Distinction of space groups (I23 and I2₁3) and (I222 and I2₁2₁2₁) using coherent convergent-beam electron diffraction

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 I2₁3) and between (I222 and I2₁2₁2₁), which belong to indistinguishable sets. It is demonstrated by computer simulations that the relative arrangement of 2-fold-rotation and 2₁-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.