摘要
碱土金属氟化物在高压下的结构行为十分丰富，是研究物质在极端条件下结构和物性的重要研究对象。利用高压技术来研究纳米材料的高压相变行为和压缩行为，是崭新的而且具有挑战的课题之一。本论文利用水热合成法制备不同尺寸的形貌均一的单分散碱土金属氟化物纳米晶。采用原位金刚石对顶砧高压实验技术对不同尺寸的碱土金属氟化物纳米晶的原位高压结构进行了研究，揭示纳米材料小尺寸效应对物质结构相变行为的影响规律。
1.利用水热合成法制备单分散碱土金属氟化物纳米晶，通过控制反应温度、反应物浓度等条件制备不同粒径、形貌均一的纳米晶。
2.利用原位高压同步辐射X-ray衍射技术，研究了粒径为8 nm和11 nmCaF_2纳米颗粒的高压相变行为。发现两种纳米晶相变压力点的差异是由于材料的尺寸不同引起的，两种纳米晶粒高压相变行为体现出了纳米小尺寸效应，表现出明显的尺寸相关性，尺寸越小其相变压力点越高。
3.利用原位高压同步辐射X-ray衍射技术和高压Raman技术，对SrF_2体材料的高压相变行为和压缩行为进行了研究。分析了包括传压介质，实验温度等因素对SrF_2高压相变行为的影响。
4.采用同步辐射X-ray衍射技术研究SrF_2纳米颗粒和SrF_2纳米板的高压相变行为。对晶格膨胀、样品暴露面和缺陷作用等影响这两种纳米晶高压行为差异的原因进行了探讨。
5.采用同步辐射X-ray衍射技术研究BaF_2纳米板的高压相变行为。探讨影响BaF_2纳米材料相变行为主要因素。
It is well known naomaterials exhibit various novel physical and chemicalproperties compared with their bulk counterparts due to their unique properties, suchas size effect, confinement effect and so on. High pressure can effectively change thedistances between molecules and atoms. The changes of structure will do strongeffects on the properties of materials. Thus, high-pressure technology is an importantand effective route for us to understand the structures, properties and even theirrelationship. In recent years, with the rapid development of nanotechnology,nanotechnology combines with high-pressure technology, and it will reveal manyattractive and novel phenomena, structures and mechanics.
As the important kind of fluoride, alkaline earth metal MF_2(M= Ca, Sr, Ba) havegreat applications in microelectric, optoelectric, biological and mineralogy due to itsanionic conductivity, high resistivity, high ionicity and low-energy phonons etc.
The structural stability and phase transformation of nanocrystals (NCs) haverecently triggered significant interests in fundamental scientific research and practicalapplications in chemistry, physics, materials science and geophysics. At ambientconditions, bulk MF_2crystallizes in the cubic fluorite structure with a space group ofFm3m. The sequence of the pressure-induced phase transition would follow thestructural progression from cubic (Fm3m) fluorite structure to orthorhombic (Pnma)α-PbCl2-type structure to hexagonal (P63/mmc) Ni2In-type structure, which in turn would be characterized by a progression in the cation coordination number from 8 to9 to 11. However, to our knowledge, there has been no report of phase transformationstudy on nanoscale system of alkaline earth metal. In this work, we studied theinfluences on the pressure behavior and compressing characteristics of the differentsizes of CaF_2/ SrF_2/ BaF_2nanocrystals.
The alkaline earth fluorides (MF_2) nanocrystals with different size weresuccessfully synthesized by a facile hydrothermal process. The MF_2nanocrystals witha controllable size were successfully synthesized by modulating the temperature andconcentration of the monomers. Moreover, high pressure studies on MF_2nanocrystalswith different size were carried out through in-situ X-ray diffraction and Ramantechniques. We found the size effect do a strong impact on the high-pressurebehaviors of MF_2.
The high-pressure behaviors of CaF_2nanocrystals with sizes of 8 nm and 11 nmhave been investigated by angle-dispersive synchrotron x-ray powder diffractionmeasurement up to 46.5 GPa and 28.5 GPa at room temperature. A pressure-inducedfluorite structure (Fm3m) to orthorhombic PbCl2-type structure (Pnma) transitionstarts at 14.0 GPa and 12 GPa, respectively. The differences of transition pressure inCaF_2nanocrystals are strongly depend on their grain size. The high-pressure behaviorof CaF_2nanocrystals show a noticeable size-dependence, the onset of transitionpressure showed a significant increase with decreasing particle size. This studyshowed that a size effect in CaF_2nanocrystals can lead high-pressure metastablematerials at ambient conditions. The bulk modulus of cubic phase in CaF_2nanocrystals strongly depend on their grain size, and the increased bulk modulus ofcubic phase indicates higher incompressibility than bulk CaF_2.
The high-pressure behavior of SrF_2has been investigated by angle-dispersivesynchrotron x-ray powder diffraction measurement up to 50.3 GPa at roomtemperature. Under pressures up to 50.3 GPa, SrF_2transforms from the cubic fluoritestructure to an orthorhombic cotunnite-type structure at about 6.8 GPa and then to ahexagonal Ni2In-type structure at 29.5 GPa. After decompression to ambientcondition, a few peaks attributed to orthorhombic phase have been retained, suggesting that the cubic and orthorhombic phase co-exist at ambient pressure. Theresidual stress in sample is not completely released upon decompression, which mightbe the reason of irreversibility at the ambient pressure. We hypothesized that thesample can recover the lower phase completely after set aside a long time. Afterrepeat in situ high-pressure X-ray diffraction and Raman spectroscopy, the phasetransformation is reversibility after complete pressure release.The isothermal bulkmodulus of the cubic, orthorhombic and hexagonal phases increased gradually,indicating higher incompressibility of SrF_2under high pressure.
