XANES AND EXAFS STUDY IN (R1, R2-DCNQI)2CU

XANES and EXAFS measurements at Cu K-edge are reported for (R1,R2-DCNQI)2Cu. The mixed valence state of Cu proposed in this compound has been confirmed by the XANES study. The systematic XANES and EXAFS studies have revealed differences in the spectra between two groups in this compound (Group I is metallic down to low temperatures, and Group II shows a metal-insulator transition). The local structural change during the metal-insulator transition in the Group II compound has been confirmed using EXAFS analysis. The clear difference in XANES spectra between two groups has been attributed to the difference in the valence states.