Reducing the background from pressure vessels using a BRIM

A collimator and beam‐stop assembly that can be inserted inside a temperature‐controlled pressure vessel, to reduce dramatically the parasitic Bragg scattering from the vessel, has been designed and evaluated. High‐energy X‐ray powder diffraction data, suitable for the Rietveld refinement of simple crystal structures, were collected using this background‐reducing internal mask (BRIM). ZrW2O8 was examined at up to 540 K and 124 MPa, using quite large pressure and temperature steps. No pressure dependence of the order–disorder transition temperature of this material was apparent. An orthorhombic to monoclinic phase transition (onset ∼83 MPa) was observed for Al2W3O12. Upon going through the transition, the bulk modulus of the material decreased from 41.8 to 20.8 GPa. Bulk moduli estimated for CaF2 and α‐Al2O3, from data collected at up to 280 MPa, were in good agreement with prior literature.