Single crystals of the nitridosilicate Ca0.27La0.03Si11.38Al0.62N16 with a filled alpha-Si3N4-type structure were obtained when preparing lanthanum nitridosilicates in a graphite furnace accidentally containing calcium residues. The lithium alpha-SiAlON LiSi9Al3O2N14 was prepared using spark plasma sintering, with the sample containing in addition a beta-SiALON, LiAlSiO4, and a glass phase. The structure of Ca0.27La0.03Si11.38Al0.62N16 was refined using MoKot single-crystal data, in space group P31c with a = 7.838(1), c = 5.703(1) Angstrom, V = 303.4 Angstrom(3), to a weighted R(F-obs(2)) = 6.0% for 475 unique reflections. The isotypic structure of LiSi9Al3O2N14 was refined with anisotropic pie thermal parameters and a = 7.8277(2), c = 5.6909(2) Angstrom to R, = 0.63% for 849 reflections for d greater than or equal to 0.5 using time-of-flight (TOF) neutron powder diffraction (NPD) data. The SiX4 (X = N or N/O) tetrahedra are regular in both structures, with Si-N distances of 1.745(1) - 1.785(3) Angstrom for the calcium-lanthanum compound and 1.741(1) - 1.765(1) Angstrom for the lithium compound. The Ca/La and lithium atoms are located on the 2b position, (1/3, 2/3, z), coordinated by seven anions with the shortest metal-anion distances of 2.38(1) and 2.05(2) Angstrom, respectively. The lithium atoms are displaced similar to0.28 Angstrom relative to the position of the Ca/La atoms, and the lithium atoms can alternatively be described as tetrahedrally coordinated.