Defects and Transport in Langasite II: Donor-doped (La3Ga4.75Nb0.25SiO14) |
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Authors: | Huankiat Seh Harry L. Tuller |
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Affiliation: | (1) Crystal Physics and Electroceramics Laboratory, Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA |
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Abstract: | The electrical conductivity of Nb doped langasite (La3Ga4.75Nb0.25SiO14) was examined as a function of temperature and oxygen partial pressure by complex impedance spectroscopy. A pO2-independent regime was found at high pO2 followed by a pO2− 1/6 dependent regime at low pO2. A defect model consistent with these results was derived in which the electron density n is fixed by the density of ionized Nb donors at high pO2 and by the generation of oxygen vacancies at low pO2. The temperature and oxygen partial pressure dependence of the electron density was obtained independently by thermoelectric power measurements. The Nb donor ionization energy was determined to be 1.52 ± 0.06 eV, confirming Nb to be a deep donor in langasite. By combining conductivity and thermoelectric power data, an expression for the electron mobility given by μe = 1.1× 10− 2exp( ) was obtained. After evaluating the temperature dependent conductivity data under reducing conditions, in light of the defect model, a value for the reduction enthalpy (Er = 6.57 ± 0.24 eV) was derived. |
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Keywords: | resonator defect equilibria electrical properties mixed ionic-electronic conductor |
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