A Raman and infrared spectroscopic study of the phosphate mineral laueite.

A

Raman

and

infrared

spectroscopic

study

of

the

phosphate

mineral

laueite

Ray

L.

Frost

a,

*

,

Ricardo

Scholz

b

,

Andrés

López

a a

SchoolofChemistry,PhysicsandMechanicalEngineering,ScienceandEngineeringFaculty,QueenslandUniversityofTechnology,GPOBox2434,Brisbane,

Queensland4001,Australia

b

GeologyDepartment,SchoolofMines,FederalUniversityofOuroPreto,CampusMorrodoCruzeiro,OuroPreto,MG35,400-00,Brazil

A R T I C L E I N F O

Articlehistory:

Received24February2015

Receivedinrevisedform1December2015

Accepted1December2015

Availableonline2December2015

Keywords: Laueite Phosphate Hydroxyl Ramanspectroscopy Infraredspectroscopy A B S T R A C T

A laueite mineral sample from Lavra Da Ilha, Minas Gerais, Brazil has been studied by vibrational spectroscopy and scanning electron microscopy with EDX. Chemical formula calculated on the basis of semi-quantitative chemical analysis can be expressed as (Mn2+

0.85,Fe2+0.10Mg0.05)P1.00(Fe3+1.90,Al0.10)P2.00(PO4)2(OH)2
8H2O.

Thelaueitestructureis basedonaninfinitechainsofvertex-linkedoxygenoctahedra,withFe3+

occupyingtheoctahedralcenters,thechainorientedparalleltothec-axisandlinkedbyPO4groups.

Consequentiallynotallphosphateunitsareidentical.TwointenseRamanbandsobservedat980and 1045cm1areassignedtothen1PO43symmetricstretchingmode.IntenseRamanbandsareobservedat

525and551cm1withashoulderat542cm1areassignedtothen4outofplanebendingmodesofthe

PO43.Theobservationofmultiplebandssupportstheconceptofnon-equivalentphosphateunitsinthe

structure.IntenseRamanbandsareobservedat3379 and3478cm1andare attributedtotheOH stretching vibrationsofthe hydroxylunits.Intense broadinfraredbandsare observed.Vibrational spectroscopyenablessubtledetailsofthemolecularstructureoflaueitetobedetermined.

ã2015ElsevierB.V.Allrightsreserved.

1.Introduction

The mineral laueite of formula Mn2+_Fe

23+(PO4)2(OH)2
8H2O

[1,2] is a hydrated hydroxy phosphate of ferric iron and manganese. The mineral is a member of the homonimous mineral group. Other minerals in this group are césarferreiraite Fe2+_(Fe3+₎

2(AsO4)2(OH)2

8H2O, ferrolaueite Fe2 +_Fe

23+(PO4)2(OH)2

8H2O, gordonite MgAl23+(PO4)2(OH)2

8H2O,

kastningite (Mn2+, Fe2+,Mg)Al2(PO4)2(OH)2
8H2O, laueite Mn2 +_Fe

23+(PO4)2(OH)2

8H2O, maghrebite MgAl2(AsO4)2(OH)2

8H2O,

mangangordonite Mn2+_Al

23+(PO4)2(OH)2

8H2O, paravauxite Fe2 +

Al23+(PO4)2(OH)2
8H2O [3], sigloite Fe3+Al23+(PO4)2(OH)2
7H2O

[4]andushkoviteMgFe23+(PO4)2(OH)2

8H2O[5–8].

ThemineralwasnamedbyHugoStrunzin1954inhonorofMax FelixTheodorvonLaue(1879–1960).Lauewasthefirsttoverify that minerals had a regular atomic arrangement as had been predictedbypreviousphysicists.Laueitewasfirstdescribedfrom HagendorfSouthpegmatite,Bavaria,Germany.Laueiteis dimor-phouswiththemineralgordonite[9].Crystalstructureoflaueite

wasdeterminedbyMoore[5–7].Moorefoundthatthereweretwo isotypesand3polymorphsforlaueite[5].Thelaueitestructureis basedonaninfinitechainofvertex-linkedoxygenoctahedra,with Fe3+_{occupyingtheoctahedralcenters,thechainsorientedparallel}

tothec-axis.Themineralshowstriclinicsymmetry,spacegroup P-1,andunitcellparametersare:a =5.28Å,b=10.66Å,c =7.14Å,

a

=107.91,

b

=110.98,

g

=71.12.

