Electrical properties and Mössbauer spectra of rutile-type Fe1−x Mn x TiTaO6 (0 ≤ x ≤ 0.3) ceramics

Abstract

Several electrical quantities of rutile-type Fe1−x Mn x TiTaO6 (0 ≤ x ≤ 0.3) ceramics were measured between room temperature and ∼ 770 K. One aim of the investigation was to study differences to data known from rutile-type FeTiTaO6 ceramics, showing giant relaxor ferroelectric-type constant 𝜖(ω) (ω is angular frequency). FeTiTaO6 (x = 0) samples showed, as expected, capacitance C p (ω) peaks at 500–600 K using Ag-paint contacts, however upon application of Pt-paint, C p (ω) increased steadily up to the maximum employed temperature of ∼ 770 K. For x = 0.02 (Ag-paint), C p (ω) peaks were detected pointing to relaxor ferroelectric behaviour. For x > 0.02 (Ag-paint), no C p (ω) peaks were observed; C p (ω) increased for all frequencies steadily with temperature up to maximum values at the highest applied temperature. Complex plane impedance plots were characterized for each composition by two semicircular arcs due to bulk and grain boundary charge processes. A marked separation of arcs was observed for FeTiTaO6 (x = 0) and 0.02; for x ≥ 0.05 this fact became much reduced. The derived DC conductivity σ DC for bulk conduction showed Arrhenius behaviour for all compositions with activation energy E A ∼ 0.4–0.7 eV and σ DC (300 K) ∼ 10−9 − 10−6Ω−1cm−1 depending on x. For x ∼ 0.05, the frequency dependence of AC conductivity σ AC (ω) was weak at and above room temperature, in contrast for x 0.05 a distinct dispersion was measured showing in part UDR-type power law dependence. 57Fe Mossbauer spectra consisted of one experimental doublet due to Fe3+; each spectrum could be adequately fitted using one doublet with Lorentzian line shape; there was enhanced line width for x = 0.05, pointing to atomic or nanoscale inhomogeneity.