CHARGE-TRANSFER FROM CU IN YBA2CU3O7-DELTA AND BA2CU3O4CL2 CRYSTALS DETERMINED BY AUGER-ELECTRON SPECTROSCOPY

A formulation is proposed to estimate the charge transfer Delta q(Cu) from Cu to some anions in metal-oxide crystals, using Auger electron s pectroscopy. In the formulation, a parameter, the Auger transition pro bability omega, is introduced, which is defined as the ratio of Auger intensity due to a certain transition to the total Auger intensity due to other transitions when the same core electrons are primarily excit ed. By applying the formulation to vacuum-cleaved surfaces of YBa2CU3O 7-delta (YBCO) and Ba2Cu3O4Cl2 (BCOC) crystals, we obtained the follow ing results: (1) YBCO cleaves between CuO2 and BaO layers, and the amo unt of Delta(q)(Cu) is 2.3 in units of elementary electric charge. The deviation of Delta q(Cu) from 2.0 suggests the existence of CU3+-like atoms; (2) for BCOC, Delta q(Cu) varies from 3.3 to 1.7 depending on the Ar ion beam sputtering time. (C) 1997 American Institute of Physic s.