XIONG Zhi-hua, ZHAO Ming-zhen, HE Jun-guo, LI Yi-peng, LI Hong-zhong

1. School of Earth and Space Science, Peking University, Beijing 100871, China

2. School of Material Science and Engineering, South China University of Technology, Guangzhou 510275, China

3. School of Earth Science and Geological Engineering, Sun Yat-sen University, Guangzhou 510275, China

4. Guangdong Provincial Key Lab of Geological Processes and Mineral Resource Survey, Guangzhou 510275, China

5. University of Houston, Department of Earth and Atmospheric Sciences，Houston, Texas 77204-5007, USA

6. Key Laboratory of Mineral Resource, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China

Raman Spectra of Bredigite at High Temperature and High Pressure

XIONG Zhi-hua1, ZHAO Ming-zhen2, HE Jun-guo3,4*, LI Yi-peng5, LI Hong-zhong4,6*

1. School of Earth and Space Science, Peking University, Beijing 100871, China

2. School of Material Science and Engineering, South China University of Technology, Guangzhou 510275, China

3. School of Earth Science and Geological Engineering, Sun Yat-sen University, Guangzhou 510275, China

4. Guangdong Provincial Key Lab of Geological Processes and Mineral Resource Survey, Guangzhou 510275, China

5. University of Houston, Department of Earth and Atmospheric Sciences，Houston, Texas 77204-5007, USA

6. Key Laboratory of Mineral Resource, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China

Bredigite was synthesized by using the Piston-Cylinder in 1.2 GPa and 1 473 K. With external heating device and diamond anvil cell, high temperature and high pressure Raman spectra of bredigite were collected at temperatures 298, 353, 463, 543, 663, 773 and 873 K and with pressure from 1 atm up to 14.36 GPa (room temperature). The SEM image showed that the sample consisted of one crystalline phase with grain size ranging from 10～20 μm. The EPMA data suggest a chemical formula of Ca7.03(2)Mg0.98(2)Si3.94(2)O16which was identical to the theoretical component of bredigite. The Raman spectroscopic results indicate there were 29 vibration bands of bredigite at high temperature. Some bands were merging, weakening and disappearing increasingly with the temperature, which was obvious in the range of 800～1 200 cm-1. The vibration bands of 909, 927 and 950 cm-1disappeared at 873, 773 and 873 K, respectively. The results primarily indicated that the structure of bredigite was stable under experimental condition. In addition, isobaric mode-Grüneisen parameters and isothermal mode-Grüneisen parameters were calculated, yielding 1.47(2) and 0.45(3) as their mean values, respectively. Anharmonic coefficients were estimated based on the high temperature and high pressure Raman experiments, showing that the contributions to anharmonic-effect induced with the Si—O vibration modes were smaller than other modes.

Bredigite; High temperature Raman; High pressure Raman; Anharmonic coefficients

Introduction

bredigite can be formed as follows

(1)

AsCa2SiO4andCa3Mg(SiO4)2werefoundinbothSkarnareaandasinclusionsindiamond,bredigitewasanticipatedtobeakindofimportantcompositionofcrustandmantle.Inaddition,bredigitealsoplayedimportantrolesincements,clinkers,slagsandfertilizersindustry.Butthepropertiesofbredigiteremainedunclear.Inthisstudy,wesynthesizedpurebredigitewithpiston-cylinderat1.2GPaand1 473K.HightemperatureRamanspectrumsofbredigitewerecollectedwithexternalthermaldevicefromroomtemperatureto873K,andhighpressureRamanofbredigiteupto14.36GPa.

Fig.1 Unit cell representation of the crystalstructure of bredigite (Without Ca)

1 Experimental

Thestartingmaterialforthehigh-Psynthesizingexperimentswithfollowingsteps:wefirstlymixedthepowdersofSiO2,MgOandCaCO3underacetoneinamolarratioof7∶1∶4,whichwerepretreatedat1atmand723Kfor5days;wesecondlypressedthismixtureintoapelletanddegasseditat1atmand1 472Kforabout48hours;wethirdlycrushedfinelythepelletunderacetoneintoapower,whichwaslaterstoredat383Kinadryingoven.Thestartingmaterialforthehigh-PsynthesizingexperimentswassealedintoaPtcapsule.Theapparatususedinoursynthesizingexperimentsispiston-cylinder,detailedintroductionsareavailableinLiuandFleet[18].Thesynthesizingconditionswere1.2GPaand1 473Kwithaheatingtimeof24hours.

TheRamansystemusedinhightemperatureandhighpressureexperimentswasequippedwithamonochromaticArionlaser.Ramansignalwereexcitedbya514.5nmmonochromaticargonionbeamandrecordedbytheCCDdetector.

