High-temperature electrical conductivity, Seebeck Coefficient, and thermal conductivity measurements were used to study the effects of different cation substituents on electrical and thermal transport in YCr03 and LaCr03. The substitution of divalent Ca and Sr for Y and La, respectively, resulted in the formation of small polarons as charge carriers. The additional substitution of Mn for Cr resulted in the formation of a second charge carrier associated with the Mn. The electrical conductivity results were consistent with thermally activated transport by hopping of a temperature-independent carrier concentration. The activation energies were 0.20 and 0.12 eV for (Y,Ca)Cr03 and (La,Sr)Cr03, respectively, and increased to about 0.50 eV with the substitution of Mn for Cr. The Seebeck coefficient increased linearly with temperature and decreased with substituent concentration for both (Y,Ca)Cr03
and (La,Sr)Cr03. The substitution of Mn for Cr resulted in aSeebeck coefficient with a more complex dependence on temperature and substituent concentration. The thermal conductivity did not change significantly with either cation substitution or temperature.
Interfacial shear strength and interfacial sliding friction stress were assessed in unidirectional Sic-filament-reinforced reaction-bonded silicon nitride (RBSN) and borosilicate glass composites and 0/90 cross-ply reinforced borosilicate glass composite using a fiber pushout test technique. The interface debonding load and the maximum sliding friction load were measured for varying lengths of the embedded fibers by continuously monitoring the load during debonding and pushout of single fibers in finite-thickness specimens. The dependences of the debonding load and the maximum sliding friction load on the initial embedded lengths of the fibers were in agreement with nonlinear shear-lag models. An iterative regression procedure was used to evaluate the interfacial properties, shear debond strength ( T~) , and sliding friction stress (T,), from the embedded fiber length dependences of the debonding load and the maximum frictional sliding load, respectively. The shear-lag model and the analysis of sliding friction permit explicit evaluation of a coefficient of sliding friction ( p ) and a residual compressive stress on the interface (a,,). The cross-ply composite showed a significantly higher cwffcient of interfacial friction as compared to the unidirectional composites. [
This report has been distributed according to the category "Physics amd Mathematics" as given in "Standard Distribution Lists for Unclassified Scientific and Technical Reports" TID-4500 (14th Ed.), October 1, 1958. A total of 650 copies was printed.
Portions of this document may be illegible in electronic image products. Images are produced from the best available original document. DISTRIBUTION This report has been distributed according to the category "Physics" as given in "Standard Distribution Lists for Unclass fied Scientific and Technical Reports" TID-4500 (18th Ed.), August 31, 1962. A total of 675 copies was printed.
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