Innovative structural and optical insights into synthesized BaTi(1-2x)SbxCrx(PO4)2 (0 ≤ x ≤ 0.5) yavapaiite phases

A series of yavapaiite-type phosphates BaTi(1-2x)SbxCrx(PO4)2 (0 <= x <= 0.5), was synthesized via solid-state reactions across divers fractions x, and studied by X-ray diffraction, Infrared, Raman UV-visible, and color (CIEL*a*b*) analyses. These compounds crystallize too in the monoclinic space group C2/m (Z = 2), with yavapaiite structure type and comparable units' cell parameters. The structure type consists of layers, arranged parallel to (a, b) plane, and formed by corner-connected Ti(Sb/Cr)O6 octahedra and PO43- tetrahedra groups. Rietveld refinements showed that the substitution of Ti4+ by Sb5+ and Cr3+ cations did not change the yavapaiite crystal structure symmetry, lattice parameters, bond lengths, and angles in studied (0 <= x <= 0.5) compositions. Specifically, the parameters increase very slightly as x increased from 0 to 0.5 without changing the yavapaiite structure-type. The SEM-EDX high-resolution images showed the formation of divers agglomerated particles with grain boundary and different sizes, and confirmed the presence of expected elements for all studied compositions (0 <= x <= 0.5). Hirshfeld surface and Fringplots analyses made on BaTi(PO4)2 crystal structure (x = 0), highlited that Ba center dot center dot center dot O/O center dot center dot center dot Ba (39.5 %) and O center dot center dot center dot O (32.1 %) are the important intercontacts contributors in the BaTi(PO4)2 crystal packing. Infrared and Raman spectra recorded at room temperature revealed characteristic bands of the PO43- tetrahedra groups, with slight changes in frequencies positions and intensities with varying the x fractions. The UV-visible absorption spectra showed the effect of Sb/Cr substitution on the optical band gap. Direct band gap values are estimated at 3.62 eV for (x = 0) and around 2.64 eV for (x = 0.1-0.5), indicating a semiconducting behavior of the substituted materials in the studied composition range. The partial substitution of Ti4+ with Sb5+/Cr3+ affects the optical properties of BaTi(1-2x)SbxCrx(PO4)2 (0 <= x <= 0.5) in the way that modifying the Sb/Cr content can remarkably reduce the optical band gap.