toIT Thz Canadinn Mine ralngist V o l . 3 6 , p p . 1 0 1 7 - 1 0 2 7( 1 9 9 8 )
DIFFRACTION TRICLINIC MUSCOVITE: X-RAYDIFFRACTION, NEUTRON AND PHOTO.ACOUSTIC FTIRSPECTROSCOPY JIAN-IIE LIANG exo FRANK C. HAWTHORNE' Depamnent of Geolngical Sciences, Universtty of Manitoba Winnipeg, Manitoba R3T 2N2
IAN P. SWAINSON Ammic Energy of Canada Limited" Chalk River Lahoratories, Chalk River, Ontario K0J IJO AssTRACT Details of the H site in muscovite were determined using single-crystal neutron-diffraction data collected at room temperanne and powder neutron-diffraction data collected at 12 K. Single-crystal neutron-diffraction data, collected at room temperature by Rothbauer (1971), were re-examined using a split-site model for H in the sp:rcegroup CAc.Lnw-temperawe neutron-ditftaction data were used to evaluate the thermal-vibrational effect on the distribution of nuclear density at the H sites. The separationof the two sites is wider (0.78 A) at l2K, but separatenuclear-density maxima were not observed. At least two unique OH strerching bands are revealed by FTIR PAS @ourier-Transform In-fraRed PhotoAcoustic Spectroscopy) experiments. The intensity ratio of the component bands changes as ttre mirror speed varies, allowing detection of individual stretching bands in severely overlapped spectra. This result confirms that there are two distinct OH groups in the structure of the muscovite examined here. Collectively, these results indicate that there are two distinct H-atom positions in the structure of this muscovite, either disordered with long-range C2llc symmetry or ordered with lower symmetry. Long-exposue precession photos recorded at room temperaflre show weak ft01 (l odd) reflections that violate c-glide symmetry, assumed to exist in muscovite designated as the polyrype 2M1. Single-crystal peak-profiling also revealed similal well-defined reflections that are confirmed to be Bragg reflections, and not due to double diffraction. Combined with previous second-harmonic generation data on muscovite, thcse results indicate Cl symme6y for this sample of muscovite. The driving force for the symmetry lowering from C2lc to Cl in muscovite involves cooperative ordering of H atoms over two distinct positions in the strucn]re. Keryords: muscovite, triclinic symmetry, H-alom positions, neutron diffraction, Rieweld structure refinement, Fourier-transform infrared photo-acoustic specEoscopy.
Sotwtans Nousavons6tudi6les d6tailsdu site occupdpar l'hydrogbnedansla muscoviteau moyende diffraction de neutronssur cristal unique I tempdratureambianteet sur poudreI 12 K. Les donn6es pr6lev6espar Rothbauer(1971) sur cristal unique d pourdvaluerun moddled sitesH partag6sdansle groupespartalC2/c.l*s donn6esde temp6ratureambianteont 6tEr6-examin6es bassetemp6ratureont 6t6utilis6espour 6valuerles effetsde vib-rationthermiquesur la distributionde densit6desnoyauxsw les sitesH. La s6paration desdeuxsitesestplusimportante(0.78A) i 12K, maisnousn'avonspasvu de maximadistinctsdansla distributiondesnoyaux.Au moinsdeuxbandesuniquesd'dtirementOH sont6videntesdenslesspectresobtenusparspectroscopie infra-rougephoto-acoustique avectransformationde Fourier.l,e rapportdesintensit6sde cesbandeschangeselonla vitessedu miroir, ce qui permetla d6tectiondes bandesindividuelles d'6tirement dansces spectressuperpos6s.Ce r6sultatconfirme Ia pr6sencededeuxgroupesOH distinctsdansla structuredela muscovite,aumoinsdansl'6chantillon choisi.Pris dansI'ensemble, cesrdsultatsmontrentqu'il y a deuxpositionsatomiquesdistinctesoccup6espar I'hydrogdnedansc€ttestructure.L'occupation une de cespositionsestsoit d6sordonn6e sur unegrande6chelleselonla sym€tie C2lc, soit ordonn6e,aveccommecons6quence sym6triemoins6lev6e.Desclich6sdepr6cessiond temp€ratureambiantemontrentdesr6flexionsfaiblesde rypebOl(l impair) en violationdu plan de glissementc, suppos6existerdansla muscoviteidentifidecommepolytype2M1.1-eprofil de r6flexions parcristauxlniques r6vdleaussiunebonnerdsolutiondepicsdistinctsoMissanti la loi deBragg,et non individuellesgdn6r6es attribuableau phdnomdnede diffraction double. Ces observations,consid6r6esavec les dom6es ant6rieuresportant sur les deuxibmesharmoniquesde la muscovite,indiquela slm6trie Cl pour cet 6chantillon.La r6ductionde la sp9trte dz CZc d'Cl dansla muscoviteimplique la mise en ordre compl6mentairedesatomesH sur deuxpositionsdistinctesdansIa structue. (Iraduit par la R6daction) Mots-cl6s:muscovite,symdtrietriclinique, positiondesatomesH, diffraction de neutrons,affinementdeRieweld, spectroscopie infra-rougephoto-acoustique avectra.nsformation de Fourier. I E-mail address.'
