Structural and magnetic changes in Li substituted YBa2Cu3Oy determined by neutron powder diffraction measurements

摘要

The crystallographic structure of orthorhombic and tetragonal samples of YBa2Cu3-xLixOy has been determined by neutron powder diffraction measurements, with lambda = 1.225 Angstrom. When the samples are synthesised in oxygen, the Li substitutes mainly for the Cu of the CuO2 planes (Cu2). When they are synthesised in air or annealed in argon at high temperature, a fraction of the Li substitutes for the Cu of the Cu-O- chains (Cu1). Moreover, the neutron data show that each substitution of a Li for a Cu entails the loss of the neighbouring apical oxygen. The magnetic structure of the tetragonal samples has been determined by neutron powder diffraction measurements with lambda = 4.738 Angstrom. With 0.09 Li/mole, weak magnetic peaks are observed at low temperature as in undoped YBCO. The Neel temperature is much lower: T-N approximate to 240 K instead of approximate to 415K for YBa2Cu3O6. The mean ordered magnetic moment on the Cu2 sites is smaller: 0.35 mu (B) instead of 0.64 mu (B) for YBa2Cu3O6. The effect of the lithium substitution is compared to that of Zn. [References: 6]