Raman spectroscopic study of mixed carbonate materials

Article abstract of DOI:10.1016/j.saa.2010.09.011

The main parameters for precipitation of mixed carbonate materials have been studied by Raman microscopy. These carbonates are compounds of barium, strontium and calcium. It has been shown that the Raman spectrum of a sample is exclusively controlled by its composition, the precipitation parameters do not affect the crystal structure. Even at relatively low levels, the calcium content of a sample can dominate the vibrational frequencies as measured by Raman spectroscopy. Calcium contents greater than 17% show this effect to a considerable degree, and give the broadest or two Raman peaks and thus the least uniform unit cells. The analysis of the lattice modes demonstrates that each Raman shift observed for a mixed carbonate sample corresponds to a specific crystal structure. Some peaks lie within two or three shifts that are observed for different crystal structures.

Full text of DOI:10.1016/j.saa.2010.09.011

Spectrochimica Acta Part A 78 (2011) 136–141
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Raman spectroscopic study of mixed carbonate materials
W. Kaabara,b,∗, S. Botta, R. Devonshirea
a High Temperature Science Laboratories, Department of Chemistry, University of Sheffield, Sheffield S3 7HF, UK
b Département de Chimie, Faculté des Sciences Exactes, Université Mentouri Constantine, Constantine 25000, Algeria
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 16 May 2010
Received in revised form 4 August 2010
Accepted 8 September 2010
The main parameters for precipitation of mixed carbonate materials have been studied by Raman
microscopy. These carbonates are compounds of barium, strontium and calcium. It has been shown that
the Raman spectrum of a sample is exclusively controlled by its composition, the precipitation parame-
ters do not affect the crystal structure. Even at relatively low levels, the calcium content of a sample can
dominate the vibrational frequencies as measured by Raman spectroscopy. Calcium contents greater than
17% show this effect to a considerable degree, and give the broadest or two Raman peaks and thus the
least uniform unit cells. The analysis of the lattice modes demonstrates that each Raman shift observed
for a mixed carbonate sample corresponds to a specific crystal structure. Some peaks lie within two or
three shifts that are observed for different crystal structures.
Keywords:
Raman microscopy
Carbonates
Calcium
Strontium
Barium
© 2010 Elsevier B.V. All rights reserved.
1. Introduction
ing calcite and aragonite with high temperature and high pressure.
They showed that the measured relative pressure and tempera-
Double and triple mixed carbonates are specially prepared emit-
ter materials used for efficient thermal electron emission of cathode
structures. In the current triple oxide cathode manufacturing pro-
cess, a matrix of barium, strontium and calcium carbonate layer
is either painted or sprayed on a metal cathode base [1]. Emission
from an oxide cathode is dependent upon the ratio of alkaline earth
carbonates present at the cathodes surface. The method by which
each carbonate is made plays a key role in its function in a cathode.
It has been found that the crystalline structure of the alkaline earth
carbonates affects the life of oxide cathode tubes [2]. The study
presented here will serve to characterise the carbonate precursor
materials using Raman microscopy.
ture shifts of the Raman lines were greater for the lattice modes
than for the internal modes of the CO3 groups. Alia et al. [9] stud-
ied synthetic aragonite–strontianite solid solution samples using
IR and FT-Raman spectroscopy; they reported that positional disor-
der induced by the random cationic substitution resulted in strong
increase of the halfwidth in several vibrational bands. Frost et al.
[10–13] have recently reported a Raman and infrared spectroscopic
study of carbonate minerals from different origins.
In this paper we have used Raman microscopy as a diagnostic
tool for mixed carbonate materials produced with different com-
positions, temperatures of precipitation and concentrations of the
precipitation agent.