As paravauxite is isostructural with laueite Mn2+_Fe3 +

2(PO4)2(OH)2
8H2O [3,12],itcouldbeindirectlyconcluded that

thestructureofparavauxiteisbasedonaninfinitechainof vertex-linkedoxygenoctahedra,withAloccupyingtheoctahedralcenters, the chain oriented parallel to the c-axis. Chains are in turn connectedtoothersbyPO4tetrahedrawhichalsobridgethrough

isolated octahedra(with Fe2+_{as centers).The laueitestructural}

formulaisMn2+_Fe3+

2(OH)2(PO4)2(H2O)6
2H2O[3],andaccordingto

analogy,theparavauxitestructuralformulaisthenFe2+_Al 2(OH)2

(-PO4₎

2(H2O)6

2H2O and the non-octahedrally bonded waters

appearinginacavityleftinthestructure.Indetaileddescription, inanalogywithlaueitestructure[3],thechainsofAl-octahedra decoratedbyflankingPO43groups(whichextendinc-direction)

meldinthea-directionbysharingonequarteroftheflankingPO4

vertices with octahedra of adjacent chains to form an [Al2(PO4)2(OH)2(H2O)2] sheet. In the resulting sheet, the PO4

* Correspondingauthor.Fax:+61731381804.

E-mailaddress:[email protected](R.L. Frost).

http://dx.doi.org/10.1016/j.vibspec.2015.12.001

0924-2031/ã2015ElsevierB.V.Allrightsreserved.

ContentslistsavailableatScienceDirect

Vibrational

Spectroscopy

tetrahedraarethree-connected.Therearetwodistinctoctahedra inthesesheets,oneofwhichissix-connectedwithinthesheet,and theotherofwhichis onlyfour-connectedandhas(H2O)attwo

vertices.

Ramanspectroscopyhasprovenveryuseful forthestudyof minerals, especially minerals containing oxyanions such as phosphate [3,4]. This paper is a part of systematic studies of vibrationalspectraofmineralsof secondaryoriginin theoxide supergene zone. Theobjective of this research is toreportthe Ramanandinfraredspectraoflaueiteandtorelatethespectrato themolecularstructureofthemineral.

2.Experimental

2.1.Samplesdescriptionandpreparation

Theminerallaueitestudiedinthisworkwasobtainedfromthe collectionoftheGeologyDepartmentoftheFederalUniversityof OuroPreto,MinasGerais,Brazil,withsamplecodeSAE-025.The laueiteoriginatedfromtheCiganamine,ConselheiroPena,Minas Gerais,Brazil.Themineraloccursinassociationwithfrondeliteina paragenesisrelatedtothehydrothermalalterationoftriphylitein Li-bearingpegmatites.Crystalsoflaueitecanmakenicespecimens withtheir colorless or light green color and glassy luster. The mineralisanuncommonspeciesincomplexzonedpegmatites.

The sample wasgentlycrushedand the associatedminerals were removed under a stereomicroscope Leica MZ4. Scanning electronmicroscopy (SEM)was appliedtosupportthe mineral chemistry.

2.2.Scanningelectronmicroscopy(SEM)

Experimentsandanalysesinvolvingelectronmicroscopywere performedintheNanoLab,REDEMAT,SchoolofMines, Universi-dade Federal de Ouro Preto, Ouro Preto, Minas Gerais, Brazil. Laueite crystals were coated with a 5nm layer of evaporated carbon.Secondaryelectronimagewas obtainedusingaTESCAN VEGA3 equipment. Qualitative and semi-quantitative chemical analyses in the EDS mode were performed with an Oxford spectrometerandwereappliedtosupportthemineral characteri-zation.

Ramanspectroscopy

Crystalsoflaueitewereplacedonapolishedmetalsurfaceon thestageofanOlympusBHSMmicroscope,whichisequippedwith 10,20,and50objectives.ThemicroscopeispartofaRenishaw 1000Ramanmicroscopesystem,whichalsoincludesa monochro-mator,a_filtersystemandaCCDdetector(1024pixels).TheRaman spectrawereexcitedbyaSpectra-Physicsmodel127He–Nelaser producing highly polarised light at 633nm and collected at a nominalresolutionof2cm1anda precisionof_1cm1inthe range between 4000 and 100cm1. Some of these phosphate mineralsfluorescedbadlyat633nm;asaconsequenceotherlaser excitationwavelengthswereusedespeciallythe785nmlaser.The poweratthesamplewas0.1mW.

