E idence o a supe cooled plas ic-c ys al phase in solid e hanol
A. S ini asan and F. J. Be mejo
Ins i u o de Es uc u a de la Ma e ia, Consejo Supe io de In es igaciones Cien ı
´ icas, Se ano 123, E-28006 Mad id, Spain
A. de And e
´s
Ins i u o de Ciencia de Ma e iales de Mad id, Sede B, Consejo Supe io de In es igaciones Cien ı
´ icas,
Uni e sidad Au o
´noma de Mad id, Facul ad de Ciencias, C-IV, Can oblanco, E-28049 Mad id, Spain
J. Dawidowski
Ins i u o de Es uc u a de la Ma e ia, Consejo Supe io de In es igaciones Cien ı
´ icas, Se ano 123, E-28006 Mad id, Spain
J. Zu
´n
˜iga
Depa amen o de Fı
´sica de la Ma e ia Condensada, Uni e sidad del Pais Vasco, Euskal He iko Uni e si a ea,
Facul ad de Ciencias, E-48960 Bilbao, Spain
A. C iado
Depa amen o de Fı
´sica de la Ma e ia Condensada, Uni e sidad de Se illa, and Ins i u o de Ciencia de Ma e iales,
Consejo Supe io de In es igaciones Cien ı
´ icas, Facul ad de Ciencias, P.O. Box 1065, E-41080 Se illa, Spain
~Recei ed 18 Oc obe 1995; e ised manusc ip ecei ed 8 Decembe 1995!
The exis ence o an o ien a ionally diso de ed cubic phase o solid e hanol is e ealed by x- ay di ac ion
and Raman spec oscopic measu emen s. Such a phase, whose exis ence was pos ula ed some ime ago on he
basis o speci ic-hea measu emen s, is p oduced by quenching below some 95 K a plas ic c ys al o med upon
mel ing and subsequen annealing o he opologically diso de ed ~glassy!solid. The ele ance o he p esen
indings o cu en discussions on glassy dynamics is analyzed in some de ail.
Despi e ecen ad ances in ou unde s anding o he mi-
c oscopic mechanisms d i ing he dynamics o glasses a
in e media e ~abo e 1 K! empe a u es,1mos s udies ega d-
ing opologically diso de ed solids ~i.e., eal glassy ma e i-
als!s ill encoun e subs an ial di icul ies when ying o go
beyond desc ip ions o he da a by means o phenomenologi-
cal app oaches. This con as s wi h a mo e de eloped unde -
s anding ega ding he dynamics o diso de ed c ys als
o med by ei he mixed2o chemically homogeneous ~plas ic
and glassy c ys als3,4!ma e ials, which in common wi h
s uc u al glasses exhibi some ea u es conside ed as inge -
p in s o he glassy dynamics. Such de elopmen s a e, how-
e e , es ic ed o ma e ials which being diso de ed in some
quan i y ~chemical composi ion, ela i e molecula o ien a-
ions, e c.!s ill ha e an unde lying c ys al la ice, hus en-
abling he calcula ion o a numbe o physical p ope ies
~i.e., coupling be ween molecula ansla ions and o a ions,
so ening o elas ic cons an s due o diso de , anomalous di-
elec ic beha io , e c.!in e ms o well-es ablished
echniques.2The ele ance o such indings o he unde -
s anding o eal glasses was no explo ed in de ail, pe haps
due o he ac ha mos o he exis ing ma e ials can ei he
be con e ed in o opological o diso de ed-c ys al s a es, ex-
cep ions o such a ule being a e ~amo phous and hexagonal
ice being an example which in ol es a he di e en ou es
o p epa a ion which pose se e e condi ions when ying o
compa e he wo in e ms o ansi ion empe a u es!.
The exis ence o some polymo phic phase in solid e hanol
which could be p epa ed unde mild he mal condi ions was
known o exis since he wo k o Haida e al.5who obse ed
calo ime ic anomalies dis inc om hose associa ed wi h
he glass ansi ion (Tg597 K!, he mel ing o he s able
c ys al (Tm5169 K!, o c ys alliza ion o he supe cooled
liquid in o such a phase (Tc '125 K!. In ac , he p esence
o a well-de ined exo he mic anomaly a some 115 K was
in e p e ed as he onse o a c ys al phase ~c ys al II!which
once g own exhibi ed a calo ime ic ansi ion in o ano he
c ys alline phase ~glassy c ys al!, showing small di e ences
in hea capaci y wi h hose o he glass ob ained by apid
cooling o he no mal liquid, bu e idencing a calo ime ic
en opy be ween ha o he glass and he s able c ys al. A
NMR elaxa ion measu emen epo ed la e on6showed ha
he dynamics o he eal glass and ha o he glassy c ys al as
sampled by he alues o he second momen o he NMR
sha ed some analogies, whe eas inspec ion o he ela i e
alues o he elaxa ion imes e ealed some sys ema ic di -
e ences be ween bo h.
