Oxidizing Intercalation of Layered Structures

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Oxidizing Intercalation of Layered Structures A.Yu. Zavrazhnov, V.N. Semenov, D.N. Turchen, V.P. Zlomanov & V.S. Pervov To cite this article: A.Yu. Zavrazhnov, V.N. Semenov, D.N. Turchen, V.P. Zlomanov & V.S. Pervov (2000) Oxidizing Intercalation of Layered Structures, Materials Technology, 15:2, 155-160, DOI: 10.1080/10667857.2000.11752872 To link to this article: http://dx.doi.org/10.1080/10667857.2000.11752872

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Date: 13 December 2016, At: 06:59

Mat. Tech & Adv. Perf. Mat. 2000 15.2: 143 - 160

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5. I. Hasegawa, T. Na kamura, S. Motojirna, and M. Kajiwara, J. Mater. Chern. 5, 193 (1995). I. Hasegawa, T. Nakamura, S. Motojima, and M. Kajiwara, 6. J. Sol-Ge l Sci. Techno!. 8, 577 (1997). I. Hasegawa, T. N akamura, and M. Kajiwara, Mat er. Res. 7. Bul!. 3 1, 869 (1996). I. Hasegawa, Y. Fukud a, and M. Kajiwara, J. Eur, Ce ram. 8. Soc. 17 , 1467 (1997) . I. Hasegawa, Y. Fukuda , and M. Kajiwara, Ce ram. Int er. 9. 25,5 23 (1999). A. Hendry and K.H . Jack in Special Ceramics 6, edited by 10. P. Popp er, (British Cera mics Research Associati on , Stoke-on-trent, 1975), p. 199.

Oxidizing Intercalation of Layered Structures Zavrazhnov A.Yu., Semenov Y.N., Turchen D.N., Zlomanov Y.P., Pervov Y.S. Voron ezh St ate University, Voronezh, Mosco w Sta te Univer sity, Dep. of Inorg. Chern., Moscow Institute of Gen eral and Inorgan ic Che mistry, Russia

T

h e intercalation of the la ye red AIJ'BV' and N VB v crysta ls by the e lectronica lly acceptor species , considered a s the unrepresentative for such structures, ha s been found. The composition and some properties of th e int ercal ate s have been investigat ed. It is shown, that in th e case of oxidizing nature of the gues t its int ercalation in such crystals is accompanied by a partial oxidizing of the host; thus the int ercalation embraces not all cryst al, but its separate, presumably, more defective part s only. The correlation between th e defect structure of th e crystal and the interc alation by th e gues t spe cies with an nonsuitable electronic structure has bee n conside red. T he possible application s of obtaine d intercalates in electronics and in catalytic proc esses are discussed.

Int roduction It is known, that for th e spontaneous int ercalation in th e host-guest interaction some steric (geometric) Address for correspondence:Zavazhnov A.Yu, Engels Street 34/85,Voronezh 39450, Russia, Fax: 5ZZ0ZZ , E-mail: [email protected]

onz

155

and electronic relationships are to be fulfilled. The steric (geometric) factors require th at host cryst al lattice should have the interlayer gaps of th e appropriate size and geometry to accept th e guest particl es). Electronic factor s means th at electron structure of th e host and guest sho uld be a good combina tion to form chemical bonds [I]. Whereas th e geome tric effect supposes an opportunity of infrin gements (int erlayer spaces could change during the intercalation), th e electronic effect ac ts co ns id e ra bly more h ard . Unfortunately th e calcul ation techniques for th e estimation of th e last effect [2, 31 are shown to be fitt ed on ly for few classes of th e structures . (Into such struc tures fall, first of all, dich alc ogenid e s o f tr an siti on met al s, which int ercal ation reacti on s are explored much in more det ail compared with othe rs layered ch alcogenides [2, 3].) For th e majority of othe rs layered co mpo unds on ly th e empirical evalua tions can be used . It is con sidered for example th at if th e van -d er-Waals gap of th e bin ary layered compound is restrict ed by atoms with high clcctron egativity, such crysta l can be spontaneously intercalat ed on ly by elec tron don ors guest species (Lewis basises) [41. In th e present paper it is shown, th at con trary to such e mpirica l point of view, so me of the layer ed chalcogenid es AIIIBvl, belon ging to th e GaS - struc tural type (GaSe, InS e - see fig. 1 (A, C) [5]), and also close to th em in a struc ture N VBv - compounds (GeAs, GeAsz [6]) ca n be intercalat ed with elec tro n acceptors (Lewis aci ds ) gues t spe cies . Unu su al featur e o f thi s intercalation is conne cted with th e fact , th at th e atoms, forming th e van-der-Waals gap in comp ounds und er conside ration, have a non -met allic na ture (Se, As). The comp osition of th e intercalat ed produ ct s and possible reason s of thi s intercalat ion are discussed in th e present paper.

