C. Stuber et W. Laqua, POINT-DEFECTS OF TEPHROITE - I - THE ELECTRICAL-CONDUCTIVITY OF MN2SIO4, Zeitschrift für physikalische Chemie, 206, 1998, pp. 197-218
Citations number
39
Categorie Soggetti
Chemistry Physical","Physics, Atomic, Molecular & Chemical
The electrical conductivity a of single crystalline Mn2SiO4 (tephroite
) grown from the melt, was investigated by impedance spectroscopy betw
een 1101 and 1197 degrees C as function of oxygen activity within the
range similar to 10(-16) less than or equal to a(O2) less than or equa
l to 0.21 (air). Mn2SiO4 is n-conducting within the low and p-conducti
ng within the high oxygen-activity regime, independent whether the sam
ple are buffered against MnO or MnSiO3. Based on our experimental resu
lts we propose a point-defect model the majority defects of which are
vacancies in the manganese sublattice V-Mn'', Mn3+-ions on Si-lattice
sites Mn-Si', holes h(.) (= Mn-Mn(.)) and electrons e'. Unlike Fe2SiO4
(fayalite), wherein according to thermogravimetric results of Nakamur
a and Schmalzried [1] associates (Fe-Fe. Fe-Si')(x) exist, our defect
model works without postulating the analogous species {Mn-Mn. Mn-Si'}(
x) to exist in tephroite. We drew this conclusion from the 1/5.5-power
law which is followed by our sigma-a(O2)-plots measured on stoichiome
tric tephroite in the high-a(O2) regime, whereas Nakamura and Schmalzr
ied derived an 1/5.0 power law from their measurements in the range of
similar oxygen activities on likewise stoichiometric fayalite. The eq
uilibrium constants for formation reactions of the aforementioned defe
cts, which emerged from our experiments were used to depict Kroger-Vin
k diagrams;they describe the dependence of defect concentrations on ox
ygen activities for both MnO resp. MnSiO3 buffered tephroite.