Tailoring effect of large polaron hopping in the conduction mechanism of Ca-modified BaTiO3 system

Tailoring effects of Ca-doping concentration on the structural, optical, and electrical properties of Ba1−xCaxTiO3 (x = 0.0 to 0.15) nanomaterials prepared via low-temperature sol–gel auto combustion technique are presented. XRD results reveal that all the prepared nanomaterials are crystallized in tetragonal structure with space group P4mm. FT-IR measurements are carried out in order to reveal the vibrational frequencies of bonds in the crystal lattice. A strong absorption peak due to Ti–O bond (TiO6 octahedron) appears at 538 cm−1 that shifts to a higher frequency with an increase in the doping of Ca ions. It is explained by the Coulomb interaction. Optical band gap of the sample increases with increase Ca doping as 3.44 eV (x = 0.0), 3.48 eV (x = 0.10), and 3.45 eV (x = 0.15). The BCT materials with x = 0.10 apparently show that the particle with short-range order can strongly influence the formation of intermediate states in the gap. Dielectric behavior is found governed by the interfacial polarization, whereas the ac conductivity supports the non-Debye process [n < 1] that is described using Jonscher’s power law. The conduction mechanism is found changing from small polaron to large polaron hopping as the Ca ions increase. Moreover, the electrical conductivity arising due to the movement of charged ions is correlated with the hopping and the lattice defects. The temperature-dependent activation energy is obtained in the range of 0.19–0.12 eV, which evidences the NTCR behavior observed for all studied materials.