NEW MIXED-VALENCE IRON-OXIDES (PB,A)SR4FE2O9-DELTA (A=CD, HG) WITH THE 0201-1201-INTERGROWTH TYPE-STRUCTURE

New mixed valence iron oxides (Pb(1-x)A(x))Sr4Fe2O9-delta have been is olated for the composition range 0 less than or equal to x less than o r equal to 0.5 and A = Cd, Hg. Powder X-ray diffraction (XRD) refineme nts and chemical analysis data demonstrated that both compounds exhibi t a significant non-stoichiometry in intermediate rock salt-type [(Pb, A)O](infinity) layers. Mossbauer spectroscopy measurements performed at 4.2 and 300 K showed the existence of several iron sites which have been assigned to individual high spin Fe(III) and to a temperature-de pendent intermediate valence state Fe(IV - Delta) due to electron hopp ing between iron sites.