Vibrational Spectroscopy

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1 Vibrational Spectroscopy 62 (2012) Contents lists available at SciVerse ScienceDirect Vibrational Spectroscopy jo ur n al hom ep age: Temperature-dependent Raman and infrared spectroscopy study on iron magnesium tourmalines with different Fe content Changchun Zhao a, Libing Liao b,, Zhiguo Xia b, Xiaoni Sun b a School of Sciences, China University of Geosciences, Beijing , China b School of Materials Sciences and Technology, China University of Geosciences, Beijing , China a r t i c l e i n f o Article history: Received 22 May 2011 Received in revised form 22 April 2012 Accepted 23 April 2012 Available online 30 April 2012 Keywords: Tourmaline Polarized Raman spectroscopy Fourier transform infrared spectroscopy Pyroelectric property a b s t r a c t Tourmalines with different Fe content have been analyzed by using Raman spectra polarized parallel to b and c-axis at 195 C, 25 C, 250 C, and 450 C and infrared spectroscopy at 25 C, 150 C, and 250 C, respectively. The Raman spectra show that the intensities of both the bands of FeO 5 (OH) and the deformation bands of [BO 3 ] 3 in b direction increase with the total Fe content, and the spectra polarized along c direction of [Si 6 O 18 ] 12 ring and [OH] shift to lower frequencies. With increasing temperature, the bands of FeO 5 (OH) in c direction shift to higher frequencies. Meanwhile, the deformation vibration bands of [Si 6 O 18 ] 12 ring enhance significantly, and the asymmetric bands of [Si 6 O 18 ] 12 ring merge into a broad one. The deformation bands of [BO 3 ] 3 and the asymmetric stretch bands of [Si 6 O 18 ] 12 ring are weakened at (bb) polarization. The intensities of infrared absorption peak of tourmalines are weakened, and some peaks shift to lower frequencies with the increase of the total Fe content. With the increase of temperature, most infrared absorption peaks shift to lower frequencies. The variation of the Raman and infrared spectra of tourmalines with temperature and Fe content indicate that more replacement of Fe for Mg in Y O 5 (OH) octahedron, leads to the deformation of Y O 5 (OH) octahedron, and further the deformation of [BO 3 ] 3 polyhedron and [Si 6 O 18 ] 12 ring which are connected with Y O 5 (OH) octahedron. Further, Mg(Fe) (OH) bonds extend with increasing temperature, leading to the deformation of [SiO 4 ] tetrahedra connected with Y octahedra Elsevier B.V. All rights reserved. 1. Introduction Tourmaline was firstly discovered in Sri Lanka, which was regarded as precious as diamond and ruby. It was noted that a gem would generate charges when it was heated, and it is called tourmaline. Now, tourmaline is a general term for tourmaline-group minerals and a group of borosilicate minerals with the structure chemical formula [1]: XY 3 Z 6 Si 6 O 18 (BO 3 ) 3 W 4, X = Na, K, Ca; Y = Mg, Fe 2+, Fe 3+, Mn, Li, Al; Z = Al, Fe 3+, Cr, Fe 2+ ; W = OH, F, O. It crystallizes in the trigonal system and its space group is R3m, with a three-fold axis in c direction. There is no symmetry axis and symmetry plane perpendicular to c-axis, and no center of symmetry [2,3]. It consists of two basic structural layers: a layer of [Si 6 O 18 ] 12 ditrigonal ring made of six silicon oxygen tetrahedra, with X type cation occupying its center, and a layer of octahedral cluster which is built of three central Y octahedra, surrounded by six outer Z octahedra. B atoms is positioned between large octahedra to form three [BO 3 ] 3 triangles. Corresponding author. Tel.: ; fax: address: lbliao@cugb.edu.cn (L. Liao). Because of its inherent electrical polarity, pyroelectric, piezoelectric, far-infrared radiation and negative ion releasing properties, tourmaline has become a kind of significant mineral material for some potential applications. Among all the properties, the pyroelectric property is the most important and earliest discovered. However, the origin and influence of tourmaline s pyroelectric property has not been understood completely. Some scholars have found that the pyroelectric property of tourmaline is related to its Fe contents; however, there is no further research about how it works [4,5]. Donnay [6] has pointed out that the pyroelectric property is mainly caused by its asymmetry and anharmonic vibration of O(1) which is shared by three octahedra in the crystal structure. Because O(1) has a polar environment, when the temperature changes, it has the largest offset among all atoms, which is up to Å and far beyond the experimental error. In addition, X-site ions (Na ions) and O(2) may also be related to the pyroelectric property of tourmaline, because they have extraordinarily large temperature coefficients, which is lack of experimental evidences. The existence of electric dipole moment suggests that polyhedra distortions occur in tourmaline, so that positive and negative charge centers do not coincide in them. Some researchers [7] have found that there exists a direct relationship between the composition and the coordination polyhedral deformation of tourmaline. The /$ see front matter 2012 Elsevier B.V. All rights reserved.