Experimental The a tte mpts of t he in t er cal ati on are ful filled thro ugh th e introdu cti on of the AIIIBvl and A ,vBv single crystals (GaS, GaSe, InSe, GeAs, SiAs, GeAs z) int o th e direct con tact with series of liquid or vapor substances. A lot of compo unds (mor e th an 40) were tested for th e role of th e guest species, th e majority of which had th e electron - acceptor prope rties: classic mineral acids , h ydro gen peroxid e, halogenides and oxiha logenides of th e elemen ts of III-VI - groups of Periodic Table, e tc.. The results of th e co ntac t, which in a series of att empts last s up to half a year, are estima ted in th e measurements of th e crystals sizes and their masses before and after being in th e medium of

156

Mat.Tech & Adv. Perf. Mat. 200015.2: 143- 160

the proposed guest species. The X-ray and spectroscopic methods are also used for that purpo se. Though the majori ty of attempts has termin ated in failure, ju st separate cases of intercalations have been detected. So, the single crystals of mo noselenides of indium and gallium are undergo ne the intercalation in their react ions with the solutions of nitri c acid or some nitrates; germa nium arsenides - in their interaction with chlorates acidified solutio ns. Such reactions with the participation of GaSe are explored in more detail. It has bee n found that in the

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action of 10-50 % nitric acid on the GaSe single crystals the noticeable swe lling of these crystals occ urs - the li nea r dime nsions of c rystals are scaled up in th e direction, parallel to the axes "c " (up to 20 or more %) . On the lateral (perpe ndicular to the axes ..c ") surfaces of the crystal the small bubbles of co lorless ga s are liberated during such interaction. Th erewith a visual transpare ncy of the even thin samples is lost; their color is changed to be cop per - metallic. Th e visual changes of the crys tals sizes at their contact with the acid are beco me noticeable in time from several seconds till an ho ur depending on the co ncentration of the acid. Protracted contact, or also use of more concentrated nitric acid calls the spontaneous splitting of the cry stal into a lot of thinn est separate plates with the subsequent complete ox idizing of GaSe up to the selenous acid salts. Similar in appearance interaction is observed also at the trea tme nt of GaS e by th e conce ntra ted wa te r solutions of nitrat es of some noble metal s (Ag ", Pd+2, Hg+1• +2). Th e InSe single crystal behaves similarly to GaS e, but it is frustrated more eas ily. Arsen ides of germanium demonstrate the similar behavior in the case of co nce ntrate d so lutio ns of potassi um c h lorate acidified with 10-20 % sulfuric acid . The produ cts of intera ction of nitric acid with the g all iu m m on osel enide (w h ic h a re indi cated a s Ga Se :H N 0 3 below ) ha ve been s tu d ie d us i ng pycn ometric den sit y, X -ray- a nd vapor pressure measurements as well as IR and other optical techniques (Table I). Th e similar investigation has been carried out with the GaSe samples, treated by the solutions of nitrates of Ag, Hg, Pd (product of intercalation are indi cated as GaS e:M e (N0 3 )n) ' T he re s ult s for

CaSe

22 _

A,%

••

Fig. I: Fragments of the GaSe structure: the structure of the -Se-Ga-Ga-Se- single flake (A,B) and the stalking sequence in the e - polytype [5]. A). C) - free-defect fragments of the GaSe structure; B). D) - the fragments with the assumed "inverse" defect. which is formed during the inversion of GaSe) - tetraedra cluster (the gallium atom falls into the van-der-Waals gap). Designations: gallium atoms are pointed as the dark circles. selenium atoms - as the bright one; defect atoms of gallium are pointed by the arrow s.

GoSe :HNO]

3.

...

