Measurement of charge of Cu and O in YBa2Cu3Oy by energy-filtering convergent-beam electron diffraction

Large-angle convergent-beam electron diffraction (CBED) patterns were observed from small areas in nanometer scale in YBa2Cu3Oy (Y123), using a new TEM. An energy filter of omega type was used to subtract background intensities caused by inelastically scattered electrons. Specimens were cooled with a liquid N stage to suppress thermal diffuse scattering that cannot be eliminated well by the energy filter. In order to measure specimen thickness, electron energy loss spectra were also measured from the same areas where CBED patterns were recorded. Charges of Cu and O on CuO chains and CuO2 planes, and charge of O on Ba-O planes were determined by analyzing the intensities of CBED patterns with the dynamical theory of electron diffraction. The obtained values are Cu2.0+ and O1.65- on CuO chains, Cu2.2+ and O1.98- on CuO2 planes and O2.0- on BaO planes. The present results indicate that the energy-filtering CBED technique is useful for determination of charge distribution along the z-direction in Y123. 30 refs.