2 C. Zhao et al. / Vibrational Spectroscopy 62 (2012) deformations of coordination polyhedra associate with each other, e.g. the distortion of [YO 6 ] has a significant impact on the deformation of other polyhedra connected to it. Therefore, coordination polyhedron deformation, particularly [YO 6 ], [SiO 4 ] and [BO 3 ] deformation may be the main reason for the electric dipole moment of tourmaline. There are three Raman active vibrational units in tourmaline structure, [Si 6 O 18 ] 12, [BO 3 ] 3 and [OH]. As early as 1969, Griffith [8] firstly measured the Raman spectra of tourmaline powder, but he only analyzed [Si 6 O 18 ] 12 group, without considering the other two. In 1995, based on Griffith s study, Peng [9] analyzed the three Raman active units in tourmalines from different areas using polarized Raman spectroscopy at room temperature. The results showed that Raman spectra of the radical [Si 6 O 18 ] 12 and [BO 3 ] 3 in tourmaline polarized parallel to c-axis are more sensitive than that parallel to b-axis, Raman spectrum of [OH] is significantly polarized parallel to c-axis direction. However, the influences of Fe content and temperature on the Raman spectra of the three radicals were not studied. In 2008, McKeown [10] studied the influence of temperature on the structure of tourmaline by polarized Raman spectroscopy and speculated that when the sample was heated close to 700 C, Fe and Al in Y and Z octahedra became disordered, part of F and OH disappeared with the increase of temperature. But he did not study the influence of Fe content on the Raman spectra of tourmaline. To elucidate the mechanism of tourmaline s pyroelectric property, the previous work in our group has studied the influence of Fe content of tourmaline on its crystal structure, inherent electric dipole moment and pyroelectric property, which will be published elsewhere. In this article, Raman spectroscopy and infrared spectroscopy are used to investigate the influence of Fe content and temperature on the vibration of radicals in tourmaline, which would provide evidences for further explanation of the mechanism of tourmaline s pyroelectric property. 2. Experimental 2.1. Sample Three cylindrical single crystals of iron magnesium tourmaline with different Fe content were obtained in PR China from Xinjiang province (No. XJ1-1, XJ2-1) and Sichuan province (No. SC1-1) province, respectively. Their chemical compositions were determined by ICP-AES (National Geological Experimental Test Center of China). The chemical formulae calculated according to chemical composition analysis data are given as follows: XJ1-1: (K 0.04 Na 0.49 Ca 0.35 ) 0.88 (Mg 2.41 Ti 0.11 Fe Fe Al 0.16 ) 2.85 (Al 5.98 Fe ) 6.00 Si 6.15 B 2.64 O 27 (OH, O, F) 3.89 XJ2-1: (K 0.01 Na 0.52 Ca 0.31 ) 0.84 (Mg 2.38 Ti 0.12 Fe Fe Al 0.13 ) 3.00 (Al 5.91 Fe ) 6.00 (Si 5.81 Al 0.19 ) 6.00 B 2.68 O 27 (OH, O, F) 3.92 SC1-1: (K 0.03 Na 0.67 Ca 0.14 ) 0.84 (Mg 1.97 Ti 0.08 Fe Fe Al 0.32 ) 2.86 (Al 5.93 Fe ) 6.00 Si 6.14 B 2.78 O 27 (OH, O, F) Polarized Raman spectroscopy and infrared spectroscopy measurement Slices were cut perpendicular to the cylinder of tourmaline crystals (c-axis), and the b-axis direction in the slice surface was determined by using a DX-3/4 type high-precision X-ray singlecrystal goniometer (experimental conditions: Cu target, 30 kv, 5 ma, precision 30 s, 2 = 10 to 140 ). The slices were cut to around 10 mm 10 mm 5 mm in size and polished. According to DTA curves of iron magnesium tourmaline [11] and the working temperature range of HR800 laser Raman spectrometer. Polarized Raman spectra were recorded on a French-made HR800 type laser Raman spectrometer (light wavelength = nm, power = 3 mw, scan time = 30 s) at 195 C, 25 C, 250 C, 450 C. Scattering geometries for the spectra listed in the text, table and figures follow the Porto notation [12]. Infrared spectra were recorded by a NICOLET 560 Fourier transform infrared spectrometer at 25 C, 150 C and 250 C, respectively. The scan range is from 400 cm 1 to 4000 cm 1 with a resolution of 4 cm 1. The scan number is 32. Powder samples (under 200 mesh) for Fourier transform infrared spectroscopy measurement are from the same crystals as those used for Raman spectroscopy experiment. The standard KBr pellet technique was employed, and the pressed pellets were then heated from room temperature to the given temperatures, and kept at the temperature for 5 min before each measurement in order to keep the temperature stable and even. 3. Results and discussion 3.1. Room temperature polarized Raman spectra of tourmalines with different Fe content Raman spectra of three kinds of tourmalines with different Fe contents at room temperature are shown in Fig. 1. Based on previous work of Peng [9] and McKeown [10], they have summarized the assignment of the Raman spectra for buergerite at room temperature. Therefore, the Raman spectra in Fig. 1 are assigned and listed in Tables 1 and 2. The shape and number of the Raman bands polarized in b (E species) and c (A 1 species) directions are different. There are more Raman bands polarized in c direction and they are stronger than those polarized in b direction. These changes show that three Raman active vibrational units ([Si 6 O 18 ] 12, [BO 3 ] 3, [OH] ) are arranged in a more orderly way in c direction than in b direction. With the increase of the total Fe content in the sample, in b direction, the relative intensity of the vibration peaks around 140 cm 1 and 760 cm 1 increase, and their peaks are weakened. From the valence state and Fe content (XJ1-1: 0.17, XJ2-1: 0.37, SC1-1: 0.49) considerations of the Y sites, it is possible to identify the vibrations of FeO 5 (OH) and the deformation vibrations of [BO 3 ] 3. As the same time, it is also showed that the anharmonic vibration can be enhanced in b direction. In c direction, the deformation vibration bands of [Si 6 O 18 ] 12 ring around 240 cm 1 and the vibration bands of [OH] around 3570 cm 1 shift to lower frequencies (Table 1), and the band near 3570 cm 1 is particularly sensitive to the X-site occupancy (Na or Vacancy) and the cation distribution over the adjacent Y sites (Mg 2+ /Fe 2+, Mg 2+ /Fe 3+ ) [10]. The increase of the total Fe content in tourmaline results in more replacement of Fe for Mg in Y sites and more deformation of Y octahedra, which leads to the deformation of the polyhedra connected with it, e.g. [BO 3 ] 3 in b direction and Si 6 O 18 ring in c direction. [OH] occupies the center of the ditrigonal rings of [SiO 4 ] tetrahedra and is surrounded by three Mg 2+ (Fe 2+ ). The complex coordination environment of [OH] in tourmaline structure results in the split of its Raman vibration peak [13,14]. Because the bond length of Fe (OH)

