Ac Conductivity for Eu2Zr2O7 and La2Ce2O7 with Pyrochlore-Type Composition

Abstract

Ac conductivity (s ac ) obtained from admittance of Eu 2 Zr 2 O 7 and La 2 Ce 2 O 7 , which have pyrochlore and fluoritetype structure, respectively, was measured as a function of frequency in the range between 5 Hz and 13 MHz and in the temperature range between 573 and 1073 K. The frequency dependence of the s ac of these oxide ion conductors showed a remarkably different behavior from that of the cation ones. By comparison of the s ac with other conductivity data obtained by dc fourprobe and impedance spectroscopic methods, it was found that the s ac in the frequency range below 10 5 Hz was strongly influenced by space charge polarization at grain boun dary and that the s ac obtained from high frequency plateau agreed with bulk conductivity, s ib , from impedance spectra and dc conductivity, s dc .

A mixed electronic and protonic conducting hydrogen separation membrane with asymmetric structure

“…However, the crystal structure of LDC is still in dispute up to now. Many XRD experiments as above support fluorite structure, due to absence of pyrochlore peaks [26,27]. Recently, D.E.P.…”

Electrical conduction and dielectric relaxation process in Ce0.8Y0.2O1.9 electrolyte system

“…In the temperature range from 240 to 360 • C, the conductivity value estimated from the low frequency plateau did not agree with that of bulk conductivity, but agreed with the conductivity estimated from the grain boundary of the impedance spectra. The conductivity dispersion in the intermediate frequency range is high for the material having higher grain boundary resistivity than the bulk resistivity [20]. So we can assume that the plateau in the low frequency range for the temperatures from 240 to 360 • C is due to the polarization of space charge due to the presence of large grain-boundary barrier.…”

“…This means that the UDR theory could not always be appropriate in the case of oxide ion conductors. The dielectric constant of oxide-ion conductors was composed of both Debye type polarization and electrode-electrolyte interfacial polarization which depends on the inverse of frequency [20]. The apparent dielectric constant (ε ) can be given as in the following equation, assuming the presence of various dipoles with multiple relaxation times [24];…”

Aliovalent doping of CeO2: DFT study of oxidation state and vacancy effects

“…Consequently, simple stability rules based on ratios of atomic radii, for example used in the study of fluorite-pyrochlore transitions, should be treated with considerable caution since they appear to be ill-defined. 43,129 Based on these results some extrapolations can be made regarding other dopant elements. Let us assume that the trend observed for the defect formation energies of group IVa and IVb dopants also hold for other groups.…”