Study of the electrical charge transport in ilvaite using impedance spectroscopy and thermopower data

• Published in: Physics and chemistry of minerals Vol. 25; no. 7; pp. 522 - 533
• Main Authors: Schmidbauer, E., Amthauer, G.
• Format: Journal Article
• Language: English
• Published: Heidelberg Springer Nature B.V 01-08-1998
• Subjects: Aluminum; Amorphous semiconductors; Charge transfer; Charge transport; Conductivity; Electrical conduction; Electrical resistivity; Electrical studies; Electrons; Energy gap; Frequency ranges; Hopping conduction; Impedance; Impedance spectroscopy; Impurities; Magnesium; Manganese; Phase transitions; Semiconductors; Spectroscopy; Spectrum analysis; Thermoelectricity
• ISSN: 0342-1791; 1432-2021
• DOI: 10.1007/s002690050144

Abstract The electrical conduction in the mineral ilvaite was studied between ≈170 and 450 K. A natural ilvaite from Elba (Italy) was found to be semiconducting with a DC conductivity 1.8×10–3 (Ωcm)–1 at 300 K, measured parallel (∥) to the [001] direction; perpendicular (⊥) to [001] it was 1.4×10–5 (Ωcm)–1, i.e. the conductivity is highly anisotropic. The conduction is effected by a hopping charge transport between localized levels in the energy gap associated with activation energies EA=0.3–0.5 eV. It is concluded that impurities (Mg,Al,Mn) may play a decisive role in the charge hopping transport ∥ [001] that is basically governed by Fe2+-Fe3+ pairs on A-sites of the lattice as the source of electrons. Although the EA-values were similar for both measured directions, the sign of thermopower is different which points to different charge transfer mechanisms. The bulk DC conductivity σDCAC for measurements ∥ [001], obtained by extrapolation of AC data using impedance spectroscopy, could only be determined at T<300 K owing to sample–electrode interfacial effects. In contrast, the bulk σDCAC⊥ [001] showed a slight break at ≈380 K that may reflect the structural phase transition monoclinic→orthorhombic at ≈345 K. From AC conductivity measurements in the frequency range 20 Hz–1 MHz at T<300 K, a dispersive character of electronic relaxation was found, resembling that of amorphous semiconductors and of impurity conduction in crystalline semiconductors where it was ascribed to charge hopping processes of electrons between localized levels of cation pairs or clusters of limited lengths.