The electrical conductivity, , of donor-doped and undoped strontium titanate (SrTiO 3 ) ceramics and, in some cases, single crystals, Sr 1−x La x TiO 3 (0 р x р 0.1), was investigated in the temperature range of 1000°-1400°C under oxygen partial pressures, P O 2 , of 10 −20 -1 bar. In conjunction with Hall data and thermopower data from related papers, a set of constants for a defect-chemical model was determined, precisely describing point-defect concentrations and transport properties of these materials. In contrast to former works, temperature-dependent transport parameters and their non-negligible influence on the determination of the constants was considered, as well as the equilibrium restoration phenomena of the cation sublattice, which can be studied only at such high temperatures. It was shown that defects in the cation sublattice completely govern the electrical behavior of donor-doped and undoped SrTiO 3 . In the latter case, frozen-in strontium vacancies act as intrinsic acceptors, determining the (P O 2 ) curves at lower temperatures. This intrinsic acceptor concentration also can be calculated with this model. The very good agreement between calculation and measurement is shown in many examples.

Several metal-organic framework (MOF) materials were under investigated to test their applicability as sensor materials for impedimetric gas sensors. The materials were tested in a temperature range of 120 °C - 240 °C with varying concentrations of O2, CO2, C3H8, NO, H2, ethanol and methanol in the gas atmosphere and under different test gas humidity conditions. Different sensor configurations were studied in a frequency range of 1 Hz -1 MHz and time-continuous measurements were performed at 1 Hz. The materials did not show any impedance response to O2, CO2, C3H8, NO, or H2 in the gas atmospheres, although for some materials a significant impedance decrease was induced by a change of the ethanol or methanol concentration in the gas phase. Moreover, pronounced promising and reversible changes in the electric properties of a special MOF material were monitored under varying humidity, with a linear response curve at 120 °C. Further investigations were carried out with differently doped MOF materials of this class, to evaluate the influence of special dopants on the sensor effect.

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We have investigated the electrical transport properties of poly(3,4-ethylenedioxythiophen)/poly(4-styrene-sulfonate) (PEDOT:PSS) with PEDOT-to-PSS ratios from 1:1 to 1:30. By combining impedance spectroscopy with thermoelectric measurements, we are able to independently determine the variation of electrical conductivity and charge carrier density with PSS content. We find the charge carrier density to be independent of the PSS content. Using a generalized effective media theory, we show that the electrical conductivity in PEDOT:PSS can be understood as percolation between sites of highly conducting PEDOT:PSS complexes with a conductivity of 2.3 (Xcm) À1 in a matrix of excess PSS with a low conductivity of 10 À3 (X cm) À1 . In addition to the transport properties, the thermoelectric power factors and Seebeck coefficients have been determined. V C 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 50: [976][977][978][979][980][981][982][983] 2012