Fan Han-Jie

A high-Tc superconducting phase in the Ba-Y-Cu-O system

The crystal structure of high-Tc superconductors in the Ba-Y-Cu-O system has been investigated by means of X-ray powder diffraction and electron microscopy. The results indicate that the superstructure based on the distorted cubic perovskite subcell is responsible for the high-Tc superconducting transition at about 90 K. The high-Tc superconducting phase is pseudo-tetragonal with triple periods (3ap) along the (001) direction. The different diamagnetic and resistance behaviour is connected with different proportions of this phase in the samples.

ELECTRON MICROSCOPY OF HUANGHOITE

Huanghoite fBaGe(CO3)F] is a new mineral discovered in China. The parameters of the hexagonal unit cell have been determined as α=5.07?, c=38.6? by using electron diffraction method. The value of c is twice as large as that determined previously by X-ray diffraction analysis. Huanghoite is composed of atoms with large difference in atomic number. The advantage of electron diffraction in investigating such kind of minerals is discussed.The stacking faults along direction c have been observed by lattice imaging technique. The possille cause of formation of such faults is proposed.