Equation of state of TiH 2 up to 90 GPa: A synchrotron x-ray diffraction study and ab initio calculations

• Published in: Journal of applied physics 2010-08, Vol.108 (4), p.043511-043511-8
• Main Authors: Kalita, Patricia E., Sinogeikin, Stanislav V., Lipinska-Kalita, Kristina, Hartmann, Thomas, Ke, Xuezhi, Chen, Changfeng, Cornelius, Andrew
• Format: Article
• ISSN: 0021-8979; 1089-7550
• DOI: 10.1063/1.3455858

We performed high-pressure studies and ab initio calculations of titanium hydride ( TiH 2 ) , an important compound in hydrogen storage research. In situ , synchrotron x-ray diffraction studies were carried out in two separate compression runs: the first up to 19 GPa in quasihydrostatic conditions and the second up to 90 GPa in nonhydrostatic conditions, and followed by the subsequent decompression to ambient conditions. The pressure evolution of the diffraction patterns revealed a cubic [face-centered-cubic (fcc), F m - 3 m ] to tetragonal (body-centered-tetragonal (bct), I 4 / m m m ) phase transition in TiH 2 occurring at or below 0.6 GPa. The high-pressure tetragonal phase persisted up to 90 GPa. Upon decompression to ambient conditions the observed phase transition appeared irreversible. A third order Birch-Murnaghan fit of the unit cell volume as a function of pressure for all experimental points, yielded a zero pressure bulk modulus K 0 = 142 ( 7 )   GPa , and its pressure derivative K 0 ′ = 3.3 ( 0.2 ) for the high-pressure tetragonal phase of TiH 2 and with K 0 ′ held at four, K 0 = 130 ( 5 )   GPa . The experimental value of bulk modulus confirmed our ab initio calculations where K 0 = 139.9   GPa , and K 0 ′ = 3.7 for the high-pressure tetragonal phase of TiH 2 .