Vol. 3, No. 5 ABSTRACTSOF PAPERSTO APPEARIN i. PHYS. CHEM. SOLIDS xli

ALKALI METALS. 10. SUPERCONDUCTIVITYIN THE NIOBIUM-RobertGinell and T.J. Quigley (Department SELENIUM SYSTEM.of Chemistry,Brooklyn College of The City E. Revolinsky, G.A. SpieringandI). J.University of New York, Brooklyn, NewYork, Beernsten(Allis-ChalmersResearchLabs.,U.S.A.). Milwaukee, Wisconsin, U.S.A.).

It hasbeenshown, usingboth Swenson’s The dependenceof superconductingtransi-dataat 4.2°Kand Bridgman’sdataat roomtern- tion temperatureson changesin compositionandperature,that the alkali metals, which do not structurewasobservedin the niobium-seleniumfollow Bridgman’sempirical law, do foliwo system. Within the compositionlimits ofTait’s Law. Both Bridgman’sempiricalequation Nb1 05Se2to NbSe2,ahexagonaltwo-layerandLevitt’s highpressureempiricalapproach struètureof the NbS2type andahexagonalfour-are shownto be specialcasesof Tait’s Law. layerstructureof a new structuretypewereBridgman’sseriesof dataup to 40,000kg/cm

2 found to be superconducting.Theywereformedis shoi~nto be aboutasreliableas his 100, 000 by heatingat temperaturesof 600-800°Candkg/cm data. Use of the Tait equation, which 850-1000°Crespectively. For the two-layeris foundedon the strict theoreticalgroundof phase,Tc variedfrom 7. 0°Kat NbSe

2to 2. 2°Kassociationtheory, allows datato be smoothed at Nb1 O5~2~For the four-layer phase,theon atheoreticalbasisratherthanon astrictly transitiontemperaturevariedbetween6. 3°Kandempiricalone. Since Tait’s Law is derived 5.9°Kover the sameapproximatecompositionwithout assumptionsfrom the generalassocia- range. Doubletransitionsindicatingafour-layertion equationof state, it hasnow beenshown to two layerphasetransformationwereassociatedthat this equationof state is applicableto gases, with samplesquenchedfrom the four-layerphaseliquids and mostlikely solids. Datafor solids region. Periodicmeasurementof transitionwhich is not consistentwith this treatment temperatureof individualsamplesindicatedthatshouldbe heldassuspector non-continuousover the transformationcontinuedat roomtemperature.thepressurerangebeingconsidered.

(Received14 December1964)(Received21 October1964)(Revised10 December1964)

11. THE ROLE OF CHEMISORPTIONIN CUR-RENT FLOW IN INSULATING CdS CRYSTALS.

9. SHAPE RESONANCESIN SUPERCONDUC- PeterMark (RCA Laboratories,Princeton,TING CYLINDERS. * NewJersey, U. S.A.).C. J. Thompson(Applied MathematicsDepartment,University of New SouthWales, Fromastudyof the dependenceon theKensington,Australia). illuminationlevel of the changein the photo-

currentduring oxygenadsorption,asemi-The energygapequationfor asuper- qualitativemodelfor photo-inducedchemisorp-

conductingcircular cylinder at zerotemperature tion on insulatingCdS crystalsis given. Theis solvednumericallyfor diametersin the range examinationof atmospheresensitivetrappingis10-17A. U. As for the uniform membrane,the extendedto thermally-stimulated-currentmeas-energygapshowspronouncedresonanceswhen urementswhich show, in agreementwith Bube,consideredasafunctionof size. The resonances thatacrystalwith an oxygenfree surfacecanoccur eachtime an eigenvaluefor motion perpen- store lOb timesmoretrappedchargethanadicular to the cylinder axispassesthroughthe crystalon whosesurfaceoxygenhasbeenphoto-Fermi surface. The peaksof the resonances adsorbed. A modelis proposedto explainthis(~ 30°K)lie well abovethe bulk valuefor the effect. The darkcurrentis similarly atmosphereenergygap(t~ 7°K),the troughsbelowthis dependent; both its magnitudeandactivationvalue (t~10.

20K). The peaksare very sharp energyare sensitiveto oxygenexposure. It is -

andfor mostvaluesof the diameter, the energy found that the adsorbedoxygenions lie 0.91eVgap is small (~10-20K), and showsa tendency below the conductionbandand, in the dark, actto remainsmall, asdeep-lyingdonorswhich surfacecompensate

the shallowerbulk donors. Photo-inducedad-(Received14 December1964) sorptionof nitrousoxide is describedandits

_____________ relevanceto barrier catalysisis briefly discus-*Thjs researchwas supportedby U.S.A.F. ned.ResearchGrant No. 62-400. (Received16 December1964)