Structure of hydrides based on V-Cr alloys
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CTURE OF INORGANIC COMPOUNDS Dedicated to the International Year of Crystallography
Structure of Hydrides Based on V–Cr Alloys S. A. Lushnikova, V. N. Verbetskiia, V. A. Somenkovb, and V. P. Glazkovb a
Faculty of Chemistry, Moscow State University, Moscow, Russia email: [email protected] b National Research Centre “Kurchatov Institute”, pl. Akademika Kurchatova 1, Moscow, 123182 Russia Received October 23, 2013
Abstract—The structure of deuterides based on V0.9Cr0.1 and V0.5Cr0.5 alloys has been investigated by neutron diffraction at room and low (77 K) temperatures. It is found that V0.9Cr0.1D2.0 deuteride has a CaF2 (Fm3m) crystal structure, which corresponds to vanadium dihydride. V0.5Cr0.5D0.7 deuteride has a NiAs (P6/3mmc) structure type, similar to chromium hydride. DOI: 10.1134/S1063774514060194
INTRODUCTION Vanadiumbased hydrides with a high hydrogen mass content (3.8%) are promising materials for stor ing hydrogen. However, the conditions of hydrogena tion of metallic vanadium and the values of pressure for vanadium mono and dihydride dissociation limit the wide practical application of these compounds. The interaction of hydrogen with multicomponent vanadium alloys (among which V–Cr–Ti alloys should be selected [1–3]) was investigated in order to make progress in this field. This study is based on the data of [4] on the influ ence of some elements on the hydrogen sorption abil ity of vanadium. According to these data, the intro duction of most elements (except for Ti, Zr, and Nb) increases the dissociation pressure of the dihydride phase. The introduction of chromium also makes vanadium dihydride less stable. A study of V1 ⎯ xCrx alloys (х = 0–0.2) [5] showed that an increase in chro mium content leads to an increase in hydrogen des orption pressure and that an alloy containing 20% Cr does not interact with hydrogen at pressures up to 70 atm. The application of the highpressure tech nique in investigations in this field is expected to gain new knowledge about metal–hydrogen systems. For example, the interaction of hydrogen with V1 ⎯ xCrx alloys (х = 0.1–0.5) was studied in [6] at pressures up to 2000 atm. Hydrogen absorption and desorption iso therms were plotted, domains of existence of hydride phases were determined, and the ΔH and ΔS values were calculated. It was found that hydride formation in the V1 ⎯ xCrx–Н2 system with х ranging from 0.1 to 0.4 occurs in two stages and is characterized by the for mation of a stable hydride phase and a hydride phase with a high dissociation pressure. At the same time, the formation of only one hydride phase and the almost complete reversibility of the hydrogen absorption–desorption reaction were
observed in the V0.5Cr0.5–Н2 system. It was noted in [5] that, if V0.9Cr0.1Н1.9 is similar to vanadium dihy dride, a hydride based on V0.5Cr0.5 alloy can be consid ered a vanadiumstabilized chromium hydride. Kaji tani et al. [7] investigated the structure of deuterides based on V1 ⎯ xCrxD0.5 and V1 ⎯ xTaxD0.5 ⎯ x alloys (x = 0.01–0.1) and fo
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