Measurement of charge of Cu and O in YBa 2Cu 3O y by energy-filtering convergent-beam electron diffraction

Abstract

Large-angle convergent-beam electron diffraction (CBED) patterns were observed from small areas in nanometer scale in YBa 2Cu 3O y (Y123), using a new transmission electron microscope (TEM) JEM-2010FEF. An energy filter of omega type was used to subtract background intensities caused by inelastically scattered electron. Specimens were cooled with a liquid nitrogen 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 CuO 2 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 Cu 2.0+ and O 1.65− on CuO chains, Cu 2.2+ and O 1.98− on CuO 2 planes and O 2.0− 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.