,-

22 . .

la lla •

',eM-·

Fig.2.:IR spectrum of GaSe and GaSe:HNO). Designations: g is a wave number. T - the relative absorbtion.

Mat.Tech & Adv. Perf . Mat. 200015 .2: 143 - 160

Technology Review s and Studie s

r

..... ."

r. ~

r,« IYII

GaSe

rt GaSe:HN0 3

."

'"

'"

."

."

'"

'"

157

bounded with the GaSe matrix. It is notable that the che mically bo unded nitrogen in the product of the insertion (GaSe:HN0 3 ) has not been detected using the quality chemical analy sis. The gas escaped on the lateral faces of the crystal gas is assumed to be molecular nitrogen or oxide NzO. Then the discussed intercalation may be described as

4"

'"

'"

2"

2"

'II.'

" ,6

1iI. 7

1iII.8

",OJ

"".6

1 . 11 ..... HKH

".7

iii.

8

11. .HKH

GaSe: HN0 3 and GaSe:Me( N0 3)n are similar. However in case of GaSe:Me(N0 3)n the penetration of the metal into the host structure has been found.

Di scu ssion As follows from the data listed in Table 1 and Fig. 2, 3 the interac tion of gallium monoselenid e with nitric acid and nitrates does not like an usual intercalati on, because both the host and the gues t are chemica lly changed as it has been found in the case of oxidizing intercalation in graphite [7]. For example, the treatment of graphite by the mixture HN0 3 + HCl0 3 leads to the chemica l gro ups (clusters) formation chemically bound ed with the graphite matri x [7, 8]:

I

( I).

>C=O,

/

-e

\\

\

.

'

\

>Se=O, - Se-OH , /

1,%

o

Taking into account the result s listed in Table lone can assume that the intercalation of HN0 3 into GaSe proceeds similarly with partial oxidizing of the host and forma tion of the clusters such as

-Ga--OH

(clust ers, bounded with the host structure) T he weak expre ssed oxid izi ng properties of GaSe:HN0 3 do not contradict to the scheme (I). ~o the vio let acidified solution TiCl 3 in the contact with GaSe:HN0 3 becomes colorle ss, that could be explained as oxida tion of Ti? up to Ti+4 with the clu sters >Se=O and (or) =SeOH. X-ray data are appeared to be some in dissonance to scheme (1). Except one reflex ( d= 11,53 5, Fig. 4 ) of the GaSe: HN 0 3 powder diffractive pattern X- Ray difraction data for the pure GaSe and GaSe: HN 0 3 are found to be the same which is not typical for intercalates forma tion. The dissonance can be overcomed if one can assume, that the oxidizing intercalation embraces the crystal not u niformly, but only its regions near to extende d defects (dis loca tion s, plane bou ndaries of polyty pes, etc.) of the cry stal (fig . 5). Th e irregular insertion can be explained by weake ning of the che mical bond s near these defects. One may also assume that the intercalation cannot be observe d in X-ray data when the content of the intercalated regions does not exceed

OH

H / -e~\

°

/

\

I

t . II

1iII. 'J

Fig3.: Spectra of GaSe and GaSe: HN0 3at the photons energy , appro achin g to the energy gap of GaSe. Design ations :arel - is the wave length, T - the relative transmission.

-oH,

\

I

."

." " .4

\

GaSe + HN03 = {-{JaOH + Se=O + - SeOH} + Nz (NzOj + IhO

50

.

9 "

Fig4.: Diffractive Pftem of GaS e:HNO j at the region of low angles. The additional peak is pointed by the arrow .

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2000 15.2: 143- 160

seve ral perce nts. It sho uld be stressed, that in spite of th e similar GaS and GaSe struc tures the gallium mon osulphid e GaS is not inte rcalated at all, whic h co rrela tes well with th e suppose d hypothesis: th e grown bulk GaSe - crysta ls usually co nta in two polytypes (e.g) with the high density of the extended defec ts [9] while GaS has one polytype (b) [10] and cont ains less exte nded defect s. One may co nclude th at the int ercalation in perfect host crystal is impossible but it is easily realized in th e case of some tr an sfor mation of th e st ruc ture, which leads to th e form ation of some defects. It is known, th at th e non -stoichi ometry of inorganic co mpo unds is caused by defects. It is interesting to co nside r in thi s co nnec tio n th e relation ship between non -sto ichiom etry of GaSe and the int ercalati on of se le n ium in t o G aS e . The sh a p e of th e ga ll ium mon oselenide homogen eity range (Fig. 6), wh ich was de termined from vapor pressure measurments [11, 12], is very unusual near th e meltin g point (1217 K). This range is expe nde d sha rply to th e Se side being enlarged up to 50,6 at. % Se at 1202 K. T his un usual sha pe of solidus is not typical for th e phase diagram s with th e small differences in eutec tic and melting point whic h in th e case of GaSe does not exceed 60 K.

