Complex dielectric function and opto-electronic characterization using VEELS for the lead-free BCZT electro-ceramic...

The current work presents the complex dielectric function and the opto-electronic properties of lead-free Ba_0.8Ca_0.2Ti_0.9Zr_0.1O₃ (BCZT) electro-ceramic, derived from valence electron energy loss spectroscopy, in transmission electron microscopy (VEELS-TEM). A single tetragonal perovskite phase, with P4mm space group, was determined by Rietveld refinement of the x-ray diffraction pattern. The VEELS-TEM experiment scanned the energy interval from 0-50 eV. The spectroscopic analysis started with the chemical identification of the atoms that conforms the BCZT solid-solution. Bulk and surface plasmons were located at 27.2 eV and 12.9 eV, respectively in the energy loss function. Complex dielectric function was obtained using Kramers-Kronig analysis from the Gatan Microscopy Suite software. Dielectric constant was calculated from the real part of the complex dielectric function, while the inter-band transitions were identified in the joint density of states function. The refraction index n and the extinction coefficient k, as a function of energy, were obtained from the complex dielectric function. The bandgap energy was determined using a polynomial fit in the optical absorption coefficient plot with an E_g = 3.2 eV.