Ting Chen, Harrington, George F., Junko Matsuda, Kazunari Sasaki, Pham, David, Corral, Erica L., and Perry, Nicola H.
Journal of the Electrochemical Society; 2019, Vol. 166 Issue 10, pF569-F580, 12p
CRYSTAL grain boundaries, SINTERING, SPACE charge, ELECTROLYSIS, PARTIAL pressure, and GRAIN size
Perovskite La0.9Sr0.1Ga0.9Mg0.1O3-δ (LSGM) is one of the fastest known oxide ion conductors, with reported enhanced p-type electronic transference numbers at grain boundaries, attributed to space charge effects. As this material is applied as a solid oxide fuel/electrolysis cell electrolyte, it is of interest to learn how its mixed conductivity may be tailored. Field assisted sintering technique/ spark plasma sintering (FAST/SPS) and conventional sintering without field or pressure were employed to prepare pellets with various grain sizes, in order to systematically assess the influence of processing route on the mixed conductivity. AC-impedance spectroscopy and the brick layer model were applied to determine local conductivities as a function of temperature, oxygen partial pressure, and dc bias. With increasing sintering temperature and grain size, the following trends were observed: larger electrical grain boundary (GB) widths, higher GB potentials, lower specific GB conductivity, greater dc-bias dependence of GB conductivity, higher pO2-dependence of GB conductivity indicating higher electronic transference numbers, and lower pre-exponential factor for specific GB conductivity. These results suggest an increasing GB space charge effect with increasing sintering temperature/grain size, which coincided with increasing compositional uniformity by TEM and EDS. The results confirm that sintering route is an important variable for tailoring mixed conduction. [ABSTRACT FROM AUTHOR]
Multilayered heterostructures of Ce0.85Sm0.15O2−δand Y0.16Zr0.92O2−δof a high crystallographic quality were fabricated on (001)-oriented MgO single crystal substrates. Keeping the total thickness of the heterostructures constant, the number of ceria–zirconia bilayers was increased while reducing the thickness of each layer. At each interface Ce was found primarily in the reduced, 3+ oxidation state in a layer extending about 2 nm from the interface. Concurrently, the conductivity decreased as the thickness of the layers was reduced, suggesting a progressive confinement of the charge transport along the YSZ layers. The comparative analysis of the in-plane electrical characterization suggests that the contribution to the total electrical conductivity of these interfacial regions is negligible. For the smallest layer thickness of 2 nm the doped ceria layers are electrically insulating and the ionic transport only occurs through the zirconia layers. This is explained in terms of a reduced mobility of the oxygen vacancies in the highly reduced ceria.
Barsotti, Domenico, Pylypiw, Harry, and Harrington, George
Analytical Letters; January 1982, Vol. 15 Issue: 17 p1411-1422, 12p
A previously reported method for the determination of nitrite ion has been extended to include nitrate ion. Nitrate is reduced to nitrite by a cadmium column and the nitrite ion determined as diphenylnitrosamine. Cadmium interference is removed by pH adjustment and the use of KDTA.
American Ancestors; Spring2012, Vol. 13 Issue 1, p7-7, 1p
The article offers information about the national campaign for the New England Historic Genealogical Society (NEHGS). Attorneys Diantha C. Harrington and George C. Harrington of Framingham, Massachusetts, are longtime members of NEHGS with broad genealogical interests. The Harringtons recognize the importance of professionally preserving unique documents.