3 30 C. Zhao et al. / Vibrational Spectroscopy 62 (2012) Fig. 1. Room temperature Raman spectra of tourmaline single crystals at different settings of polarization. Table 1 The wavenumbers (cm 1 ) and the possible assignments of the bands observed in the Raman spectra of the tourmaline crystals belonging to A 1 species [a(cc)ā]. Sample XJ1-1 XJ2-1 SC1-1 Temperature 195 C 25 C 250 C 450 C 195 C 25 C 250 C 450 C 195 C 25 C 250 C 450 C FeO 5OH (Si O) ring deformation (Si O) ring of the symmetric (Si O) ring of the asymmetric 215(s) 215(s) 212(s) 212(s) 214(s) 214(s) 211(s) 211(s) 215(s) 215(s) 212(s) 211(s) 244(s) 243(s) 241(s) 240(s) 243(s) 241(s) 240(s) 240(s) 243(s) 241(s) 240(s) 240(s) (s) 370(s) 368(s) 365(s) 371(s) 370(s) 367(s) 364(s) 370(s) 370(s) 367(s) 364(s) (s) 701(s) 697(s) 692(s) 704(s) 701(s) 697(s) 692(s) 704(s) 701(s) 697(s) 692(s) (Si O) 1040(s) 1045(s) 1043(s) 1035(s) 1048(s) 1045(s) 1034(s) 1030(s) 1035(s) 1031(s) 1025(s) 1028(s) [OH] vibration 3579(s) 3578(s) 3575(s) 3572(s) 3577(s) 3575(s) 3572(s) 3571(s) 3571(s) 3569(s) 3569(s) 3566(s) Note: s refers to strong. is longer than that of Mg (OH), the Raman vibration peaks of [OH] shift to lower wavenumbers. However, O6 is connected to Y polyhedron and T polyhedron, and the bond of Fe (OH) may lead to the bond shortening of Si O6 (single crystal X-ray diffraction test: XJ1-1: Å, XJ2-1: Å, SC1-1: Å), which led to the decrease of the T polyhedron intrinsic electric dipole moment in c direction Temperature dependent polarized Raman spectra of tourmalines The Raman spectra of tourmalines at different temperatures are shown in Fig. 2 and Tables 1 and 2. In c direction, with the increase of temperature (Fig. 2(a) (c)), number of peaks in the Raman spectra reduced gradually and most of the peaks become broader. Table 2 The wavenumbers (cm 1 ) and the possible assignments of the bands observed in the Raman spectra of the tourmaline crystals belonging to E species [a(cb)ā]. Sample XJ1-1 XJ2-1 SC1-1 Temperature 195 C 25 C 250 C 450 C 195 C 25 C 250 C 450 C 195 C 25 C 250 C 450 C FeO 5OH 146(s) 150(s) 148(s) 146(s) 148(s) 150(s) 148(s) 148(s) 150(s) 150(s) 149(s) 149(s) (Si O) ring deformation 215(s) 214(s) 214(s) 211(s) 214(s) 211(s) 211(s) 211(s) 211(s) 211(s) 212(s) 210(s) 375(s) 375(s) 372(s) 371(s) 375(s) 374(s) 372(s) 371(s) 377(s) 374(s) 372(s) 372(s) (Si O) ring of the symmetric (Si O) ring of the asymmetric (Si O) [BO 3] 3 of the deformation (s) 775(s) 767(s) 760(s) 750(s) 759(s) 759(s) 757(s) 785(s) 785(s) 780(s) 777(s)

4 C. Zhao et al. / Vibrational Spectroscopy 62 (2012) Fig. 2. Polarized Raman spectra of different kinds of tourmalines at the measured temperature: (1) 195 C, (2) 25 C, (3) 250 C and (4) 450 C, (a), (b), (c) are corresponding to XJ1-1, XJ2-1 and SC1-1 for the Raman-active A 1 species (c direction), respectively, and (d), (e), (f) are corresponding to XJ1-1, XJ2-1 and SC1-1 for the Raman-active E species (b direction), respectively. Most bands shift to lower frequencies, such as the vibration peaks of [OH] near 3570 cm 1 (XJ1-1: cm 1, XJ2-1: cm 1, SC1-1: cm 1 ). Among them, the variation of Raman peak for XJ1-1 is the biggest one, while that of SC1-1 is the smallest one. Simultaneously, the variation is precisely reflected in the same temperature range, the smaller Fe content tourmaline possesses, the greater