Eskolaite

Abstract: This contribution reports for the first time on the synthesis and the main physical properties of single-phase pure α-Cr2O3 nanoparticles synthesized by a facile, rapid and eco-friendly process using Callistemon viminalis flower's extract as an effective oxidizing/reducing agent. These crystalline nanoparticles exhibit a cubic-like platelet shape with sharp edges with an average particle diagonal size of ∼92.2 nm. The room temperature physical properties of these pure highly crystalline Eskolaite α-Cr2O3 nanoparticles were carried out using complementary techniques such as high-resolution transmission electron microscopy (HRTEM), energy-dispersive X-ray spectroscopy (EDS), XRD, FTIR-ATR, Raman and XPS.

Abstract: The best known cause for colors in insulating minerals is due to transition metal ions as impurities. As an example, Cr3+ is responsible for the red color of ruby (α-Al2O3:Cr3+) and the green color of eskolaite (α-Cr2O3). Using X-ray absorption measurements, we connect the colors of the Cr x Al2−x O3 series with the structural and electronic local environment around Cr. UV–VIS electronic parameters, such as the crystal field and the Racah parameter B, are related to those deduced from the analysis of the isotropic and XMCD spectra at the Cr L2,3-edges in Cr0.07Al1.93O3 and eskolaite. The Cr–O bond lengths are extracted by EXAFS at the Cr K-edge in the whole Cr x Al2−x O3 (0.07≤x< 2) solid solution series. The variation of the mean Cr–O distance between Cr0.07Al1.93O3 and α-Cr2O3 is evaluated to be 0.015 A (≈1%). The variation of the crystal field in the Cr x Al2−x O3 series is discussed in relation with the variation of the averaged Cr–O distances.