Crystallochemistry and structural studies of two newly CaSb_0.50Fe_1.50(PO₄)₃ and Ca_0.50SbFe(PO₄)₃ Nasicon phases

Abstract

Crystallographic structures of two new orthophosphates Ca0.50SbFe(PO4)3 and CaSb0.50Fe1.50(PO4)3 obtained by conventional solid state reaction techniques at 900 °C, were determined at room temperature from X-ray powder diffraction using Rietveld analysis. The two compounds belong to the Nasicon structural family. The space group is R3 for Ca0.50SbFe(PO4)3 and R3c for CaSb0.50Fe1.50(PO4)3. Hexagonal cell parameters for Ca0.50SbFe(PO4)3 and CaSb0.50Fe1.50(PO4)3 are: a=8.257(1) Å, c=22.276(2) Å, and a=8.514(1) Å, c=21.871(2) Å, respectively. Ca2+ and vacancies in {[Ca0.50]3a[◻0.50]3b}M1SbFe(PO4)3 are ordered within the two positions, 3a and 3b, of M1 sites. Structure refinements show also a quasi-ordered distribution of Sb5+ and Fe3+ ions within the Nasicon framework. Thus, in {[Ca0.50]3a[◻0.50]3b}M1SbFe(PO4)3, each Ca(3a)O6 octahedron shares two faces with two Fe3+O6 octahedra and each vacancy (◻(3b)O6) site is located between two Sb5+O6 octahedra. In [Ca]M1Sb0.50Fe1.50(PO4)3 compound (R3c space group), all M1 sites are occupied by Ca2+ and the Sb5+ and Fe3+ ions are randomly distributed within the Nasicon framework.

A Reitveld quantitative XRD phase-analysis of selected composition of the Sr(0.5+x)Sb(1−x)Fe(1+x)(PO4)3(0 < x < 0.50) system

“…3). It should be noticed that similar results are already obtained in the case of the Ca (0.5+x) Sb (1−x) Fe (1+x) (PO 4 ) 3 (0 ≤ x ≤ 0.50) system [8]. In order to clarify this assumption, a quantitative phaseanalysis using the Rietveld method (RQXRD) of selected compositions of the Sr (0.5+x) Sb (1−x) Fe (1+x) (PO 4 ) 3 system has been undertaken.…”

“…1". Recently, the structural characteristics by powder X-ray diffraction (XRPD) study using the Rietveld method for A 0.50 SbFe(PO 4 ) 3 (R3 space group) and ASb 0.50 Fe 1.50 (PO 4 ) 3 phases (R3c space group) (A = Ca, Sr) were realised [8,9]. In all A 0.50 SbFe(PO 4 ) 3 samples, A 2+ cations occupied principally one-half of the M1 3a sites and the Sb 5+ and Fe 3+ cations are orderly distributed within the SbFe(PO 4 ) 3 framework.…”

“…In the ASb 0.50 Fe 1.50 (PO 4 ) 3 phases, the A 2+ cations are located in the M1 sites whereas the Sb 5+ and Fe 3+ cations are statistically distributed within the Nasicon framework. In the Ca (0.5+x) Sb (1−x) Fe (1+x) (PO 4 ) 3 (0 < x < 0.50) system, a qualitative phase-analysis of the XRPD patterns have clearly shown the absence of a continuously solid solution [8]. In fact, XRD spectra of selected compositions of this system is composed principally of their two end members Ca 0.50 SbFe(PO 4 ) 3 (R3 space group) and CaSb 0.50 Fe 1.50 (PO 4 ) 3 (R3c space group).…”

Preparation, characterization, impedance and thermal expansion studies of Mn0.5MSb(PO4)3 (M=Al, Fe and Cr)

“…An attempt is made to fit these powder XRD patterns using Rietveld analysis. The d-lines of MnASP are similar to that of CaSb 0.5 Fe 1.5 (PO 4 ) 3 [18] and therefore its structural parameters are taken as starting parameters for Rietveld analysis. This analysis gave a reasonable fit to rhombohedral lattice with space group R3c.…”

Structure, infrared and Raman spectroscopic studies of newly synthetic AII(SbV0.50FeIII0.50)(PO4)2 (ABa, Sr, Pb) phosphates with yavapaiite structure

“…Indeed analysis of the obtained XRD pattern shows principally the presence of a mixture of the already known Ca 0.50 SbFe(PO 4 ) 3 Nasicon phase and two Ca 2 P 2 O 7 (PDF number 81-2257) and SbOPO 4 (PDF number 84-830) phosphates which are identified as minority phases[16,34,35]. Our experimental result shows that [Sb 0.5 Fe 0.5 (PO 4 ) 2 ] 2À yavapaiite framework appears well adapted to bigger Sr 2þ , Pb 2þ and Ba 2þ cations.…”