- Email: [email protected]
Valence force field and raman spectra of β Ga2O3
419
3ourmlofMolecubrStmcture,79(1982)419-422 EkevierScientific PublishingCompany,Amsterdam-RintedinTheNetherlands
OF 8 G”z03
VALENcEmmFlELDANDRAMANsPEcTRA
D.DOHYandG.LUC?GEAU Laboratoire de Chirnie Physique de 1 'Universit6 Paris XIII, -SE
A single crystal of -Ox 4 and 1000 K. A Flete
(m)
hasbeens~edbyRmanspecWoscopybetween
valence force field has been cibtaine3.The temperature
dependanceofthe~bandhalfwidthsIscrnusudlandhasbeendiscussedinternsof mnicity,
creation of defects and order-disorder phase transition.
A single crystal was cbtained from Professor Revmlevschi was cut andorient&
folla&ngix&catrixaxes.
TheC2axiswas
(ref. 1). The crystal controlldw~th
~larizmgmicrosmpe~Iaueexperiments.~spectrawere~~wltha C&erg
T800 spzctrtmtleter using 5145 and 4880 A laser lines. In-a-red
werereaxd&onaPerkinElmer580
spectra
instrumznt and a F.I.R. 30 Polytec interfemmztex
for the 20-300 an-l frequency range.
lhe unit cell countain two Ga203 units, it is represented in Fig. la, the stnxture is represented by the C'u,space group. Atonrsare all in Cs sites (ref. 2), and the coupling through the center of inversion gives rise to Ag + B, rrpdes m na3einC
s
andtoB
vibrationalmodes
Fig.
1. (aI tit
+A
rmdesfrcmnone
cZnbe"classifiedas
A"rmMe
1 IntheC
2h factorgroupthe
follu.+s :rvib = 10~g + 5~~ + 4Au + 8~~.
cell of Ga203. (b)perspectivetiewofoc&edraandtetxaedra.
0022-2860/82/000~000/$02.7501982
an A'
Elsevier
ScientifxPublishingCompany
Fig. 2. Polarised Rmmn
spectra of B Ga203 at 300 K.
The structure is made of octaedra (Ga&
sharing one edge and of chains of corner
sharing tetraedra as shun in Fzg. lb. Assuming that the largest Ga ObmZs ina first stage , it is possible to consider Ga O2 groups.
(2.05 i)
canbeignored
RESULTS PolarisedRaman
spectra at 300 K are reported ti Fig. 2. 300 K 1-R spxtnnn
nujol mull of ~lycrystalline mystal
sample is given in Fig. 3. F&man spztza
have been recorded every 25 K frcm 5 to 1000
V&rational
of
of single
K.
analysis
At 5 K one separates 14 of the band is a swsition
active fumkrmmizl
rrodes..TAe475 cm-1
of Ag and Bg rrodes.Fig. 2 reports the relative intensity of
thedifferentmnents mpnts interm
15 F&man
of the scattermgmtricesmasuredat300
of symxtryis
readilyobtained.Threeregions
K.Theassigncanbe
recognized in
FLamnspectm.Thel~fmqmncy
region belcw &IO cm -'. (characterized bynarrmbands)
must
(vibratiors and trans,$ 'dons of chains of tetmedra).
be related tilatticeties
The second region (above 600 cm-'> is assiqnable to the Ga 0 (tetraedra) stretching rmdes. The third region (between 600-300 cm?') corresponds to bending vibrations_ Their description in these simple te.nx is reported along with the D.E.P. found from nomal
cxordimteanalysis
Vakn~
intablel.
force field calculations
~ecal~ationswereperforrrreduslng~ouchi'sprogramrre. consbts
range is between 2.2 and 1.65 r&m
AO-l for tee&on
The stretching force (
421 0.6-1.3
O-1 miyn A
fK1203,
work is in progress.
for octaedron (Ga O&.
Fig. 3. Infra-red spxtrum
The force field has been transfered to
at 300 K. Fig. 4. Halfwidth variation.
Tmpxature
effect
Ageneralbroadeningof
Rarranbandsis
cbservedwhen
thetemperatureis
highest absolute broadening is observed for the "internal &es"
at high frequenq.
