Crystal structures of Ca<sub>4+<i>x</i> </sub>Y<sub>3–<i>x</i> </sub>Si<sub>7</sub>O<sub>15+<i>x</i> </sub>N<sub>5–<i>x</i> </sub>(0 ≤ <i>x</i> ≤ 1) comprising of an isolated [Si<sub>7</sub>(O,N)<sub>19</sub>] unit
Acta crystallographica. Section E, Crystallographic communications