ii ABSTRACTS OF PAPERSTO APPEAR IN J. PHYS. CHEM. SOLIDS Vol.6, No.12

Fe1~phasehasbeencarriedout in the tempera- nearestneighborsitesof ~0. 035 eV accountsture range700-1350°Cusingsolid stateelectro- well for the experimentallyobservedquantities.chemicaltechniques. The resultsconfirm the Theconfigurationalentropy is an appreciablepresenceof threewustiteregionsseparatedby fraction (~10%at 300°K) of the total entropyorder- disordertransitions. Partial molar en- content.thalpiesandentropiesof solutionof oxygen in.Fe1_~Oare reported. (Received4 September1968)

(Received29 April 1968)(Revised18 September1968) 7. OPTICAL CONDUCTWITY IN ALKALI

METALSH. B~1ttnerandE. Gerlach(Battelle-

5. MAGNETO-ACOUSTIC INVESTIGATION Institut e.V., FrankfurtamMain,OF THE FERMI SURFACE AND SPIN Germany)SPLITTING OF THE LANDAU LEVELSIN p-TYPE AND n-TYPE PbTe It is shownthat the Mayer Naby peakin\V. Schllz (Philips Zentrallaboratorium the optical conductivity of alkali metalsarisesHamburg, Hamburg54, Vogt-Kollnstr.30) from transitionsfrom the Fermi seato the

Brillouin zoneboundaries.Quantumoscillationsof the magneto-

acousticattenuationhavebeenmeasuredin p-type (Received29 May 1968)and n-type samplesof leadtelluride. Fromthe (Revised14 August 1968)periodsof theseoscillations, measuredas afunction of theangle ~ betweenthe direction ofmagneticfield andthe [100] axis of the crystal, 8. STRUCTURAL AND MAGNETIC PRO-the shapeof the Fermi surfacehasbeeninvesti- PERTIESOF NON-STOICHIOMETRICgatedasa function of the carrier concentration. PRASEO-DYMIUM MONOPHOSPHIDEA strongnon-ellipsoidalbehaviorwas observed Enrico FranceschiandGiorglo L. Olcesefor bothp-typeandn-type material. Furthermore, (Istituto di Chimicafisica, Universita’spin splitting of the Landaulevels wasmeasured. di Genova,Genova,Italy)The splitting wasfound to be around~ the Landau-level spacinganddecreasesslightly with decrea- An investigationon the occurrenceof non-sing carrier concentration. stoichiometryin solid praseodymiummonophos-

phide wascarriedout by evaluatingthe variation(Received14 August1968) of the lattice constantanddensitywith the corn-(Revised17 September1968) position. A rangeof solid solutionby vacancies

in thephosphorussub-latticewasfoundbetweenthe compositionscorrespondingto PrPand

6. ON THE THERMODYNAMIC PROPER- PrPO.B5 phases. MagneticpropertiesandtheirTIES OF THE SOLID ELECTROLYTE dependenceon non-stoichiornetryweredeter-RbAg4I5 mined in thetemperaturerange4.2°- 500°K:forH. Wiedersichand W.V. Johnston the quasi-stoichiometricphasesthere is no evi-(ScienceCenter, North Americal Rock- denceof magneticorderinganda superconductingwell Corporation,ThousandOaks, transitionseemsto occur below 7°K,while anCalifornia 91360, U. S.A.) antiferromagneticcouplingof praseodymiumions

becomespossiblewhenthe interionic distancesThenon-randomdistribution of Ag~ions decreaseby introductionof vacanciesin the phos-

on threecrystallographicallynonequivalentsets phorussub-lattice.of tetrahedralsites in RbAg4I5 is a consequenceof bothsiteenergydifferencesandmutualrepul- (Received5 August 1968)sion of silver ions on nearestneighborsites. A (Revised13 September1968)methodsimilar to the quasicheniicalapproxima-tion, usedin the theoryof order-disordertrans-formations, hasbeenappliedto obtainthe con- 9. FERRIMAGNETIC STRUCTURE OFfigurationalentropyandexcessspecific heat Mn2Co2Cassociatedwith the disorderof the silver ions. N. S. SatyaMurthy, R. J. Begum, C. S.Site energydifferencesof —~0.027 and ‘~0.042 eV Somanathan,B. S. Srinivasanandbetweenthe different typesof silver sitesanda M. R. L. N. Murthy (BhabhaAtomic Re-mutual repulsionenergybetweensilver ions on SearchCentre, Trombay, Bombay74,India)

Vol. 6, No. 12 ABSTRACTS OF PAPERSTO APPEAR IN J. PHYS. CHEM. SOLIDS

The carbideMn2Co2C hasbeenfound valuesfor the momentsare:4.0~Bfor the cor-

to be ferrimagneticwith aNéel temperatureof ner Mn atom, 3. 36 ~B for the facecentreMn535°C by meansof neutrondiffraction. It hasa and1.24 ~B for eachCo atom. The smaller mo-cubic unit cell with an Mn atom at the cubecar- mentsof the facecentreatomsarisefrom thenerandthe carbonatom at the bodycentre. The Influenceof thecarbonatom. Polarizedneutronsfacecentresitesare takenup by theother Mn and were usedto chooseastructurehavingcubicsyrn-the two Co atomsin a statisticalmanner. The metry overoneof tetragonalsymmetry.Mn momentsare alignedantiparallelto eachotherwhile the two Co momentsare parallelto (Received20 August1968)the cornerMn moment. Themostreasonable