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abstracts
The exploration of multi-dimensional phase diagrams is a topical subject. However, the simultaneous variation of several control parameters such as temperature, pressure and light irradiation requires a suitably optimized sample environment, particularly when the aim of the experiment is to obtain structural information. We report on a new such sample environment, developed in the context of neutron diffraction measurements, in which the sample can be submitted to pressures up to 7 kbar, temperatures down to 1.7 K and light irradiation in the 660 to 852nm wavelength range, simultaneously. The Ti-Zr alloy pressure cell combines a high mechanical resistance over a wide temperature range with an acceptable neutron background level. The pressure medium is helium gas, ensuring the best possible hydrostatic conditions over a very broad temperature range. The low-temperature environment is obtained from an ILL-type `orange cryostat'. After focusing into an optical fiber, laser light is transmitted to the sample through a sapphire optical window implemented in the pressure cell. The laser flux density at the sample position is of ~30mW/cm2. The geometry of the set-up is optimized to offer a wide optical access (+/- 500 vertical, +/-1650 horizontal), particularly well suited for Laue neutron diffraction techniques. First results obtained on the pressure-photo-induced spin crossover of a model coordination complex will be presented.
abstracts
The large area neutron Laue diffractometer based on CCD detectors (CYCLOPS [1]) has been developed and recently completed at the ILL. High-quality Laue patterns covering an angular range of 3600 horizontally and 920 vertically, can be obtained in only few seconds. The diffractometer excels for fast survey of reciprocal space and fast data collections through phase transitions as well as in-situ experiments on single crystals with time resolution similar to that obtained with powder diffraction. The detector is being upgraded with new faster CCD cameras having a larger dynamic range. A protocol for detector corrections from spatial distortions and uniformity response has been established which allows to obtain accurate integrated intensities leading to good structural refinements. Examples of results of phase transitions and structural investigations will be presented.
