Tuning phase fractions and leakage properties of chemical solution deposition-derived mixed-phase BiFeO₃ thin films

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Phase-pure epitaxial bismuth ferrite (BiFeO₃, BFO) thin films with a homogeneous mixed-phase structure were synthesized on (001)-oriented lanthanum aluminate (LaAlO₃, LAO) substrates using chemical solution deposition. The phase development of the BFO thin film and its leakage current characteristics have been systematically investigated as a function of thickness (number of spin-coated layers) and the heat treatment process (heating temperature and dwell time). The results show that the tetragonal-like (T′) phase fraction changes dramatically from 35% (45 nm thick single layer) to 10% (250 nm thick four-layer films). In a two-layer film (80 nm) configuration, the T′-phase fraction was further tuned. When annealing at 640 °C for 30 min, this mixed-phase BFO film, despite its high T′-phase fraction (28%), shows the lowest leakage current (<0.1 A/cm² at <500 kV/cm), comparable to 200 nm pulsed laser deposition-grown pure R-BFO thin films. In contrast to the observed bulk-limited Ohmic or space-charge-limited-conduction (SCLC)-predominant mechanism in pure R′-phase and low T′-phase fraction BFO thin films, the high T′-phase fraction (∼28%) mixed-phase BFO film displays an interface-limited Schottky emission to an SCLC mechanism transition with increasing electric field.