1a

AB C

Ia~c -

- --

I a~

a

b

FigS.: The stalking seq uence near th e plane bounda ry be twee n e- and g. polytype in the cry ta l of GaSe (A); and form ation of the int ercalated area of the crysta l, locat ed near th is de fect. Design at ion s: plan e boundary pointed a th e dotted line, th e int ercalated field of the crysta l is outlined by the rect angle; a ABC and a AB are th e lattice pa rameters, co rresponds to th e slab mutual arra ngement of the g. an d e- polvtvpes respect ively, a'ABC and a'ABare this parameters for the intercalat ed field of th e crystal.

It has bee n supposed, th at th e ano mal retrograd e solubility of Se in GaSe in th e narrow tempe rature region is exp la ined by th e interl ayered ent rance of selenium at high tem peratures. It is known, that heatin g of layered crystals leads to anisotro pic expansion and can increase van- de r-Waals gaps [13, 14] . Thus th e co nc en t ra t ion of th e in terlayer Se at oms can be dra stically in cr eased wh ich is co rre la te d with th e tem per atur e dep e n de nce of th e d efect s energy formation. The formation ene rgies o f the defects, respon sible for th e excess of gallium * (Ga, or Vs) and selenium * (Se, or VG) ' are decreased from 260 kj/mo l up to 150 kj/mol. in th e first and from 690 kj/mol, up to 400 kj/mol. in th e second case respectively while th e temp erature was increased from 1140 K to 1180 K. The expe rimenta lly observed intercalati on of th e GaSe structure by Se or HNO J (which belon g to th e guest species with accepto r cha rac te r) seems not to be agreed with th e empirical evaluations [4] and can be explained by rearrangement of th e host structure: 1. It has been supposed , th at th e acce pto r guest provo kes tran sferri ng a pa rt of th e gallium ato ms from their initial intr aslab locati on to th e int erlayered one (fig. 1 B, D). (Th e spontaneous formation of such defects is also accepted under th e high ternp eratures.) The inversion of Sp3 - hybrid gallium a to m in tetraedra clu ster is simila r to th e we ll-known pro cess of the "in verse inside o ut" of the ammonia molecu le. It sho uld be noted, tha t th e form ati on of such defect sho uld be connect ed with th e breakin g of th e Ga-G a bonds. 2. T he formation of the new che mical bonds between th e guest particl e and th e gallium at om in the vertex of th e "inverse" tetrahedron can in turn partly compensate th e ene rgy expe nditure of th e Ga -Ga bond breaki ng. T h is process is energetically advantageo us when th e gues t h as an ex pressed function of th e elect rons acce pto r. Remaining free valence s of th e guest co uld int eract with th e inverse atom of an other layer, con necting th e separa te slabs. Similarly one cou ld explain th e insertion of nitric acid in to the GaSe crystal and th e int ercalat ion of chloric acid solutions int o germa nium arsen ides. . In concl usion of this part it is worth noting, t hat th e idea of t he host matrices modifica t ions for th eir subsequent inte rcalation is not new [ 151. However th ere are some differences between th e presented result s and dat a [ 151: - th e induced struc tura l changes could be smoot hly varying; and - th e structure modi ficati on occurs not in the bu lk host crysta l, but on th e alte rna ting additional planes whic h

Mat.Tech & Adv. Perf. Mat.

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159

2000 15. 2: 143 - 160

appea r a t t h e interca lation o f n onsroic h iometric o r impurity guest atoms (m ol ec u lar s) [16]).

Applied Aspect The Oxidi zing Intercalation Products May Be Used As Catalyt ic Species.

