Fehr, K. T.; Hochleitner, Rupert; Schmidbauer, E.
Electrical properties of rutile-type relaxor ferroelectric-like Fe 0.9W0.05TiMO6 (M = Ta,Nb) ceramics.
In: Journal of Electroceramics, Vol. 30, Nr. 4: S. 191-205
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Electrical properties of rutile-type Fe0.9W 0.05TiMO6TiMO6(M=Ta,Nb) ceramics were measured at and above room temperature and the results are compared with those gained previously on rutile-type relaxor ferroelectrics FeTiMO6(MTa,Nb). The aliovalent W6 cationsin the current compounds might change the suggested polar nanodomains, giving rise to very high dielectric constant ε(ω), and further electrical quantities can possibly shed additional light on the nature of the mechanism leading to extraordinary values in ε(ω). In part similar electrical data were established such as very high ε(ω) but also different results were noted. Apart from ε(ω), the electrical response was analysed by measuring losses, dissipation factor δ, DC conductivity σDC and AC conductivity σAC(ω) using impedance spectroscopy, and thermopower; the results are discussed in conjunction with literature data. The role of grain boundaries and sample-electrode processes was investigated in particular with respect to the sample capacitance. Eventual microstructural local inhomogeneities were checked by means of 57Fe Mössbauer spectroscopy. For both compounds, the temperature dependence of bulk σDC showed Arrhenius behaviour with activation energy EA∼ 0.35 eV and σDC (295 K) ∼ 5× 105Ω-1cm -1; grain boundaries exhibited slightly higher EA but the value of σDC was a factor of up to ∼ 10 lower at all temperatures. From σAC(ω) data, a power law frequency dependence of grain boundary conductivity was derived. Relaxation processes were established from loss and δ data. The thermopower is negative and varies weakly with temperature, pointing to long-range charge transfer by a hopping-type mechanism of electron polarons.