Wet chemical synthesis of La9.83−xSrxSi6O26+δ (0≤x≤0.50) powders, characterization of intermediate and final products

In this paper we reported the preparation and extensive characterization of La9.83−xSrxSi6O26+δ (0≤x≤0.50) precursors, intermediate and final products. The sintering reactions, the phase formation, the structure as well as the powders' morphology were studied by means of thermogravimetric analysis, X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). Moreover, the effect of stoichiometry on precursor's structure and morphology as well as on intermediate and final products was reported. As was concluded pure La9.83Si6O26+δ, La9.38Sr0.45Si6O26+δ and La9.33Sr0.50Si6O26+δ could be prepared after sintering at 1400 °C for 20 h while La9.68Sr0.15Si6O26+δ and La9.53Sr0.30Si6O26+δ compounds contained minor traces (<3.5%) of La2Si2O7 secondary phase. Concerning the synthesis, there have been no previous reports on the preparation of pure La9.83Si6O26+δ, La9.38Sr0.45Si6O26+δ and La9.33Sr0.50Si6O26+δ compounds. The final powders consisted of spherical particles and an increase of Sr content seemed to inhibit sintering phenomena. The existence of interstitial oxygen at intermediate crystallographic positions of apatite structure had great effect on SiO4 sub-structure distortion. The increase of Sr content led to a major reduction of interstitial oxygen quantity and the refutation of silicon tetrahedron distortion.

Graphical AbstractSingle phase apatite type lanthanum silicates (ATLS), La9.83–xSrxSi6O26+δ (0≤x≤0.50), were prepared after sintering at 1400 °C for 20 h (the final powders consist of spherical particles and an increase of Sr content seems to inhibit sintering phenomena)Figure optionsDownload full-size imageDownload as PowerPoint slide