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High-pressure resonance Raman spectroscopic study of ultramarine blue pigment Mirela M. Barsan, Ian S. Butler, Denis F.R. Gilson ⇑ Department of Chemistry, McGill University, 801 Sherbrooke St., W. Montreal, QC, Canada H3A 0B8

h i g h l i g h t s

g r a p h i c a l a b s t r a c t

" The pressure dependence of thr

600

Wavenumbers/cm -1

resonance Raman spectrum of ultramarine is reported for the ﬁrst time. " The dm/dP values are small, indicating weak interactions with the sodalite lattice. " For combination bands, the dm/dP values equal the sum (or difference) of the values of the individual fundamental peaks.

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a r t i c l e

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Article history: Received 15 May 2012 Received in revised form 17 August 2012 Accepted 24 August 2012 Available online 1 September 2012

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Pressure/GPa

a b s t r a c t The resonance Raman spectrum of ultramarine has been studied as a function of pressure up to 5 GPa. The overtone progressions of the m1 fundamental and the combination bands of S 3 and the m1 band of S 2 were measured and the pressure dependences were determined. The symmetric stretching mode of S 3 is nearly harmonic. No phase transition was observed over the measured pressure range. Ó 2012 Elsevier B.V. All rights reserved.

Keywords: Ultramarine High-pressure Raman spectroscopy

Introduction The semi-precious mineral lapis lazuli, has been used in jewellery since the sixth century and in painting since the 11th century. Ultramarine, the modern synthetic form, was developed independently by Guimet and by Gmelin in 1928. The host solid is the aluminosilicate sodalite, Na8{Al6Si6O24}Cl2, and the colour is due to the radical ions S 3 and S2 , which replace the chloride ions and occupy the cages in the sodalite structure. The colour centres were identiﬁed by electron spin resonance measurements [1,2] and resonance Raman spectra [3–5]. In synthetic ultramarines, the pigments show a range of colours from violet to pink depending on the ratio of S 3 to S2 , and with the possible involvement of a third species either S4 or S 4 [4,5]. Other chalcogenide ions can replace ⇑ Corresponding author. Tel.: +1 514 398 6239. E-mail address: [email protected] (D.F.R. Gilson). 1386-1425/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.saa.2012.08.078

the sulphur ions [6]. When trapped in the sodalite cages, these radical ions are isolated and this provides an opportunity for studying such unstable species. Resonance Raman spectra show progressions with overtones of fundamentals and combination bands and this allows the determination of the harmonic frequencies and the anharmonicities [3–5]. For a non-linear tri-atomic molecule, the wavenumbers are given [9] by Eq. (1).

mðv 2 ; v 3 Þ ¼ v 1 x1 þ v 2 x2 þ v 3 x3 þ v 1 ðv 1 þ 1ÞX 11 þ v 2 ðv 2 þ 1ÞX 22 þ v 3 ðv 3 þ 1ÞX 33 þ v 1 v 2 X 12 þ v 1 v 3 X 13 þ v 2 v 3 X 23

ð1Þ

where xi are the harmonic frequencies in the lowest vibrational state and Xij the anharmonicity constants and x1, x2 and x3 are the symmetric stretching, bending and asymmetric stretching modes, respectively.

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For the progression of a single mode, e.g. m1, the symmetric stretching vibration,

mðv 1 ; 0; 0Þ ¼ v 1 x1 þ ½v 1 ðv 1 þ 1ÞX 11

ð2Þ

Thus a plot of m1/v1 versus v1 will be a straight line with slope X11 and intercept x1 + X11. For the combination band progression, (m2 + v1m1)

1 2

mðv 1 ; 1; 0Þ ¼ v 1 x1 þ x2 þ ½v 1 ðv 1 þ 1ÞX 11 þ 2X 22 þ ½3=2v 1 þ X 12 1 1 v 1 X 13 þ X 23 2 2

ð3Þ

A plot of the wavenumbers of the combination band [(m2 + v1m1) m2]/v1 versus v1 will be a straight line with slope of X11 and intercept of x1 X11 + X12. Thus, Clark and Franks [3] derived values of 550 and 0.75 cm1 for the harmonic frequency and harmonicity of the m1 mode, respectively. The vibration is close to being harmonic. From Eq. (3) the combinations (m1 + m2) and (m1 m2) can be written

1 2

ð4Þ

and

1 1 1 mð1; 1; 0Þ ¼ x1 x2 þ 2X 11 2X 22 þ X 12 þ X 13 X 23 2 2 2

Table 1 Pressure dependence (intercepts and slopes) of the combination bands of ultramarine. Wavenumbers, cm1