Ou aim he e is o es ablish he na u e o he c ys al II and
glassy c ys al phases o his ma e ial. I , as expec ed, a su-
pe cooled plas ic c ys al ~SPC!can be o med by eezing
he o a ional eedom o he plas ic c ys al ~PC!, i would
hen p o ide an excellen benchma k ma e ial whe e quan i-
a i e s udies on he ole o di e en deg ees o eedom
~posi ional and o ien a ional!on he dynamics o he glass a
in e media e empe a u es could be ca ied in de ail.
Spec oscopic g ade e hanol was used wi hou u he pu-
i ica ion, a oiding exposu e o a mosphe e o p e en cap-
u e o wa e apou . The x- ay di ac ion measu emen s
we e pe o med using a S oe di ac ome e , using he Cu
K
a
line l51.5418 Å, being he samples con ained in glass
PHYSICAL REVIEW B 1 APRIL 1996-IVOLUME 53, NUMBER 13
53
0163-1829/96/53~13!/8172~4!/$10.00 8172 © 1996 The Ame ican Physical Socie y
capilla ies cooled by an Ox o d Ins umen s c yos eam
coole . The Raman spec a we e eco ded on an X-YDilo
spec ome e equipped wi h an enhanced pho odiode a ay.
Sli wid hs gi ing nominal esolu ions o 1.8 and 3.7 cm21
we e employed o c ys al and glass spec a, espec i ely.
Exci a ion was achie ed by an A 1sou ce lasing a 514 nm
and deli e ing some 10 mW o he sample which was con-
ained wi hin 5 mm qua z ubes. These we e kep wi hin a
Ox o d Ins umen s lux c yos a used o keep empe a u es
be ween 10 K and ambien . The sca e ed ligh was collec ed
on he S okes side a igh angles.
Sample p epa a ion ega ding he no mal glass and s able
~monoclinic!c ys al phases is s aigh o wa d since i only
in ol es a quench below Tg597 K a a a e no slowe han
6 K min21~glass!and a subsequen annealing a some 130
K o a leas a hal hou ~c ys al!. As ega ds he p epa a ion
o he supe cooled-plas ic-c ys al phase, ou own expe ience
indica es ha ep oducible esul s a e ob ained i he supe -
cooled liquid o med upon mel ing he no mal glass is al-
lowed o anneal o some minu es a T5100 K ollowed by
a apid quench below he Ta597 K ansi ion. A mac o-
scopic phase sepa a ion occu s du ing annealing whe e a
anslucen solid phase seg ega es om he clea liquid.
Figu e 1 shows a plo compa ing he x- ay sca e ed in-
ensi ies o he h ee phases o solid e hanol. The monoclinic
c ys al spec um is ully compa ible wi h he c ys al s uc u e
desc ibed in Re . 7 which co esponds o a uni cell con ain-
ing ou molecules, wo o which a e independen in he
asymme ic uni o Pc symme y. The e e ed wo molecules
ha e a di e en in e nal s uc u e ~con o ma ion!, showing
dihed al CuCuOuH angles o some 297° ~gauche!and
179° ~ ans!wi h also signi ican a ia ion o he bond-angle
alues.7The c ys al s uc u e shows in ini ely bonded zigzag
chains joined by OuH•••O bonds o leng h 2.716 Å. In ull
con as , he glass shows a b oad spec um wi h a main di -
ac ion peak cen e ed a Q'1.65 Å21and a wid h o
'0.5 Å21. The pa ame e s o such a peak a e close o hose
ound o a chemically ela ed glass ~me hanol!discussed in
some de ail in he pas ,8and which we e ound o ep esen 9
a sys em o long, winding chains, wi h a co ela ion leng h
@de ined by he ex en in eal space whe e he g( ) in e mo-
lecula dis ibu ion unc ion shows no iceable oscilla ions#o
some 15 Å. The exis ence o a high-symme y c ys al phase
is demons a ed by he di ac og am o Fig. 1 ~middle!,
which shows ha mos o he in ensi y a ises om wo B agg
e lec ions a Q51.651 Å21~in ense!and Q52.335 Å21
~weak!, alongside wi h small aces o con amina ion by
minu e amoun s o he monoclinic phase and a b oad, di use
backg ound. Such a di ac ion pa e n can be unde s ood as
a ising om a body-cen e ed-cubic s uc u e wi h la ice con-
s an a55.381 Å, he ~110!and ~200!, espec i ely, being he
obse ed e lec ions. Assuming wo molecules pe uni cell,
he assignmen would co espond o a solid wi h a mac o-
scopic densi y o 982.5 kg m23, close o he alue a Tgas
ex apola ed om abula ed alues o he no mal supe -
cooled liquids10 (
5958.2 kg m23). The alue o he la -
ice cons an men ioned abo e becomes e y close o ha o
5.377~4!Å co esponding o he adimension o he mono-
clinic cell.7On he o he hand, he close loca ion o he ~110!
e lec ion wi h he wa e ec o cha ac e is ic o he peak
maximum in he glass phase p o ides a clea example o he
physical meaning o he i s di ac ion peak in glasses, an
issue which was he ocus o some ecen con o e sies.11 In
ac , compa ison o di ac og ams o glass and cubic c ys al
clea ly sugges s ha only he wid h o such a peak should
bea a clea physical signi icance in a glass.
