A. Huanosta

Electric transport properties of the β-LnNb3O9 phases (Ln = La, Ce, Pr, and Nd)

The electric properties of the cation deficient perovskites of the formula β-LnNb3O9, where Ln is La, Ce, Pr, or Nd, were investigated by means of the impedance spectroscopy technique. The electric conductivity behavior of the β-LnNb3O9 phases shows a clear trend in the activation energy for electric transport that can be easily correlated to the small changes in the unit cell volume. The β-LnNb3O9 series shows similar dielectric loss behavior, with the exception of the β-CeNb3O9 phase. The β-CeNb3O9 compound shows an electronic contribution to the electric conduction which seems to be present in the entire range of temperatures investigated.

Characterisation of magnetic materials by impedance spectroscopy

Abstract Impedance spectroscopy has been used to investigate the magnetic properties of (Ni,Zn)Fe 2 O 4 . Two magnetic relaxations were observed corresponding to domain wall bulging and domain rotation. At higher applied fields a second magnetic mechanism, involving irreversible domain movement, was also observed. An equivalent circuit consisting of two RL parallel elements and a Warburg-type magnetic impedance has been used to model these phenomena.

Electrical properties of the solid solution Li4 − 3xInxSiO4

Abstract Polycrystalline solid solutions with formula Li4 − 3xInxSiO4: 0 ≤ x ≤ 0.15 were prepared by solid state synthesis. These materials were found to exhibit lithium ion vacancies. From ac impedance measurements conductivities with values around 1 × 10 −5 Ω −1 cm −1 at 250 °C, are found.

Curie-Weiss behavior in polycrystalline barium titanate from ac measurements

Abstract The dielectric constant of undoped, polycrystalline barium titanate in the paraelectric phase was obtained from the complex impedance plane representation in the 180–400°C temperature range, between 5 Hz and 13 MHz. A Curie-Weiss behavior is observed, with a Curie constant C o = 10.48 × 104 (K). These results are discussed and compared with results obtained with fixed frequency measurements.

Analysis of dielectric parameters and ion hopping rates in the β-LnNb3O9 phases (LnLa, Ce, Pr and Nd)

Abstract The electric transport characteristics of β - LnNb 3 O 9 ( Ln = La , Ce , Pr and Nd ) orthorhombic phases, measured by ac impedance spectroscopy, were recently reported. In this work, a detailed analysis of dc component, obtained directly from ac data, is given. The dc conductivity of β - CeNb 3 O 9 is quite close to the bulk conductivity at low temperatures. Different behaviour is shown in the other three cases. The hopping rate characteristics of the charge carriers and an estimation of the relative carrier concentration are also presented. Exhaustive analysis has been made on admittance versus frequency plots to extract hopping rate and dc values. The β - LnNb 3 O 9 compounds show Arrhenius behaviour in their hopping rate and dc characteristics. Finally, the behavior with temperature and frequency of dielectric parameters like tan δ and permittivity are discussed.

Ac impedance spectroscopy studies of the solid solution Li2Zr1−xTixO3

Abstract ac impedance spectroscopy studies were carried out in polycrystalline samples of Li 2 Zr 1− x Ti x O 3 :0 x α =1×10 −6 (ω cm) −1 at 400°C rising to α =1×10 −3 (ω cm) −1 at 750°C. It was found that the conductivity and the E a values decrease with increasing Ti 4+ content. The dielectric constant decreases sharply with increasing Ti content. Using the same ac data the hopping rate characteristics and dc component were investigated.