A method to determine long-range order parameters from electron diffraction intensities detected by a CCD camera.

To determine long-range order parameters from electron diffraction intensities, the authors have developed a CCD camera system to detect precisely electron diffraction intensities, a method for quickly and precisely measuring specimen thickness, and a computer programming to calculate long-range order parameters from the ratio of superlattice and fundamental diffraction intensities. Thickness variation over a diffraction area is taken into consideration in the calculation of electron diffraction intensities on the basis of the multi-slice method, and long-range order parameters are calculated by the successive approximation method. The absorptive form factors are also calculated from experimental data of diffraction intensities by parameter fitting, and the effect of absorption on the calculation of long-range order parameters is examined. The values of Cu(3)Au alloys aged at 523 and 653 K that were obtained by averaging long-range order parameters determined for several diffraction areas with the developed method are close to the reported data obtained by the X-ray diffraction method. The main causes for the deviation of long-range order parameters determined for several diffraction areas are also discussed.