Dielectric and microstructural properties of barium titanate zirconate thin films on copper substrates

Barium titanate zirconate, Ba(Ti_1−xZr_x)O₃ (0 ≤ x ≤ 0.25), thin films were deposited via the chemical solution deposition (CSD) method directly on copper foils. The films were processed in a reductive atmosphere containing nitrogen, water vapor, and hydrogen gas at 900 °C to preserve the metallic copper substrate during crystallization. Increasing the fraction of BaZrO₃ revealed several effects, including an increase in unit cell dimensions, a decrease in both the temperature and value of the maximum permittivity, as well as a decrease in the average grain size of the films. The decrease in the relative permittivity was attributed to a grain size effect as opposed to zirconium substitution. In film compositions containing 25 mol% BaZrO₃, the permittivity below T_max became dispersive, and the ferroelectric transitions became increasingly diffuse. These characteristics suggest relaxor-like behavior. The dielectric tunability of Ba(Ti_1−xZr_x)O₃ was studied at room temperature and at T_max for each composition. There was little variation in the tunability with measurement temperature; however compositions that were ferroelectric at room temperature saw a decrease in hysteresis at T_max, and all compositions showed an increase in permittivity.