The title compounds are prepared by calcining stoichiometric amounts of Fe2O3, Sb2O3, NH4H2PO4, and SrCO3 or BaCO3 or Pb(NO3)2 in air (staged complex schedule max.

a b s t r a c tThe synthesis and structural study of three new A II (Sb V 0.5 Fe III 0.5 )(PO 4 ) 2 (A]Ba, Sr, Pb) phosphates belonging to the AeSbeFeePeO system were reported here for the first time. Structures of [Ba], [Sr] and [Pb] compounds, obtained by solid state reaction in air atmosphere, were determined at room temperature from X-ray powder diffraction using the Rietveld method. Ba II (Sb V 0.5 Fe III 0.5 )(PO 4 ) 2 features the yavapaiite-type structure, with space group C2/m, Z ¼ 2 and a ¼ 8.1568 (4) Å; b ¼ 5.1996(3) Å c ¼ 7.8290(4) Å; b ¼ 94.53(1) . A II (Sb V 0.5 Fe III 0.5 )(PO 4 ) 2 (A]Sr, Pb) compounds have a distorted yavapaiite structure with space group C2/c, Z ¼ 4 and a ¼ 16.5215(2) Å; b ¼ 5.1891(1) Å c ¼ 8.0489(1) Å; b ¼ 115.70(1) for [Sr]; a ¼ 16.6925(2) Å; b ¼ 5.1832(1) Å c ¼ 8.1215(1) Å; b ¼ 115.03(1) for [Pb]. Raman and Infrared spectroscopic study was used to obtain further structural information about the nature of bonding in selected compositions.

<p class="Mabstract">Three new A^II(Sb_0.5Cr_0.5)(PO₄)₂ (A^II = Ba, Sr, Pb) yavapaiite phases, abbreviated as [ASbCr], have been successfully synthesized by a conventional solid-state reaction in air atmosphere. Their crystal structures have been investigated by Rietveld analysis from the X-ray powder diffraction method. Results show that Ba(Sb_0.5Cr_0.5)(PO₄)₂ crystallizes in monoclinic <em>C</em>2<em>/m</em> space group (Z = 2) with cell parameters a = 8.140(1) Å; b = 5.175(1) Å; c = 7.802(1) Å and β = 94.387(1)°. Structures of A^II(Sb_0.5Cr_0.5)(PO₄)₂ (A^II= Sr, Pb) compounds are comparable, and both crystallize in a distorted yavapaiite structure with <em>C</em>2<em>/c</em> space group (Z = 4). Obtained monoclinic cell parameters are: a = 16.5038(2) Å; b = 5.1632(1) Å; c = 8.0410(1) Å; β = 115.85(1) for [SrSbCr] and a = 16.684(2) Å; b = 5.156(1) Å c = 8.115(1) Å; β = 115.35(1)° for [PbSbCr]. Infrared and Raman spectroscopic study was undertaken to provide information about vibrations bonds within the studied yavapaiite materials.</p>

Synthesis and structural study of the new Ba(NbV 0.50MIII 0.50)(PO4)2 (MIII = Al, Cr, Fe, In) phosphates, abbreviated as [BaNbM], were reported here for the first time. Structures of [BaNbM] compounds, obtained by solid-state reaction in air atmosphere, were determined at room temperature from X-ray powder diffraction using the Rietveld method. The four studied compoundsfeature the yavapaiite-type structure, with space group C2/m ( 3 C2h , N°12) and Z = 2. Their framework can be described as consisting of dense slabs of Nb(M)O6 octahedra and PO4 tetrahedra interconnected via corner-sharing, alternating along the c-axis with layers of Ba cations in ten-fold coordination. Raman and Infrared spectroscopic study were used to obtain further structural information about the nature of bonding in selected compositions. Assignments of Nb-O, M-O and P-O Raman and Infrared bands, in [BaNbM] compounds, were based on those already known in the literature for niobium and phosphates oxides. Some empirical relationships, connecting Raman stretching frequencies to the obtained Nb-O and P-O distance values, were also used for assignments of various Raman bands