There have been numerous spectroscopic investigations of pure
carbonates. Amongst the earlier experimental investigations are
those of Couture [3] on aragonite, strontianite and witherite. In
view of their isomorphism a comparative study of the Raman spec-
tra of those three simple carbonates was given by Krishnamurti
[4]. Griffith [5] published the first compilation of FT Raman spec-
tra of minerals, including several carbonates. Adler and Kerr [6]
reported the IR spectra of a dozen of simple and double carbon-
ates and showed that differences in the spectra were a function of
cation size. Later, Scheetz and White [7] published a detailed Raman
and IR study of alkaline-earth double carbonates of natural origin.
Gillet et al. [8] studied the behaviour of simple carbonates includ-
2. Experimental
A standard preparation method [14] is to precipitate carbonates
from an aqueous solution of the alkali earth nitrates with ammo-
nium carbonate. Raw materials of high purity (99.99%) were used
throughout these studies, sourced from the Aldrich Chemical Com-
pany.
The powdered carbonate material is prepared by co-
precipitation from aqueous solutions in respective nitrates
with ammonium carbonate according to the following reaction:
(Ba, Sr, Ca)NO3(aq) + NH4HCO3(aq) → (Ba, Sr, Ca)CO3(s) + NH4HNO3(aq)
Briefly, the method for precipitation of the carbonate powders
is as follows: Ba, Sr, Ca nitrate weighed out in the required ratios
by mass and then dissolved in 50 ml deionised water. The solu-
∗
Corresponding author at: Département de Chimie, Faculté des Sciences Exactes,
Université Mentouri Constantine, Constantine 25000, Algeria. Tel.: +213699854214.
E-mail address: w kaabar@yahoo.co.uk (W. Kaabar).
1386-1425/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2010.09.011

W. Kaabar et al. / Spectrochimica Acta Part A 78 (2011) 136–141
137
0.00
of-plane bend (ꢀ2), a doubly degenerate asymmetric stretch (ꢀ3)
and a doubly degenerate bending mode (ꢀ4). The symmetries of
these modes are A1ꢀ (R) + A2ꢀꢀ (IR) + Eꢀ (R, IR) + Eꢀꢀ (R, IR) and occur at
1064, 879, 1415 and 680 cm−1 respectively. The symmetric stretch-
ing vibration is very intense in the Raman spectrum, while the
asymmetric stretching is weak. The asymmetric bending although
Raman-allowed is very weak.
The internal modes can be related to the vibrations of the free
carbonate ion, by simply comparing the band frequencies. The site
symmetry of the CO3 group is determined by the cation environ-
ment and modifies the selection rules (i.e. the number of bands
observed), and the frequencies to a small extent, when compared
with the free group.
1.0
2
5
0.8
21
0.25
0.6
0.50
13
4
0.4
3
15
TP2
14
0.75
In this study the relative Raman shifts and the full width at half
maximum (FWHM) of the prominent peak corresponding to the ꢀ1
band are compared for the different samples.
16
10
11
8
0.2
22
20
9
6
7
19
18
12
1
1.00
0.00
17
3.1.1.1. Pure carbonates. Fig. 2 shows the ꢀ1 fundamental in the
0.0
Raman spectra of the pure carbonates. The peaks from the three
0.25
0.50
Ba content
0.75
1.00
samples are well separated, with centres located at 1059.77 cm−1
,
1071.28 cm−1 and 1086.09 cm−1, for pure barium (Emitter 17),
strontium (Emitter 2) and calcium (Emitter 1) carbonates respec-
tively. Farmer [16] showed that the (CO3)2− symmetric stretching
band varied according to the ionic radius of the cation. The higher
the ionic radius the lower the wavenumber of the symmetric
stretching mode. The ionic radii of Ba2+, Sr2+ and Ca2+ ions are
149 pm, 132 pm and 114 pm respectively. Each Raman spectrum
shows a single narrow peak with FWHM values of between 3.5 and
Fig. 1. Ternary phase diagram showing the content of mixed carbonate powders
prepared with different compositions.
tion is heated to required temperature with continuous stirring.
