Abstract: | 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 Sc1.368Y0.632SiO5, 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. Sc1.368Y0.632SiO5 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. |