Abstract. Qualitative XRD phase-analysis of four (x = 0.10, 0.20, 0.30, 0.40) selected compositions of the Sr (0.5+x) Sb (1−x) Fe (1+x) (PO 4 ) 3 (0 < x < 0.50) system was undertaken. XRD data shows the absence of a continuously solid solution. In fact, each composition is composed only of a mixture of the two end members, Sr 0.50 SbFe(PO 4 ) 3 (R3 space group) and SrSb 0.50 Fe 1.50 (PO 4 ) 3 (R3c space group), type-phases. Rietveld refinement method, using the XRPD technique, has been used for a quantitative phase-analysis of these compositions. In order to evaluate the relative errors of this experimental result, a set of standard phase-mixtures of both end compositions of the system was also quantified by the Rietveld method. Obtained results show the usefulness of this method for quantitative phase-analysis, particularly in geology including other classes of materials such clay and cement.

<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>