[email protected]
1018
TIIE CANADIAN MINERALOGIST
hrrRolucnoN LocatingH atomsin mineralshasalwaysbeendifficult, as H is a very weak scattererof X-rays. It is usually omitted from structuremodelsil X-ray studiesof muscovite(Giiven 1971,Richardson& Richardson l982,Uang & Hawthome1996),althoughSchultzer aI. (1989)did include the H atom in their modelof the muscovitestructure.Single-crystalneutrondiffraction (Rothbauerl97I) gaveaccurateinformation about the positionof H in muscovite,but with a very largeanisotropic displacementof the H atom [amplitudeup to 14 times greaterthan thoseof other atomsin the structure, althoughthe powder neutron-diffractionstudy of Cattiet al. (1994)doesnot showsuchlargeanisotropy of the H atoml. Schultzet al. (1989)reportedon a sample of muscovitewith g'islinissymmetry,which would requiretwo distinctH-atompositions.Despiteextensive spectroscopic work (Serratosa & Bradley1958,Bassett 1960,Vedder& McDonald1963,Wada& Kamitakahara 1991),the questionof OH orientationand the number of unique OH groups in muscoviteremain unclear.
(apfu)oF THE TABLE1. UNITFORMULAE MUSCOVITE CRYSTALS WHICHABE DISCUSSED HERE
SI 14lAl :T t6tAl FA
Mn
3.068
_@?_ 4.000 1.954 0.029 0.013
W Li
>M K Na rc Ca F OH
2.979 1.021 4.000
3.037 0.963 4.000
1.929 0.002 0.006 0.003
1.884 0.14i1 0.005 0.014
n naE '_1_.sse_ 1.r?s
0.876 0.096 0.010
'-
0.892 0.077 0.021
_w9.1
0.982
0.991
0256 n.744)
0.1@
4S9_
.ry. 2.180
.: 2.046 N RRO
0.092
: 0.981 0.196
g-@I 2.000
(1996); LH:Liang &Halvthome References: (1971) ssT:schulE efal.(1989); R:Rothbauer
EleeRftmlrAL The muscovitesampleused here is from the Himalaya mine, Mesa Grande,California. Liang & Hawthorne(1996)reportedthe chemicalcomposition andboth single-crystalandRieweld refinementsof the structure.Table I lists theunit formula ofthis andother muscovitesamplesdiscussed in the text,
difftaction (a doublediffraction canonly be observedat one specific psi-angle,whereasa Bragg diffraction is observedthroughoutthe completerangeof psi angles). Powderneutrond.ifftactionot ]2 K
Powderneutron-diffractiondatafor muscovitewere collectedat 12 K in a liquid-Hecryostatusingthe sample of Liang & Hawthome(1996)loadedinto a vanaA single-crystalprecessioncamerawas usedto ob- dium can. The intensity data were collectedover a tain zero-levelprecessionphotographsusingh-filtered 48-hourperiodon thehigh-resolutionpowderdifftactoMoKa X-radiation,Exposuresof up to one week were meter at the C2 beam-holeof the NRU reactor at the takento testfor possibledeviationsfrom C2,lcsymme- Chalk River Laboratories,Ontario. A wavelengthof try, focusingparticularlyon /z0lreflections.Diffraction 1.5022(l)A, calibratedwith Al2O3powder,was used patternsat precessionanglesof 25 and 30" were in the datacollection.The detectorcollectsdatasimulobtainedto identify double-diffractioneffects,asa spe- taneouslyover an 80"rangeof scatteringangleswith an cific double diffraction cannot occur at two differenr angularseparationof the wires