Nanoscale polarisation switching and leakage currents in (Ba_0.955Ca_0.045)(Zr_0.17Ti_0.83)O₃ epitaxial thin films

This paper investigates the crystal structure, ferroelectric, temperature-dependent leakage current conduction mechanism and the piezoresponse force microscopy (PFM) behaviours of (Ba_0.955Ca_0.045) (Zr_0.17Ti_0.83)O₃–BZT–BCT (_x=0.15) films at the vicinity of the morphotropic phase boundary (MPB) of the [(1  −  x) BaZr_0.20Ti_0.80O₃–xBa_0.70Ca_0.30TiO₃] (_x=0.15) composition. Epitaxial BZT–BCT thin films were grown on conductive La_0.5Sr_0.5CoO₃ (LSCO) layers coated onto MgO (1 0 0) single-crystal substrates by pulsed laser deposition (PLD). High resolution x-ray diffraction (HR-XRD) reciprocal space maps (RSMs) confirmed the epitaxy with in-plane tetragonal symmetry (c  <  a), and Raman spectra also revealed a tetragonal perovskite crystalline lattice structure. Polarisation studies demonstrate that BZT–BCT films exhibit a high saturation polarisation of 148 µC cm⁻² and a high recoverable (discharged) energy-storage density of 39.11 J cm⁻³ at 2.08 MV cm⁻¹. Temperature-dependent P–E hysteresis loops resulted in a decrease in polarisation. Temperature-dependent leakage current behaviour was obtained and possible conduction mechanism is discussed. PPFM images revealed switchable ferroelectric piezoelectric contrasts after the application of a  ±9 V dc voltage on the conductive tip of the piezoresponse force microscope