ð5Þ

From Eqs. (4) and (5), the summation band wavenumbers would equal the sum of the wavenumbers of the two fundamental plus the anharmonicity term X12 whereas the difference band would be simply equal the difference. In principle, this provides a determination of the term X12. We have previously studied the effect of pressure on the resonance Raman spectrum of potassium permanganate trapped in potassium bromide and perchlorate lattices [7] and report here a similar study on the S 3 ion in ultramarine. High pressure studies of ultramarine have been limited to the electrical conductivity measurements at temperatures in excess of 700 K [8]. Experimental Ultramarine pigment was purchased from Pigments Fragonard, Pébéo, France. Raman spectra were measured with a Renishaw inVia spectrometer using an argon ion laser 514.5 nm line and calibrated with a silicon wafer. The spectra were analysed using the Renishaw WiRe software. High pressure spectra were obtained using a Diamond Anvil Cell (DAC) from High-Pressure Diamond Optics, Tucson, AZ. The sample, together with a ruby chip as calibrant [10], was contained in a 300 lm thick stainless-steel gasket located between the diamonds, and the DAC was mounted on the translation stage of a Leica microscope (long-working-distance, 20 objective). Spectra were recorded with a slit width of 50 lm and a laser power of 25 mW. Results and discussion The 514 nm line excites into the broad absorption band of S 3 in the region of 600 nm but not the absorption of S at ca. 400 nm, 2 thus resonance effects are observable only for the former species. The progression up to 6m1 and the combination band up to (m2 + 4m1) were observed except the combination band (m2 + 2m1) which was obscured by the strong scattering from the diamond, Fig. 1. The assignments, wavenumbers and pressure dependence of the fundamental and combination peaks are given in Table 1. The plot of m1/v1 versus v1, according to Eq. (2), gave values of 548.9 ± 0.4 and 0.54 ± 0.1 cm1 for x1 and X11, respectively. These

dm//dP cm1 GPa1

256.4 ± 0.6 287.1 ± 1.4 547.5 ± .3 583.8 ± 1.4 583.8 ± 1.4 802.9 ± 1.1 836.6 ± 1.9 1127 ± 0.3 541.9 ± 0.6

Assignment

m2

2.14 ± 0.20 1.09 ± 0.56 0.38 ± 1.0 1.78 ± 0.53 1.78 ± 0.53 2.75 ± 0.40 4.41 ± 0.74 1.18 ± 0.34 0.59 ± 0.21

(m1 m2)

m1 m, S2 m3 (m1 + m2) (m2 + m3) (m1 + m3) Sodalite

values are in reasonable agreement with those reported by Clark and Franks [3].The pressure dependence is given by Eq. (6)

ð1=v 1 Þdv 1 =dP ¼ x01 þ dx1 =dP þ ðv 1 þ 1ÞdX 11 =dp

ð6Þ

where x01 is the harmonic frequency at zero pressure. The m1 fundamental showed a very small pressure dependence, the difference between the wavenumbers at ambient pressure and 5 GPa was ca. 2 cm1. The higher harmonics will show increased pressure dependence but the peaks become weaker and broader. A plot of m1/v versus pressure should give lines of slope dx1/dP + vdX11/dP and

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1 2

mð1; 1; 0Þ ¼ x1 þ x2 þ 2X 11 þ 2X 22 þ 2X 12 þ X 13 þ X 23

Fig. 1. Resonance Ramam spectrum of ultramarine at 4.9 GPa. The strong peal from the diamond anvil, at 1330 cm1, has been ‘‘zapped’’.

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þ

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Pressure/GPa Fig. 2. Pressure dependence of the fundamentals m1 and m2 and their combination bands (m1 m2) and (m1 + m2). The dashed lines are the sum or difference of the dm/dP values of the fundamentals.

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Raman intensity / arb. units 400

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Wavenumbers/cm-1 Fig. 3. Raman spectra of the region 400–700 cm1. Lower curve ambient pressure. Upper curve 4.9 GPa.

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intercept x01 þ dX 11 =dP but, since X11 is small, the derivative term can be ignored and a plot of (1/v1)(v1m1) versus P gave values of 547.2 ± 0.22 and 0.59 ± 0.09 cm1 for x01 and dx1/dP, respectively. Fig. 2 shows the pressure dependence of the fundamentals m1 and m2 and their sum and difference bands, respectively. From Eqs. (4) and (6) the wavenumbers of the difference band is equal simply to the difference between the two fundamentals and, therefore, the pressure dependence should be equal to the difference between the dm/dP values; 1.76 cm1 GPa1 versus the experimental value of 1.09 cm1 GPa1 (since m2 has a higher dm/dP value, the pressure dependence of the difference band is negative). The summation band includes the anharmonicity term X12, which is assumed to be small, and the dm/dP value of the combination band (m1 + m2) is 2.75 cm1 GPa1 versus the sum dm1/dP and dm2/dP of 2.47 cm1 GPa1. The anti-symmetric stretching vibration, m3, is observed in the infrared spectra but not in the Raman spectra. However, Ledé and co-workers [11] have claimed, based on investigations of samples with different concentrations of S 2 , that the Raman band is coincident with the stretching vibration of S 2 at 584 cm1 and have assigned other peaks, at 326, 837and 1128 cm1, as combination bands involving m3, Table 1. The 326 cm1 peak was not observed in the present study. The effect of highpressure on the Raman spectra should show a separation of the coincident peaks providing that they have different pressure dependence. A closer examination of the region around the S 3 symmetric stretch at 548 cm1 showed that this peak does separate further with increasing pressure but does not clearly become two peaks, Fig. 3. Furthermore, the 548 cm1 peak is slightly asymmetrical in shape and can be ﬁtted with a weak shoulder at 541 cm1. This peak is probably the 4-ring breathing mode of the sodalite as that is the strongest peak in the sodalite Raman spectrum [12]. The pressure dependence of the wavenumbers for this peak is negative. The peak at 837 cm1 has been assigned [13] as the combination (m2 + m3) and the 2m1 overtone peak at 1094 cm1 has a shoulder 1129 cm1, which separates with increasing pressure and has been assigned as (m1 + m3). Fig. 4 shows the experimental data for m1 and m2 and the combination bands (m1 + m3) and (m2 + m3). The dm/dP values of the combination bands are 4.41 and 1.18 cm1 GPa1, respectively, compared with the sums of the dm/dP values of the fundamentals 3.92 and 2.16 cm1 GPa1. While the (m2 + m3) value is in reasonable agreement, the (m1 + m3) value is not. An electron spin resonance study of the S 3 ion in ultramarine showed a strong dependence of the linewidth of the S 3 radical on temperature so that the S anion must be rotating in the soda3

