Alternative explanation for the relaxor ferroelectric behavior in FeTiNbO6 rutile ceramics: The influence of electrode contacts

The radio-frequency permittivity-temperature profiles of acceptor-donor codoped ${\mathrm{TiO}}_{2}$-based rutiles commonly produce higher than expected values ($>{10}^{3}$ at 300 K) often with conflicting interpretations. A combination of dielectric spectroscopy (DS) and impedance spectroscopy (IS) with different electrode materials is used to reinvestigate the electrical properties of ${\mathrm{Fe}}^{3+}\text{\ensuremath{-}}{\mathrm{Nb}}^{5+}$-doped rutile in the form of ${\mathrm{FeTiNbO}}_{6}$ ceramics that show permittivity-temperature characteristics that are consistent with relaxor ferroelectrics (RFE). IS results reveal semiconducting grains with an activation energy of $\ensuremath{\sim}0.16\phantom{\rule{0.28em}{0ex}}\mathrm{eV}$, and relative permittivity of similar magnitude and temperature dependence to undoped ${\mathrm{TiO}}_{2}(<250)$. Reducing the work function of the electrode material by replacing Au with InGa has a dramatic effect on the IS and DS data. We propose the apparent RFE behavior observed by DS and previously attributed to the formation of nanoclustering of the cations is an extrinsic effect primarily associated with the development of Schottky barriers between the semiconducting ceramics and Au contacts.