Once nitrate solution is stable at required temperature, ammonium
carbonate solution is added drop-wise at an approximate rate of
2 ml/min. On completion of the precipitation, heating is turned off
and sample is left to cool to room temperature with rigorous stir-
ring. Sample is filtered and collected precipitate was oven dried
at 40 ◦C for 12 h. Additional cathode components may be included
such as ZrO2, which is known to extend cathode life [15]. From
the above, it can be observed that the main parameters which
will affect the precipitation process are: the ratio of alkali earth
nitrates, the temperature of precipitation and the concentration of
the precipitating agent.
4.5 cm−1
.
The results from these pure carbonate samples can be used for
comparison to the double and triple component samples prepared.
3.1.1.2. Double component samples with similar ratio. These com-
prise Emitters 4, 12 and 13, which are composed of 50:50 Sr:Ca,
50:50 Ba:Ca, and 50:50 Ba:Sr respectively. Raman spectra of the ꢀ1
band for each of these are given in Fig. 3.
Emitter 13 gives a narrow peak, FWHM of 6.5 cm−1, at a Raman
shift between that of pure barium and strontium carbonates. This
is due to the fact that the Ba2+ and Sr2+ ions are of a similar size.
The exchange of these two species in a lattice structure therefore
causes only minor changes to the crystal structure, and the pres-
Raman spectra of the carbonate powder samples prepared are
acquired with a Renishaw RM1000 series, using 514.5 nm excita-
tion from an Ar+ laser. Rayleigh scattered light rejection is with
the aid of a holographic notch filter, the cut-off from which is
approximately 190 cm−1. Spectral manipulation such as base line
adjustment, smoothing and normalisation are performed using the
software package GRAMS (Galactic Industries Corporation).
1086.09
1071.28
1059.77
3. Results and discussion
1.0
0.8
0.6
0.4
0.2
0.0
CaCO3
SrCO3
BaCO3
3.1. Change of composition
Raman microscopy is performed on 23 carbonate powder sam-
ples of varying compositions, the temperature of precipitation is
68 ◦C and the concentration of ammonium carbonate solution is
0.25 mol/dm3 (Table 1). The various compositions are represented
as a ternary diagram of the relative amounts of the three alkali earth
carbonates present in each of the samples prepared. This is given
in Fig. 1.
The Raman spectra of well mixed powder samples acquired
show clear differences between samples of differing composition.
In general, the spectra may be separated into two regions. Those
bands at wavelengths above 600 cm−1 are due to the internal
motions of the molecular carbonate ion. Those below 600 cm−1 are
due to motions involving the entire unit-cell usually referred to as
lattice modes.
1110
1100
1090
1080
1070
1060
1050
1040
Wavenumber / cm-1
3.1.1. Carbonate anion internal modes
2−
The free ion, CO3
with D3h symmetry exhibits four normal
Fig. 2. Raman spectra of carbonate anion symmetric stretching band for single com-
vibrational modes; a symmetric stretching vibration (ꢀ1), an out-
ponent carbonate powder samples.

138
W. Kaabar et al. / Spectrochimica Acta Part A 78 (2011) 136–141
Table 1
Raman shifts and FWHM for Emitter samples with different compositions.