Repeated acquisitions on the crystals using the highest magnification (50) wereaccumulatedtoimprovethesignalto noise ratio of the spectra. Spectra were calibrated using the 520.5cm1lineofasiliconwafer.Previousstudiesbytheauthors providemoredetailsoftheexperimentaltechnique.Alignmentof all crystals in a similar orientation has been attempted and achieved.However,differencesinintensitymaybeobserveddueto minordifferencesinthecrystalorientation.

ARamanspectrumoflaueiteisprovidedintheRRUFFdatabase. Thespectrumonlycoversthe1200–100cm1spectralrange.This spectrumisprovidedinSupplementaryinformationasFig.S1. Infraredspectroscopy

InfraredspectrawereobtainedusingaNicoletNexus870FTIR spectrometerwithasmartendurancesinglebouncediamondATR cell.Spectraoverthe4000–600cm1rangewereobtainedbythe co-additionof128scanswitharesolutionof4cm1andamirror velocity of 0.6329cm/s. Spectrawere co-added toimprove the signaltonoiseratio.

Spectralmanipulationsuchasbaselinecorrection/adjustment and smoothing were performedusing theSpectracalc software packageGRAMS(GalacticIndustriesCorporation,NH,USA).Band component analysis was undertaken using the Jandel ‘Peakfit’ softwarepackagethatenabledthetype offittingfunctiontobe selected and allows specific parameters to be fixed or varied accordingly.Bandfittingwas doneusing aLorentzian–Gaussian cross-productfunctionwiththeminimumnumberofcomponent bandsusedforthefittingprocess.TheGaussian–Lorentzianratio was maintained at values greater than 0.7 and fitting was undertakenuntilreproducibleresultswereobtainedwithsquared correlationsofr2_{greaterthan0.995.}

5.Resultsanddiscussion 5.1.Chemicalcharacterization

TheBSIimageoflaueitesamplestudiedinthisworkisshownin Fig.1. Qualitative and semi-quantitative chemical composition showsaFeandMnphosphatephasewithminoramountsofMg andAl.ThechemicalanalysisisrepresentedasanEDXspectrumin Fig. 2. On the basis of semiquantitative chemical analyses the

Fig.1.SEMimageofBrazilianlaueite.

chemicalformula wascalculatedand canbeexpressedas(Mn2 +

0.85,Fe2+0.10Mg0.05)P1.00(Fe3+1.90,Al0.10)P2.00(PO4)2(OH)2
8H2O.

Vibrationalspectroscopy

The Raman spectrum of laueite over the 4000–100cm1 spectralrangeisreportedinFig.3a.Thisspectrumwasobtained usingthe633nmlaser.Thespectrumshowscomplexitywithmany bandsbeingobserved.Thisfigureshowsthepositionandrelative intensitiesoftheRamanbands.Itisnoteworthythattherearelarge partsofthespectrumwherenointensityisobserved.TheRaman spectrumistherefore,subdividedintosectionsdependingupon thetype of vibrationbeing analysed. The infraredspectrum of laueite over the 4000–600cm1 spectral range is displayed in Fig.3b.Thespectrumisnotshownbelow600cm1.Thereasonfor thisisthatweareusingareflectiontechniqueandtheATRcell absorbsallincidentradiationbelowthiswavenumber.Thereare parts of this infrared spectrum where little or no intensity is observed. Thisspectrum maybe thus subdivided into sections dependinguponthetypeofvibrationbeinganalyzed.Asummary ofthespectroscopicdataisgiveninTable1.

TheRamanspectrum ofthelaueitemineralsampleover the 3800–2500cm1 spectral range is reported in Fig. 4a. Intense Ramanbandsareobservedat3478,3430and3379cm1andare assigned to thestretching vibration of the hydroxyl units.The bands at3080 and 3297cm1are assigned towater stretching vibrations. The infrared spectrum over the 3800–2500cm1 spectral range is reported in Fig. 4b. The infrared spectrum is complex with overlapping bands observed. Band component analysisenablescomponentbandstoberesolved.Infraredbands are observed at 3532, 3470, 3387, 3241 and 3035cm1 are attributedtotheOHstretchingvibrationsofthehydroxyl units, althoughthebandat3035cm1mayassignedtowaterstretching vibration.Breitingeretal.studiedhemineralwardite.Althoughthe structure of wardite is different to that of laueite, it is not unreasonabletomakeacomparison.Breitingeretal.[10]found infraredbandsat3520(vw),3545(s),3585(sh)and3613cm1(m). Breitinger et al. states that the

n

(OH) modes in the two

Fig.2.EDXanalysisofBrazilianlaueite.