of 0.1".The scattering precession angles. rangeof 8 to I l8o wascoveredby seningthe detectorin A secondset low- andhigh-anglepositionsin sequence. Peakprofiling of weakh)l (l odd) reflectionsusing a of data was collectedwith the detectorat positionsof singk -crystal difftactometer 0.05"offsetto thoseof the fust set,giving intensitydata at a stepintervalof 0.05"20. The samemuscovitecrystal usedin the precession work wasmountedon anautomatedsingle-crystalfour- Fouri er -Transform I nfrared Photo-Acousrtc circle diffractometer.Peakprofiles of thevery weakhDl Spectroscopy( FTIR PAS) (l odd) reflectionswere 6ftainedby step-scanning the corresponding peskssysl a29-nnge ofup to 2ousing Fourier-TransformInfrared Photo-AcousticSpec100to 120stepswith a countingtime of 5 minutesper troscopy(FTIR PAS) differs from conventionalFIIR step.For one of suchreflection, 201, scansin different spectroscopyin that the IR band-intensitydistribution orientationsocorrespondingto different psi-angles is not only a function of absorbanceof the sampleand (rotation about the diffraction vector), were taken to IR frequency(asin transmissionIR spectroscopy),but ensurethat the reflection observedis not due to double is also strongly dependenton the thermal-diffusion Precessinn photography
1019
TRICLINIC MUSCOVTTE
lengths(in femtometen)arcbs = 5.803,LU= -3.7409, bsi= 4.1491,bpt = 3.449,bx = 3.71(Koester1977). y"= tl@Elpe @ ( 1 ) The single-crystalneutron-diffractiondataof Rothbauer wherek, p, C arethe thermalconductivity,densityand ( I 971) wereusedfor refinementof the H positionin the specific heat of the sample,respectively,and ; ,, (__) l_ffiN -W)tll JS7'2'^
Flc. 6. Difference-Fouriermaps projecteddown [100], showing the nuclear-density (contoursfrom -10.0 to -2.0) and distributionin muscoviteat (A): room temperature (B): l2K(contoursfrom-11.0to-1.0).Thecontourintervalis0.l arbitraryunits. half-height) of the O-H stretchhg band in muscovite is ahnost twice as large as in phlogopite (Rouxhet 1970, Bassett 1960, Serratosa& Bradley 1958), irrespective of sample temperahre (ftom 273 to 77 K). The band is also asymmetrical, with the slope toward higher frequency being more gradual than the slope toward lower frequency (Vedder & McDonald 1963). Two OH orientations were suggested by Serratosa & Bradley (1958), in analogy to the OH orientations in lepidolite. Infrared spectroscopy of muscovite at liquid-He
temperature may result in increased spectral resolution and provide more conclusive specral hformation on this issue. H position at 12 K At 12K. an elongate nuclear-density distribution for the H atom was obtained (Fig. 68), similar to that observed at room temperature. The muscovite sample used in the present study has a chemical composition
TRICLIMC MUSCOWTE
r025
Wavenumber(cm-1) Ftc. 7. FTIR PAS of muscovite-2Mr at room temDerature.
t: .CI
Wavenumber(cm.l) FIG. 8. FIIR PAS spectra of muscovite-2M1 in the OH-stretching region at room temrreratue.
