The effects of composition gradients of BaxSr1−xTiO3 thin films on their microstructures, dielectric and optical properties

Ferroelectric thin films of BaxSr1−xTiO3 (BST) with artificial gradients in composition normal to the growth surface were prepared on Si and fused quartz substrates by a sol–gel technique. Auger electronic spectroscopy observation shows that composition gradients of Ba and Sr are gradual and uniform without obvious interfaces between the different layers. X-ray diffraction analysis reveals that polycrystalline and perovskite formed at 730 °C. Annealing at higher temperature enhanced grain growth, the lattice parameter decreases with increasing annealing temperatures. The small signal dielectric constant and dielectric loss at 100 kHz were found to be 300 and 0.02. The graded thin film shows a relatively high tunability of 35% at an applied field of 240 kV cm−1. The optical properties were determined at room temperature in the wavelength range of 200–2000 nm from spectrophotometer measurements of the transmittance. The transmittance of the graded thin films increased, and a much weaker and flatter absorption band was found in the absorption spectra.