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Pressure/GPa Fig. 4. Pressure dependence of the fundamentals m2 and m3 and their combination bands (m1 m3) and (m2 + m3). The dashed lines are the sum or difference of the dm/dP values of the fundamentals.

lite lattice, even at liquid helium temperature [13]. A similar study [14] of S 3 contained in a Zeolite A lattice, concluded that the S3 species reorients between 12 possible orientations in the sodalite cage with an estimated barrier of 2.4 kJ mol1. The freedom of movement could explain the low values of the pressure dependence of the wavenumbers. The smaller S 2 ion showed much larger pressure dependence. In this case, the anharmonicity constant is much larger, 2.1 cm1 [3], which suggests that the anharmonicity decreases with increasing pressure. High-pressure studies of sodalite itself by infrared spectroscopy [15] and X-ray diffraction [16,17] did not indicate the existence of any phase changes over the pressure range from 0 to 5 GPa. No phase transition was observed for ultramarine over the same pressure range. Monte Carlo methods predict an order–disorder transition in ultramarine at about 750 K [18]. Acknowledgment This work was supported by operating and equipment Grants from Natural Sciences and Engineering Research Council of Canada (Discovery Grant #228253). References [1] S.D. McLaughlin, D.J. Marshall, J. Phys. Chem. 74 (1970) 1359. [2] U. Hofman, E. Herzenstiel, E. Schönemann, K.H. Schwarz, Z. Anorg, Allg. Chem. 369 (1969) 119. [3] R.J. H Clark, M.L. Franks, Chem. Phys. Lett. 34 (1975) 69. [4] R.J.H. Clark, D.G. Cobbold, Inorg. Chem. 17 (1978) 3169. [5] R.J.H. Clark, T.J. Dines, M. Kurmoo, Inorg. Chem. 22 (1983) 2766. [6] D. Reinen, G.-G. Lindner, Chem. Soc. Rev. 28 (1999) 75. [7] M.M. Barsan, I.S. Butler, D.F.R. Gilson, J. Phys. Chem. B 110 (2006) 9291. [8] R.S. Bradley, J.P. Clark, D.C. Munro, D. Singh, Geochim. Cosmochim. Acta 36 (1972) 471. [9] G. Herzberg, Molecular Spectra and Molecular Structure II Infrared and Raman Spectra of Polyatomic Molecules, Van Nostrand Company, Princeton, NJ, 1966. [10] G.J. Piermarini, S. Block, J.D. Barnett, R.A. Forman, J. Appl. Phys. 46 (1975) 2774. [11] B. Ledé, A. Demortier, N. Gobeltz-Hautecœur, J.-P. Lelieur, E. Picquenard, C. Duhayon, J. Raman Spectrosc. 38 (2007) 1461. [12] D. Liu, D. Seoung, Y. Lee, X. Liu, J.-W. Lee, Y.-H. Yoon, Y. Lee, J. Phys. Chem. C. 116 (2012) 2159. [13] A.B. Wie˛ckowski, W. Wojtowicz, J. S´liwa-Nies´ciór Magn. Reson. Chem. 37 (1999) S150. [14] J. Goslar, S. Lijewski, S.K. Hoffmann, A. Jankowska, S. Kowalak, J. Chem. Phys. 130 (2009) 204504. [15] Y. Huang, J. Mater. Chem. 8 (1998) 1067. [16] S. Werner, S. Barth, R. Jordan, H. Schulz, Z. Kritstallog. 211 (1996) 158. [17] O. By, J. Eun, J. Moon, M. Mancio, S.M. Clark, P.J.M. Monteiro, Cement Concrete Res. 41 (2011) 107–112. [18] M.C. Gordillo, C.P. Herrero, J. Phys. Chem. 97 (1993) 8310.