Because o he small numbe o obse ed B agg e lec-
ions, u he de ails ega ding he s uc u e o such a cubic
phase could only be de i ed om addi ional independen
measu emen s. Be ween hose, a compa ison o he Raman
spec a o he solid wi hin i s h ee ~cubic, monoclinic, and
glass!phases was chosen and he mos ele an esul s a e
displayed in Fig. 2. The immedia e consequence o such a
compa ison ega ds he exis ence o a s ong s a ic diso de
in he cubic phase as demons a ed by he absence o well-
esol ed phonon peaks below some 40 meV. Tha such a
diso de is o s a ic ~o ien a ional!na u e is u he a i ied by
he absence o any he mal anomaly o his phase below ou
ac ual T580 K, which should be p esen i subs an ial o a-
ional mo ions we e s ill p esen . I seems hen clea ha he
cubic phase ep esen s a SPC o glassy c ys al phase, whe e
he la ge o a ional mo ions p esen abo e 97 K ha e ozen
in o a s ongly o ien a ionally diso de ed phase. In ac , spec-
a measu ed du ing annealing ime show in addi ion o he
peaks shown in he SPC phase an addi ional s ong di use
backg ound. The amoun and kind o diso de ~i.e., s a is ical
o h ough some p e e en ial di ec ion!canno be in e ed
om he a ailable da a, al hough he simili ude be ween he
FIG. 1. X- ay di ac ion pa e ns o ~a! he posi ionally diso -
de ed glass a 80 K, ~b! he supe cooled cubic c ys al phase a 80 K,
and ~c! he s able ~monoclinic!c ys al a 120 K. The small peak a
Q'1.786 Å21in ~b!comes om a small con amina ion o he
monoclinic c ys al phase.
53 8173BRIEF REPORTS
low- equency Raman spec a ~below some 20 meV!and he
coincidence o he posi ion o he in ense B agg e lec ion
wi h he maximum o S(Q) in he canonical glass pinpoin s
he exis ence o ema kable co ela ions be ween molecula
o ien a ions as i is known o occu in he glass phase o
o he alcohols.9,12
The Raman spec a o he glass and SPC solid show a he
simila shapes o he equency dis ibu ions. Because o he
iso opy o he glass and he o ien a ional diso de in he
SPC, he Raman in ensi ies could be conside ed o be di-
ec ly ela ed o he ib a ional densi y o s a es h ough he
usual exp ession ZR(
)}I(
)
/@n(
)11#, whe e in he
absence o addi ional in o ma ion a quad a ic equency de-
pendence o he C(
) ligh - o- ib a ion coupling unc ion
is assumed ~i.e., comple e andomness o couplings!. No ice
om he inse in Fig. 2 ha he main di e ence be ween
canonical and SPC spec a ega ds he posi ion o he
maxima which in he SPC phase is shi ed some 1 meV
abo e ha o he canonical glass, as well as a a he small
excess o modes below 6 meV o he glass wi h espec o he
SPC.
An assessmen o he physical soundness o such esul s is
p o ided by e alua ing he ha monic con ibu ion o he
cons an - olume hea capaci y om he ZR(
) es ima e o
he ib a ional densi ies o s a es desc ibed abo e. To a oid
p oblems ega ding he no maliza ion o ZR(
) o absolu e
uni s only he a ios C
g/C
SPC o hea capaci ies o he glass
and SPC a e conside ed. Such a quan i y yields a alue o
1.34 o be compa ed wi h ha o 1.60 de i ed om da a
gi en in Re . 13. On he o he hand, he maxima o
C (T)/T3cu es appea in he SPC phase shi ed some 1.8
K abo e ha o he s uc u al glass, a ac also bo ne ou by
calo ime ic measu emen s whe e he maxima o he SPC
sample is loca ed a some 6.5 K whe eas ha o he glass
appea s a '4.5 K.
