Structural, surface analysis, vibrational and optical properties of inorganic yavapaiite compounds Ba(MFe) 0.5 (PO 4 ) 2 (M: Nb, Sb)

This paper reports on synthesis, structural, Raman-Infrared spectroscopic, and optical properties of Ba(FeM)0.5(PO4)2 (M: Nb, Sb) abbreviated as [BN] and [BS]. The two phases, refined from XRD diffraction by the Rietveld method, crystallise in the monoclinic yavapaiite structure of C2/m Space group (Z = 2). Their structure type consists of layers, arranged along (a, b) plane, and built up of corner-connected Fe(Nb/Sb)O6 octahedra and PO43- tetrahedra. Theoretical group analysis considering Cs-site symmetry of PO43- groups as in [BN] and [BS] phases. A comparative discussion of observed bands is improved based on other yavapaiite materials. Direct gap energies, 3.51 eV [BN] and 3.45 eV [BS], suggest these samples as semiconducting materials. The electric σel(λ) and optical σop(λ) conductivities present two maxima below 400 nm, and then decrease in the visible range. The weak permittivity and conductivity observed above 400 nm indicate excellent dielectric characteristics in (400–800 nm) range. The Metallisation criteria (M < 1) indicated the non-metallic behaviour, which suggests that these compounds are promising materials in catalysis and optoelectronic applications.