Neutron total scattering of crystalline materials in the gigapascal regime

Abstract

Neutron total scattering of disordered crystalline materials provides direct experimental access to the local (short-range) structure. The ways in which this local structure agrees (or disagrees) with the long-range crystal structure can provide important insight into structure-property relationships. High-pressure neutron diffraction using a Paris-Edinburgh (P-E) pressure cell allows experimenters to explore the ways in which materials are affected by pressure, can reveal new synthetic routes to novel functional materials and has important applications in many areas, including geology, engineering and planetary science. However, the combination of these two experimental techniques poses unique challenges for both data collection and analysis. In this paper it is shown that, with only minor modifications to the standard P-E press setup, high-quality total scattering data can be obtained from crystalline materials in the gigapascal pressure regime on the PEARL diffractometer at ISIS. The quality of the data is assessed through the calculation of coordination numbers and the use of reverse Monte Carlo refinements. The time required to collect data of sufficient quality for detailed analysis is assessed and is found to be of the order of 8 h for a quartz sample. Finally, data from the perovskite LaCo 0.35 Mn 0.65 O 3 are presented and reveal that PEARL total scattering data offer the potential of extracting local structural information from complex materials at high pressure.

Recovering local structure information from high-pressure total scattering experiments

“…The absence of pronounced Bragg peak broadening (i.e. strain) in the diffraction patterns confirms hydrostatic compression of the sample, in contrast to measurements of -quartz without a PTM (Playford et al, 2017). This is further supported by the strong structural correlations observed in the PDFs shown in Fig.…”

“…For each sample, the density and composition were estimated from the difference between the masses of the loaded gasket pre-and post-compression, and were used to normalize PDFs for subsequent treatment. As part of a simplified data treatment, and following established data reduction procedures (Playford et al, 2017), we did not correct for inelasticity effects, as these were likely to be small for the relatively heavy sample materials, nor did we correct for sample absorption since the attenuation due to the press is likely to dominate over any sample effects. Accordingly, no absorption correction was required to obtain high-quality Rietveld fits (see the supporting information).…”

“…Amorphous/glassy materials account for the bulk of these studies because they are not particularly susceptible to the effects of strain (Salmon et al, 2012;Zeidler et al, 2014). Recently, Playford et al (2017) showed, using the PEARL instrument at ISIS, that usable PDFs can be obtained for some simple crystalline systems. However, even some of these exhibited signs of strain broadening.…”

PEARL: the high pressure neutron powder diffractometer at ISIS

“…[60,61] Current capabilities now extend to measuring data from partially disordered crystalline materials and analysing these with the reverse Monte Carlo method. [62,63]…”

Calculation of pair distribution functions for multiphase systems

“…Furthermore, because of the development of total scattering measurement instrumentation it has become possible to extend the use of total scattering studies to time-and space-resolved cases (Chupas et al, 2007). At the same time, sample environments of greater complexity are being used to obtain total scattering data (Playford et al, 2017). These advances are likely to require studies of multicomponent samples or analysis of data sets where not all the instrumental contributions have been subtracted (Proffen et al, 2005).…”