X線粉末回折データより格子定数及び空間群を求めるプログラム : 斜方晶系の場合

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A program for finding the unit-cell constants and the possible space groups of orthorhombic substances from X-ray powder diffraction data is presented. The program is written in N_<88>-BASIC. The program is based on the assumption that reflections with indices h00, hk0 and h0l exist in the observed diffraction lines. Trial unit-cell parameters a are obtained by assuming that all low-angle observed lines have indices h00. Then, the b and c parameters for a particular a parameter are derived by assuming that the observed lines have indices 0k0, 00l, hk0 or h0l. For each set of the a, b and c parameters thus obtained, 2θ_<cal> are calculated for various indices hkl and compared with 2θ_<cal> Then, if all 20θ_<obs> up to the 20th line are explained in terms of 2θ_<cal> within given window widths ±Δ2θ, the a, b and c parameters are saved as a possible set of the unit-cell constants. After the above calculation, the systematic extinctions for the space groups belonging to the orthorhombic system are applied to the calculated reflections, and the unit cells with high reliability indices R are selected. Final unit-cell constants and possible space groups are obtained by least-squares refinement of the cell parameters and reexamination of the reliability indices using input data up to about 35th line. The reliability index R used in the program is given by R = ( Number of observed reflections) / ( Number of calculated reflections for a given space group) , where the calculated reflections are those having essentially different d-values. Note that the above program includes a program which gives information concerning the presence of insufficient higher-angle diffraction lines, such as those produced by impurities or those having uncertainty in 2θ due to weak diffraction intensities.
社団法人日本セラミックス協会の論文
1988-01-01

X線粉末回折データより格子定数及び空間群を求めるプログラム : 斜方晶系の場合

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