Abstract
Both nominally undoped and 1%Sr-doped langasite were found to exhibit acceptor behavior and correspondingly mixed ionic-electronic conductivity under experimentally accessible conditions. At high pO2, the conductivity of nominally undoped langasite was pO2-independent (ionic behavior) but became increasingly pO2-dependent (n-type behavior) under reducing conditions. The substitution of strontium on lanthanum sites, increased the ionic and introduced a p-type electronic conductivity behavior at the highest pO2’s, while completely depressing the n-type electronic conductivity – observations consistent with predictions of the proposed defect model based on oxygen vacancy formation in response to negatively charged acceptor impurities.
Sr-doped langasite was found to have a higher activation energy for oxygen ion transport (1.27 ± 0.02 eV) than nominally undoped langasite (0.91 ± 0.01 eV). This difference could not be successfully explained by applying a simple defect association model but required the assumption of long range defect interactions.
Using the defect model, a number of key equilibrium constants (reduction (5.7 ± 0.06 eV), oxidation (2.18 ± 0.08 eV), electron-hole generation (3.94 ± 0.07 eV), and defect mobilities (oxygen vacancies and holes) were derived and summarized.
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Seh, H., Tuller, H.L. Defects and transport in langasite I: Acceptor-doped (La3Ga5SiO14). J Electroceram 16, 115–125 (2006). https://doi.org/10.1007/s10832-006-4081-x
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DOI: https://doi.org/10.1007/s10832-006-4081-x