Structure of Lu₄Si₂O₇N₂ analyzed by the Rietveld method using the time-of-flight neutron powder diffraction pattern

The crystal structure of a lutetium silicon oxynitride (Lu₄Si₂O₇N₂) was analyzed by the Rietveld method using time-of-flight (TOF) neutron powder diffraction data. The compound crystallizes in a monoclinic cell, space group P2₁/c (No. 14-1) with a = 7.4243(1), b = 10.2728(1), c = 10.6628(1) Å, and β = 109.773(1)° at 297 K. One nitrogen atom in Lu₄Si₂O₇N₂ occupies the bridging site between the two Si atoms, and the other one is statistically situated at the terminal sites of Si₂O₅N₂ ditetrahedra. In the local structure, Si₂O₅N₂ ditetrahedra consist of SiO₃N and SiO₂N₂ tetrahedral units sharing the N atom. Lu atoms are in sixfold, sevenfold (×2) and eightfold coordinations of O/N atoms. X-ray powder diffraction data were also analyzed with the model obtained by the neutron diffraction.