Single-Crystal High-Pressure Studies of Na3ScF6

The crystal structure of Na 3 ScF 6 was investigated by high-pressure single-crystal X-ray diffraction techniques in the range from ambient conditions to 68.2 kbar. Pressure was measured by the ruby fluorescence method. The single-crystal structure determination at 27.9 kbar resulted in the cell parameters a =5.484(1) A, b =5.732(1) A, c =7.948(2) A, and β =90.96(3)° and the same space group symmetry, P 2 1 / n (Z=2), as at ambient conditions. The 19 structural parameters needed to describe a model with isotropic displacement parameters were refined by least-squares techniques. For the 143 most significant observed unique reflection amplitudes, the R value became 0.047. When the pressure was increased from ambient to 27.9 kbar, the change in the geometry and the relative change in the volume of the coordination polyhedron around the six-coordinated Sc 3+ ion were negligible. Significant changes of the coordination volumes around the Na + ions were observed. The volume decreases for the six-coordinated and the eight-coordinated Na + ions were similar, viz., 7 and 8%. The layered stacking of the larger, low-charged F − and Na + ions along [103] offers an explanation for the pattern which determines the changes of the unit cell parameters with pressure. The relative change in unit cell volume versus pressure in the range from ambient to 68.2 kbar was fit to the Birch type equation of state. The isothermal bulk modulus at ambient pressure and its pressure derivative were determined to be B 0 =46.0(7) GPa and B ′ 0 =3.3(2), respectively.