TY - JOUR

T1 - Transport numbers and ionic conduction of eutectic methacomposites {(1 − x)MeWO4 · xWO3}) (Me = Sr, Ba; x = 0−0.55)

AU - Pestereva, N. n.

AU - Zhukova, A. yu.

AU - Neiman, A. ya.

PY - 2007/11/1

Y1 - 2007/11/1

N2 - Transport numbers of oxygen ions, to2-, in methacomposites (1 - x)MeWO4 • xWO3, where Me = Sr and Ba and x = 0-0.55, are determined in the temperature interval 600 to 900°C by a method of the emf of an oxygen-air galvanic cell. It is demonstrated that the region of small contents of the additive (x ≤ 0.2) is predominantly characterized by oxygen-ion conduction (tO2 - = 1), which gives way to electronic conduction (t e = 1) at x > 0.35. It is confirmed once again that subeutectic compositions (1 - x)MeWO4 • xWO 3 where Me = Sr and Ba and x = 0-0.2 belong in the class of ion-conducting methacomposites. The threshold of percolation of electronic conduction (t e ≥ 0.5, tO2 - < 0.5) occurs at x t ≥ 0.3. Dependences of the transport numbers of the oxygen ions on the volume ratio between components in both composites resemble one another; specifically, the threshold composition contains nearly 20 vol % of WO3. The dramatic amplification (by 1-1.5 orders of magnitude) of the ionic conductivity in the methacomposites occurs at small contents of tungstic oxide (x ≤ 0.01). A chemical transport removal of excess tungstic oxide, which is segregated in the form of the surface compound MeW-s, from the surface of the MeWO4 grains destroys MeW-s, leading to a 10-15-fold drop of the ionic conductance. At x ≥ 0.05, the oxygen-ion conductance in the methacomposites is practically independent of their composition. A model for the formation and architecture of the methacomposites is qualitatively modified. The modified model takes into account doubled surface activity and mobility of the MeW-s phase with respect to MeWO4 and WO3.

AB - Transport numbers of oxygen ions, to2-, in methacomposites (1 - x)MeWO4 • xWO3, where Me = Sr and Ba and x = 0-0.55, are determined in the temperature interval 600 to 900°C by a method of the emf of an oxygen-air galvanic cell. It is demonstrated that the region of small contents of the additive (x ≤ 0.2) is predominantly characterized by oxygen-ion conduction (tO2 - = 1), which gives way to electronic conduction (t e = 1) at x > 0.35. It is confirmed once again that subeutectic compositions (1 - x)MeWO4 • xWO 3 where Me = Sr and Ba and x = 0-0.2 belong in the class of ion-conducting methacomposites. The threshold of percolation of electronic conduction (t e ≥ 0.5, tO2 - < 0.5) occurs at x t ≥ 0.3. Dependences of the transport numbers of the oxygen ions on the volume ratio between components in both composites resemble one another; specifically, the threshold composition contains nearly 20 vol % of WO3. The dramatic amplification (by 1-1.5 orders of magnitude) of the ionic conductivity in the methacomposites occurs at small contents of tungstic oxide (x ≤ 0.01). A chemical transport removal of excess tungstic oxide, which is segregated in the form of the surface compound MeW-s, from the surface of the MeWO4 grains destroys MeW-s, leading to a 10-15-fold drop of the ionic conductance. At x ≥ 0.05, the oxygen-ion conductance in the methacomposites is practically independent of their composition. A model for the formation and architecture of the methacomposites is qualitatively modified. The modified model takes into account doubled surface activity and mobility of the MeW-s phase with respect to MeWO4 and WO3.

UR - https://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=tsmetrics&SrcApp=tsm_test&DestApp=WOS_CPL&DestLinkType=FullRecord&KeyUT=000251190800015

UR - http://www.scopus.com/inward/record.url?partnerID=8YFLogxK&scp=36349036641

U2 - 10.1134/S1023193507110158

DO - 10.1134/S1023193507110158

M3 - Article

VL - 43

SP - 1305

EP - 1313

JO - Russian Journal of Electrochemistry

JF - Russian Journal of Electrochemistry

SN - 1023-1935

IS - 11

ER -