x ABSTRACTSOFARTICLESTO BE PUBLISHEDIN THE J.PHYS. CHEM. SOLIDS Vol. 32,No. 12

reflectivity dataof Horita [2]. Usingthe Clausius— 6. RAMAN AND MID-INFRARED SPECTRO-Mossottirelation,we calculatetheelectronicpolariz- SCOPICSTUDY OFTHE PHASETRAN-ability for pyrite.Alsoevaluatedare the pressureand SITIONSIN OCTAFLUORONAPHTHALENElattice parameterdependenceof theenergygap.We pre- AT ELEVATED PRESSURESdict thetemperatureof decompositionof naturalpyrite D.M. AdamsandA.C. Shaw,Departmentofin inert atmospherefrom Mossbauerstudies. Chemistry,The Universityof Leicester,

Received30April 1979 LeicesterLE1 7RH,England;G.A. MackenzieandG.S.Pawley,Departmentof Physics,TheUniversity of Edinburgh,EdinburghEH9 3JZ,

4. EFFECTSOFFINITE TEMPERATURES,Scotland,U.K.

VALENCE BANDS AND ENERGYGAPSONTHE INDIRECT EXCHANGEINTERACTION Ramanandmid-infraredspectraof C10F8havebeenIN INTRINSIC SEMICONDUCTORS obtainedunderhydrostaticpressuresup to 17 kbarin a

diamondanvil cell. The C10P81to II phasechange,pre-R. Moreira Xavier,C.A. Taft andS. Lara,CentroBrasileiro dePesquisasFisicasAv. viously observedby neutrondiffraction at about0.8

kbar,hasbeenconfirmed.No evidencewasfound toWenceslauBras,71,Urca,Rio deJaneiro,Brasil.supporttheexistenceof a further phasechangebetween

The indirectexchangeinteractionbetweenlocalized 4 and6 kbar indicatedby theneutronwork, althoughmagneticmomentsvia virtual excitationsfrom the this is certainlynotprecludedasthe extraspectralvalencebandin intrinsicsemiconductorsis calculated featuresexpectedin this caseare extremelysmall. Thetaking into accountthetemperature,energygaps,finite modeGruneisenparameters,~ allow a cleardistinctionvalencebandsandeffectivemasses.The inclusionof betweeninternalandexternalmolecularmodes,andImite temperatureeffectschangessignificantly thephase scaleroughly in accordwith Zallen’srelation~y v~

2.andmagnitudeof theoscillations.For smallgapsemi-

Received10 April 1979conductorstheoscillatory characterandthepossibilityof ferro-magneticaswell asanti-ferromagneticcoupling 7. ELECTRONIC POLARIZABILITIES ANDareobtained.The exchangeinteractionoscillateswith SIZESOFIONS IN ALKALINE EARTHtemperaturesuggestinginterestingapplicationsof this HALIDES AND ALKALI CHALCOGENIDESmodel.

Jai ShankerandS.C. Agrawal, DepartmentofReceived2May 1979 Physics,Agra College,Agra-282002,India.

An analysisof theelectronicpolarizabilitiesand5. ETUDED’UN GROUPEMENT(Ru

3012)”3 EN sizesof ionsin the crystalsof alkalineearthhalidesand

PRESENCEDE DEGENERESCENCE alkali chalcogenideshasbeenperformedusinga relationORBITALE ET DE COUPLAGESPIN-ORBITE betweenpolarizability andionic radius.The electronic

M. Drillon, J. Darriet,R. GeorgesandP. Hagen- polarizabilitiesand sizesof ionsare calculatedusingthemuller, DépartementSciencede Matériaux, free statedatareportedby Pauling.The quantitiesE.N.S.C.S.,1, rue BlaisePascal,B.P. 296/R8 obtainedin the presentstudyare foundto vary from67008StrasbourgCedex,France. crystalto crystal,thusshowingthe deviationsfrom the

additivity rule. The resultsare discussedandcomparedA trinuclearcluster(Ru

3012)’3 occursin the with thoseobtainedby other investigators.

Ba4NbRu3O12andBa4TaRu3O12compoundswherethe

oxydationstatesof rutheniumare + III and+ IV. The Received28 September1979exchangeinteractionbetweenmagneticsitesis described Revised21 June1979by a Hamiltonian,which takesaccountof the orbitaldegeneracyof the

2T2g (Ru3~)and3Tig (Ru4~)terms. 8. A THEORETICALSTUDY OFALKALINE-EARTH CATIONS IN CRYSTALLINE

Fortheseions, thespin-orbitcoupling is the dominantSODIUM CHLORIDE, POTASSIUM

effect andit appearsthat the low temperaturemagneticCHLORIDE AND POTASSIUMBROMIDE

susceptibilitydependsessentiallyon the orbital reduc-tion factor andthe distortionof the coordinationocta- C.R.A. Catlow, Departmentof Chemistry, Uni-hedra.Thereis apparentlyno first orderperturbation versity CollegeLondon,20 GordonStreet,of the groundstatedueto the interactionbetweenmag- LondonWCIH OAJ, United Kingdom;J.Corishneticions, andJ.M. Quigley,Departmentof Chemistry,

University College Dublin, Belfield, Dublin 4,Received9 February 1979 Ireland;P.W.M. Jacobs,Departmentof