HR: 1330h
AN: T42A-0277    [PDF]
TI: $\alpha$-$\beta$ Inversion in Quartz From Low Frequency Electrical Impedance Spectroscopy
AU: * Bagdassarov, N
EM: nickbagd@geophysik.uni-frankfurt.de
AF: Nikolai Bagdassarov, Institut fuer Meteorologie und Geophysik, Universitaet Frankfurt, Feldbergstrasse 47, Frankfurt am Main, 60323 Germany
AB: The $\alpha-\beta$ phase transformation in polycristalline quartz has been studied in the pressure range from 0.5 to 2.5 GPa by the use of the low frequency electrical impedance spectroscopy in the range from 10$^{-2}$ to 10$^{5}$ Hz. The electrical conductivity (dispersion) obtained at low frequencies (low frequency dispersion or LFD) is due to the grain boundary electric charge transport and electrode polarization. The temperature dependence of LFD exhibits a different slope on an Arrhenius plot $ln(\sigma_{LFD}\times T)$ vs. $1/T$ above and below T$_{c}$, where T is the absolute and T$_{c}$ is the inversion temperature. The point where the slope changes, coincides with the T$_{c}$, i. e. the temperature point of $\alpha$-$\beta$ inversion in quartz. The obtained inversion temperature T$_{c}$ from this method compares well with the previous measurements of T$_{c}$ using DTA and laser interferometry. The LFD data in insulating materials with ionic conductivity due to impurities may be a useful method for characterization of structural displacive phase transitions in quartz-like structures, for example, berlinite AlPO$_{4}$ and FePO$_{4}$. The results of this study in SiO$_{2}$ demonstrated workability of the LFD method, and the experimentally determined slope of $dT_{c}/dP$ in the range of from 0.5 to 2.5 GPa is $\sim 233.5\deg$/GPa. The activation volume of the electrical conductivity in $\alpha$ phase is several times larger than in $\beta$ phase indicating that in two phases differing proportion of ion types (alkalis and H$^{+}$) may be responsible for the overall electric charge transport along grain boundaries.
DE: 3904 Defects
DE: 3914 Electrical properties
DE: 3924 High-pressure behavior
DE: 5109 Magnetic and electrical properties
SC: Tectonophysics [T]
MN: 2003 Fall Meeting