HIGH-VOLTAGE HIGH-RESOLUTION ELECTRON-MICROSCOPY STUDY OF ALKALINE-EARTH COPPER OXIDES

Two families of alkaline-earth copper oxides are studied by using high -voltage high-resolution electron microscopy. One is Srn-1 CunO2n-1(n = 2, 3), the so-called spin-ladder compounds, and the other is ACuO(2) (A = Ca-Sr) crystallizing in the infinite-layer structure, which is a parent structure for all copper oxide superconductors. It is demonstr ated in the former compounds that oxygen columns as well as metal colu mns are directly imaged in a ''structure'' image. Moreover, twin-relat ed lattice defects, which can be the origin of free Cu2+ spins observe d previously in magnetic measurements, have been detected in SrCu2O3. An interesting irradiation effect under a 1,000-kV electron beam has b een observed in the infinite-layer compound. An unusual structural pha se transformation to a NaCl-type lattice is induced, accompanied by th e formation of nm-size twin domains. (C) 1998 Wiley-Liss, Inc.