Conductivity enhancement in fluorite-structured Ba1−xLaxF2+x solid solutions |
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Authors: | KED Wapenaar JL Van Koesveld J Schoonman |
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Institution: | Solid State Department, Physical Laboratory, State Univesity, 3508 TA Utrecht, The Netherlands |
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Abstract: | The ionic conductivity of single crystals of the fluorite-structured solid solutions Ba1?xLaxF2+x(10?3 <×<0.45) has been studied as a function of temperature and composition in the range 300–900 K. Three regions can be discerned in the concentration dependence of the ionic conductivity: a dilute concentration region (x<10?3), where classic relations between solute content and ionic conductivity hold; an intermediate concentration region (10?3<x?5×10?2), where large changes occur in the conductivity activation enthalpy and the magnitude of the conductivity; and a concentrated solid solution region (x?5×10?2) characterized by enhanced ionic motion. In the dilute region the migration enthalpy for interstitial fluoride ions is determined to be 0.714 eV, while a value of 0.39 eV is found for the (LaBaFi)X association enthalpy. The defect chemistry in the intermediate concentration region is shown to be controlled by a superlinear increase of the concentration of mobile defects, while in the concentrated solid solution region a composition-independent amount of ≈1 mole% of interstitial fluoride ions with enhanced mobility, carry the current. |
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