Structural,optical, microstructure,and giant dielectric behavior of parent,Cu and Sr doped La0.55Li0.35TiO3-δ

Optimization of energy storage performance in dielectric ceramics has been a focus in recent decades due to the benefits of high energy storage density, efficiency, and exceptional temperature stability. In this work, we report huge dielectric constant in La_0.55Li_0.35TiO_3-δ and sharp decrease in its value with the substitution of Sr and Cu at Ti position. These samples La_0.55Li_0.35TiO_3-δ (LLTO), La_0.55Li_0.35Ti_0.9Cu_0.1O_3-δ (LLTCO) and La_0.55Li_0.35Sr_0.1Ti_0.9O_3-δ (LLSTO) were prepared by solid state reaction method. The interfacial polarization of lithium ion aggregation close to the grain boundaries and the dipoles of Li ions in the sample are suggested to be the source of the enormous dielectric values. Parent composition (LLTO) shows highest dielectric constant value (6.29 × 10⁵ at frequency 10 Hz, 7.30×10⁴ at 1 kHz) recorded at room temperature while the lowest dielectric loss value (0.124) was observed for LLSTO at frequency 1 kHz. Structural characterization has been done using X-ray diffraction (XRD) technique to investigate the crystal structure of the prepared compositions. The XRD patterns show the similar crystal structure for all the compositions with the parent composition LLTO. The optical band gap is calculated by Kulbeka Munk function and Tauc plot using UV–visible diffuse reflectance spectroscopy technique. The maximum band gap value (3.32 eV) is obtained for parent composition while doping of Cu and Sr at Ti site in La_0.55Li_0.35TiO_3-δ decreases the band gap value. Optical microscopy shows the micron size grains in these samples. Doping of Sr and Cu in perovskite structure of LLTO brings tunability in dielectric and optical properties.