the pyroelectric coefficient is. The bands of FeO 5 (OH) near 129 cm 1 distinctly shift to higher frequencies. The possible reason is that with the increase of temperature, Fe 2+ in Y octahedron was gradually oxidized into Fe 3+, leading to the contraction of Y octahedron (the radius of Fe 3+ is less than that of Fe 2+ ) [15]. Such a contraction shortened the length of Fe O bond, which led to the shift of FeO 5 (OH) deformation vibration to higher wavenumber. Therefore, the contraction of Y polyhedron will be associated with the distorted Z, T polyhedron; thereby it will affect the total inherent dipole moment of tourmaline and pyroelectric properties [16]. In addition, the intensities of the deformation bands of [Si 6 O 18 ] 12 ring around 210 cm 1 and 240 cm 1 significantly enhance. The increase of temperature may extend Mg(Fe) (OH) bonds in Y octahedron, leading to the deformation of [SiO 4 ] tetrahedra which is connected with Y by corner sharing, therefore intensifying the deformation vibration of the bridge oxygen. Raman spectra also show that, three small asymmetric vibration peaks of [Si 6 O 18 ] 12 ring at cm 1 tend to merge a broader band. This may be due to the difference of the four Si O bond lengths in [SiO 4 ] tetrahedron. For example, for XJ1-1 sample, single crystal structure analysis at room temperature manifested that the distances between Si and the four surrounding O (O4, O5, O6, O7), are , , and (d 1, d 2, d 3, d 4 ), d 1 is obviously different from d 2 and d 3 approximately equal to d 4. So there are three different Si O (Si O4, Si O5, Si O7) bond lengths, corresponding to the three peaks in Raman spectra. According to the report of McKeown [10], O4 vibrates in +c direction, while O5

5 32 C. Zhao et al. / Vibrational Spectroscopy 62 (2012) vibrates in c direction. The movement of O4 and O5 in c direction leads to the vibration of Si O bond. With the increase of temperature, d 1, d 2, d 4 tend to be equal, and the three corresponding Raman bands progressively merge one band. Based on the bond lengths of (Si O) consideration, the (Si O) asymmetric band near 692 cm 1 shall be vested in the vibration of the Si O6. The above changes showed that the anharmonic vibration [SiO 4 ] tetrahedra can be enhanced in c direction. Fig. 2(d) (f) indicate that the deformation vibration bands of [BO 3 ] 3 around 720 cm 1 and 770 cm 1 are weaken and split with the increase of temperature. Simultaneously, the asymmetric stretch vibration peaks of [Si 6 O 18 ] 12 ring around 990 cm 1 of XJ1-1 and XJ2-1 are also weakened. So it seems that temperature mainly affects the deformation vibration of [BO 3 ] 3 and the asymmetric vibration of [Si 6 O 18 ] 12 ring. These variations further indicate that the temperature will cause anharmonic vibrational enhancement of [BO 3 ] 3 and [Si 6 O 18 ] 12 in b direction. In order to compare the bands anharmonicity, as given in Fig. 3, we have drawn the plot of the wavenumber shift versus Fig. 3. Variation of Raman shift of (Si O) ring the asymmetric vibration versus temperature in c direction. Fig. 4. Infrared spectra of tourmalines with different Fe content at variant temperatures, (1) 25 C, (2) 150 C, and (3) 250 C, and infrared spectra in the range of cm 1 of XJ1-1, XJ2-1 and SC1-1 are shown in (a) (c); the parts in the range of cm 1 are shown in (d) (f), respectively.