In consequence, and wi h he abo e p o isos in mind, i
seems clea ha he cubic SPC phase o e hanol he e s udied
co esponds o he same one explo ed by calo ime ic
means.5,13 This being he case, he di e ence in speci ic hea s
a Tgdiscussed by Joha i and o he s14 upon mel ing he glass
and ha a ising om he SPC-plas ic c ys al ansi ion can be
a ionalized on a mo e quan i a i e basis. In ac , compa ison
o he jumps in Cpa he glass ansi ion and o a ional a es
poin s Tg5Ta597Ko 35and23JK
21mol21e idences
ha some 66% o he jump upon mel ing he glass can be
accoun ed by he onse o apid molecula o a ions. Such a
pe cen age becomes e en la ge ~75%! o he jump in en-
opy, and goes o some 63% o he con igu a ional en opy.
In conclusion, he exis ence o a o ien a ionally diso -
de ed phase in a sys em conside ed since many decades ago
as one o he clea es examples o a glass- o ming liquid has
been demons a ed. F om he p esen da a as well as om
ha al eady a ailable, he SPC solid can be igh ly consid-
e ed as a phase wi h an in e media e kind o diso de be-
ween he g ound s a e ~monoclinic c ys al!and he glass. In
his espec , i s de ailed s udy will open up he possibili y o
sepa a ing he e ec s o posi ional and o ien a ional diso de
on di e en magni udes usually conside ed in s udies on
glassy dynamics.
This wo k was suppo ed in pa by DGICYT G an No.
PB92-0114-C04.
1Fo a ecen compendium o discussions on his opic, see P o-
ceedings o he II In e na ional Discussion Mee ing on Relax-
a ion in Complex Sys ems, edi ed by K.L. Ngai e al. @J. Non-
C ys . Solids 172-174,~1994!#.
2R.M. Lynden-Bell and K.H. Michel, Re . Mod. Phys. 66, 721
~1994!.
3The Plas ic C ys alline S a e, edi ed by J.N. She wood ~Wiley,
New Yo k, 1979!.
4A. Loidl and R. Bo
¨hme , in Diso de E ec s on Relaxa ional
P ocesses, edi ed by R. Riche and A. Blumen ~Sp inge -Ve lag,
Be lin, 1994!, p. 659.
5O. Haida, H. Suga, and S. Seki, J. Chem. The modyn. 9, 1133
FIG. 2. Raman equency dis ibu ions ZR(
)
5I(
)
/@n(
)11#a 10 K o ~a! he glass phase, uppe ame
~b! he SPC phase mid ame, and ~c! he monoclinic c ys al. The
inse in ~b! ep esen s an enla gemen o he equency dis ibu ions
o he glass and SPC phases. In ensi ies a e gi en in a bi a y uni s.
8174 53
BRIEF REPORTS
~1977!. Also M. Hugo, K. Schlu
¨ e , and A. Wu
¨ linge , Z. Phys.
Chem. ~Neue Folge!175, 235 ~1992!.
6T. Eguchi, G. Soda, and H. Chiha a, Mol. Phys. 40, 681
~1980!.
7P.G. Jo
¨nsson, Ac a C ys allog . B 32, 232 ~1976!.
8F.J. Be mejo, A. C iado, M. Ga cia-He nandez, J. Alonso, C. P i-
e o, and J.L. Ma inez, J. Phys. Condens. Ma e 6, 405 ~1994!,
and e e ences he ein.
9F.J. Be mejo, J. Alonso, A. C iado, F.J. Mompean, J.L. Ma inez,
M. Ga cia-He nandez, and A. Chahid, Phys. Re . B 46, 6173
~1992!, and e e ences he ein.
10Tables Annuelles de Cons an es e Donne
´es Nume
´ iques, edi ed
by Ch. Ma ie e al. ~Gau hie -Villa s, Pa is, 1912!, Vol. 3,
p. 10.
11S.R. Ellio , J. Phys. Condens. Ma e 4, 7661 ~1992!; F.J. Be -
mejo, M. Ga cia-He nandez, F.J. Mompean, D. MacMo ow,
and J.L. Ma inez, Phys. Re . B 51, 11 932 ~1995!.
12F.J. Be mejo, A. C iado, A. de And e
´s, E. Enciso, and H. Schobe ,
Phys. Re . B 53, 5259 ~1996!.
13M.A. Ramos and S. Viei a, in Nanos uc u ed and Non-
C ys alline Ma e ials, edi ed by M. Vazquez e al. ~Wo ld Sci-
en i ic, Singapo e, 1995!, p. 212. Also, M.A. Ramos, Q.W.
Zhow, J.A. Mo eno, and S. Viei a, in P oceedings o he Wo k-
shop on Non-equilib ium Phenomena in Supe cooled Fluids,
Glasses and Amo phous Ma e ials, Pisa, I aly, 1995 ~Wo ld Sci-
en i ic, Singapo e, in p ess!.
14G.P. Joha i, Philos. Mag. B 41,41~1980!; G.P. Joha i and J.
Pe ez, Mol. Phys. 83, 235 ~1994!.
53 8175BRIEF REPORTS