Electrical properties of rutile-type relaxor ferroelectric-like Fe0.9W0.05TiMO6 (M = Ta,Nb) ceramics

Autor: K. Th. Fehr, Rupert Hochleitner, E. Schmidbauer
Rok vydání: 2013
Předmět:
Zdroj: Journal of Electroceramics. 30:191-205
ISSN: 1573-8663
1385-3449
DOI: 10.1007/s10832-013-9783-2
Popis: Electrical properties of rutile-type $\mathrm {Fe}_{0.9}{\kern 1pt} \mathrm {W}_{0.05}\\\mathrm {TiMO}_{6} (\mathrm {M} {} = {} \mathrm {Ta,Nb})$ ceramics were measured at and above room temperature and the results are compared with those gained previously on rutile-type relaxor ferroelectrics $\mathrm {FeTiMO}_{6} (\mathrm {M} {} = {} \mathrm {Ta,Nb})$ . The aliovalent ${\rm W}^{6+}$ cationsin the current compounds might change the suggested polar nanodomains, giving rise to very high dielectric constant $\epsilon (\omega )$ , and further electrical quantities can possibly shed additional light on the nature of the mechanism leading to extraordinary values in $\epsilon (\omega )$ . In part similar electrical data were established such as very high $\epsilon (\omega )$ but also different results were noted. Apart from $\epsilon (\omega )$ , the electrical response was analysed by measuring losses, dissipation factor $\tan \delta $ , DC conductivity $\sigma _{DC}$ and AC conductivity $\sigma _{AC}(\omega )$ 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 Mossbauer spectroscopy. For both compounds, the temperature dependence of bulk $\sigma _{DC}$ showed Arrhenius behaviour with activation energy ${E_{A}}\sim $ 0.35 eV and $\sigma _{DC}$ (295 K) $\sim 5\times 10^{-5} \Omega ^{-1}\text{cm}^{-1}$ ; grain boundaries exhibited slightly higher ${E_{A}}$ but the value of $\sigma _{DC}$ was a factor of up to $\sim 10$ lower at all temperatures. From $\sigma _{AC}(\omega )$ data, a power law frequency dependence of grain boundary conductivity was derived. Relaxation processes were established from loss and $\tan \delta $ data. The thermopower is negative and varies weakly with temperature, pointing to long-range charge transfer by a hopping-type mechanism of electron polarons.
Databáze: OpenAIRE
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