Correlation between electronic polarizabilities and ionic radii in alkali halides

viii ABSTRACTS OF ARTICLES TO APPEAR IN J. PHYS. CHEM. SOLIDS Vol. 19, No.3 C 11 = 4.31 C12 = 2.54 C~= 2.14 indicated how one may define the irreducible stresses C33 = 4.47 C13 = 2.18 C~ = 2.41 and strains in an unambiguous manner by using the differential strain-energy function. In a cubic material C1, = C33, C~ = C~ and C12 = C13: the elastic behaviour of this tetragonal compound close- Received 13 February 1975 ly resembles that of a cubic material, as might be antici- Revised 30 January 1976 pated from its structure. This similarity is further illus- 6. OPTICAL ABSORPTION AND ESR STUDY trated by reference to the symmetry of phase velocity and Young’s modulus surfaces. Examination of the OF F CENTRES IN BaC1F AND SrC1F elastic constants and reduced elastic constants of these CRYSTALS compounds shows a regular trend the elastic stiffness L. Taurel and M. Yuste, Laboratoire 1e decreases as the number of vacant sites increases. There Physique Cristalline, Université Paris-Sud, is an approximately linear relationship between the re- bãt.490, 91405 Orsay, France; M. Rahmani, duced bulk modulus and the number of sited vacancies. Centre Nucléaire de l’Université de T~héran, Amir Abad, Teheran, Iran; and D. Lemoyne, Received 23 June 1975 Laboratoire d’Optique Physique de l’E.S .P.C .1., Revised 30 January 1976 10, rue Vauquelin, 75231 Paris Cédex 05, France. 4. CORRELATION BETWEEN ELECTRONIC POLARIZABILITIES AND IONIC RADII IN Magnetic and optical properties of two types ot F ALKALI HALIDES centres, called F(F) and F(Cl), created in BaC1F and SrC1F tetragonal crystals are described. Jal Shanker and M.P. Verma, Department of The experimental position of the absorption bands Physics, Agra College, Agra-282 002, India. and the [g] principal values of each centre are the An analysis of the electronic polarizabilities and following at 78 K: sizes of ions in alkali halides has been carried out by considering a relationship according to which the elec- InBaC1F, F(Cl): tronic polarizability of an ion should vary as the nth power of its radius. The values of crystal radii, pohariz- = 438 nm, X1 = 550 nm, abilities and the exponent n have been calculated using g11 = 1.9690 ± 0.0003, gj = 1.9798 ± 0.0003; the free ion data reported by Pauling. The values of n are F(F): found to be nearly 3 in most of the crystals suggesting f430 nm the validity of the polarizability radius cube relation. = 532 nm, A1 = The polarizabilities and crystal radii calculated in the k446 nmj’ present study agree well with those estimated by earlier g11 = 1.9836 ± 0.0003, g1 = 1.9695 ± 0.0003. investigators. Received 28 July 1975 InSrC1F, F(CF): Revised 30 January 1976 = 380nm, A1 =465nm. g11 = 1.996±0.002, g1= 1.993 ± 0.002; 5. AN EXTENSION OF MOMENTS CALCU- LATIONS FOR OPTICAL ABSORPTION F(F): BANDS [345 nml X1~—4lOnm, Aj~ t363nmJ’ Jordan J. Markham, Department of Physics, Illinois Institute of Technology, Chicago, g1~= 1 .997 ± 0.001, g1 = 1 .993 ± 0.001. Illinois 60616, U.S.A. In this paper the developments of Schnatterly, (II and! refer to the light polarization or the magnetic ;hichter and Henry are extended by using a more general field direction with respect to the fourfold axis of the Formulation of the principle of spectroscopic stability crystal). (for a site of symmetry Oh). The linear effects for any This attribution disagrees with that proposed by type of stress is obtained next. The expressions indicate Nicklaus and Fischer, but accounts for the values of the how one can test the theory experimentally a critical energy levels of F(F) and F(CV) in BaC1F and SrC1F manner. This has not been done. The theory shows that calculated by S. Lefrant and A.H. Harker. one cannot expect to get more information on KC1 from Received 15 October 1975 stress experiments than is now available. Finally, it is Revised 30 January 1976

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Transcript of Correlation between electronic polarizabilities and ionic radii in alkali halides

Page 1: Correlation between electronic polarizabilities and ionic radii in alkali halides

viii ABSTRACTSOFARTICLES TO APPEARIN J.PHYS. CHEM. SOLIDS Vol. 19,No.3

C11 = 4.31 C12 = 2.54 C~= 2.14 indicatedhow one may definethe irreduciblestresses

C33 = 4.47 C13 = 2.18 C~= 2.41 andstrainsin an unambiguousmannerby usingthedifferential strain-energyfunction.

