Aging characteristics of ferroelectric epitaxial BaTiO₃/YBa₂Cu₃O₇ heterostructures

The nature of ferroelectric aging of epitaxial BaTiO₃/YBa₂Cu₃O₇ heterostructures grown by laser deposition was investigated as a function of microstructure in the dielectric layer. Molar amounts of SrTiO₃ were then substitutionally added to analyze the effect on the microstructure and electrical properties. Corresponding shifts in c/a ratio and curie temperature were correlated to changes in aging rate (%ΔC/decade time). Microstructural analysis was provided by high-resolution x-ray diffraction (HRXRD), and Rutherford backscattering spectroscopy (RBS). Results indicate a moderate upward shift in c/a ratios from theoretical values due to increasing lattice strain across the bilayer interface. Minimum channel yields in RBS spectra were maintained between 6-8% for BaTiO₃ purities above 60%. Dielectric measurements were conducted using an impedance analyzer equipped with an isothermal chamber capable of maintaining ±1 °C. The dielectric properties were consistent with c-axis oriented BaTiO₃ values (k = 120, D = .02) Minimum aging rates are observed at the lower c/a ratio compositions to be as low as .07%ΔC/decade.