from first principles PP-I-1

PP-III-27Oxygen Isotope Exchange and Pressure Relaxation of Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3–Eremin V.A. 1 , Ananyev M.V. 1 , Kurumchin E.Kh. 1 , Yoo Ch.-Y. 2 , Bouwmeester H.J.M. 21 Institute of High Temperature Electrochemistry UB RAS, Yekaterinburg, Russia2 University of Twente, the Netherlandswedney@yandex.ruBarium―strontium cobaltites doped with iron are promising cathode materials for advancedelectrochemical devices. Detailed understanding of the processes occurring on the boundarybetween oxygen in the gas phase and the oxide is necessary to improve the performance ofdevices in which these materials are used. In this work the oxygen exchange kinetics ofBa 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3–δ has been investigated.The oxide samples were analyzed by the following methods: i) the phase composition wasdetermined by X-ray powder diffraction on a Rigaku diffractometer using CuKα-radiation atroom temperature in air; ii) the elemental composition was checked by X-ray fluorescencespectrometry on a XRF-1800 spectrometer; iii) the microstructure of the samples was studied bySEM on a JSM 5900LV with INCA Energy spectrometer. Prior to the SEM investigations, thesamples were grinded and polished on a Struers machine after epoxy impregnation in vacuum.The kinetics of the interaction between gaseous oxygen and Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3–δ has beenstudied by i) pressure relaxation (T = 450―750°C, Po 2 = 10 –3 ―10 –1.5 atm) andii) 16 O- 18 O isotopic exchange with gas phase analysis (T = 550―800°C, Po 2 = 10 –3 ―10 –1.5 atm).The rates of equilibration, interphase exchange, and of the three exchange types [1], and theoxygen diffusion coefficient have all been evaluated from the experimental data. The first andthird exchange types are found to prevail in oxygen exchange on Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3–δ . Thedependences of the rates of equilibration, interphase exchange and overall exchange onoxygen partial pressure have a power-law form. The order of the equilibration ratedependence is close to ½, which corresponds to the order for the overall exchange rate. Forthe interphase exchange rate and the third exchange type rate the orders are close to unity. Theinterphase exchange rates are found to be in good agreement with previous values measuredby the pulsed isotope exchange method [2]. In this work, the mechanism of oxygen exchangeis discussed for two cases: pressure relaxation and isotope exchange with gas phase analysis.References:[1] G.P. Boreskov etc. // Russ. Chem. Rev. 37(8) (1968) 613.[2] H.J.M. Bouwmeester etc. // PCCP. 11 (2009) 9640.179