Name
Nominal ratio Ba:Sr:Ca
Raman shift prominent peak (cm−1
)
FWHM Prominent peak (cm−1
)
Emitter 1
Emitter 2
0:0:100
0:100:0
100:0:0
0:50:50
50:0:50
50:50:0
17:17:66
55:20:25
66:5:29
17:66:17
80:10:10
66:29:5
33:33:33
66:17:17
45:45:10
50:30:20
66:0:34
66:4:30
66:15:19
66:24:10
66:30:4
66:34:0
100:0:0
1086.09
1071.28
1059.77
1084.95
1087.23
1066.74
1084.95
1083.81
1084.95
1072.42
1062.16
1064.43
1078.11/1086.09
1063.31/1080.40
1067.83
4.384
4.164
3.601
21.983
20.417
6.545
15.689
20.637
22.422
6.482
9.175
8.455
7.547
9.176
8.035
Broad
7.499
9.642
6.963
11.248
7.532
4.821
3.764
Emitter 17
Emitter 4
Emitter 12
Emitter 13
Emitter 6
Emitter 8
Emitter 9
Emitter 5
Emitter 7
Emitter 11
Emitter 3
Emitter 10
Emitter 21
Emitter 14
Emitter 18
Emitter 19
Emitter 20
Emitter 16
Emitter TP2
Emitter 15
Emitter 22Pure Ba + ZrO2
1088.33
1060.92/1087.11
1062.05/1085.97
1063.19/1085.05
1064.32
1064.21
1059.77
1059.72
ence of the two bond types result in the observation of an “average”
frequency. The Ca2+ ion however is considerably smaller, and along
with the different structural variations of CaCO3, this produces dif-
ferent results than in the Ba:Sr case.
For both Emitters 12 and 4, Raman peaks are considerably
broader, FWHM of approximately 21 cm−1, and are close to the
Raman shift observed for the single component CaCO3 sample.
This remarkable increase in the band width has previously been
reported in the Raman spectra of double carbonates [7,9]. This
suggests that the size of the Ca2+ ion play a dominant role in the
vibrational frequencies observed by Raman microscopy.
Carbonate samples Emitter 7 and 11 show Raman shifts between
those of the single component BaCO3 and SrCO3 samples. These
contain cumulative amounts of Ba and Sr of 90% and 95% of the
total composition, with only small proportions of Ca making up the
remainder. At these low levels Ca has only a small effect on the
vibrational frequencies.
The Raman spectra of Emitter 3 and 10 are different to all those
above in the fact that they both show two maxima. Emitter 3 has
equivalent amount of all three materials. Sr is the highest Raman
scatterer, but the effect of Ca on the Raman spectrum to shift the
peak towards its pure position has been observed. The presence
of Ba serves to add to the Sr shift which reduces the domina-
tion of the spectrum of large amounts of Ca seen for the double
component samples. The spectrum therefore represents a “com-
promise” of the system between these effects. Emitter 10 contains
a lower proportion of Ca and an increased proportion of Ba and
Sr combined. The spectrum is expanded in the direction of the
pure Ba position as this is now the dominant component, but the
second feature as a result of the presence of Ca is still clearly visi-
ble.
The variation of Raman spectrum observed for samples with
similar Ba composition (66%) is a result of the variation of Sr/Ca
ratio, given all other parameters were kept constant. From these
results it may be confirmed that the proportion of calcium con-
tent in a triple component carbonate sample dominates the Raman
spectrum. Calcium contents greater than 10% show a Raman spec-
trum with two maxima, the prominent peak is expanded in the
direction of the pure Ba position as this is the dominant compo-
nent. This effect is not observed when the proportion of Ca is 10%
or less. Emitter 21 (45:45:10) shows a Raman shift similar to the
50:50 Ba:Sr sample this is due to the small Ca content of 10%. Emit-
ter 14, with more important calcium content of 20%, gives a Raman
peak centred close to the single component CaCO3 sample, similar
to the results for Emitter 8.
In summary, lower Ba content causes the Raman shift to move
to higher wavenumbers, Ca contents greater than 17% causes the
Raman shift to be close to that of 100% Ca. The Raman peak is only
in the region of the 100% Sr shift when Sr content is greater or equal
66%. The presence of two peaks indicates that the proportions of Ba,
Ca and Sr are similar, or Ba content is 66% while Ca and Sr contents
are within 5% of each other, or Ba content is 66% and Ca content is
∼30–34%.