Hightemperatureenvironmentusedinourexperimentwascreatedbyakindofheatingdevice[19].Andhigh-pressureRamanspectrawerecollectedwiththeuseofdiamond-anvil-cell.Coupleofsmallrubysphereswasplacedinthesamplechamberalongwiththe4∶1methanolandethanolaspressuremediumtomonitoranddeterminethepressurevariations(Maoetal. 1978).AbackscatteringgeometrywasusedtocollectRamandataandeachspectrumwascollectedatabout15mins.TheRamanpeakswereanalyzedwithVoigtprofilesusingthePeakFitprogram.

2 Result and discussion

2.1 Sample detection

Someportionsofthesynthesizedsampleswereselectedrandomlyandexaminedbyascanningelectronmicroscope(Quanta650FEG).AsshowedinFig.2,theproductsynthesizedisasinglephase,withthesizeofthegrainrangefrom10to20μm.

Fig.2 SEM image of bredigite, showingits grain size is 10～20 μm

Besides,Ramanspectrumscollectedrandomlyonthesurfaceofthesampleturnedouttobesame,whichindicatedthestructureofsamplesynthesizedwereidentical.Finally,electronmicroprobeanalyseswereconductedon10arbitrarilyselectedgrainsofthesample,andtheiraveragewasCa7.03(2)Mg0.98(2)Si3.94(2)O16,whichwasinaccordancewiththeidealformulaofbredigite.Allthetestesprovethesuccessinsynthesizingbredigite.

Fig.3 High temperature Raman spectrums of bredigite

2.2 High-temperature high-pressure Raman

HightemperatureRamanspectrumswerecollectedfromroomtemperatureupto873K(298, 353, 463, 543, 663, 773and873K).AsshowedinFig.3, 29peakscouldbedetectedinhightemperatureexperimentstotally,andthepeakpositionshifttowardtolowerfrequency.Withanalysis,wefoundthatnonewpeaksappearedastemperatureincreased,butsomeprimitivepeaksdisappearedbecauseoftheweakeningoftheirintensity;meanwhile,somepeaksmergedtogetherwiththeincreasingoftemperature. .

Comparedwithmineralswithsimilarcompositionandstructure,wefoundthatthebandsoftherangefrom500to1 200cm-1couldbeassignedtotheSi-Ostretching,whichwereinternalmodes;andthebandsappearedintherangefrom50to500cm-1couldbeattributedtothestretchingofMg-OandCa-O,aswellasthetranslationandrotationsofSiO4andMgO6[24-26].

AsshowninTable1andFig.4,vibrationpeakwasinlineardriftasthetemperaturewaschanging.BasedontheresultofhightemperatureRamanexperiments,thestructureofbredigiteshouldbeastableonewithintheinvestigatedtemperaturerange.

Table 1 Temperature and pressure dependences of vibrational frequency shifts, and anharmonic parameters of bredigite

Isobaric Grüneisen parameter can be calculated as

(2)

In whichν0iand ?νi/?Twas the mode frequencies at ambient conditions and theretemperature-dependent frequency shift, respectively,αisthere was the thermal expansion coefficient. For there was no high temperature experiment performed to investigate the thermal expansion coefficients. So take the minerals including monticellite and pyroxene as references[28-30], the thermal expansion coefficients was assumed as 3.96×10-5K-1in this study.

Fig.4 Raman frequency shifts as functions of temperature

The results of the calculated isobaric Grüneisen parameters were listed in Table 1. Values corresponding to the internal modes range from 1.5 to 3.22, lattice modes range from 0.63 to 1.21. The average value of all isobaric Grüneisen parameters is 1.47(3).

High pressure Raman spectrums were showed as Fig.5. Totally, 25 peaks were collected in high pressure experiments, with 17 peaks distributed in the range of 200～600 cm-1and 8 peaks in the range of 800～110 cm-1. All the peaks shift toward high frequency as pressure increases without the appearance of new peaks or the disappearance of primitive peaks. The fitting results showed that the relationship between peak shifting and pressure is a linear one, and the Frequency shifts as a function of pressure of bredigite were shown in Table 1. The results of high pressure Raman also primitively indicate that the structure of bredigite can be stable as pressure increase up to 14.36 GPa.

Similarly as to thermal expansion coefficients, we also took minerals including monticellite and pyroxene as reference[31-33], the bulk modulus of bredigite was assumed as 109 GPa in this study. The mode-Grüneisen parameter (γi) can be obtained from the following equation

(5)

Fig.5 Representative Raman spectra of bredigite at high pressures (room temperature) in the range of (a) 200～800 cm-1; (b) 700～1 150 cm-1

Fig.6 Raman frequency shifts ad a function of pressure of bredigite

Whereν0iand dνi/dPare mode frequencies at ambient conditions and their pressure-dependent frequency shift, respectively,KTstand for the bulk modulus. These parameters were calculated using polynomial fitting of the Raman frequencies as a function of pressure. The obtained dνi/dPandγivalues Table 1.

