Ceramics-Silikáty 48 (4) 159-164 (2004)

P-T PHASE DIAGRAM AND GOLD VALENCE STATE OF NEW GOLD MIXED-VALENCE COMPLEXES, Cs₂[Au^IX₂][Au^IIIY₄](X, Y = Cl, Br, I; X ą Y)

K. Ikeda, Y. Ono, M. Enomoto, N. Kojima, Y. Kobayashi, M. Seto, K. Koyama, Y. Uwatoko

Cs₂[Au^IX₂][Au^IIIX₄](X = Cl, Br, and I) is well known for the perovskite-type gold mixed-valence system. This system undergoes pressure-induced and photo-induced Au valence transition from the mixed valence state of Au^I,III to the single valence state of Au^II. Recently, we have succeeded in synthesizing new gold mixed-valence complexes having perovskite-type structure, Cs₂[Au^IX₂][Au^IIIY₄](X, Y = halogen, X ą Y), in organic solvent by using a new method. This hetero-halogen bridged gold mixed-valence system was confirmed by means of Raman spectroscopy. From the analysis of 197Au Mössbauer spectra, it was elucidated that the charge transfer interaction between Au^I(5dx²-y²) and Au^III(5dx²-y²)in the a-b plane becomes dominant for the Au^I-Au^III interaction in Cs₂[Au^IX₂][Au^IIIY₄] (X, Y = Cl, Br, and I) in the order of X = Cl < Br < I, where Y is fixed. In order to elucidate the Au valence transition for Cs₂[Au^IX₂][Au^IIIY₄], we have investigated the X-ray diffraction and Raman spectra under high pressure. Moreover, we have synthesized TlAuX₃(X = Cl and Br) having cubic perovskite structure and highly conducting behavior. The Au valence state in TlAuX₃ is considered to be Au^II at ambient pressure.

Keywords: Valence transition, Phase diagram, Mixed valence, Perovskite-type structure