JOURNAL OF MATERIALS SCIENCE: MATERIALS IN ELECTRONICS 10 (1999) 121±132 Hydrazine method of synthesis of c-Fe 2 O 3 useful in ferrites preparation. Part III ± study of hydrogen iron oxide phase in c-Fe 2 O 3 K. S. RANE, V. M. S. VERENKAR, R. M. PEDNEKAR, P. Y. SAWANT Department of Chemistry, Goa University, Goa 403206, India E-mail: ksrane@unigoa.ernet.in Direct current electrical conductivity s measurements as a function of temperature have been carried out on g-Fe 2 O 3 prepared from precursors, iron (II) carboxylatohydrazinates, g-FeOOH and hydrazinated g-FeOOH. The conductivity variation obeys an Arrhenius equation, s I  s o e DE=kT and the plots of log s versus 1=T of the as prepared g-Fe 2 O 3 , which are in general linear, during the very ®rst heating up to 350  C and cooling to room temperature (RT) do not overlap. This indicates a hysteresis behavior of conductivity, thereby suggesting involvement of two different conductivity mechanisms. When the heat treated sample was equilibrated in a known partial pressure of moisture at * 200  C and then conductivity measured from RT, the log plots during heating and cooling did not overlap and a hysteresis behavior similar to the as prepared g-Fe 2 O 3 is observed again in the conductivity. Water is considered to be crucial during the synthesis of g-Fe 2 O 3 through magnetite, Fe 3 O 4 : Protons, H  , are thought to be introduced in the spinel Fe 3 O 4 making it defective and the oxidation product of this is g-Fe 2 O 3 which retains few protons in its spinel structure. From the structural similarity of such proton incorporated g-Fe 2 O 3 and lithium ferrite, LiFe 5 O 8 , Fe 3  8 Fe 3 12 Li 1 4 O 32 , a formula HFe 5 O 8 , Fe 3  8 Fe 3 12 H 1 4 O 32 is suggested. A hydrogen iron oxide of formula H 1x Fe 5x 3 O 8 , where x *0:1 is probably formed as a maximum limit. Protons are removed during the very ®rst heating of the as prepared sample in the present studies and hence the conductivity of proton free g-Fe 2 O 3 is different and therefore a hysteresis behavior is observed. Moisture equilibration reintroduces the protons. The lithiated samples in the present studies were found to substitute for protons in g-Fe 2 O 3 and no hysteresis behavior is observed in such samples even after moisture equilibration. 1. Introduction Although a simple elimination of water on dehydration of g-FeOOH topotactically transforms it readily into g-Fe 2 O 3 , commercial manufacturing of the oxide resorts to the following multistep process, a-FeOOH  ? oxidation a-Fe 2 O 3  ? reduction Fe 3 O 4  ? O g-Fe 2 O 3 1 In general, g-Fe 2 O 3 synthesized from g-FeOOH shows lower saturation magnetization values than that obtained from controlled oxidation of Fe 3 O 4 . A plausible reason given for such superior properties for the g-Fe 2 O 3 obtained from Fe 3 O 4 oxidation is based on the consideration of easy diffusion of Fe 3 ions through the spinel framework already present in Fe 3 O 4 to give well ordered vacancies on the so called ``lithium sites''* of g-Fe 2 O 3 [1, 2]. On the other hand, defect spinel g-Fe 2 O 3 with a framework of FeO 6  octahedra with edge and corner sharing, that formed from the corrugated layers of [FeO 6 ] octahedra of g-FeOOH on dehydration, has insuf®cient time and occasion for Fe 3 ions to diffuse through the developing framework of g-Fe 2 O 3 to occupy the lithium sites for giving a well ordered g-Fe 2 O 3 and hence a low saturation magnetization. g-Fe 2 O 3 is a vacancy ordered defect spinel similar in structure to the inverse spinel, magnetite, Fe 3 O 4 . A unit cell structure of this ferrouso-ferric oxide, Fe 3 O 4 is written as Fe 3  8 Fe 3 8 Fe 2 8 O 32 , where  and  represent tetrahedral and octahedral sites of the spinel, respectively. On oxidation of Fe 3 O 4 , the Fe 2 ions from the octahedral sites oxidize to Fe 3 ions and for every 3Fe 2 ions that oxidizes to 2Fe 3 ions, one vacancy &, is created resulting in g-Fe 2 O 3 , Fe 3  8 Fe 3 8 Fe 3 51=3 h 8=3 O 32 . A crystal structure similarity between lithium ferrite, LiFe 5 O 8 , Fe 3  8 Fe 3 12 Li 1 4 O 32 and g-Fe 2 O 3 , Fe 3  8 Fe 3 12 Fe 3 4=3 h 8=3 O 32 suggests [3± 10] that the Fe 3 4=3 and h 8=3 are in fact the ``lithium sites'' of g-Fe 2 O 3 . As mentioned earlier, the Fe 3 O 4 oxidation allows Fe 3 and & vacancies to order on the lithium sites by simple diffusion of Fe 3 through the spinel *Actually Fe 64 O 96 fFe tetrahedral 24 Fe octahedral 36 Fe Li-sites 4 8 Li-sites O 96 g. controlled 0957±4522 # 1999 Kluwer Academic Publishers 121