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A local structure analysis method based on convergent-beam electron diffraction (CBED) has been used for refining isotropic atomic displacement parameters and five low-order structure factors with sin θ/λ ≤ 0.28 Å−1 of potassium tantalate (KTaO3). Comparison between structure factors determined from CBED patterns taken at the zone-axis (ZA) and Bragg-excited conditions is made in order to discuss their precision and sensitivities. Bragg-excited CBED patterns showed higher precision in the refinement of structure factors than ZA patterns. Consistency between higher precision and sensitivity of the Bragg-excited CBED patterns has been found only for structure factors of the outer zeroth-order Laue-zone reflections with larger reciprocal-lattice vectors. Correlation coefficients among the refined structure factors in the refinement of Bragg-excited patterns are smaller than those of the ZA ones. Such smaller correlation coefficients lead to higher precision in the refinement of structure factors.

A structure-analysis method using convergent-beam electron diffraction (CBED) developed by Tsuda et al. [Tsuda & Tanaka (1999), Acta Cryst. A55, 939-954; Tsuda, Ogata, Takagi, Hashimoto & Tanaka (2002), Acta Cryst. A58, 514-525] has been applied to the determination of the electrostatic potential and electron density of crystalline silicon. CBED patterns recorded at nine different incidences are simultaneously used to improve the accuracy of the refinement. The Debye-Waller factor and low-order structure factors of silicon have been successfully refined only using CBED data. The electrostatic potential and electron-density distribution have been reconstructed from the refined parameters. The latter clearly shows the bonding electrons between the nearest neighbor atoms. The obtained results are compared with the results of other CBED and recent X-ray diffraction experiments. The influence of the number of refined low-order structure factors on the electron density is discussed. The effect of the reduction of experimental data points on the accuracy of the refined parameters is also examined.

Convergent-beam electron diffraction (CBED) is well known as a powerful tool to determine space groups of crystals. However, it cannot distinguish several sets of space groups. It is shown theoretically that the coherent CBED method can distinguish between space groups (I23 and I2(1)3) and between (I222 and I2(1)2(1)2(1)), which belong to indistinguishable sets. It is demonstrated by computer simulations that the relative arrangement of 2-fold-rotation and 2(1)-screw axes can be distinguished by examining the relative phases of specific reflections through the interference fringes of coherent CBED patterns. This fact implies that these space groups can be distinguished by the coherent CBED method.

The method to refine crystal structure parameters (atom positions and Debye–Waller factors) using convergent-beam electron diffraction (CBED), which is applicable to crystal structure analysis of a small specimen area down to a few nm in diameter, is studied. The line profiles of higher-order Laue-zone reflections are recorded using imaging plates. Theoretical intensities are calculated based on the dynamical theory of electron diffraction with the aid of the generalized Bethe approximation to shorten calculation time. The structural parameters are determined by fitting the experimental profiles with the theoretical ones using a nonlinear least-squares method. The present method has been applied to the low-temperature phase of SrTiO3. The structural parameter or the rotation angle of the oxygen octahedron has been determined to be \varphi = 1.12 (4)°, which shows good agreement with that obtained from electron spin resonance experiments.