsilon (perpendicular to)/epsilon (parallel to) decreases with the film-growth oxygen pressure, consistent with the structural anisotropy. The films prepared at 50 mT, with epsilon (perpendicular to) approximate to epsilon (parallel to), have the highest permittivity, tunability, and figure of merit. (C) 2001 American Institute of Physics.