Hydrothermally grown BaZrO₃ films on zirconium metal: Microstructure, x-ray photoelectron spectroscopy, and Auger electron spectroscopy depth profiling

BaZrO₃ films were grown on zirconium metal substrates by immersing thin Zr foils in an alkaline solution under hydrothermal conditions. The films were produced at temperatures ranging from 200 °C to 270 °C in a 0.25 M barium hydroxide solution for 3 to 8 h. The resulting films did not have visible pores or defects, and displayed a grain structure which depended on the treatment conditions, especially temperature. X-ray photoelectron and Auger spectroscopies revealed that (a) after removing the surface layer, films were clean, not displaying OH groups nor carbon contamination; (b) the Ba concentration steadily decreased as the depth increased, and did not behave as in BaTiO₃ or SrTiO₃ films prepared under similar conditions; and (c) the BaZrO3/Zr interface was very broad. Grazing angle x-ray diffraction analysis showed BaZrO₃ (cubic), ZrO₂ (hexagonal), and Zr (hexagonal), suggesting a layered structure: BaZrO₃/ZrO₂/Zr. The relative dielectric constant was ≍70 and was independent of the frequency between 100 Hz and 1 MHz. The dielectric loss factor (tan δ) was between 0.01 and 0.02. Dielectric breakdown occurred between 25 and 40 MVm⁻¹.