The results of the calculated mode Grüneisen parameters were listed in Table1. Values corresponding to the internal modes range from 0.2 to 0.45, lattice modes range from 0.47 to 0.80. The average value of all mode Grüneisen parameters is 0.45(8).

2.3 Anharmonic parameter

Anharmonic parameter is an important parameter in thermodynamic system, which stands for the anharmonic extent induced by temperature and pressure. According to the equation[34]

(4)

Fig.7 Anharmonic parameters of bredigite

Combining the result of high temperature and high pressure experiments, the estimated anharmonic parameters of different modes were listed in Table 1 and Fig.7. The values of internal modes range from -0.84 to -3.57, and the values of lattice modes range from -3.81 to -6.27.

It’s obvious that the absolute value of internal modes was smaller than that of lattice modes. The results indicate that the vibrations of Si-O have more contributions to heat capacity than other vibrational-modes.

3 Conclusions

(1) Bredigite was synthesized with piston-cylinder under 1.2 GPa and 1 473 K;

(2) High temperature Raman spectrums were collected form room temperature to 873 K, providing the shift rates and isobaric Grüneisen parameters. The average of all isobaric Grüneisen parameters was 1.47(3). The result of high temperature Raman experiment showed that no phase transition happened in bredigite’s structure within the investigated temperature range;

(3) With diamond anvil cell, high pressure Raman spectrums were collected up to 14.36 GPa, giving the shift rates and mode- Grüneisen parameters, the average of all mode Grüneisen parameters was 0.45(8). The result of high pressure Raman experiment showed that the structure of bredigite could keep stable as pressure up to at least 14.36 GPa;

(4) Anharmonic parameters were calculated based on the results of high temperature and high pressure experiments, the result showed that the anharmonic effects of vibration induced by Si-O were smaller than other vibration modes.

[1] Tilley C E. Mineralogical Magazine, 1929, 22: 77.

[2] Sabine P A, Styles M T, Young B R. Mineralogical Magazine, 1985, 49: 663.

[3] Tilley C E, Vincent H C G. Mineralogical Magazine, 1948, 28: 255.

[4] Douglas A M B. Mineralogical Magazine, 1951, 29: 875.

[5] Bridge T E. American Mineralogist, 1966, 51: 1766.

[6] Sarakar S L, Jeffrey J W. Journal of the American Ceramic Society, 1978, 61: 177.

[7] Moore PB, Araki T. American Mineralogist, 1976, 61: 74.

[8] Lin H C, Foster W R. Journal of American Ceramic Society, 1975, 58: 73.

[9] Taylor J H. American Mineralogist, 1935, 20: 120.

[10] Mason B. American Mineralogist, 1957, 42: 379.

[11] Joswig W, Stachel T, Harris J W, et al. Earth and Planetary Science Letters, 1999, 173: 1.

[12] Brenker F E, Vincze L, Vekemans B, et al. Earth and Planetary Science Letters, 2005, 236: 579.

[13] Lee K W, Park S H, Yoon H S, et al. Optis Express, 2012, 20: 6248.

[14] Lee K H, Im W B. Journal of American Ceramic Society, 2013, 96: 503.

[15] Yi D, Wu C, Ma B, et al. Journal Biomaterials Applications, 2014, 28: 1343.

[16] Wu C, Chang J, Wang J, et al. Biomaterials, 2005, 26: 2925.

[17] Schlaudt C M, Roy D M. Journal of the American Ceramic Society, 1966, 49: 430.

[18] Liu X, Fleet M E. Journal of Mineralogical and Petrological Science, 2009, 104: 25.

[19] Wang F, Liu X, Lv M D, et al. Spectroscopy and Spectral Analysis, 2015, (In review).

[20] Mao H K, Bell P M, Shaner J W, et al. Journal of Applied Physics, 1978, 49: 3276.

[21] Klotz S, Chervin J-C, Musch P, et al. Journal of Physics D: Applied Physics, 2009, 42: 075413.

[22] Angel R J, Bujak M, Zhao J, et al. Journal of Applied Crystallography, 2007, 40: 26.

[23] Godwal B K, Speziale S, Clark S M, et al. Journal of Physics and Chemistry of Solids, 2010, 71: 1059.

[24] Mohanan K, Sharma S K. American Mineralogist, 1993, 78: 42.

[25] Kolesov B A, Geiger C A. Physics and Chemistry of Minerals, 2004, 31: 142.

[26] Kleppe A K, Jephcoat A P, Smyth J R. Physics and Chemistry of Minerals, 2006, 32: 700.

