The modification of apparent thermionic constants for oxygenated tungsten by the temperature variation of adsorptive equilibrium

Abstract

When the temperature variation of a saturated thermionic current i per unit area is represented by plotting log ( i /T 2 ) against 1/T, it has been customary to identify the slope and the vertical intercept of the graph with the electronic work function ϕ and the logarithm of the emission constant A, respectively, in Richardson’s equation i = AT 2 e - ϕ /k T . This identification has been reasonably successful for materials of a high degree of homogeneity, since they exhibit straight “Richardson plots” whose measurement offers values of A and ϕ not inconsistent with electronic data from other sources. On the other hand, certain materials exhibit curved plots, indicating at once that no fixed A and ϕ can be recorded. Others, with which we are here concerned, give plots which appear straight over an observed range but suggest values of A and ϕ , disagreeing so radically with established theory or with indirect experiments that they have been regarded as anomalous. We prove in one instance that an extension of the range reveals such a plot as part of a curve, and that the curve contains implicit quantities not solely electronic and therefore not expressed by even a sequence of simple Richardson equations. Hence the slopes and intercepts of tangents to this curve are not identifiable with values of ϕ and log A.