1. The rare earth ions lie between the disilicate groups and the sheets of octahedra to form (8+3)-coordinated A(1)-polyhedra and 10-coordinated A(2)-polyhedra.
2. The rare earth ions lie between the disilicate groups and the sheets of octahedra to form (8+3)-coordinated A(1)-polyhedra and 10-coordinated A(2)-polyhedra.