6 C. Zhao et al. / Vibrational Spectroscopy 62 (2012) Table 3 Observed infrared absorption features (cm 1 ) in various tourmalines at different temperatures and their assignments. Assignment XJ1-1 XJ2-1 SC C 150 C 250 C 25 C 150 C 250 C 25 C 150 C 250 C Si O Si bending Si O Si stretch Si O stretch B O stretch O H stretch (s) 505(s) 501(s) 505(s) 501(s) 499(s) 507(s) 503(s) 501(s) 715(s) 714(s) 712(s) 715(s) 714(s) 712(s) 715(s) 714(s) 712(s) (s) 984(s) 984(s) 985(s) 984(s) 982(s) 985(s) 984(s) 982(s) (s) 1265(s) 1265(s) 1265(s) 1265(s) 1265(s) 1265(s) 1265(s) 1263(s) (s) 3572(s) 3570(s) 3568(s) 3570(s) 3570(s) 3560(s) 3566(s) 3566(s) temperature for three kinds of tourmaline when they are cooled from 450 C to 195 C. It is clearly found that the asymmetric vibration peaks of [Si O] shift to higher wavenumber. However, compared with the heating process, its peak position changed at the same temperature, which indicated that the of [Si O] bonds were asymmetric vibration. According to Ackermann [17] and Voigt [18], pyroelectric property of tourmaline mainly originates from its thermal expansion and the change of its inherent electric dipole moment generated by thermal stress. The above Raman spectra of tourmalines at different temperatures show that the increase of temperature not only causes the extension of some bonds, and the expansion of the crystal lattice, but also the deformation of structure polyhedra, which is probably one of the main factors affecting tourmaline s pyroelectric property Temperature dependent Infrared spectra of tourmalines with different Fe contents The infrared absorption in tourmaline is mainly caused by vibrations of Si O bond, Si O Si bond of [SiO 4 ] tetrahedron, B O bond of [BO 3 ] triangle, O H bond of hydroxyl and M O bond of [MO 6 ] octahedron [19]. The infrared spectra of tourmalines with different Fe contents and at variant temperatures are shown in Fig. 4 and Table 3. At the same temperature, infrared absorption peaks of tourmalines are weakened and some peaks shift to lower frequencies with the increase of the total Fe content. It proves that with the increase of the total Fe content, the infrared activities of the radicals in tourmalines are weakened. As infrared absorption is due to the change of the permanent dipole moment in radicals, the above results indicate that the increase of the total Fe content decreases the change of the permanent dipole moment of the radicals in tourmaline, which leads to the weakening of its pyroelectric effect. For the same tourmaline, with the increase of temperature, the Si O band around 507 cm 1, 715 cm 1 and 758 cm 1, the Si O Si band at cm 1, the O H vibration band around 3633 cm 1 move to lower wavenumbers. The fact indicated that the bond lengths of Si O, Si O Si and OH increased, and the vibration peaks of Si O Si in the cm 1 wavenumber range can be ascribed to asymmetric vibration. Therefore, it is believed that the peak is generated by the movement of the Si O6 Si antisymmetric. With increasing temperature, the movement of O6 along the +c direction resulted in the increase of the electric dipole moment of T polyhedra in the c direction (this conclusion is also consistent with the Raman test results), and the crystal cell also expands as the temperature increases. As Si O bond and Si O Si bond become longer, the Si O Si band around 758 cm 1 is weakened, which means the dipole moment of Si O Si bond decreases. For example, for XJ1-1 sample, with the increase of temperature, the Si O Si bending band around 420 cm 1 becomes narrower and more symmetrical, so that the energy difference ( E) between the molecular vibrational energy levels caused by Si O Si bending vibration becomes smaller, and the molecular internal structure (T polyhedron) changes [20]. When the three samples are heated from 195 C to 450 C, respectively, most Raman bands in b, c directions and infrared bands gradually be broadened and their intensities decrease with the increase of the temperature. Especially, some bands are divided into several small bands. This phenomenon indicates that the anharmonic vibrations of the crystal internal ionic units are enhanced with increasing temperature. As shown in Fig. 5 (Table 4), both the deformation vibration peaks of (Si O) ring at cm 1 in c direction and deformation vibration peaks of Fig. 5. The bandwidth variation versus temperature: (a) Si O ring deformation in c direction, (b) [BO 3] 3 deformation in b direction.

