Insight into OLPT model conduction mechanism and dielectric relaxation of lead borate glass containing Cr and Ge ions

Lead borate glass with compositions 25B 2 O 3 –73.8PbO– x GeO 2 -(1.2 − x ) Cr 2 O 3 ( x ≤ 1.2 mol. %) is fabricated by the melt quenching procedure. The electrical conductivities ( σ dc , σ ac ) of fresh samples are measured in the frequency range 100 Hz–1.0 MHz and temperature range 303–393 K. The anomalous behavior observed in the dc activation energy at x = 0.6 mol% is argued to the formation of bridging and non-bridging oxygen bonds. These bonds are formed due to substitution of GeO 2 to the expense of Cr 2 O 3 ions in the PbO–B 2 O 3 network. The dependence of ac conductivity on frequency is analyzed through the power law: σ ac α ω s where s ≤ 1.0. The experimental results of s for the considered samples have shown that overlapping large polaron tunneling (OLPT) is the possible conduction model in the considered frequency and temperature ranges. The strength of the OLPT model established on the normal Mayer–Neldel (MN) rule is analyzed and discussed. Furthermore, results of the real and imaginary dielectric constant composed with Cole–Cole diagrams for investigated samples are presented and discussed.