3.1.1.3. Triple component samples. Table 1 summarises the Raman
shift and the full width at half maximum of the ꢀ1 band for samples
with three components. The effect of sample composition on the
observed Raman shifts may be explained as follows:
Emitters 6, 8, and 9 contain over 20% calcium, and this result in
the Raman peak being centred close to the single component CaCO3
sample. The Raman spectrum acquired from Emitter 5 is centred on
the position of the single component SrCO3 sample. This is due to
the very high Sr content in this sample, and the fact that SrCO3 is
the strongest Raman scatterer of the three carbonate materials [9].
1084.95
1.0
1066.74
(equimolar Sr,Ca)CO3
(equimolar Ba,Ca)CO3
(equimolar Ba,Sr)CO3
1087.23
0.8
0.6
0.4
0.2
0.0
1110 1100 1090 1080 1070 1060 1050 1040
Wavenumber / cm-1
Fig. 3. Raman spectra of carbonate anion symmetric stretching band for equimolar
carbonate powders.

W. Kaabar et al. / Spectrochimica Acta Part A 78 (2011) 136–141
139
CaCO3
35000
TP1 (48ºC)
180.01
206.54
TP2 (68ºC)
281.83
154.99
30000
TP3 (80ºC)
1064.21
Emitter 23 (71ºC fast)
25000
20000
15000
10000
5000
0
214.52
236.20
244.74
180.33
148.44
SrCO3
BaCO3
140.00
1431.02
160.60
233.76
258.31
690.46
153.20
135.36
179.67
224.90
1600 1400 1200 1000
800
600
400
200
0
Wavenumber / cm-1
600
500
400
300
200
100
0
Wavenumber / cm-1
Fig. 5. Raman spectra of carbonate samples prepared at different precipitation tem-
peratures and speed.
Fig. 4. Raman spectra of lattice modes for single component carbonate powder
samples.
each Raman shift can be calculated to arise from a mixing of
two or more shifts from the individual pure carbonate sub-
stances (aragonite, strontianite and witherite) in their respective
ratios. For example: Emitter 10 (17.2% Ca, 16.9% Sr, 66% Ba) has
a peak at 235.06 cm−1 (nearest literature peak is aragonite at
272 cm−1, strontianite at 248 cm−1 and witherite at 222 cm−1):
A previous study, carried out by Murabayashi [17,18] using scan-
ning electron microscopy, demonstrated the variation in carbonate
powder morphology with composition for a large range of samples.
The extension of the study using Raman microscopy has provided
a further analysis of composition variations.
Two samples, Emitters 17 and 22 were prepared with a composi-
tion, 100% BaCO3, but 2% zirconia was added to the 22 sample prior
to precipitation. Analysis by Raman microscopy (Table 1) indicates
that the addition of zirconia does not influence the precipitated Bar-
ium carbonate structure, and exists in the materials as a separate
inclusion.
(0.172 × 272) + (0.169 × 248) + (0.66 × 222) = 235.22 cm−1
.
3.2. Temperature and speed of precipitation
Three samples were prepared to determine the effect of the
temperature of precipitation on the Raman spectra. The compo-
sition (4% Ca, 30% Sr, 66% Ba) and concentration of the ammonium
carbonate solution (0.25 mol/dm3) were kept constant.
Raman microscopy was performed on each of the samples, and
Fig. 5 shows the resulting spectra. The rising baseline is a result of
the exact focus of the laser on the sample, and so the differences in
3.1.2. Lattice modes
Fig. 4 shows the Raman low frequency spectral region cor-
responding to the pure carbonate substances. A pair of intense
Raman bands is observed for each of the cases of CaCO3, SrCO3 and
BaCO3. These bands are at 206.54 and 154.99 cm−1 in CaCO3, 180.33
and 148.44 cm−1 in SrCO3 and 153.20 and 135.36 cm−1 in BaCO3.
These bands match perfectly with previous results for aragonite,
strontianite and witherite [4,9]. The very weak intensity bands at
509.5 cm−1 in CaCO3 and at 510.77 cm−1 in SrCO3 are not in the lit-
erature. In relation to CaCO3, the band at 281.83 cm−1 corresponds
to a calcite structure. CaCO3 can exist in different structures under
similar condition, the occurrence of both aragonite and calcite
is very common. Calcite/aragonite intergrowth is almost always
observed when carbonation is carried out in the temperature range
30–80 ◦C [19].
