The Band Gap of BaPrO₃ Studied by Optical and Electrical Methods

Abstract

We report on measurements of the electrical and optical properties of BaPrO3. The temperature dependences of the electrical conductivity σ and the Seebeck coefficient α of polycrystalline samples were studied over a wide temperature range (300°C–1050°C). At lower temperatures, the observed charge transport can be described as thermally activated hopping of electron‐based small polarons with an activation energy of 0.37 eV. An observed change in temperature dependence of both σ and α around 700°C was observed and interpreted as a transition from extrinsic to intrinsic carrier transport. The intrinsic conduction can be modeled with an apparent electrical band gap of ~2 eV. Optical absorption and emission spectroscopy in the UV–VIS–NIR range revealed a series of characteristic absorption thresholds and the type of optical transitions was identified by combining transmittance and diffuse‐reflectance spectroscopy methods. An absorption edge of indirect type with onset at 0.6 eV is attributed to small polaron effects. The higher lying absorption thresholds of direct origin positioned at around 1.8 and 3.8 eV are correlated with thermal activation parameters from electrical measurements and discussed in terms of the band gap of BaPrO3.

Toward Zero-Strain Mixed Conductors: Anomalously Low Redox Coefficients of Chemical Expansion in Praseodymium-Oxide Perovskites

“…The calculated changes in conductivity from redox reactions were applied to the respective Arrhenius plots, and this adjustment resulted in less than 4% change in the calculated activation energies for both samples; this change is within the error of experimental measurements and is considered negligible. Second, intrinsic carrier generation was ruled out because the observed activation energies were significantly lower than half the expected band gaps: for undoped BPO, the gap has been reported to be about 2 eV 74 and undoped PGO is predicted to have a band gap >3 eV by first-principles DFT calculations, 75 in agreement with calculations made in this work. Further, considering the simulations in the present work, since O-2p holes are expected to form in both materials, PGM and BPY would be more appropriately described by using high U values.…”

Dielectric Properties of Compacts Sintered after High-Pressure Forming of Lithium Fluoride

“…Usually, the optical band gap is higher than the electrical band gap [15], most typically four times higher [16]. Here, in case of LiF 700-2, the optical gap is 3.65 eV, and the electrical gap is 0.277 eV at room temperature.…”