High pressure resonant X-ray emission studies of WO₃ and hydrogenated WO₃

Abstract

We performed two high pressure resonant X-ray emission experiments (RXES) on tungsten oxide (WO₃), and a mixture of WO₃ and ammonia borane (NH₃BH₃), respectively. In the first experiment, WO₃ (confined by a Be gasket) was pressurized and RXES spectra were collected from ambient pressure up to 54.8 GPa via incident X-ray excitation of the W L_III line at 10.207 keV and collection of emission spectra from the L_α1 line near 8.398 keV. The spectra display significant alterations, in particular, a diminishment of one of the spectral lines with pressure suggesting some electronic state changes with pressure in WO₃ which were largely reversible upon decompression of the sample to ambient pressure. For the second experiment, a powder mixture of WO₃ and NH₃BH₃ was pressurized and irradiated to release H₂. An RXES pattern was recorded at 4 GPa which displayed little difference between the RXES spectrum recorded of pure WO₃ in the first experiment. However, at 10 GPa, a dramatic change occurred in the RXES spectrum suggesting that the H₂ reacted with and/or intercalated into the WO₃ lattice. These studies suggest the possibility of harnessing useful hard X-ray photochemistry as a novel means to dope semiconductors.