Hopping conduction in insulating rf-sputtered zinc oxide films

Structural and morphological studies, and temperature/frequency dependence of electrical conductivity of Ba0.97La0.02Ti1-x Nb4x/5O3 perovskite ceramics

Conductivity measurements of our polycrystalline perovskite ceramic systems with a composition of Ba0.97La0.02Ti1-x Nb4x/5O3 (x = 5, 7 and 10, in mol%) were performed, in order to investigate frequency and temperature dependence. Our ferroelectric ceramics were fabricated by the molten-salt method (chemical reaction followed by an evaporation and filtration reaction); X-ray diffraction patterns indicated that a single phase was formed for pure BaLT1-x Nb4x/5 ceramics. The electrical behavior of the ceramics was studied by impedance spectroscopy in the 500-610 K temperature range. The conductivity was investigated which can be described by the Jonscher law. Both AC and DC electrical conductivities are completely studied as a function of frequency and temperature. The conductivity exhibits a notable increase with increasing Nb-rates. The low-frequency conductivity results from long-range ordering (close to frequency-independent) and the high-frequency conductivity is attributable to the localized orientation hopping process. Impedance analysis was performed revealing conductivity data which fitted the modified power, σ AC(ω) = Aω n . The frequency dependence of the conductivity plot has been found to obey the universal Jonscher power law. Both AC and DC electrical conductivities are thoroughly studied as a function of frequency as well as temperature. The AC conductivity reveals that correlated barrier hopping (CBH) and non-overlapping small polaron tunneling (NSPT) models are suitable theoretical models to elucidate the conduction mechanisms existing in our compounds. Significantly, by increasing the temperature, the DC conductivity was increased, which verifies the semiconducting nature of the materials.