similar to that of the sampleused by Rothbauer (1971), although the unit-cell parameters of the two samples do differ somewhat (Table 2). The individual O-H distances at 12 K are not significantly different from those at room temperature; however, the H(1)-H(2) sepalation is significantly larger at low temperature(0.78 A) than at room temperature(0.44 A). Such an increasein separation at low temperature supports a split H-atom model. Nevertheless,even with a 0.78 A separation,it was still not possible to resolve two maxima (Frg. 6B). Infrared spectroscopy The FTIR PAS spectrum of muscovite at 2.5 kllz (Ftg. 7) shows a shoulder to the high-frequency side of
the absorption envelope, and it is separatedfrom the principal maximum by an inflection point; this feature indicates the presence of (at least) two distinct bands in the spectrum. This conclusion is re-inforced by the series of spectra recorded with gradually decreasing interferometer-mirror speed @ig. 8). The intensity of the high-frequency shoulder increases relative to the maximum intensity of tle envelope as the mirror speed decreasesfrom 2.5 kHz to 5 Hz. Note that wavenumber increases toward the right-hand side in Figure 8, and that slower mirror-speed favors higher IR ftequencies. The increase in relative intensity of the right shoulder of the envelope indicates that there are two (or more) unique bands in the muscovile spectrum, in turn indicating more than one symmetrically distinct OH group.
1026
TIIE CANADIAN MINERALOGIST
Cooperativeeffectsin themuscovitestructure What drives the needfor subgroupsymmetryin muscovite? Schts,lz etaL (1989)suggested thatthelower symmetryis dueto the presence of cationsat theM(l) site of one layer and not at the M(l') sits,of the other layer. As the total amountof scatteringat the M(1) site in their refinementis low (0.7 e A-3;, it is difficult to seehow sucha low occupancy(0.035Li atomsperformula unit, apfu, eqwvalentto 0.4 electronsper formula unit) at onesite could drive a lowering of the symmetry of the crystal, as symmetry-breaking mechanisms require cooperativebehavior throughoutthe whole crystal. Energy calculations(Abbott et aI. 1989)and the resultsof neutroncrystal-structurerefinementindicate thattherearetwo independentH-atompositionsin muscovite. However,theseresultsdo rwt tndtcatewhether such positionsare long-rangeorderedor disordered within the structure.The presenceof c-glide-violating reflectionssuggeststhat theseH-atom positionsare actually long-rangeorderedin the structure.Thus, it seemsreasonableto proposethat the symmetrybreakingmechanisminvolvesthis orderingof the H atoms.Unlike theM(l)-M(l') ordering-mechanism proposedby Schulzer al. (1989),the atomsinvolved in a H-bonding mechanismare distributed uniformly throughoutthe completecrystal, and hencecan a"ffect the macroscopicpropertiesofthe crystal throughlocal cooperativeinteractions. Whatcancausecooperativeorderingof H atomsinto two symmetricallydistinctpositions?Inspectionof the structureof muscovitesuggeststhat it must involve short-rangeorder of Al and Si over the Z sites in the structure. In this regard, the results of Abbott et al. (1989)suggestthatthe H-atomorderingcouplesto the local Al-Si arrangement.In this regard, Schnlz et al. (1989)founda disordered distributionofAl-Si overthe tetrahedrain their Cl refinementof muscoviteusing X-ray data Thus,altho.lrghit now seemsestablishedthat muscovitecanhaveCl symmetry,andthat the driving force for the reductionin symmetryinvolves cooperative orderingof H over two distinct positionsin the muscovitestructure,the causeof this orderedarrangementof H is still obscure. AcrNowr.sDGevENTs
interpretation of the data. IBD NRC allowed us access to the FTIR PAS instrument. This work was supported by the Natural Sciences and Engineering Research Council of Canada in the form of a Graduate Scholarship to J-JL and in the form of Operating, Major Equipment and Infrastructure grants to FCH. RnrmsNcES C.W.(1989):TreatAssolT, R.N.Jn.,Posr,J.E.& BURNHAM, calculations.An. ment of hydroxyl in structure-energy Mineral.74, l4l-150. BAssEm,W.A. (1960):Role of hydroxylorientationin mica alteration.GeoLSoc.Am,,Bull. 71,449456. Bsg, D.L. (1993):Rietveldrefinementof the kaolinitestuctureat 1.5K. ClaysClayMincrals 41,738-744. R.E.(1979):Acentricity Honsey,R.S.&Nswr,rHAM, in the micas: an optical secondharmonic study. Am. Mineral. g. lO52-1O55.
