Effect of Fe3+-doped Ca12Al14O33 cement on optical and thermal properties

Abstract

This study aims to investigate the effect Fe ions doped into Ca12Al14O33 (C12A7, 12CaO-7Al2O3) cement compound on its thermal and optical properties. Polycrystalline samples of Ca12Al14−xFexO33 (where x = 0.0, 0.5, and 1.0) were prepared via a solid state reaction in an oxygen atmosphere. The lattice constant of Ca12Al14O33 determined using an XRD technique was in excellent agreement with first-principles calculations. With increasing Fe concentrations, the lattice constants were found to have increased. Additionally, the optical gaps of Ca12Al14−xFexO33, (x = 0, 0.25, 0.5, and 1.0) were 3.9 eV, 3.77 eV, 3.75 eV and 3.63 eV, respectively. It was clearly seen that the optical gap decreased with increasing Fe concentrations. As revealing by first-principles calculations, the optical gap was directly related to the electronic transition from the occupied electronic state of extra-framework O2− ions (as free O2− ions inside nano-cage) to the conduction band. Moreover, we also found that the thermal conductivity Ca12Al14−xFexO33 was reduced when the larger atomic mass and atomic radii Fe was substituted into Al sites. Hence, this indicated that Fe3+-substitution into Al3+ sites of Ca12Al14O33 cement directly affected both its optical gap and thermal conductivity.