It is known, th at t h e in tercal a ti on of gra ph ite by palladium c h loride with th e subse q ue n t reduc ti o n o f Pd z + - io ns gives a good ca ta lytic reagent for a lo t o f reduc tio n reaction s in orga nic syn thesis [7, 171 . For the syn thesis of th e sim ila r ca talyst on t h e GaSe ba se t h e Met hods and devices The absorptio n spec trums (fig. 2); lR - spectrophotometer UR-20; wave range is 400-4000 em:'

last o ne has been treated by the sa tur a ted water solu tio n of Pd (N 0 3) z: In ter c ala ted palladium [G aSe: Pd (NO})zl h as been reduced by the excess o f TiCl 3 solution. The q ua ntitative compo sition of the product (Pdo.opaSe ) h as been determined by the x-ray-fluorescent analysis. The catalytic activity of the Pd intercalated into GaSe was tested using the S 1 -reaction when phenyl gro u p subs titutes for c h lorine into orthochloro-phenol: (eq.3). It h as bee n fo und , that the efficiency of proposed cata lyst is qu ite comparable with the pa lladium-graphite o ne in the interaction (3) (see appendix 1).

Results

Int erpr etation

a) the in tercalate absorb s the light almost en tirely in th e spectral ran ge near the of 3600 cm' (fig. 2) ; b) Ga-Se ba nds (400-460cm '!) a re smoot hed and are shifted to more longwave region rela tive to pure GaSe. In t e rc al a t ed sa mp le s are m or e transparen ced t han t he pure GaS e with the sa me th ic kness; c)in the GaSe:H N0 3 spect rum the new peak at g»2300 em:'. was found.

a) high conce nt ration of the OH groups in th e GaSe :HN03 -; b) considerable number of disrupted bonds in the int ercalate s. The shift of th e abso rp tion maximum into mor e lon g-wave region co uld be explained by orne red istribution of t he el ectr oni c d en sity in th e inte rca lated samples; c) th e similar peak, fixed on the powder of seleno us acid may be refered to th e > Se= O or \ -YlSe-O H bond. /

Ligh t transmission measurm ents; th e radiati on ene rgy was close to t h e e ne rgy ga p o f Ga Se; spectro photometer VSU-2M

a) more smoo th abso rpti on edge in the int ercalat ed samples in co mpa rison with pure GaSe (fig. 3); b) the presence of th e "steps" on the curve of th e absorption (fig. 3).

a) the destortion of the GaSe structure by intercalated nitric acid ; b) considerable concen tration of impurity level s in the energy ga p of t he intercalate s.

Pycnometric measurement s, size of powder- 0.0 1 - 0. 1 mm. T he using liq u id is th e pure e t ha no l. Measure me nts have been mad e after an ho ur of boiling in etha nol. A precision class of the picnometer is 0.0 1.

T he den sity of .GaSe after the treat ment by ni t ric ac id was decrea sed from 4.95 ± 0 .05 g/cru' till 4.30 ±0.05 g/cm' . (X-ray density of pure GaSe is 5.03 g/cm')

Increase of th e van -der-waals gap.

Vapor pressu re measurrn en ts of interca late s. T he q ua rtz membran ous zero - gauge with the free volume is used. Time expo use was several hours

Noticeable fugitiveness - from - 600 K (pure GaSe practica lly is nonv olatile). The tran sfer of the compou nds into a vapour is pro longed wit h h ea ti ng up to 773 K. Process is not in equilibrium: at the cooling th e pressure is not reproduced.

T he q uant itative X-ray- fluo resce n t ana lysis of the samples GaSe:Me (N0 3)n (VRA -30, firm Ca rl-Zeiss)

onreversible co nde nsa tion OH groups with form at ion of wat er and oxyge n bound ed with the h ost struc ture are possible. Calcul ated in this assumption con centration of O H - groups is 5-8 at. %.

The insert ion of th e noble metals (Pd, Hg, Ag) int o th e ho t structure of in the amo un ts up to 5 at. %.

Table 1: The results of the GaSe intercalation.

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Mat.Tech & Adv. Perf. Mal. 2000 15.2: 143 - 160

160

Ph-CI + Pho\BNa

Ph-Ph

\

(3).