Fig. 4 reports scxe halfwidth curves as function of temperature. FYeguenq rermin less than 2 % between 100-800 K for rrostof the modes except bard which shifts of 5 %. In any case all the expermental
shifts
for the 143 a-i-l
studies of anharrmnicity in
ionic crystal such as quartz, fluorites, silicates (ref. 3) shm
that the frequency
shifts are large (rmre than 6 8 between 200-1000 K) and are due to Wo related to the way in which the frequency changes with volme oftenexpressed
raiseJ. The
terms, one is
(due to expansion) it is
ILLterms of Griineisenparameters and is exp9zt&
to be large for lckr
frequency external rrcdes (ref. 4). the second one is a direct
anhan~~ruc
mntaming
contributions (the last
cubic CaT dependaxe)
and quartx
(bT2 dependaxe)
terms being negligible for law frfquency external ties). shifts for Ga203 mntrastwith tirational
effect
These mderate
frequency
large broadenings and thus neither anhanmnicity
nor
dephasing (ref. 5) can explain both large broadenings and small freqclency
shiftS. Creation of defects could be Involved, ~IIthis respect a
GJeak
scattering is
observed in the Kayleigh wings above 600 K. Under this model the different broadetigs would be related to their different dispersion curve. Hmever Plateau for a 0x-n
nmr&r
the presence of a
of bands remain to explain. A.T.D measurements exclude
the possiblllty of a first order phase tranSition, a secorrdorder one could be in~lVed,
It muld
be of the order-disorder type, pretrans~tional effms
rroreor less pronounced depending on the type of the nonnal &es.
muld
be
422 -1 lix&a-Red
and&man
; dculatdfrequenciesardpotential-energy
wncies
distiibution
r
--SF 763 R' 760 1-R 720 1.R 668 1-R 657 R 651 R 640 1.R 628 R 525 I.R 475 R 475 R 455 1.R 415 R 372 1.R 353 R n.o.1.R 346 R 318 R 3 0 1.R 2 !I 0 IOR 250 1.R 199 R 169 R 155 1.R 147 R 114 R 111 R =
731 692 656 654 644 626 628 526 474 468 500 406 374 360 352 353 308 337 300 216 195 166 155 152 114 113 z
D.E.P 24v + 20~ 17"; -I-29P 22v" 62v + 16S" 41VT + 22vl + 1581 65vT + 178O 64vT + 16~; 75vT 91vT + 208 + l8b 34vT + 36~' + 20a2 39vT + 306O + l76l 34P + 29d + 15d; 33v" + 18s; 33rs" 59v3 + 326 + 166 16v" + 64~' + 256; 22vT + 396O 20v" + 32v3 + 218 17vT + 24v" + 1962 i6L$ + 36v0 + 1562 38a" + 216; 29v + 32&l 15v" + 396l + 276 26vT + 52~' + 71d2 33vT + 21a" + 166l 31v" + 816l + 986f 626': + 646; Ked barn,, n.0 =
ml
Au As Bs ml As Bu As Bs Au As g Au As As Bu BU
Au As As Bu
1
5 .
=
=
beMing.
OnlycontGbutions&porequdL
This work was supported
’
M.
Ga-O-Gs
2 s. Gel&r, 3 F. Gervais,
J. Chm.
Phys.,
B. Piriou
4 G. Leibfried,
?a?
6 V as
(0 I2
I o11)2
"asG"I(OI)2 + 16d2
6Gp(oI )2 twist. E"IIOI)2 r=W
// GaI(OI)2
roc?dng_LGaI(OI)2 -.(+I --=?I + 296 + 206; -.lib.mI trans.lib.mI
+ 3363 + 2363
not
beding,
to15
by N.A.T.O.
Saurat and A. Revcolevschi,
attribution vsGP(oI)2
ObSE 6
fed,vT =
=
Ga
tetraearo
+bending,
tr etcmng 6; 9 y?2
% ar~rep&d.
(nb RG 259.80)
Rev. Int. Hautes Temper.
et Refract.,
8(1971)291-304
33(1960) 676-684
and F. Cabannes,
Phys. Stat. Sol.,
(b)55(1973)143-154
J. Phys. Chem. Sol., supp.1(1965)237-244
5 s. Marks, P.A. Cornelius
and C.B. Harris,
J. Chem. Phys.,
73(1980)3069-3081.
