The crystal structure of new quantum memory-storage material Sc_1.368Y_0.632SiO₅

Monoisotopic scandium yttrium oxyorthosilicate crystals as a material for quantum memory storage with high optical quality were grown by the Czochralski method. This material, of composition Sc_1.368Y_0.632SiO₅, is characterized by congruent melting and a melting point 60 K below the temperature for the ideal solid-solution series Y₂SiO₅-Sc₂SiO₅. The structure of the crystals was refined on the basis of high-quality single-crystal X-ray diffraction data. Sc_1.368Y_0.632SiO₅ belongs to B-type RE₂SiO₅ (space group C2/c). Scandium and yttrium cations are distributed among two 8f sites with coordination numbers 7 and 6 for which the occupancy parameters ratios Sc:Y and average bond lengths are, respectively, 0.473:0.527 and RE1-O = 2.305 (2) Å, and 0.895:0.105 and RE2-O = 2.143 (2) Å. It is shown that the character of the occupancy of the positions of the cations with coordination numbers (CN) 6 and 7 for these solid solutions can be approximated by a polynomial dependence, the magnitude of the coefficients of which depends on the difference in the ionic radii of the cations. A preliminary electron paramagnetic resonance (EPR) study shows that activator ions with a large ionic radius at a concentration less than 0.1% occupy a position with CN = 7.