35000
CP4: 0.129 mol/dm3
CP5: 0.064 mol/dm3
CP1: 0.881 mol/dm3
30000
1064.26
CP3: 0.257 mol/dm3
25000
CP2: 0.512 mol/dm3
20000
Table 2 gives the positions of the Raman vibrations for the var-
ious Emitters. As no crystal structure information is available on
any of the emitter materials, one has to make use of correlations
which have been established between Raman spectral features
observed in the emitters and known crystal structures of related
carbonate compounds. Raman shifts characteristic of various crys-
tal structures were from the Database of Raman spectroscopy, X-ray
diffraction and chemistry of minerals website [20] and other refer-
ences [9,21–24].
15000
140.26
690.96
163.12
10000
234.76
5000
0
Where possible, specific crystal structures were assigned to
each Raman shift observed in the Emitters. Some peaks in
Table 2 lie within two shifts that are observed for two differ-
ent crystal structures. It may suggest that the crystal structure
in the emitter is some way between the two extremes, and
1600 1400 1200 1000
800
600
400
200
0
Wavenumber / cm-1
Fig. 6. Raman spectra of carbonate samples precipitated with ammonium carbonate
solutions of differing concentration.

140
W. Kaabar et al. / Spectrochimica Acta Part A 78 (2011) 136–141
Table 2
Observed Raman shifts in the Emitters.
Emitter
1
2
3
4
5
6
7
8
% Ca
% Sr
% Ba
100.0
–
–
–
100.0
–
33.4
33.3
33.3
50.1
50.0
–
17.0
66.1
17.0
66.8
17.1
17.0
10.1
10.2
80.0
25.0
20.0
55.2
154.99
180.39
206.54
281.83
509.55
705.56
712.43
1086.09
1435.84
1462.07
Arag
Arag
Arag
Cal
Arag
Carb
Carb
Carb
Carb
Carb
148.44
180.33
214.52
236.20
244.74
258.31
510.77
710.13
Stron 155.36 Arag
Stron 191.77 Alsto 268.01 Cal III
Stron 273.76 Arag
Stron 510.78 Stron 692.95 Carb
Stron 701.08 Carb
Stron 711.25 Carb
Stron 1078.11 Carb
Carb 1086.09 Carb 1084.95 Carb
Carb 1451.84 Carb 1397.12 Carb
188.09 Arag
180.09 Arag
189.04 Arag
164.46 Baryt 183.81 Stron
246.50 Stron 266.92 Stron 231.60 Cal III 257.53 Baryt
509.98 Arag. Stron 507.55 Arag
508.39 Arag
702.08 Carb
712.39 Carb 1062.16 Carb
874.18 Carb 1386.66 Carb 1083.81 Carb
1084.95 Carb
510.20 Stron 691.88 Carb
696.45 Carb
1072.42 Carb
1447.25 Carb
689.61 Carb
707.84 Carb
874.18 Carb
707.94 Carb
710.19 Carb
871.22 Carb
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
1448.06 Carb
–
–
–
–
–
–
–
–
–
–
–
–
1071.28
1445.91
Carb
–
–
–
–
Emitter
9
10
11
12
13
14
15
16
% Ca
% Sr
% Ba
29.0
5.0
66.0
17.2
16.9
66.0
5.0
28.8
66.0
50.1
–
50.1
–
50.1
50.0
20.0
30.0
50.0
–
34.3
66.7
10.3
24.2
66.6
194.19
259.98
691.88
705.54
873.23
1084.95
1325.34
–
Alsto
Mix
Carb
Carb
Carb 1063.31
Carb 1080.40
Carb 1432.64
–
–
164.39
235.06
690.75
704.41
Baryt
Cal
Carb
Carb
Carb 1064.43
Carb 1433.73
Carb
–
–
166.76
234.39
509.59
690.75
Baryt
Cal III
Stron
Carb
Carb
Carb
–
189.10
267.05
510.84
693.03
712.37
874.18
Baryt
Cal III
Arag
Carb
Carb
Carb
Carb
–
142.89
171.81
237.28
509.67
693.02