3ourmlofMolecubrStmcture,79(1982)419-422 EkevierScientific PublishingCompany,Amsterdam-RintedinTheNetherlands
OF 8 G”z03
VALENcEmmFlELDANDRAMANsPEcTRA
D.DOHYandG.LUC?GEAU Laboratoire de Chirnie Physique de 1 'Universit6 Paris XIII, -SE
A single crystal of -Ox 4 and 1000 K. A Flete
(m)
hasbeens~edbyRmanspecWoscopybetween
valence force field has been cibtaine3.The temperature
dependanceofthe~bandhalfwidthsIscrnusudlandhasbeendiscussedinternsof mnicity,
creation of defects and order-disorder phase transition.
A single crystal was cbtained from Professor Revmlevschi was cut andorient&
folla&ngix&catrixaxes.
TheC2axiswas
(ref. 1). The crystal controlldw~th
~larizmgmicrosmpe~Iaueexperiments.~spectrawere~~wltha C&erg
T800 spzctrtmtleter using 5145 and 4880 A laser lines. In-a-red
werereaxd&onaPerkinElmer580
spectra
instrumznt and a F.I.R. 30 Polytec interfemmztex
for the 20-300 an-l frequency range.
lhe unit cell countain two Ga203 units, it is represented in Fig. la, the stnxture is represented by the C'u,space group. Atonrsare all in Cs sites (ref. 2), and the coupling through the center of inversion gives rise to Ag + B, rrpdes m na3einC
s
andtoB
vibrationalmodes
Fig.
1. (aI tit
+A
rmdesfrcmnone
cZnbe"classifiedas
A"rmMe
1 IntheC
2h factorgroupthe
follu.+s :rvib = 10~g + 5~~ + 4Au + 8~~.
cell of Ga203. (b)perspectivetiewofoc&edraandtetxaedra.
0022-2860/82/000~000/$02.7501982
an A'
Elsevier
ScientifxPublishingCompany
Fig. 2. Polarised Rmmn
spectra of B Ga203 at 300 K.
The structure is made of octaedra (Ga&
sharing one edge and of chains of corner
sharing tetraedra as shun in Fzg. lb. Assuming that the largest Ga ObmZs ina first stage , it is possible to consider Ga O2 groups.
(2.05 i)
canbeignored
RESULTS PolarisedRaman
spectra at 300 K are reported ti Fig. 2. 300 K 1-R spxtnnn
nujol mull of ~lycrystalline mystal
sample is given in Fig. 3. F&man spztza
have been recorded every 25 K frcm 5 to 1000
V&rational
of
of single
K.
analysis
At 5 K one separates 14 of the band is a swsition
active fumkrmmizl
rrodes..TAe475 cm-1
of Ag and Bg rrodes.Fig. 2 reports the relative intensity of
thedifferentmnents mpnts interm
15 F&man
of the scattermgmtricesmasuredat300
of symxtryis
readilyobtained.Threeregions
K.Theassigncanbe
recognized in
FLamnspectm.Thel~fmqmncy
region belcw &IO cm -'. (characterized bynarrmbands)
must
(vibratiors and trans,$ 'dons of chains of tetmedra).
be related tilatticeties
The second region (above 600 cm-'> is assiqnable to the Ga 0 (tetraedra) stretching rmdes. The third region (between 600-300 cm?') corresponds to bending vibrations_ Their description in these simple te.nx is reported along with the D.E.P. found from nomal
cxordimteanalysis
Vakn~
intablel.
force field calculations
~ecal~ationswereperforrrreduslng~ouchi'sprogramrre. consbts
range is between 2.2 and 1.65 r&m
AO-l for tee&on
The stretching force (
421 0.6-1.3
O-1 miyn A
fK1203,
work is in progress.
for octaedron (Ga O&.
Fig. 3. Infra-red spxtrum
The force field has been transfered to
at 300 K. Fig. 4. Halfwidth variation.
Tmpxature
effect
Ageneralbroadeningof
Rarranbandsis
cbservedwhen
thetemperatureis
highest absolute broadening is observed for the "internal &es"
at high frequenq.
