ABSTRACT
The difficulty of small-angle neutron scattering (SANS) is that diffraction is recorded at very small angles which means that shielding of the pressure cell material hit by the neutron beam is virtually impossible. In addition, the signal from standard pressure cell alloys interferes in general strongly with the sample signal which makes the substraction of the background difficult. A large field of applications for SANS under pressure concerns research on soft condensed matter where the sample is liquid and the relevant pressure range a few 0.1 GPa. For such purposes there are a number of solutions which are conceptually very similar. The key ingredient in these cells is the use of windows made of single crystalline material. The only material which has sufficient strength and which can be obtained in large sizes is sapphire. The pressure cell by Gabke et al. [73] shown in Figure 8.1 is one of the simplest designs and illustrates the basic principle of such cells. Two sapphire windows enclose a sample volume in the form of a disk. The sample is injected into the pressure chamber by a hole from the side and remains in permanent contact with an external pressure manometer and a hydraulic compressor. The sapphires are kept into their position by two closure nuts which have central bores for the incoming and diffracted beam. There is the possibility to change the temperature by circulating water of the desired temperature around the cell. Earlier versions with similar design were presented by Vennemann et al. [74] (max. pressure 0.2 GPa), Takano et al. [75] (max. pressure 0.2 GPa and temperatures up to 520 K), as well as Pe´py and Baroni [76] (max. pressure 0.15 GPa) and Bonetti and Calmettes [77] (max. pressure 0.3 GPa).
