ISSN 0862-5468 (Print), ISSN 1804-5847 (online) 

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


P-T PHASE DIAGRAM AND GOLD VALENCE STATE OF NEW GOLD MIXED-VALENCE COMPLEXES, Cs₂[AuIX₂][AuIIIY₄](X, Y = Cl, Br, I; X ≠ Y)
 
Ikeda Kazuhiro 1, Ono Yuuki 1, Enomoto Masaya 1, Kojima Norihichi 1, Kobayashi Yasuhiro 2, Seto Makoto 2, Koyama Kazuko 3, Uwatoko Yoshiya 3
 
1 Graduate School of Arts and Sciences, The University of Tokyo, Tokyo 153-8902, Japan
2 Research Reactor Institute, Kyoto University, Osaka 594-0494, Japan
3 Institute for Solid State Physics, The University of Tokyo, Chiba 277-8581, Japan

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

Cs₂[AuIX₂][AuIIIX₄](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 AuI,III to the single valence state of AuII. Recently, we have succeeded in synthesizing new gold mixed-valence complexes having perovskite-type structure, Cs₂[AuIX₂][AuIIIY₄](X, Y = halogen, X = 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 AuI (5dx²-y²) and AuIII(5dx²-y²)in the a-b plane becomes dominant for the AuI-AuIII interaction in Cs₂[AuIX₂][AuIIIY₄] (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[AuIX₂][AuIIIY₄], 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 AuII at ambient pressure.


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