Fig. 4 reports scxe halfwidth curves as function of temperature. FYeguenq rermin less than 2 % between 100-800 K for rrostof the modes except bard which shifts of 5 %. In any case all the expermental
shifts
for the 143 a-i-l
studies of anharrmnicity in
ionic crystal such as quartz, fluorites, silicates (ref. 3) shm
that the frequency
shifts are large (rmre than 6 8 between 200-1000 K) and are due to Wo related to the way in which the frequency changes with volme oftenexpressed
raiseJ. The
terms, one is
(due to expansion) it is
ILLterms of Griineisenparameters and is exp9zt&
to be large for lckr
frequency external rrcdes (ref. 4). the second one is a direct
anhan~~ruc
mntaming
contributions (the last
cubic CaT dependaxe)
and quartx
(bT2 dependaxe)
terms being negligible for law frfquency external ties). shifts for Ga203 mntrastwith tirational
effect
These mderate
frequency
large broadenings and thus neither anhanmnicity
nor
dephasing (ref. 5) can explain both large broadenings and small freqclency
shiftS. Creation of defects could be Involved, ~IIthis respect a
GJeak
scattering is
observed in the Kayleigh wings above 600 K. Under this model the different broadetigs would be related to their different dispersion curve. Hmever Plateau for a 0x-n
nmr&r
the presence of a
of bands remain to explain. A.T.D measurements exclude
the possiblllty of a first order phase tranSition, a secorrdorder one could be in~lVed,
It muld
be of the order-disorder type, pretrans~tional effms
rroreor less pronounced depending on the type of the nonnal &es.
muld
be
422 -1 lix&a-Red
and&man
; dculatdfrequenciesardpotential-energy
wncies
distiibution
r
--SF 763 R' 760 1-R 720 1.R 668 1-R 657 R 651 R 640 1.R 628 R 525 I.R 475 R 475 R 455 1.R 415 R 372 1.R 353 R n.o.1.R 346 R 318 R 3 0 1.R 2 !I 0 IOR 250 1.R 199 R 169 R 155 1.R 147 R 114 R 111 R =
731 692 656 654 644 626 628 526 474 468 500 406 374 360 352 353 308 337 300 216 195 166 155 152 114 113 z
D.E.P 24v + 20~ 17"; -I-29P 22v" 62v + 16S" 41VT + 22vl + 1581 65vT + 178O 64vT + 16~; 75vT 91vT + 208 + l8b 34vT + 36~' + 20a2 39vT + 306O + l76l 34P + 29d + 15d; 33v" + 18s; 33rs" 59v3 + 326 + 166 16v" + 64~' + 256; 22vT + 396O 20v" + 32v3 + 218 17vT + 24v" + 1962 i6L$ + 36v0 + 1562 38a" + 216; 29v + 32&l 15v" + 396l + 276 26vT + 52~' + 71d2 33vT + 21a" + 166l 31v" + 816l + 986f 626': + 646; Ked barn,, n.0 =
ml
Au As Bs ml As Bu As Bs Au As g Au As As Bu BU
Au As As Bu
1
5 .
=
=
beMing.
OnlycontGbutions&porequdL
This work was supported
’
M.
Ga-O-Gs
2 s. Gel&r, 3 F. Gervais,
J. Chm.
Phys.,
B. Piriou
4 G. Leibfried,
?a?
6 V as
(0 I2
I o11)2
"asG"I(OI)2 + 16d2
6Gp(oI )2 twist. E"IIOI)2 r=W
// GaI(OI)2
roc?dng_LGaI(OI)2 -.(+I --=?I + 296 + 206; -.lib.mI trans.lib.mI
+ 3363 + 2363
not
beding,
to15
by N.A.T.O.
Saurat and A. Revcolevschi,
attribution vsGP(oI)2
ObSE 6
fed,vT =
=
Ga
tetraearo
+bending,
tr etcmng 6; 9 y?2
% ar~rep&d.
(nb RG 259.80)
Rev. Int. Hautes Temper.
et Refract.,
8(1971)291-304
33(1960) 676-684
and F. Cabannes,
Phys. Stat. Sol.,
(b)55(1973)143-154
J. Phys. Chem. Sol., supp.1(1965)237-244
5 s. Marks, P.A. Cornelius
and C.B. Harris,
J. Chem. Phys.,
73(1980)3069-3081.