Revealing the effect of conductive mechanism on the voltage endurance of ferroelectric thin films via controlling the deposition temperature for reaching high energy storage capability†

Abstract

Dielectric capacitors are considered superior to Li-ion batteries for replacing conventional internal combustion engines because they have no drawbacks of long charging times. Compared to the material's state of bulk ceramics and flexible composite films, dielectric capacitors in the form of thin films offer greater flexibility for regulation beyond domain and interface engineering. In this work, we grew 0.75Ba_0.15Ca_0.85Zr_0.1Ti_0.9O₃–0.15Bi(Zn_2/3Ta_1/3)O₃ (BCZT–BZT) thin films on 100 nm SrRuO₃(SRO)-coated (001)-STO substrates at various deposition temperatures. Due to lattice mismatch, all films consist of a strained layer and a relaxed layer, with varying proportions, and the strained layer is considered to degrade the voltage endurance of the thin films. The J–E curve results indicate a conduction mechanism transition from Schottky emission to Ohmic contact, with the formation of a depletion layer, which is higher in resistivity, at the bottom of BCZT–BZT60 and BCZT–BZT65. Considering a phase evolution from T-phase to O-phase from the bottom up, directly observed in the TEM images, electric field redistribution with voltage endurance was thought to occur in these two thin films, which is confirmed by the mathematical derivation. The synergistic effects of the variation between the strained and relaxed layers, along with the transitions in the conduction mechanism, result in BCZT–BZT65 achieving the highest breakdown strength (E_b) of 7.01 MV cm⁻¹ and a recoverable energy density (W_rec) of 101.79 J cm⁻³. Additionally, BCZT–BZT65 demonstrates high reliability in harsh environments and excellent discharge performance with a discharge time (t_0.9) of only 0.45 μs.