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 Al ₂W ₃O ₁₂. Upon going through the transition, the bulk modulus of the material decreased from 41.8 to 20.8 GPa. Bulk moduli estimated for CaF ₂ and-Al ₂O ₃, from data collected at up to 280 MPa, were in good agreement with prior literature.