Structural and spectroscopic investigation of lanthanum-substituted strontium-oxybritholites

Abstract

Lanthanum-substituted strontium-oxybritholites, Sr 10-x La x (PO 4 ) 6-x (SiO 4 ) x O with x = 0, 2 and 4, prepared by solid state reaction were investigated by chemical analysis, powder X-ray diffraction, Raman and 29 Si MAS NMR spectroscopies. The refinements of powder XRD patterns of the substituted compounds by the Rietveld method showed that the lanthanum occupied the two metal sites, i.e. (4f) and (6h) sites into the apatite structure, with a clear preference for the (6h) sites. A progressive shift of the free oxygen O(4) towards the centre of the triangles formed by the metal-atoms in the (6h) positions was observed when the lanthanum content increased. It led to the formation of a Sr/La(2)-O(4) strong bond, which might have increased the stability of these compounds. The bands of Raman spectra were assigned to the vibration modes of PO 4 and SiO 4 groups. The comparison of the results of 29 Si MAS NMR analysis with those obtained with the 31 P previously reported, suggested that both species occupied the same crystallographic sites.

Mechanochemical synthesis and ionic conductivity of lanthanum phosphosilicate oxyapatites

“…The explanation of the effect of substitution on the a-axis is not as obvious because of the different sizes of the substituted ions. The comparison of the obtained parameter values with those determined by K. Boughzala for the same compounds, prepared at high temperature [37],…”

Anhydrous Europium Phosphates: A Comprehensive Report on Syntheses, Crystal Structures, and Phase Relations

“…The mixed‐valent europium(II,III) oxide phosphate is structurally related to Eu II 5 (PO 4 ) 3 X ( X = F, Cl, OH), Ca II 10 (PO 4 ) 6 O, and Sr II 10 (PO 4 ) 6 O [ a = 9.750(4) Å, c = 7.278(3) Å] . Its lattice parameters are slightly smaller than those of strontium(II) oxide phosphate.…”

“…Along the zone axis 0 0 l no intensity outside the Bragg reflections due to structure modulation was observed, pointing to a rather random disorder. We assume a similar disorder as in Sr II 10 (PO 4 ) 6 O but with a higher occupancy for the corresponding oxygen atom to compensate the additional charge per formula unit due to the incorporation of Eu 3+ at the expense of Eu 2+ [according to Eu II 10– x Eu III x (PO 4 ) 6 O 1+ x /2 ]. Despite this uncertainty, the simulation of the XRPD pattern (Figure ) based on the structure model from SXRD matches the observed pattern nicely.…”

Synthesis, Rietveld refinements and electrical conductivity of news fluorobritholite based on lead Ca7-xPbxLa3(PO4)3(SiO4)3F2 (0 ≤ x ≤ 2)

“…Several studies have analyzed the occupancy of lanthanide ions between the two crystallographic sites in the apatitic structure. Several works indicate that the La atoms are distributed between the two crystallographic sites M(1) and M(2) in apatite structure, with a clear preference for the larger site M(2), demonstrating that the nature of the channel anion plays a significant role in the distribution of La 3+ between the two cationic sites [25,26]. Furthermore, Ardhaoui et al [27,28] indicated that the introduction of La 3+ in the apatite structure has a strong influence on its stability.…”