Electrical conductivity of synthetic mullite single crystals - Kölner UniversitätsPublikationsServer

Malki, Mohammed, Schreuer, Juergen ORCID: 0000-0002-8611-6842 and Schneider, Hartmut (2014). Electrical conductivity of synthetic mullite single crystals. Am. Miner., 99 (5-6). S. 1104 - 1109. CHANTILLY: MINERALOGICAL SOC AMER. ISSN 1945-3027

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DOI:10.2138/am.2014.4442

Abstract

The electrical conductivity of 2/1-mullite (approximate composition 2Al(2)O(3)center dot SiO2) was measured using plane parallel, polished plates cut perpendicular to [100], [010], and [001] from a large single crystal grown by the Czochralski method. Impedance spectra were recorded in the 1 Hz to 1 MHz frequency range at temperatures from 550 to 1400 degrees C in air. The conductivity vs. temperature curves display changes of their slope between 850 and 950 degrees C depending on the crystallographical direction. The low-temperature region (T < 850 degrees C) of conductivity is characterized by low-electrical conductivities (sigma(av) approximate to 5.4 x 10(-9) Omega(-1)cm(-1), average conductivity at 550 degrees C) with sigma([010]) > sigma([100]) > sigma([001]) and low-activation energies (approximate to 0.66 eV, average value). In the high-temperature region (T > 950 degrees C) the electrical conductivity is significantly higher (sigma(av) approximate to 1.1 x 10(-9) Omega(-1)cm(-1), average conductivity at 1400 degrees C) with sigma([001]) > sigma([100]) approximate to sigma([010]), and with higher activation energies (approximate to 1.6 eV). While the conductivity in the low-temperature region essentially is electronic, ion conductivity dominates the conductivity in the high-temperature region. We believe that the ionic conductivity is essentially due to hopping of 0 atoms from structural sites linking the tetrahedral double chains in mullite toward adjacent oxygen vacancies especially in c-axis direction. These oxygen hoppings are associated with complex structural re-arrangements, which control and slow down the velocity of the processes. Thus the electrical conductivity of mullite at high temperature is much lower than, e.g., that of Y-doped zirconia, but is significantly higher than that of alpha-alumina.

Item Type:

Journal Article

Creators:

Creators	Email	ORCID	ORCID Put Code
Malki, Mohammed	UNSPECIFIED	UNSPECIFIED	UNSPECIFIED
Schreuer, Juergen	UNSPECIFIED	orcid.org/0000-0002-8611-6842	UNSPECIFIED
Schneider, Hartmut	UNSPECIFIED	UNSPECIFIED	UNSPECIFIED