[27] Noel Y, Catti M, D’ArcoPh, et al. Physics and Chemistry of Minerals, 2006, 33: 383.

[28] Ye Y, Schwering R S, Smyth J R. American Mineralogist, 2009, 94: 899.

[29] Lager R A, Carmichael E P. American Mineralogist, 1978, 63: 365.

[30] Cameron M, Sueno S, Prewitt C T, et al. American Mineralogist, 1973, 58: 594.

[31] Hazen R M. American Mineralogist, 1976, 61: 1280.

[32] Sharp Z D, Hazen R M, Finger I W. American Mineralogist, 1987, 72: 748.

[33] Walker A M, Tyer R P, Bruin R P, et al. Physics and Chemistry of Minerals, 2008, 35: 359.

[34] Gillet P, Richet P, Guyot F, et al. Journal of Geophysical Research, 1991, 96: 11805.

*通訊聯(lián)系人

S511

A

白硅鈣石的高溫高壓拉曼光譜研究

熊志華1，趙明臻2，何俊國(guó)3, 4*，李羿芃5，李紅中4, 6*

1. 北京大學(xué)地球與空間科學(xué)學(xué)院, 北京 100871

2. 華南理工大學(xué)材料科學(xué)與工程學(xué)院, 廣東 廣州 510275

3. 中山大學(xué)地球科學(xué)與地質(zhì)工程學(xué)院, 廣東 廣州 510275

4. 廣東省地質(zhì)過程與礦產(chǎn)資源探查重點(diǎn)實(shí)驗(yàn)室，廣東 廣州 510275

5. University of Houston, Department of Earth and Atmospheric Sciences, Houston, Texas 77204-5007, USA

6. 中國(guó)科學(xué)院地質(zhì)與地球物理研究所，中國(guó)科學(xué)院礦產(chǎn)資源研究重點(diǎn)實(shí)驗(yàn)室, 北京 100029

利用活塞圓筒裝置在1.2 GPa，1 473 K的條件下合成了白硅鈣石。采用外加熱裝置和金剛石壓腔結(jié)合拉曼光譜分析技術(shù)，采集了白硅鈣石298，353，463，543，663，773以及873 K溫度區(qū)間的常壓及1 atm～14.36 GPa(常溫)壓力區(qū)間的拉曼譜圖。掃描電鏡下，該研究合成的樣品為結(jié)構(gòu)一致的單一相，顆粒大小為10～20 μm。電子探針分析結(jié)果表明，樣品的組成為Ca7.03(2)Mg0.98(2)Si3.94(2)O16，該組分完全吻合白硅鈣石理論組分。Raman分析結(jié)果表明，高溫時(shí)白硅鈣石的拉曼譜圖中具有29個(gè)振動(dòng)峰。隨著溫度的升高，部分振動(dòng)峰出現(xiàn)了合并或者弱化消失的現(xiàn)象。該現(xiàn)象尤其以800～1 200 cm-1范圍內(nèi)的909，927和950 cm-1振動(dòng)峰峰位最為明顯，這些振動(dòng)峰分別在873，773以及873 K時(shí)弱化消失。據(jù)此，白硅鈣石的結(jié)構(gòu)在實(shí)驗(yàn)溫壓范圍內(nèi)穩(wěn)定，且隨著溫度和壓力的升高，其拉曼振動(dòng)峰峰位分別呈現(xiàn)往低頻和高頻方向線性飄移的趨勢(shì)。除此之外，根據(jù)高溫和高壓拉曼實(shí)驗(yàn)的結(jié)果，分別計(jì)算了白硅鈣石拉曼振動(dòng)峰峰位的等壓mode-Grüneisen參數(shù)和等溫mode-Grüneisen參數(shù)，其算術(shù)平均值分別為1.47(2)和0.45(3)。最后結(jié)合高溫和高壓拉曼實(shí)驗(yàn)的結(jié)果，計(jì)算了白硅鈣石的非諧系數(shù)，結(jié)果表明，Si-O振動(dòng)模式對(duì)于非諧效應(yīng)的貢獻(xiàn)要小于其他振動(dòng)模式。

白硅鈣石；高溫拉曼；高壓拉曼；非諧系數(shù)

2015-07-03，

2015-11-29)

Foundation item：National Natural Science Foundation of China(410090371, 41273072, 41303025)

10.3964/j.issn.1000-0593(2016)10-3404-06

Received：2015-07-03; accepted：2015-11-29

Biography：XIONG Zhi-hua, (1987—), female, a PhD candidate at school of Earth and Space Science, Peking University e-mail: zhihuaxiong@pku.edu.cn *Corresponding authors e-mail: waynelee01@163.com；lihongzhong01@aliyun.com