A simple theory of alkali halide gas molecules in the spirit of Born-Mayer lattice theory is presented. The molecule is considered to be constituted of ions, each of which is polarized by the electrostatic field of the other. This deformation polarization has two important consequences: (1) the net dipole moment of the molecule becomes appreciably lower than that given by the product of the electric charge e, and the internuclear separation a; (2) the repulsion constants (determined from empirical data) become different from the corresponding constants for the crystal. The theory yields satisfactory results for the binding energy, vibration frequency, and dipole moment, μ, in all instances where necessary data are available. In cases where the internuclear distances are not known experimentally, they are calculated from the theory using experimental binding energies. It is possible to assign to the ions Goldschmidt-like radii, the sums of which reproduce reasonably well both the calculated and the observed internuclear distances. Finally, item (1) above explains why Pauling's criterion for the fraction of ionic character, f=μ/ea, is not a very good measure of ionicity for these completely ionic substances.
Emission and evaporation characteristics of a porous tungsten cathode impregnated with the composition 5BaO·2Al2O3 are presented and are interpreted in terms of the cathode mechanism. Barium necessary for activation is generated by the reaction, 23 Ba3Al2O6+13 W=13 BaWO4+23 BaAl2O4+Ba,and is transported through partially clogged pores, the length of which increases with time, predominantly via Knudsen flow. During transport, oxygen is acquired from the tungsten, leading to a substantial content of BaO in the evaporant. The BaAl2O4 component of the impregnant is inert. Emission is substantially lower than that of an L cathode, presumably because of release of a poisoning agent accompanying the activator.
An examination of the validity range of the Shockley theory reveals that it is applicable to the emitter and collector regions for all current values of interest, whereas it is valid in the base region only for very small currents. In the present paper the treatment of the base region is extended so as to apply to arbitrary injection level and to include the effect of surface recombination. Two predictions are made: (a) the surface recombination velocity should increase with injection level; and (b) the alpha cut-off frequency for a transistor with plane parallel junctions should increase with emitter current by a factor of two.
It has long been known that the quantitative separation of cadmium and mercury by procedures which depend upon the different solubilities of their sulfides is in many cases impossible (3,4,5,6). Because of the near equality in atomic radii of the two metals, it is to be expected that substitutional solid solutions should easily be formed. The investigations of Bottger and Druschke (3) and of Ahrens (1) point strongly to the occurrence of solid solutions in the zinc blende structure as the explanation of the induced precipitation of cadmium sulfide by mercuric sulfide and the failure of boiling dilute nitric acid to extract all the cadmium from a mixed precipitate of these sulfides. Since both sulfides are polymorphous, solid solutions might be expected to exist in any one of the crystal structures exhibited by the pure components. It therefore appeared of interest to us to study the structures of the phases obtained by coprecipitation of the two sulfides under a variety of conditions, and to compare them with the structures formed by the separate precipitation of each substance under the given conditions. During the course of the investigation, observations were made bearing on the polymorphism of both sulfides.CADMIUM SULFIDE Cadmium sulfide is dimorphous (8), crystallizing in a hexagonal form (wurtzite structure) and also in a cubic form (zinc blende structure). Milligan (7) has reported some of the conditions under which each modification is precipitated by hydrogen sulfide from neutral or acid solutions of various cadmium salts.No data on the stability relations of the two modifications have been heretofore available. By direct observation of the transition
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