706.69
710.15
1066.74
1435.42
Stron
Mix
Mix
Stron 1088.33
Carb 1443.84
Carb
Carb
Carb
Carb
163.10
272.48
692.94
Baryt
Arag
Carb
Carb
Carb
–
–
–
–
138.52
160.75
205.17
691.50
698.59
703.12
1059.77
1428.77
–
Mix
Mix
Mix
Carb
Carb 1064.32
Carb 1430.18
Carb
Carb
–
144.78
160.21
234.80
690.58
Alsto
Arag
Cal
Carb
Carb
Carb
–
–
–
–
–
–
–
–
1087.23
–
–
–
–
–
–
–
–
–
–
–
–
–
Emitter
17
18
19
20
21
22
% Ca
% Sr
% Ba
–
–
34.2
–
66.0
29.9
4.0
66.0
19.5
15.5
66.1
10.2
45.5
45.6
–
–
98.1
100.0
135.36
153.20
179.67
224.90
690.25
699.48
1059.77
1420.23
–
With
With
With
With
Carb
Carb
Carb
Carb
–
138.49
155.05
184.47
229.64
691.02
700.92
1060.92
1087.11
1424.50
Cal III
Arag
Mix
Baryt
Carb
Carb
Carb
Carb
Carb
139.68
156.18
184.67
230.27
690.58
1062.05
1085.97
1425.83
–
Cal III
Calcite
Stron
Baryt
Carb
Carb
Carb
Carb
–
141.36
158.46
233.65
690.58
1063.19
1085.05
1429.02
–
Arag
142.01
164.11
239.55
693.08
1067.83
1442.66
–
Arag
Baryt
Cal II
Carb
Carb
Carb
–
135.59
152.70
178.88
224.46
690.51
693.92
699.62
1059.72
1419.83
With
With
With
With
Carb
Carb
Carb
Carb
Carb
Cal III
Baryt
Carb
Carb
Carb
Carb
–
–
–
–
–
–
–
Arag = aragonite, Cal = calcite, Carb = carbonate, Stron = strontianite, Alsto = alstonite, Baryt = barytocalcite, With = witherite, Mix = mixture.
slope for the three samples do not represent differences in struc-
ture. All spectral features occur at the same position and the relative
magnitudes of features in each spectrum are consistent across the
three samples. Thus the use of different precipitation temperatures
with the same composition does not affect the crystal structure.
The speed of precipitation may also affect the Raman spectra
of the carbonate materials, and the standard drop-wise addition of
ammonium carbonate is thought to be essential to the precipitation
process. To test this, one sample was prepared at a measured tem-
perature with the same composition as the temperature samples
above, but the ammonium carbonate solution was added in one
step, rather than the usual drop-wise addition. The Raman spec-
trum acquired from the sample Emitter 23 at 71 ◦C is given in Fig. 5,
with the previous temperature samples for reference. It can be seen
that the same spectral features are observed in the same positions
with the same intensity ratios. The speed of precipitation, at a given
composition, does not appear to alter the crystal structure.
carbonate solution. Raman spectra were obtained for each sample,
and these are shown in Fig. 6. The spectra are very similar indicating
that the crystal structure is consistent throughout all five samples.
4. Conclusions
The study of the main parameters for precipitation of alkali earth
carbonate materials has uncovered several important features. The
Raman spectrum of a mixed carbonate material is only composition
dependent. The precipitation parameters are shown not to affect
the crystal structure.
