Superstructure of a phosphor material Ba3MgSi2O8 determined by neutron diffraction data

Ba3MgSi2O8, a phosphor host examined for use in white-light devices and plant-growth lamps, was synthesized at 1225 °C in air. Its crystal structure has been determined and refined by a combined powder X-ray and neutron Rietveld method (P3¯, Z=3, a=9.72411(3) Å, c=7.27647(3) Å, V=595.870(5) Å3; Rp/Rwp=3.79%/5.03%, χ2=4.20). Superstructure reflections, observed only in the neutron diffraction data, provided the means to establish the true unit cell and a chemically reasonable structure. The structure contains three crystallographically distinct Ba atoms—Ba1 resides in a distorted octahedral site with S6 (3¯) symmetry, Ba2 in a nine-coordinate site with C3 (3) symmetry, and Ba3 in a ten-coordinate site with C1 (1) symmetry. The Mg atoms occupy distorted octahedral sites, and the Si atom occupies a distorted tetrahedral site.

Graphical AbstractCrystal structure of Ba3MgSi2O8 viewed along the c direction. Superstructure reflections, observed only in the neutron diffraction data, provided the means to establish the true unit cell and a chemically reasonable structure.Figure optionsDownload full-size imageDownload as PowerPoint slide