Rutiles of the system Tio2-FeNb2O6-NbO2 : Structural,magnetic and electron transport properties

A wide domain of rutile solid solution has been isolated in the system TiO₂-FeNb₂O₆-NbO₂. The cristallographic parameters, characteristic of the classical rutile cell, have been determined by X-ray diffraction. The Mössbauer and magnetic susceptibility study shows that in the whole domain iron exhibits the divalent state. A second type of site for Fe(II) has been observed on the limit $\text{Ti}{}_{\mathrm{1?x}}{}^{\mathrm{IV}}\text{Fe}{}^{\mathrm{II}}{}_{\mathrm{<mtext>x</mtext><mtext>3</mtext>}}$Nb^V, which has been interpreted by a small loss of oxygen involving the formation of trivalent titanium. The study of the conductivity and the thermoelectric power confirms the classical band model proposed for the rucile structure, involving in this case narrow Π^H bands. The evolution of σ and α as well as that of the c parameter shows that two domains, I and II, must be distinguished, in which the Π^H bands involve the Ti-3d and Nb-4d orbitals, respectively. The first domain is indeed characterized by the presence simultanously of Ti^IV, Ti^III and Nb^V and corresponds to the triangle Ti^IVO₂-Fe^IINb^V₂O₆Ti ^III_0.5Nb^V_0.5O₂ second domain in which all the titanium ions are in the trivalent state is characterized by the presence of Ti^III, Nb^IV and Nb^V simultanously and corresponds to the triangle Nb^IVO₂-Fe^II₂Nb^V₂O₆-Ti^III_0.5Nb^V_0.5O₂.