High energy storage density and efficiency of 0.5Ba(Zr0.2Ti0.8)O3–0.5(Ba0.7Ca0.3)TiO3 thin films on platinized sapphire substrates

Manganese-doped 0.5Ba(Zr_0.2Ti_0.8)O₃–0.5(Ba_0.7Ca_0.3)TiO₃ (BZT–BCT) ferroelectric thin films deposited on platinized sapphire substrates by chemical solution deposition and multistep-annealed at 850 °C, are investigated. The 100 nm and 340 nm thick films are crack-free and have columnar microstructures with average lateral grain sizes of 58 nm and 92 nm, respectively. The 340 nm thick films exhibit a relative permittivity of about 820 at 1 kHz and room temperature, about 60% higher than the thinner films, which is attributed to the dielectric grain size effect. The thinner films exhibit a larger coercive field and remanent polarization of about 110 kV cm⁻¹ and 6 μC cm⁻² respectively, at 1 MV cm⁻¹ compared to 45 kV cm⁻¹ and 4 μC cm⁻² for the thicker films. The 340 nm thick films exhibit a maximum polarization of about 47 μC cm⁻² at 3.5 MV cm⁻¹ and slim polarization loops, resulting in high energy storage properties with 46 J cm⁻³ of recoverable energy storage density and 89% energy storage efficiency.