TWIN, SUPERSTRUCTURE AND TRANSIENT TETRAGONAL MONOCLINIC TRANSITION IN ELECTRON-DOPED ND2-XCEXCUO4-DELTA

The well-known modulation structure in electron-doped Nd2-xCexCuO4-del ta has been found to consist of four-fold twins and two-dimensional su perstructures as evidenced by electron diffraction and transmission el ectron microscopy (TEM). Twins and superstructures are both generated by a second-order tetragonal-monoclinic transition, producing the mono clinic structure in different transient forms and changing the intensi ty of superstructure reflections and the thickness of twin domains at the same time. This behavior allows us to build Nd (Ce) cation displac ement models for the superstructures with the help of their forbidden rules. The influence of the structural properties on the manifestation of superconductivity is also discussed.