FIGURE 3. Rietveldrefinements Samples 1 and 2. Black crosses = Observed signal; red line = modeled diffraction pattern; tick marks = 2-angles of observed reflections. (a) Sample 2: wavelength was 0.34531 Å. The whole pattern, including background (not shown here) was fitted. For MgSiO₃-perovskite we find an R_F² of 0.09, for the 3 x 1 kinked post-perovskite R_F² is 0.24, and for KBr 0.04. The fitted cell parameters of the 3 x 1 phase are 9.608(16) x 6.043(13) x 4.248(8) ų, β = 98.689(14)°, the cell parameters of pervoskite are 4.442(1) x 4.651(1) x 6.438(1) ų, and the cell parameter for KBr is 2.7979(3) Å. The standard deviation is given in brackets. (b) Sample 1: wavelength was 0.3888 A. Background was subtracted in advance of Rietveld refinement because of a strong modulation from excitation halos around the intense peaks for the pressure medium. The weighted profile refinement parameter wRp was 0.09 and ² = 31.3. The R_F² for the 2 x 1 phase was 0.25. The cell parameters are 6.804(5) x 6.289(7) x 4.161(4) ų, β = 96.17(9)°. The cell parameter for NaCl is 2.727(1) Å and for perovskite 4.445(3) x 4.598(4) x 6.372(3) ų.