Structural, morphological, Infrared-Raman, and UV studies of three yavapaiite phosphates Ba(SbV0.5MIII0.5)(PO4)2 (M: Sc, In, Yb)

Abstract

Three novel phosphates Ba(Sb_0.5M^III_0.5)(PO₄)₂ (M^III: Sc, In, Yb), denoted [BaSbM], were synthesized by solid-state reactions method. X-ray powder diffraction data refined by the Rietveld method showed that these compounds crystallize at room temperature in isotopic yavapaiite structures of C2/m (Z = 2) space group, consisting of three polyhedra types, BaO₁₀, tetrahedral anions PO₄³⁻ and Sb(M)O₆. The two last groups are corner-sharing and alternating along c-axis with Ba cations layers, in ten-fold coordination (6 + 4) with six short [2 × Ba–O(1), 4 × Ba–O(3)] and four long [Ba–O(1)] lengths. The relationships between compositions and [BaSbM] parameters showed linear increasing of (b, c), due to progressive increasing of <Ba–O> and <Sb(M)–O> distances with M³⁺ radii. The unit’s volume variation related to b/c parametres is slightly influenced by β angle distortion held between [BaSbIn] and [BaSbYb] phases. Surfaces morphology and chemical compositions of [BaSbSc] and [BaSbIn] are studied by SEM-EDX techniques. SEM-EDX mapping images highlited dispersion homogeneity and composition elements importance for [BaSbSc] phase. The BFDH crystal morphology predicted for [BaSbSc] gives hight facets (h k l) with their center-to-plane distance d_hkl and morphological importance (MI). The Raman-Infrared study is developped to obtain more information on bond’s nature in phases [BaSbSc] and [BaSbIn] regarding other yavapaiite materials. The bands assignment is made based on vibrational modes analysis considering C_s site symmetry of PO₄³⁻ groups. The UV–visible direct and indirect optical gap energies varying in 3.15–3.55 eV, suggesting thee three phases as semi-conducting materials.