Structural, vibrational, and optical studies of newly synthesized Yavapaiite-type phases BaSb2/3X1/3(PO4)2 (X = Mn, Co, Cu, Zn)

The synthesis and structural characterization of four newly synthesized phosphates, BaSb2/3X1/3(PO4)2 phases where X represents Mn, Co, Cu, and Zn, are presented here for the first time. These BaSb2/3X1/3(PO4)2 phases, denoted as [BaSbMn], [BaSbCo], [BaSbCu], and [BaSbZn], were prepared by a solid-state reaction at 900 degrees C in air atmosphere. The crystal structures of these [BaSbX] materials were investigated using Rietveld analysis based on conventional X-ray powder diffraction. The structural analysis revealed that all four compounds are isostructural, exhibiting the Yavapaiite-type structure with a monoclinic C2/m space group. Raman and infrared spectroscopy were employed to elucidate the bonding characteristics within the [BaSbX] phases. UV-vis-NIR spectroscopy provided insights into the electronic properties of the compounds, revealing charge transfer and dd transitions in Mn2+, Co2+, and Cu2+ ions. In contrast, Zn2+ exhibited full d orbitals. The absorption spectra revealed UV bands indicative of charge transfer, with optical bandgap values spanning from 3.8 eV to 4.6 eV. This range signifies a distinctive semiconducting property inherent in the synthesized materials. Analysis of the Urbach tails revealed the presence of localized states, with lower values indicating higher crystallinity, giving valuable insights into the electronic behavior of the compounds.