Fig.3.(a)Ramanspectrumoflaueiteoverthe4000–100cm1spectralrange(b)

independentpairsofsymmetry-correlatedOHgroupsclassifyas 2a+2b; withthecorrelation splittingbetween a and b species dependingonthedistancesineachofthepairs[10].The

n

(OH) regionofIRspectraoflaueiteshowstwosharpbands(3241and 3387cm1) with two weak shoulders or satellites (3470 and 3532cm1).Itislikelythatthetwosharpinfraredbandsaredueto two independentand non-equivalent OH units. The two sharp shoulderbandsmaybeattributedtotheFe–OH–Fegroups.

These bands at 3241 and 3387cm1 are assigned to water stretchingvibrations.Itisprobablethatsomeofthecomponent bandsareduetoovertonesandcombinationofthewaterbending and librational modes. The position of the water stretching vibrationprovidesevidenceforstronghydrogenbondingandthat waterisinvolvedindifferenthydrogenbondingarrangements.The bandsprovideanindicationthatwaterisverystronglyhydrogen bondedinthelaueitestructure.Itispossiblethatthebandsreflect thetwoisotypesoflaueiteasdemonstratedbyMoore[5].

The Ramanspectrum of the laueite in the 1800–1300cm1 spectralrangeisillustratedinFig.5a.TwoRamanbandsarefound at1633and1692cm1.Thesebandsareascribedtowaterbending modes.Theinfraredspectrumofthelaueitemineralsampleover the1800–1300cm1spectralrangeisshowninFig.5b.Infrared bandsareobservedat1589and1624cm1.Thebandsinthisregion resultfromcorrelationsplittingasaresultoftheshortdistanceand orientationoftheH2Omolecules.

TheRamanspectrumoflaueiteinthe1250–650cm1regionis displayedinFig.6a.Thespectrumisdominatedbytwointense bandsataround980and1045cm1.Thesetwobandsareassigned to the

n1

PO43 symmetric stretching vibrations. The Raman

spectrumoflaueitefromtheRRUFFdatabaseisprovidedinthe supplementary information as Fig. S1. Two intense bands are observedat976and1089cm1withashoulderbandat1003cm1. ThisspectrumdiffersfromourspectrumasshowninFig.6a.Two intensebandsareobservedreflectingtwonon-equivalent phos-phateunitsinthelaueitestructure,aswasdemonstratedbyMoore [5]. Galy [11] first studied thepolarized Raman spectra of the H2PO4 anion. Choi et al. reported the polarization spectra of

NaH2PO4crystals.CascianiandCondrate[12]publishedspectraon

brushiteandmonetitetogetherwithsyntheticanhydrous mono-calciumphosphate(Ca(H2PO4)2),monocalciumdihydrogen

phos-phate hydrate (Ca(H2PO4)2

H2O) and octacalcium phosphate

(Ca8H2(PO4)6
5H2O).Theseauthorsdeterminedbandassignments

forCa(H2PO4)andreportedbandsat1002and1011cm1asPOH

andPOstretchingvibrations,respectively.ThetwoRamanbandsat 1086 and 1167cm1 are attributed to both the HOP and PO antisymmetricstretchingvibrations. CascianiandCondrate[12] tabulatedRamanbandsat1132and1155cm1andassignedthese bandstoPOsymmetricandthePOantisymmetricstretching vibrations.

Breitinger et al. used FT-Raman to obtain their spectra of warditeandfoundoverlappingRamanbandsat999and1033cm1 andassignedthesebandstothe

n1

PO43symmetricstretchingand

n3

PO43antisymmetricstretchingmodes.Thedifferenceinthe

spectrabetweenourwork andthat of Breitingeret al. maybe attributedtotheimprovedtechnologyofthespectrometerwith greaterresolution.Otherbandsoflesserintensityareobservedat 997,1021,1069and1096cm1.Theselattertwobandsareassigned tothe

n3

PO43antisymmetricstretchingvibrations.Thefirsttwo

bandsareattributedto

n1

HOPO33stretchingvibrations.

Breitingeretal.assignedthebandat999cm1intheRaman spectrumofwarditetoAlOHdeformationmodes.Inthisworkthe bandat997cm1isquitesharpandwellresolved.Agroupoflow

Table1

Vibrationalspectroscopicdataoflaueite(latticemodesnotlisted).

