Oxygen-defective LaMnO3-x with twin structure was studied using an HREM. On the basis of direct observation with a 200-kV HREM and with the aid of computer simulation, an optimum imaging condition was found, where metal La and Mn atoms and oxygen atoms were imaged as dark spots and bright spots, respectively. The through-focus observation and intensity profile observed from the image contrast support the view that the oxygen vacancies could be detected from the intensity distribution of bright spots in the observed image, which represents the positions of the oxygen atoms. A structure image under the optimum imaging condition reflected the twin structure with oxygen vacancies in LaMnO3-x. Twin structures were found to consist of two kinds of twin planes, (110) and (112), including oxygen vacancies.
