Joint seminar of Fritz Haber Institute and Institute for Molecular Science, Japan. Charge order (CO) has been recognized as one of the most important competing order in superconductive cuprates. In YBa₂Cu₃O_6+x (YBCO), CO could only be investigated by x-ray diffraction in under-doped YBCO with low critical temperatures (T_C), but not in highly-doped YBCO with high T_C suitable for device applications, due to the competing superconductive phase. Therefore, the most fundamental physical mechanisms governing CO, for example, the role of so-called charge reservoir (Cu-O chain) layers in CO and the spatial interplay of CO and SC, in highly-doped YBCO are still unclear. [more]