Laueite Laueite Probableassignment

Raman Infrared 3515 3532 n(OH) 3478 3470 n(OH) 3430 vðH2OÞ 3379 3387 vðH2OÞ 3297 vðH2OÞ 3080 3035 vðH2OÞ 1692 1650 d_ðH2OÞ 1613 1624 dðH2OÞ 1096 1090 v3ðPO4Þ 1064 1074 v3ðPO4Þ 1045 1026 v3ðPO4Þ 1021 993 v1ðPO4Þ 997 959 v1ðPO4Þ 980 918 g_ðH2OÞ 864 864 g_ðH2OÞ 774 g_ðH2OÞ 731 669 g_ðH2OÞ 551 g_4ðPO4Þ 542 g_4ðPO4Þ 525 g_4ðPO4Þ 472 v2ðPO4Þ 456 v2ðPO4Þ 404 v2ðPO4Þ 357 v1ðFeOÞ 335 v1ðFeOÞ

Fig.4.(a)Ramanspectrumoflaueiteoverthe3800–2600cm1spectralrange(b)

Infraredspectrumoflaueiteoverthe3800–2500cm1range.

intensitybandsat1069and1096cm1andareassignedtothe

n3

PO43 antisymmetricstretchingmodes.Breitingeretal. didnot

reportany bands in these positions in theRamanspectrum of wardite.Theseworkersreportedinfraredbandsat1058(strong) withshouldersat1129and1168cm1andassignedthesebandsto

d

Al2OH deformation modes. A low intensity broad band at

864cm1isassignedtoawaterlibrationalmode.Intheworkof Breitingeretal.,abroadlowintensitybandwasfoundataround 800cm1andwasalsoattributedtowaterlibrationalmodes.

The infrared spectrum of laueite over the 1250–650cm1 spectralrangeisdisplayedinFig.6b.Theinfraredspectrumshows somesimilaritytothatoftheRamanspectrum.Theinfraredband at around 1026cm1 is attributed to the

n1

PO43 symmetric

stretchingmode.Theinfraredbands at1072and1090cm1are attributedtothe

n3

PO43antisymmetricstretchingmodes.The

seriesofinfraredbandsat774,846and918cm1areassignedto thewaterlibrationalmodes.Someofthesebandsmayalsobedue to the

d

Fe2OH deformation modes, in harmony with the

assignment of Breitinger et al. He and co-workers stated that thedeceptivelysimplestrongIRbandcenteredat1059cm1for warditecontainsatleastfourcomponentsof

n

(PO4)generatedby

lifting of the originally threefold degeneracy of

n3

(PO4) and

activationof

n1

(PO4)duetothegeneralpositionofPO4andagainat

least four components of the deformation modes

d

(Al2OH)

involvingthetwopairsofthenon-equivalentOHgroups.Inthis

work we have obtained much greater resolution and these componentsareresolvedintothecomponentbands.

TheRamanspectral regionof thephosphatebendingmodes overthe800–100cm1spectralrangeisreportedinFig.7.Intense

Fig.5.(a)Ramanand (b) infraredspectrumof laueite,bothover the1800–

1300cm1range.

Fig.7.Ramanspectrumoflaueiteoverthe800to100cm1range.

Fig.6.(a)Ramanand(b)infraredspectrumoflaueite,bothoverthe1250–650cm1

Ramanbandsareobservedat551,542and525cm1areassigned tothe

n4

outofplanebendingmodesofthePO43andHOPO32

units.IntheRRUFFspectrumoflaueite,Ramanbandsarefoundat 462,516and577cm1.

TheRamanbandat993cm1isassignedtothe

n1

symmetric stretchingmodeof thePOH units,whereastheRamanbandat 1009cm1isassignedtothe

n1

symmetricstretchingmodeofthe PO43units.Galy[11]firststudiedthepolarizedRamanspectraof

theH2PO4anion.Choietal.reportedthepolarizationspectraof

NaH2PO4crystals.CascianiandCondrate[12]publishedspectraon

brushiteandmonetitetogetherwithsyntheticanhydrous mono-calciumphosphate(Ca(H2PO4)2),monocalciumdihydrogen

phos-phate hydrate (Ca(H2PO4)2

H2O) and octacalcium phosphate

(Ca8H2(PO4)6

5H2O).Theseauthorsdeterminedbandassignments

forCa(H2PO4)andreportedbandsat1002and1011cm1asPOH

andPOstretchingvibrations,respectively.ThetwoRamanbandsat 1086 and 1167cm1 are attributed to both the HOP and PO antisymmetricstretchingvibrations.Cascianiand Condrate[12] tabulatedRamanbandsat1132and1155cm1andassignedthese bandstoPOsymmetricandthePOantisymmetricstretching vibrations.