7 34 C. Zhao et al. / Vibrational Spectroscopy 62 (2012) Table 4 The bandwidth variation wavenumber values (cm 1 ) of Si O ring deformation in a(cc)ā and [BO 3] 3 deformation in a(cb)ā for different temperature. The bandwidth variation Temperature XJ1-1 XJ2-1 SC1-1 Si O ring deformation [BO 3] 3 deformation 195 C C C C C C C C [BO 3 ] 3 at cm 1 in b direction are broadened with increasing temperature. Among them, the deformation vibration peak of (Si O) in c direction is broadened with the maximum value for XJ1 in C. But in b direction, the largest deformation bandwidth vibration of [BO 3 ] 3 for XJ1 is obtained at C. SC1 sample has the maximum variation between 250 C and 450 C. The above variation behavior and difference should be due to different Fe contents in three kinds of tourmaline samples. If the sample has high Fe content, more Fe 2+ will be oxidized into Fe 3+ from 250 C to 450 C, which will in turn lead to the greater distortion of Y polyhedron. Then it will further affect the distortion of the associated [BO 3 ] 3 triangular with Y polyhedron. Therefore, as the temperature increases, the anharmonic vibration of the [BO 3 ] 3 will be large in b direction. Accordingly, the above comparison of IR and Raman wavenumbers showed a minor Raman-IR exclusion, which indicates that the structure is far from a centrosymmetric structure that could have important consequence for the pyroelectric behavior. 4. Conclusions In conclusion, the tourmalines with different Fe contents have been analyzed by using polarized Raman spectroscopy and IR spectra at different temperature, respectively. Temperature dependent polarized Raman spectra results showed that replacement of Fe for Mg in Y sites leads to the deformation of Y octahedron and the deformation of [BO 3 ] 3 and [Si 6 O 18 ] 12 ring connected with it. The bond lengths of Mg(Fe) (OH) in Y octahedra become longer, leading to the deformation of [SiO 4 ] tetrahedra which are connected with Y octahedra by corner sharing. The deformation of [SiO 4 ] tetrahedron narrows its Si O bond length difference. When the temperature keeps at the same value, infrared absorption peaks of tourmalines have become weakened with the increase of iron content, and some of the peaks shift to the lower frequencies. It means that the increase of Fe content in tourmaline would decrease the change of the permanent electric dipole of the radicals in tourmaline, which results in the weakening of its pyroelectric effect. The above results verify that the increase of bond length will result in the increase of its electric dipole moment. Acknowledgements This work was supported by the National Natural Science Foundations of China (Nos and ). We also sincerely thank Institute of Physics Chinese Academy of Sciences for their contribution to part experimental work. References [1] F.C. Hawthorne, D.J. Henry, Eur. J. Mineral. 11 (1999) [2] L.B. Liao, Crystal Chemistry and Crystal Physics, Geological Press, Beijing, China, 1999, pp (in Chinese). [3] T. Nakamura, T. Kubo, Ferroelectrics 137 (1992) [4] A. Tatli, J. Phys. Chem. Solids 46 (1985) [5] A. Ertl, J.M. Hughes, F. Pertlik, F.F. Foit JR., S.E. Wright, F. Brandstätter, B. Marler, Can. Mineral. 40 (2002) [6] G. Donnay, Acta Crystallogr. A33 (1977) [7] K.D. Hawkins, I.D.R. Mackinnon, H. Schneeberger, Am. Mineral. 80 (1995) [8] W.P. Griffith, J. Chem. Soc. A (1969) [9] M.S. Peng, H.Y. Wang, Acta Mineral. Sinica 4 (1995) [10] D.A. McKeown, Phys. Chem. Miner. 35 (2008) [11] X.N. Sun, Thesis: A study of temperature-change Raman and infrared spectrum of tourmalines with different iron content, China University of Geosciences, Beijing, China, 2008, pp (in Chinese). [12] D.L. Rousseau, R.P. Bauman, S.P.S. Porto, J. Raman Spectrosc. 10 (1981) [13] Z.J. Ji, S. Jin, Z. Zong, Acta Mineral. Sinica 5 (2002) (in Chinese). [14] C. Wang, Thesis: Silicate and aluminum silicate minerals by Raman spectroscopy, China University of Geosciences, Beijing, China, 2005, pp (in Chinese). [15] A. Tatli, A.S. Pavlovic, Phys. Rev. B 38 (1988) [16] C.C. Zhao, D. Zhang, L.B. Liao, J. Chin. Ceram. Soc. 36 (2008) (in Chinese). [17] W. Ackermann, Ann. Phys. 46 (1915) [18] W. Voigt, Ann. Phys. 46 (1915) [19] W.W. Li, R.H. Wu, Y. Dong, Geol. J. Chi. Univ. 3 (2008) [20] J.L. Robert, Y. Fuchs, J.P. Gourdant, Phys. Chem. Miner. 23 (1996) 309.