\

OH

OH

The Second Possible Appli cation Of The Intercalation Products M ay Deal With Elect ronics. For prod uction of electronics devices are needed structures with sequential alterna tion of layers with the diffe rent properties. These are the ceramic capacitors whic h are the se que nce of th e alt ernating layersInsul ator - metal - insul ator...) or photomultiplier s which are alternating layers: Insulator - se miconductor - insulator...). Th e discu ssed int ercalation reaction s could be proposed for preparation of sandwich struc tures, using for exa mple the following steps: a). The grow ing of semiconducting layered crystal with the planar alternating defects [16]. b). The oxidi zing intercalation for the interlayer

T,K

1210

1---1 -2

GaSe+ 1 1185

Acknowledgements: Authors are gra tef ul to Dr. Shevchen ko N.V. for ass istance in catalitic investigations.

References: I. Rouxel1.Intercalated layeredmaterials.( Ed Levy E: Donlrecht (Holland). 1979). v.6.p. 201. 2 Yoffe A D."Ann. Chim" (France). 7. No 2-3(1982),: Chemistry andphysicsofsulfides, selenidesandtelluridesolids.Int,Colloq. CNRS. Paris, Sept 14-17.1981.pp.215-238. 3. Pervov V.S.• Volkov v.v..FaI'kengof AT.• et, aI., Neorg. Mater; v32, No.6. pp.675.fJ79 (1996). 4. V.M Koshkin.• Yu. N. Drnitriev, Chemistry and physics of compounds with looosecrystal structure. "SeriesChern. Rew....v.19.part2. ed.byM.E.\blpin, 138 p.( Harwood Acad, I\1b.Switzerland, 1994). 5. LeithR.MA. III-VI-rompounds."Preparationandcrystalgrowth of thematerials withlayered structure" (Ed LevyE: Dordrecht-Boston, 1977),

pp.225-254.

I-----i

GaSe+ L

1160

Ga l+GaSe 1125

49.50

distance expenditure and the insertion of the success ive guest. c) . Th e in s ert ion of th e s uita ble org ani c compound, which can be polymer ized under radia tion, into the expanded interiayered spaces. Th e sta rting monomer should be selected in accorda nce to the required properties of the polymeric films (dielectric or met all ic) fo r s u bs eq ue n t ly prep ared s a nd w ic h structures . d). The selective polymerization of the required sites under a hard radiation. e) . Removal of the residued intercalated monom er for exa mple by vacuum treatment.

50.00

50.50

•X Se' at .0, 10

Fig 6: Homogeneity regionofGaSeaccording to thedataofthevapor-pressure investigation. Deslgnatlons: I - experimental points; 2 - the instrumental errors,

.

6. WndstenT.Chern. Commun, Unif.Stockholm, V. 15.No 1O.-p.14, (1975). 7. Graphiteand itscrystalcompounds. A R Ubbelohde RRS.•FA. Lewis. (Oxford, at the claredonpress. 1960).256p. 8. Hamwi A . Marchand v..: Pap. 8th Int. Symp. Intercalation Compounds, Vancouver. 28May- I June, 1995 J. Phys.and Chern. Solids; 57. N 6- 8.- No.867-872(1996). Terbell 1.CJM.•Lieth RM A. Phys.statussolidi(a).- 1972.- No 9. 1O.- p529-535. 10. Kuhn A .ChevalierR , Desnogers Ch.•Terrell1.CJM.ActaCryst B32,No.6, -pp.1910-1911(1 976). II . Zavrazhnov A Yu., Thrchen D.N., Goncharov Eu. G.. Fcdomva M,v.. Suvorov AV.1.ofgenernl chem (Russia),v.68, No 6.pp.920-9"..5(1998). 12 Zavrazhnov A Yu.•Tureben ON .•GoncharovEu.G., Prigorogova TA 1.ofgeneral chern.(Russia).Expected in v.W, No 12 (1999). Belenkii G, SalayevE..Sullimanov R A Solid StateCommun, 13. v53.No l l. pp,967-971(1985). 14. KellyB.T.. WakkerP.L1. ofGubon.-I 970.- V.8.N02 -p.211 -226. 15. Brec R Proc of the IO-th Coorse of Erise summer School on intercalation.in layeredmaterials (Ed by M.S. Dresselhaus. - NantesCedex, 1986).- p.I 25-I34. 16. ChizhevskayaSN.•Shelimova L E..Zaitseva IA Ncorg.Mater.• v.30.No II . pp.1379-1387 (1994). 17. 1.Phys. and Chern.Solids6-8,v57,pp.899-90I (1996)