Abstract
This contribution deals with the synthesis, properties and investigation of the field of solid solutions formed between the three end-members of apatite-type alkaline earth element-yttrium-silicate oxybritholites with the hexagonal structure (P63/m). The stoichiometric composition of these compounds corresponds to the formula AEEδY10−δ(SiO4)6O3−0.5δ, where AEE=Ca, Sr and Ba and parameter δ→2. These compounds and their solid solutions crystallize from non-equilibrium high temperature flux as the main product of sinter-crystallization process. Increasing ionic radius of AEE cations has significant effect to the lattice parameters, properties and miscibility of apatite phases. While there is non-limited miscibility of solid solutions formed between Ca2Y8[SiO4]6O2 and Sr2Y8[SiO4]6O2, the highest content of barium in the binary solution with these species is limited to 28% and 38%, respectively. The connecting line of these points marks out the borderline for the field of solid solutions in the ternary system. All attempts for the preparation of pure Ba2Y8[SiO4]6O2 end-member via the ceramic method were not successful.
Highlights
Apatite is the most abundant phosphate mineral, which accounts for more than 95% of total phosphorus (P is the tenth most abundant element on Earth) in the Earth's crust [1]
The course of synthesis of AEE apatite-type yttrium silicate phases during thermal treatment was investigated by TG–DTA and EGA (SDT Q600, Thermal Instruments connected with the measuring cell (FTIR-TGA interface) of infrared spectrometer iS10, Thermo Scientific via steel capillary). 30 mg of sample was inserted into alumina cup heated in air (100 cm3 minÀ1 free of CO2 and water vapor) with the rate of 10 1C minÀ1
The end-member phases in the investigated ternary diagram of alkaline earth element-yttrium-silicate oxybritholite system (Fig. 2(a), samples S1, S2 and SiO4]3O3À0.5δ analog (S3)) have stoichiometric composition given by the formula AEEδY10Àδ(SiO4)6O3À0.5δ, where AEE 1⁄4 Ca, Sr and Ba and δ-2
Summary
Acid, etc.) and food production (production of phosphate fertilizers) [2]. apatites and their synthetic analogs represent a major class of ionic compounds [3] of interest to many disciplines including medical and biomaterials sciences [4,5,6,7,8,9,10], geology [11], cosmology [3], environmental [12] and nuclear sciences [3], preparation of apatite phosphors [13], pigments [14] catalysts in organic synthesis [15] and magnetooptical materials [16]. In the previous work [34], the synthesis, properties and the role of non-equilibrium flux formed during the sintercrystallization process of SrY4(SiO4)3O (or by “double formula” the Sr2Y8(SiO4)6O2) oxyapatite phase was described This contribution deals with the preparation, properties and examination of the field of solid solutions miscibility between three end-members of alkaline earth element-yttrium-silicate phases (AEEδY10Àδ(SiO4)6O3À0.5δ, where AEE 1⁄4 Ca, Sr and Ba and the value of δ-2). Investigated by the methods of thermal analysis, X-ray diffraction analysis, infrared spectroscopy and electron microscopy These results were used for the definition of range of miscibility region of ternary solid solutions and for the investigation of effect of AEE2þ cation on the system stoichiometry, i.e. the variation of parameter δ in the formula of apatite unit and the lattice parameters
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