It has been shown that, even at relatively low levels, the cal-
cium content of a sample can dominate the vibrational frequencies
as measured in the Raman spectrum. This is due to the discrep-
ancy in size between the Ca2+ ion and the Sr2+ and Ba2+ which are
significantly larger and similar to each other.
The analysis of the lattice modes demonstrates that the presence
of calcium forces considerable changes in the formation of the car-
bonate lattice. Each Raman shift observed for a sample corresponds
to a specific crystal structure. Some peaks lie within two or three
shifts that are observed for different crystal structures.
3.3. Concentration of precipitation solution
Five samples were prepared with the same composition (4% Ca,
30% Sr, 66% Ba) and precipitated at approximately same temper-
ature, 70 ◦C, but with differing concentrations of the ammonium
This work shows that with the Raman spectra used as a refer-
ence, one can analyse an unknown alkali earth carbonate sample

W. Kaabar et al. / Spectrochimica Acta Part A 78 (2011) 136–141
141
using Raman microscopy. If these studies could be extended to
directly analyse oxide materials, structural information could be
inferred non-destructively from Raman spectra acquired from a
sample surface.
[10] R.L. Frost, M. Dickfos, Polyhedron 26 (2007) 4503–4508.
[11] R.L. Frost, M. Dickfos, J. Raman Spectrosc. 38 (11) (2007) 1516–1522.
[12] R.L. Frost, M.C. Hales, D.L. Wain, J. Raman Spectrosc. 39 (1) (2008) 108–
114.
[13] R.L. Frost, M. Dickfos, Spectrochim. Acta A 71 (1) (2008) 143–146.
[14] A. Hermann, D. Wagner, The Oxide-Coated Cathode, vol. 1, Chapman and Hall,
London, 1951.
References
[15] E.F. Lowry, Illum. Eng. 48 (6) (1951) 288–294.
[16] V.C. Farmer, Mineralogical Society Monograph 4: The Infrared Spectra of Min-
erals, 1974.
[1] F. Poret, J.M. Roquais, Appl. Surf. Sci. 251 (2005) 31–41.
[2] D. Shafer, J. Turnbull, Appl. Surf. Sci. 8 (1981) 225–230.
[3] L. Couture, Ann. Phys. Ser. 12 (2) (1947) 5–94.
[4] D. Krishnamurti, Proc. Ind. Acad. Sci. A 31 (1960) 285–295.
[5] W.P. Griffith, J. Chem. Soc. A (1970) 286–291.
[6] H.H. Adler, P.F. Kerr, Am. Mineral. 48 (1963) 839–853.
[7] B.E. Scheetz, W.B. White, Am. Mineral. 62 (1977) 36–50.
[8] P. Gillet, C. Biellmann, B. Reynard, P. McMillan, Phys. Chem. Minerals 20 (1993)
1–18.
[9] J.M. Alia, Y. Diaz de Mera, H.G.M. Edwards, P. Gonzalez Martin, S. Lopez Andrés,
Spectrochim. Acta A 53 (1997) 2347–2362.
[17] M. Murabayashi, Shin Nippon Denki Giho 4 (2) (1969) 169–176.
[18] M. Murabayashi, H. Shirai, Shin Nippon Denki Giho 6 (1) (1971) 27–31.
[19] D. Chakrabarty, S. Mahapatra, J. Mater. Chem. 9 (1999) 2953–2957.
[20] Database of Raman Spectroscopy, X-ray Diffraction and Chemistry of Minerals
Website, http://rruff.info/index.php.
[21] M.Y. Fong, M. Nicol, J. Chem. Phys. 54 (2) (1971) 579–585.
[22] L.G. Liu, T.P. Mernagh, Am. Mineral. 75 (1990) 801–806.
[23] E.E. Coleyshaw, W.P. Griffith, R.J. Bowel, Spectrochim. Acta
1909–1918.
A 50 (1994)
[24] R. Frech, E.C. Wang, Spectrochim. Acta A 36 (1980) 915–919.