NEUTRON DIFFRACTION DETERMINATION OF THE CELL DIMENSIONS AND THERMAL EXPANSION OF THE FLUOROPEROVSKITE KMGF3 FROM 293 TO 3.6 K

Abstract

The cell dimensions of the fluoroperovskite KMgF3 synthesized by solid state methods have been determined by powder neutron diffraction and Rietveld refinement over the temperature range 293–3.6 K using Pt metal as an internal standard for calibration of the neutron wavelength. These data demonstrate conclusively that cubic $ Pm\overline{3} m $ KMgF3 does not undergo any phase transitions to structures of lower symmetry with decreasing temperature. Cell dimensions range from 3.9924(2) Å at 293 K to 3.9800(2) Å at 3.6 K, and are essentially constant within experimental error from 50 to 3.6 K. The thermal expansion data are described using a fourth order polynomial function.