The Electronic Properties of Barium Sulfide

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Abstract
Barium sulfide has been prepared in a form suitable as a cathode emitter as well as in the form of compressed pills. It has a work function of 2.1 ev with a wide variation possible in activation. The most active materials had an emission at temperatures of 900°K and greater comparable to that from pure BaO. Pure nickel and platinum only were used as base metals. An equimolar mixture of BaS‐SrS had a work function of 2.6 ev, and x‐ray analysis indicated solid solution formation. The electrical conductivity of BaS was found to vary between wide limits depending on the degree of activation and the denseness of the specimen but was much less than for BaO. At 1000°K the specific conductivity of a compressed pill was 10−5 ohm−1 cm−1. The thermoelectric power was found to be constant with temperature although it decreased with increase in the activity of the specimen. The warmer electrode was always positive. Pure BaS had a thermoelectric power of 2.5 mv per degree between 970° and 1270°K. The effect of added impurities of iron on the electrical characteristics was studied. By mass‐spectrometer studies, the evaporation rate of BaS was found to be much less than that of BaO, indicating a vapor pressure of the sulfide about 100 times less than that of the oxide. The heat of sublimation was found to be 104 kcal/mole.