Localization of Small Impurities of Water and Carbon Dioxide in Channels of the Structure of Natural Cordierite
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zation of Small Impurities of Water and Carbon Dioxide in Channels of the Structure of Natural Cordierite A. P. Dudkaa, *, M. A. Belyanchikovb, V. G. Thomasc, Z. V. Bedranb, and B. P. Gorshunovb aShubnikov
Institute of Crystallography, Federal Scientific Research Centre “Crystallography and Photonics”, Russian Academy of Sciences, Moscow, 119333 Russia b Moscow Institute of Physics and Technology, Dolgoprudny, Moscow oblast, 141701 Russia c Institute of Geology and Mineralogy, Russian Academy of Sciences, Novosibirsk, 630090 Russia *e-mail: [email protected] Received January 28, 2020; revised February 17, 2020; accepted February 20, 2020
Abstract—An accurate X-ray diffraction study of cordierite mineral, the simplified chemical formula of which is Mg2Al4Si5O18, is performed. The main octahedral position contains magnesium, iron, and aluminum ions, as well as traces of manganese. Alkaline cations are localized within large channels formed by six AlO4 and SiO4 tetrahedra at the level z = 0. Water and carbon-dioxide molecules are located within the same vertical channels as sodium ions but at the level z = 1/4; they alternate from one cell to another. The CO2 molecule is elongated along the a axis of the cell and rotates around the central carbon atom (0, 0, 0.25) by an angle of ~10°. Several orientations of the water molecule are observed. The mutual ordering of the molecules is hindered in the range 91–295 K due to intense interorientational transitions and the duration of residence of the water molecules in incoherent intermediate states. Keywords: cordierite, water molecules, localization of hydrogen atoms, X-ray analysis, ferroelectricity, structure of minerals, calibration of experimental facilities DOI: 10.1134/S1027451020040035
INTRODUCTION Minerals with nanoscale channels and pores, into which individual atoms or small molecules can enter (e.g., in the process of synthesis), play an important role in geological processes. In practice, such materials can be used as, e.g., matrices for the storage of radioactive waste, molecular filters, and chemical gauges/sensors. Currently, such objects attract attention from a fundamental standpoint because the specific interaction between the contents of nanoscale channels and pores is possible. In some cases, such molecules (atoms) are located quite far from each other, hence, there is almost no chemical interaction between them. However, long-range electric or magnetic forces can potentially lead to their mutual ordering. Switchable magnetic or electric domains are some options of the practical application of nanoporous materials. Systems, in which nanoscale channels contain water molecules possessing a significant electric dipole moment (1.85 D), should be noted separately. It is considered that distributed systems of interacting water molecules can play a noticeable role in the transmission of signals in living organisms, as well as find application in nanoscale electronic devices. Minerals containing water molecules in nanoscale channels are also model systems for
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