Interstitial oxide positions in oxygen-excess oxy-apatites

Preparation of aluminium lanthanum oxyapatite tapes, La10AlSi5O26.5, by tape casting and reaction sintering

“…Selected parts of the La 10 AlSi 5 O 26.5 tapes with the best properties (M-34-U2-10BP and M-34-U2-20BP), were grinded and their powder patterns were analyzed by the Rietveld method using the structural descriptions previously reported. 27 The occupation factors for lanthanum, silicon and aluminium sites were conveniently modified to describe the nominal stoichiometry. Only the overall parameters (histogram scale factor, background coefficients, unit cell parameters, zero-shift error, and peak shape pseudo-Voigt coefficients) and weight fractions of side phases (if necessary) were refined.…”

Electrical properties of Al-doped oxyapatites at intermediate temperature

“…As far as the conductivity mechanism in Al-doped oxyapatites is concerned, lowering charge on the tetrahedral sites in oxyapatites was already pointed out in literatures [8,22,23] implying local distortion of the SiO 4 tetrahedral group and thus greatly affecting the oxide migration. Several studies consider that migration of interstitial oxygen O i is the major mechanism for ionic conductivity [9,[24][25][26][27].…”

The structure and texture genesis of apatite-type lanthanum silicates during their synthesis by co-precipitation

“…Numerous studies of structure and transport properties of these compounds demonstrated that their high ion conductivity is associated with the presence of cation vacancies and/or interstitial oxygen atoms in the hexagonal apatite structure, while the structure tolerance to isomorphous substitutions allows to vary the density of defects and, thus, to modify their transport properties [17][18][19][20][21][22][23][24][25][26][27]. Both lanthanum substitution and especially doping on the silicon site with lower valence cations (Ga 3+ , Al 3+ , Fe 3+ ) help to increase the oxygen ion conductivity of apatite-type lanthanum silicates making them promising as solid electrolytes for intermediate temperature SOFCs [18,[23][24][25][26].…”

“…The conventional method of apatite-type rare-earth silicates preparation is high-temperature solid-phase synthesis [3,5,7,12,[14][15][16][17][18][19][20][21][22][23][24][25]. However, this method does not allow controlling textural characteristics and spatial uniformity of chemical and phase composition of produced silicates playing a crucial role in performance of functional ceramics, phosphor materials as well as bulk or supported catalysts.…”