Biryukov Yaroslav P, Zinnatullin Almaz L, Levashova Irina O, Shablinskii Andrey P, Bubnova Rimma S, Vagizov Farit G, Ugolkov Valery L, Filatov Stanislav K, Pekov Igor V
Institute of Silicate Chemistry of the Russian Academy of Sciences (ISC RAS), Makarova Emb., 2, Saint Petersburg, 199034, Russian Federation.
Institute of Physics, Kazan Federal University, Kremlyovskaya Str., 18, Kazan, 420008, Russian Federation.
Acta Crystallogr B Struct Sci Cryst Eng Mater. 2023 Oct 1;79(Pt 5):368-379. doi: 10.1107/S2052520623006455. Epub 2023 Aug 17.
This paper reports an investigation of the chemistry, crystal structure refinement and thermal behavior (80-1650 K) of ludwigite from the Iten'yurginskoe deposit (Eastern Chukotka, Russia). Its chemical composition was determined by electron microprobe analysis, giving an empirical formula (MgFeMn)(FeAlMg)O(BO). A refinement of the crystal structure from single-crystal X-ray diffraction data (SCXRD) was provided for the first time for ludwigite from this deposit (R = 0.047). The structure can be described as a framework composed of [MO] octahedra and isolated [BO] triangles located in triangular interstices of the framework. Based on a comprehensive analysis of SCXRD and Mössbauer spectroscopy data, the M1 site is occupied by Mg, M2 and M3 by Mg and Fe, M4 by Fe, Mg and Al. There are also oxo-centered [O4M] and [O2M] polyhedra building up a framework with the [BO] triangles located in its hexagonal interstices. No indications of magnetic ordering are found in the temperature range investigated. The Fe → Fe oxidation occurs above 600 K, and is accompanied by a decrease of the unit-cell parameters and subsequent incomplete solid-phase decomposition with the formation of hematite, warwickite and magnetite. The mineral melts at temperatures above 1582 K. The thermal expansion of ludwigite is slightly anisotropic, which is explained by a dense packing of the [MO] octahedra as well as a virtually perpendicular orientation of the oxo-centered double chains to each other. At room temperature, maximum expansion is along the c axis (α = 9.1 × 10 K) and minimum expansion is in the ab plane (α = 8.6 × 10, α = 7.6 × 10 K), which is due to the preferred orientation of the [BO] triangles. A comparison of the thermal behavior of three oxoborates of the ludwigite group, namely azoproite (Mg,Fe)(Fe,Ti,Mg,Al)O(BO), vonsenite (Fe,Mg)(Fe,Mn,Sn,Al)O(BO) and ludwigite (MgFeMn)(FeAlMg)O(BO), is provided.
本文报道了对俄罗斯楚科奇东部伊滕尤尔金斯克矿床硼铁矿的化学性质、晶体结构精修及热行为（80 - 1650 K）的研究。通过电子微探针分析确定了其化学成分，得出经验式为(MgFeMn)(FeAlMg)O(BO)。首次对该矿床的硼铁矿进行了基于单晶X射线衍射数据（SCXRD）的晶体结构精修（R = 0.047）。该结构可描述为由[MO]八面体和位于骨架三角形间隙中的孤立[BO]三角形组成的骨架。基于对SCXRD和穆斯堡尔谱数据的综合分析，M1位点由Mg占据，M2和M3由Mg和Fe占据，M4由Fe、Mg和Al占据。还有以氧为中心的[O4M]和[O2M]多面体构成一个骨架，[BO]三角形位于其六边形间隙中。在所研究的温度范围内未发现磁有序迹象。Fe→Fe氧化在600 K以上发生，并伴随着晶胞参数减小以及随后不完全的固相分解，形成赤铁矿、硼镁铁矿和磁铁矿。该矿物在1582 K以上温度熔化。硼铁矿的热膨胀略有各向异性，这是由[MO]八面体的紧密堆积以及以氧为中心的双链彼此几乎垂直的取向所解释。在室温下，最大膨胀沿c轴（α = 9.1×10 K），最小膨胀在ab平面（α = 8.6×10，α = 7.6×10 K），这是由于[BO]三角形的择优取向。还对硼铁矿族的三种氧硼酸盐，即偶氮硼镁石(Mg,Fe)(Fe,Ti,Mg,Al)O(BO)、硼镁锰矿(Fe,Mg)(Fe,Mn,Sn,Al)O(BO)和硼铁矿(MgFeMn)(FeAlMg)O(BO)的热行为进行了比较。