In a cubic materialC1, = C33,C~= C~andC12 = C13:theelasticbehaviourof this tetragonalcompoundclose- Received13 February 1975ly resemblesthat of a cubicmaterial,asmight beantici- Revised30January1976patedfrom its structure.This similarity is further illus- 6. OPTICAL ABSORPTIONAND ESRSTUDYtratedby referenceto thesymmetryof phasevelocityandYoung’smodulussurfaces.Examinationof the OF F CENTRESIN BaC1FAND SrC1Felasticconstantsandreducedelasticconstantsof these CRYSTALScompoundsshowsa regulartrendtheelasticstiffness L. Taurel andM. Yuste,Laboratoire1edecreasesasthe numberof vacantsitesincreases.There PhysiqueCristalline,UniversitéParis-Sud,is anapproximatelylinearrelationshipbetweenthe re- bãt.490,91405Orsay,France;M. Rahmani,ducedbulkmodulusand thenumberof sitedvacancies. CentreNucléairede l’Université deT~héran,

Amir Abad, Teheran,Iran;andD. Lemoyne,Received23 June1975

Laboratoired’OptiquePhysiquede l’E.S .P.C.1.,Revised30January1976 10, rue Vauquelin,75231 ParisCédex05,

France.4. CORRELATIONBETWEENELECTRONIC

POLARIZABILITIES AND IONIC RADII IN Magneticandopticalpropertiesof two typesot FALKALI HALIDES centres,calledF(F) andF(Cl), createdin BaC1Fand

SrC1F tetragonalcrystalsaredescribed.Jal ShankerandM.P. Verma,Departmentof The experimentalpositionof the absorptionbandsPhysics,AgraCollege,Agra-282002, India. andthe [g] principalvaluesof eachcentrearethe

An analysisof the electronicpolarizabilitiesand following at 78K:sizesof ionsin alkali halideshasbeencarriedoutbyconsideringa relationshipaccordingto which the elec- InBaC1F,F(Cl):tronic polarizability of anion shouldvaryasthe nthpowerof its radius.Thevaluesof crystal radii, pohariz- = 438nm, X1 = 550 nm,abilities andtheexponentn havebeencalculatedusing g11 = 1.9690±0.0003, gj = 1.9798±0.0003;the freeion datareportedby Pauling.The valuesof n are F(F):found to be nearly3 in mostof thecrystalssuggesting f430 nmthevalidity of the polarizability radiuscuberelation. = 532 nm, A1 =

Thepolarizabilitiesandcrystalradii calculatedin the k446nmj’presentstudyagreewell with thoseestimatedby earlier g11 = 1.9836±0.0003, g1 = 1.9695±0.0003.investigators.

Received28 July 1975 InSrC1F, F(CF):Revised30 January 1976 = 380nm, A1 =465nm.

g11 = 1.996±0.002,g1= 1.993±0.002;5. AN EXTENSION OFMOMENTS CALCU-

LATIONS FOROPTICAL ABSORPTION F(F):BANDS [345 nml

X1~—4lOnm, Aj~t363nmJ’JordanJ.Markham,Departmentof Physics,Illinois Instituteof Technology,Chicago, g1~= 1 .997±0.001, g1 = 1 .993±0.001.Illinois 60616,U.S.A.

In this paperthedevelopmentsof Schnatterly, (II and!refer to the light polarizationor themagnetic;hichterandHenryare extendedby usinga moregeneral field directionwith respectto the fourfold axisof theFormulationof theprinciple of spectroscopicstability crystal).(for a siteof symmetryOh). Thelineareffectsfor any This attributiondisagreeswiththatproposedbytypeof stressis obtainednext.The expressionsindicate NicklausandFischer,butaccountsfor thevaluesof thehow onecantestthe theoryexperimentally a critical energylevels of F(F) and F(CV) in BaC1FandSrC1Fmanner.Thishasnotbeendone.The theoryshowsthat calculatedby S. Lefrant andA.H. Harker.onecannotexpectto get moreinformation on KC1 from Received15 October1975stressexperimentsthanisnow available.Finally, it is Revised30 January 1976