ИСТИНА

Aluminum takes the first place among metals and the third place among the elements after oxygen and silicon by the prevalence in the Earth's crust. The concentration of aluminum in the Earth's crust, according to various researchers, reaches 16.4 wt. %. Aluminates may be the hosts of aluminum under the conditions of the transition zone and lower mantle of the Earth. Experiment on synthesis of the phases in the Ca-Al-O (±Fe) system were carried out using a high pressure - high temperature 1000-t multi-anvil Sumitomo press and 1200-t multi-anvil Haymag press at Bayerisches Geoinstitute (BGI). The phases of CaAl2O4, Ca2Al6O11 and Ca(Al,Fe)2O4 were synthesized at 1600°C and 15, 24 GPa, respectively. The method of single-crystal X-Ray diffraction allowed us to refine the structures and to determine the crystal chemical formulae of the phases. All studied phases with the stoichiometry AB2O4 have the CaFe2O4-type structure. The structures of the synthesized phases were refined by the method of single-crystal X-Ray diffraction using synchrotron radiation. The compressibility of the Ca(Al,Fe)2O4 phase was studied up to ~60 GPa.