& Jor${sroN,C.T. (1993):Rietveldrefinementand Fourier-transforminfrared spectroscopicstudy of the dickite structureat low temperatue.Clays CIay Minerah 41.297-3M. & voN DnFrr;, R.B. (1989): Rietveld refinement of
thenon-hydrogenatomicpositionsin kaolinite. ClaysClay Minzrals37,289-296. Carn, M., Frnnenrs, G., Hur-1,S. & Pevrse, A. (1994): Powderneutrondiffraction studyof 2Mt muscoviteat room pressureandat 2 GPa.Eur. J. Mincral.6, l7l-178. CH@r,Er,M., Roussr-r,G. & Bm,rneno,L. (1986):Fouriera more complete transformphotoacousticspectroscopy: method for quantitativeanalysis.Can. J. Phys. 64, l08l-1085. G.A. &Lnr, JruIryGuccmlrmu, S., ScHUlzE,w.A., HARRrs, Csorutc (1983): Noncentriclayer silicates:an optical secondharmonicgeneration,chemical,and X-ray study. Clays Clay M irrcrah 31, 251-26O. GiIvB.r,N. (1971):The crystalstructureof 2M1phengiteand 2Mr muscovite.Z. Krisnllogr.lY, 196-212. lltrr, R.J & Howann,C.J. (1986):A computerprogramfor RietveldanalysisoffixedJength X-ray andneutrondiffraction patterns.Awtralian Atomic Energy Commission, Luta: HeightsResearchlaboratories (Menai,New South Wales,Australia), Rep.MLl2.
We thank Steve Guggenheim,Don Peacor,R.J. Swope,anonymousreviewersand the unanonymous editor Bob Martin for their commentson this manu- KoEsrER,L. (1977): Neutron scatteringlengths and fundamentalneufroninleractions./z SpringerTractsin Modem script. Dr. Petr Cemf, University of Manitob4 kindly Physics- NeutronPhysics(W.S.Hohler,ed.).Springer, suppliedthe muscovitesample.AECL Chalk River Heidelberg,Germany(1-55). Iaboratories is acknowledgedfor the low-temperature neutron-diffractionbeamtime. Michael Sowa,Institute Lrer.rc,Jnr,r-Jm& Hawrnonwr, F.C. (1996): Rieweld refinefor Biodiagnostics,National ResearchCouncil of ment of rnicaceousmaterials:muscovite-2Mr,a compariCanada(IBD, NR.C)helpedcollect the PAS spectra sonwith single-crystalstructurerefinefrent Can.Mberal. y.tl5-122. andofferedvaluableadviceon experimentaldesignand
TRICLINIC
RrcrenosoN,S.M. & RrcsanosoN,J.W., Jn. (1982):Crystal structueof a pink muscovitefrom Archer'sPos! Kenya: implicationsfor reversepleochroismin dietahedral micas. Am-Mitrcral.67,69-75.
MuscowfE
1027
SrENcER, N.D. (1986): Listening in on solid materials. CHEMTECH (Jwe), 378-384.
Twc, Y.C. & Roycs,S.H.(1982):QuartitativeFourierransform IR photoacousticspectroscopyof condensedphases. Rorrmnunn,R. (1971):Untersuchung eines2M1-Muskovits Appl.Oprtcs2L,77-8O. mit Neutronenstrahlen. Neues.Jahrb. Mineral., Morntslu. t43-155. VDDm' W. & MCDoNALD, R.S.(1963):vibrationsof theOH ionsin muscovite.J. Chem.Phys.38,1583-1590. Rorncrsr, P.G. (1970):Hydroxyl stretchingbandsin micas:a quantitativeinterpretation,CIayMtttzral. 8, 375-388. Waoe, N. & Kawrararnna, W.A. (1991):Inelasticneufionstudiesof muscoviteandvermiculite a-ndRaman-scattering Scrwr4 P.K, Sr-!rDs, P.G.&Tnrfi\r
