In situ Neutron Diffraction as a Probe on Formation and Decomposition of Nitrides and Hydrides: A Case Study

In order to perform real-time studies of solid-gas reactions involving light elements such as hydrogen and nitrogen, gas pressure and gas flow cells were developed for in situ neutron powder diffraction. The gas pressure cell is based on a sapphire single crystal tube as a sample holder and provides high quality diffraction patterns with very low background up to 16.0 MPa hydrogen (deuterium) gas pressure and temperatures up to 400 degrees C. The gas flow cell contains a silica tube as sample container and is optimized for flowing ammonia as reaction gas. While it produces higher background owing to the silica, it allows much higher temperatures of up to 750 degrees C to be used. For both cells heating is realized contactless and without any contribution to the diffraction patterns by two lasers and so high-quality diffraction data allowing for a detailed Rietveld analysis can be collected on D20 (Institute Laue-Langevin) with a one minute time resolution. Examples are presented demonstrating the potential of the in situ gas cells, ranging from the nitridation of vanadium and iron powders with flowing ammonia, to the deuteration of palladium and the hydrogen storage material LaNi5.