Breitingeretal.assignedthesebandsat551,542and525cm1 to

n

(Al(O/OH)6) stretching vibrations. No phosphate bending

modesintheworkofBreitingeretal.werereported.TheRaman spectrum of crystalline NaH2PO4 shows Raman bands at 526,

546and618cm1(dataobtainedbytheauthors).Aseriesofbands forlaueite are observed at472 and 456cm1.These bands are attributedtothe

n2

PO43andH2PO4bendingmodes.TheRaman

spectrumofNaH2PO4showsRamanbandsat482and460cm1and

areattributedtothe

n2

PO43bendingmodes.Ramanbandsat317,

446and515cm1reportedbyBreitingeretal.wereassigned to vibrationalmodesoftheAlO6/AlOH6units.IntenseRamanbandsat

357and339cm1areassignedtotheFeOandMnO

n1

stretching vibrations.ThelowintensityRamanbandat731cm1maybea secondwaterlibrational mode. Inthe RRUFFspectrum,intense Ramanbandsareobservedat257and335cm1.

Intheinfraredspectrum(Fig.6b)aseriesofbandsareobserved at696,643and620cm1.Thesebandsareattributedtothe

n4

out of plane bending modes of the PO43 units. Breitinger et al.

assignedbandsinthisregionto

n

(Al(O/OH)6)stretchingvibrations.

InharmonywithBreitingeretal.assignments,theinfraredbands observed at 732, 795 and 893cm1 are attributed to water librational modes.The Raman spectrum of laueitein the 300– 100cm1regionisshowninFig.7.IntenseRamanbandsobserved at253cm1forthelaueitearerelatedtotheOFeOskeletal stretchingvibrations.Otherbandsinthispartofthespectrumare notedat226,240,265and279cm1.Theintensebandinallthe spectraat161cm1isconsideredtobeduetoHOHhydrogen bonds.OtherRamanbandsareobservedat110,115,138,172and 186cm1.Thesebandsaresimplyassignedtolatticevibrations. 7.Conclusions

Ramanspectroscopycomplementedwithinfrared spectrosco-py hasbeen used to study themolecular structure of mineral laueitefromBrazil.Themineralspecimenwasalsoanalysedusing SEMwith EDXtechnology. Chemicalformula calculated onthe basisofsemi-quantitativechemicalanalysisofthestudiedsample

can be expressed as (Mn2+

0.85,Fe2+0.10Mg0.05)P1.00(Fe3 +

1.90,Al0.10)P2.00(PO4)2(OH)2
8H2O.

Thelaueitestructureisbasedonaninfinitechainsof vertex-linked oxygen octahedra, with Fe3+ _{occupying the octahedral}

centers,thechainorientedparalleltothec-axisandlinkedbyPO4

groups.TwointenseRamanbandsobservedat980and1045cm1 areassignedtothe

n1

PO43symmetricstretchingmode.Intense

Ramanbandsareobservedat525and551cm1withashoulderat 542cm1areassignedtothe

n4

outofplanebendingmodesofthe PO43.Theobservationofmultiplebandssupportstheconceptof

non-equivalentphosphateunitsinthestructure.Asaconsequence atthemolecularlevelnon-equivalentphosphateunitsexistinthe structureandmultiplephosphatevibrationalmodesareobserved.

Acknowledgments

Thefinancialand infra-structuresupportof theDisciplineof Nanotechnologyand MolecularScience,Scienceand Engineering FacultyoftheQueenslandUniversityofTechnology,isgratefully acknowledged.TheAustralianResearchCouncil(ARC)isthanked for funding the instrumentation. The authors would like to acknowledgetheCenterofMicroscopyattheUniversidadeFederal deMinasGerais(http://www.microscopia.ufmg.br)forproviding theequipment andtechnicalsupportfor experimentsinvolving electronmicroscopy.R.ScholzthankstoCNPq-ConselhoNacional deDesenvolvimentoCientíficoeTecnológico(grantsNos.306287/ 2012-9and402852/2012-5)andPROPP/UFOP,projectNo.03/2014. AppendixA.Supplementarydata

Supplementarydataassociatedwiththisarticlecanbefound, in the online version, at http://dx.doi.org/10.1016/j.vibspec. 2015.12.001.

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