Decomposition of the hexagonal copper hydride at high pressure

The process of decomposition of hexagonal copper hydride has been observed in situ in a diamond anvil cell (DAC) using the energy dispersive X-ray diffraction (EDXRD) method. The presence and intensity of diffraction lines of the hexagonal CuH0.8 phase have been taken as a probe for the decomposition process. The intensity of diffraction lines decreases abruptly in the vicinity of 8.4 GPa, indicating complete decomposition of the hydride. The determined value of decomposition pressure is equal to 8.4 +/- 0.6 GPa. The standard Gibbs energy of formation of 54.0 +/- 1.3 kJ mol(-1) (H-2) calculated for copper hydride has been compared with the result obtained from calorimetric studies. The large discrepancy between the two values suggests that the decomposition pressure does not describe 'true' equilibrium conditions in this system. (C) 2004 Elsevier Ltd. All rights reserved.