Yuan Yao, Kloß Simon D, Attfield J Paul
Centre for Science at Extreme Conditions and School of Chemistry, University of Edinburgh, Peter Guthrie Tait Road, Edinburgh EH9 3FD, UK.
Department of Chemistry, Ludwig-Maximilians-Universität München, Butenandtstraße 5-13, Munich 81377, Germany.
Philos Trans A Math Phys Eng Sci. 2023 Oct 16;381(2258):20220329. doi: 10.1098/rsta.2022.0329. Epub 2023 Aug 28.
Sodium azide (NaN) is a versatile nitrogen source that can be used for the synthesis of new nitrides under high-pressure and temperature conditions. Reactions between lanthanum nitride (LaN) and sodium azide (NaN) at 800°C under 8 GPa pressure have led to the discovery of two defect rocksalt phases which are the first reported ternaries in the La-Na-N system. Preliminary structure assignments have been made based on fits to powder X-ray diffraction profiles. One phase is LaNaN with vacancies at octahedral La sites and interstitial tetrahedral Na cations. This phase has a tetragonally distorted rocksalt structure (space group 4[Formula: see text], = 3.8704(2) and = 5.2098(3) Å for nominal = 0.10) and the distortion decreases with increasing Na content (space group 4[Formula: see text], = 3.8060(2) Å, = 5.2470(3) Å for nominal = 0.14), further giving a cubic phase ( = 5.3055(2) Å) for nominal = 0.25. This coexists with another cubic [Formula: see text] phase ( = 5.1561 (5) Å), tentatively identified as rocksalt 'NaN' stabilized by a small amount of La; NaLaN with ≈ 1%. These initial investigations reveal that the high-pressure La-Na-N phase diagram may be rich in defect rocksalt-type materials although further work using neutron diffraction will be needed to confirm the structures. This article is part of the theme issue 'Exploring the length scales, timescales and chemistry of challenging materials (Part 1)'.
叠氮化钠（NaN₃）是一种用途广泛的氮源，可用于在高温高压条件下合成新的氮化物。在8吉帕压力和800°C下，氮化镧（LaN）与叠氮化钠（NaN₃）之间的反应导致发现了两种缺陷岩盐相，这是La-Na-N体系中首次报道的三元化合物。已根据粉末X射线衍射图谱的拟合结果进行了初步的结构归属。其中一个相是LaNaN₃，八面体La位点有空位，间隙有四面体Na阳离子。该相具有四方畸变的岩盐结构（空间群I4/mcm，对于标称x = 0.10，a = 3.8704(2) Å和c = 5.2098(3) Å），并且畸变随着Na含量的增加而减小（空间群I4/mcm，对于标称x = 0.14，a = 3.8060(2) Å，c = 5.2470(3) Å），对于标称x = 0.25进一步形成立方相（a = 5.3055(2) Å）。它与另一个立方相（a = 5.1561(5) Å）共存，初步鉴定为少量La稳定的岩盐“NaN₃”；NaLaN₃中La含量约为1%。这些初步研究表明，高压La-Na-N相图可能富含缺陷岩盐型材料，尽管需要使用中子衍射进行进一步的工作来确认结构。本文是主题为“探索具有挑战性材料的长度尺度、时间尺度和化学性质（第1部分）”的一部分。
