In situ observations of temperature- and pressure-induced phase transitions in TiH2: Angle-dispersive and synchrotron energy-dispersive X-ray diffraction studies |
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Authors: | Patricia E. Kalita,Andrew L. Cornelius,Cé dric L. Gobin |
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Affiliation: | a Department of Physics, University of Nevada Las Vegas, Las Vegas, NV 89154-4002, USA b Geophysical Laboratory, Carnegie Institution of Washington, Washington, DC 20015-1305, USA c Department of Chemistry, University of Nevada Las Vegas, Las Vegas, NV 89154-4010, USA |
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Abstract: | We investigated the behavior of the structure of titanium hydride (TiH2), an important compound in hydrogen storage research, at elevated temperatures (0-120 °C) and high pressures (1 bar-34 GPa). Temperature-induced changes of TiH2 as indicated in the alteration of the ambient X-ray demonstrated a cubic to tetragonal phase transition occurring at about 17 °C. The main focus of this study was to identify any pressure-induced structural transformations, including possible phase transitions, in TiH2. Synchrotron X-ray diffraction studies were carried out in situ (diamond anvil cell) in a compression sequence up to 34 GPa and in subsequent decompression to ambient pressure. The pressure evolution of the diffraction patterns revealed a cubic (Fm-3m) to tetragonal (I4/mmm) phase transition at 2.2 GPa. The high-pressure phase persisted up to 34 GPa. After decompression to ambient conditions the observed phase transition was completely reversible. A Birch-Murnaghan fit of the unit cell volume as a function of pressure yielded a zero-pressure bulk modulus K0=146(14) GPa, and its pressure derivative K′0=6(1) for the high-pressure tetragonal phase of TiH2. |
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Keywords: | C. High-pressure D. Phase transitions |
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