Instrumentation development for neutron scattering at high pressure

Abstract

Neutron scattering at extremes of pressure is a powerful tool for studying the response of structural and magnetic properties of materials on microscopic level to applied stresses. However, experimental neutron studies require a relatively large sample volume, which makes it necessary to use rather large presses. One of the most commonly used high-pressure devices in neutron diffraction experiments is the Paris-Edinburgh (P-E) press. This compact hydraulic press has been successfully used at various neutron facilities across the world for over 20 years. However, there are some limitations imposed by the design of the press and this project addressed two of them. The first objective of this research was to solve the problem of the spatial restriction on the scattered beam imposed by the tie-rods of the P-E press which results in the limited access to the reciprocal space of a single-crystalline sample. In order to overcome this challenge a rotating device has been designed and built to work with the existing P-E press mainframe. The purpose of the device is to rotate the anvils at a high load in a controlled fashion so that neutron diffraction data can be collected from the sample at particular angles. A number of technical challenges had to be overcome in the design process. One of the problems was caused by the significant friction in the commercially available thrust roller bearings at loads above 25 tonnes. To resolve this issue a set of custom-designed hydraulic bearings has been developed. In these bearings a thin layer of oil separates the two parts that can rotate with respect to each other.