We synthesized SrF_2nanoparticles and nanoplates with an average size of around11 nm and 21 nm in a fluorite-type structure. The high-pressure behaviors ofnanocrystalline SrF_2samples have been investigated by angle-dispersive synchrotronx-ray powder diffraction measurement up to 46 GPa at room temperature. Two phasetransitions from fluorite-type toα-PbCl2-type and Ni2In-type phases of the SrF_2nanoparticles occur at 10 and 34.3 GPa, which is much higher than that in bulk SrF_2(6.8 GPa and 29.5 GPa). Upon decompression, the pureα-PbCl2-type metastablephase is retained when the pressure is released. In contrast, the two phasetransformations of nanoplates occur at 6.3 GPa and 27.7 GPa, and the high-pressurebehavior of SrF_2nanoplates is similar to that observed in bulk material. The SrF_2nanoparticles exhibit amazing pressure responses which are different than those forbulk materials. Decreasing particle size reduces the hosted ratios of defect anddislocation in SrF_2nanoparticles. In SrF_2nanoplates with sizes of 21 nm, the hosteddefect (or dislocation) acts to behave similar to that in bulk. The defect site couldserve as a weak point and induce a stress concentration, so a new phase prefers tonucleate at such a defect site. Therefore, high pressure phase nucleated in SrF_2nanoplates certainly has a reduced nucleation pressure relative to that in SrF_2nanoparticles.
The high-pressure behavior of BaF_2nanoplates has been investigated byangle-dispersive synchrotron x-ray powder diffraction measurement up to 21.2 GPa atroom temperature. BaF_2nanoplates transforms from the cubic fluorite structure to anorthorhombic cotunnite-type structure at about 5.8 GPa and then to a hexagonal Ni2In-type structure at 14.4 GPa, which is much higher than that in bulk BaF_2. Upondecompression, the pureα-PbCl2-type metastable phase is retained when the pressureis released. This study showed that a size effect effect in BaF_2nanoplates can lead theenhancement of transition pressure and high-pressure metastable materials at ambientconditions.
引文
[1] Hou S, Zou Y, Liu X, et al. CaF2 and CaF2:Ln3+(Ln =Er, Nd, Yb) hierarchicalnanoflowers: hydrothermal synthesis and luminescent properties [J].CrystEngComm, 2011, 13: 835-840.
[2] Quan Z W, Yang D M, Yang P P, et al. Uniform colloidal alkaline earth metalfluoride nanocrystals: nonhydrolytic synthesis and luminescence properties [J].Inorg. Chem., 2008, 47: 9509-9517.
[3] Gao P, Xie Y, Li Z. Controlling the size of BaF2nanocubes from 1000 to 10 nm[J]. Eur. J. Inorg. Chem., 2006, 2006(16):3261-3265.
[4] Yang X C, Hao A M, Wang X M, et al. First-principles study of structuralstabilities, electronic and elastic properties of BaF2under high pressure [J].Computational Materials Science, 2010, 49:530-534.
[5] Madelung O, Bo¨rnstein L. Numerical Data and Functional Relationships inScience and Technology [M]. New Series, Group. III: Springer-Verlag, Berlin,1983.
[6] Justel T, Nikol H, Ronda C. New developments in the field of luminescentmaterials for lighting and displays [J]. Angew. Chem. Int. Edn, 1998, 37(22):3085-3103.
[7] Singh R, Sinha S, Chou P, et al. Preparation of BaF2films by metalorganicchemical vapor deposition [J]. J. Appl. Phys., 1989, 66: 6179-6181.
[8] Kawano K, Ohya T. Tsurumi T, et al. X-ray excitation fluorescence spectra of theEu2+-stabilized VKcenter in alkaline-earth fluoride mixed-crystal systems [J].Phys.Rev. B, 1999, 60(17):11984-11992.
[9] Retherford R S, Sabia R, Sokira V P. Effect of surfacequality on transmissionperformance for (111) CaF2[J]. Applied Surface Science, 2001, 183(3):264-269.
[10] Westerhoff T, Knapp K, Moersen E. Optical materials for microlithographyapplications [J]. Proc. SPIE, 1998, 10:3424.
[11] Duparre A, Thielsh R, Kajser N, et al. Surface Finish and Optical Quality of CaF2of UV-lithography Applications [J]. Proceeding of SPIE, 1998, 3334:1048-1051.
[12] Engel A, Knapp K, Aschke L, et al. Development and investigation of highquality CaF2used for 157nm micro lithography [J]. Proceeding of SPIE, 2001,4346:1183-1189.
[13] Mouchanow A, Hilburger U, Driedrich J, et al. Experimental verification of thenumerical model for a CaF2crystal growth process [J]. Crystal ResearchTechnology,2002, 37(1):77-82.
[14] Oldham W G, Schenker R E. 193 nm lithographic system lifetimes as limited byUV compaction [J]. Solid state technology, 1997, 40:95-102.
[15] Dressler L, Rauch R, Reimann R, On the Inhomogeneity of Refractive Index ofCaF2Crystals for High Performance Optics [J]. Cryst. Res. Technol., 1992,27(3):413-420.
[16] Stenzel E, Gogoll S, Sils J, et al. Laser damage of alkaline-earth fluorides at 248nm and the influence of polishing grades [J]. Applied Surface Science, 1997,109/110:162–167.
[17] Jiang J, Zhang G, Poulain M, Cerium-containing glasses for fast scintillators [J].Journal of Alloys and Compounds, 1998, 275-277:733-737.
[18] Dorenbos P. Light output and energy resolution of Ce3+-doped scintillators [J].Nuclear Instruments and Methods in Physics Research A,2002,486(1-2):208-213.
[19] Schotanus P, Van Eijk C W E, Hollander R W. Development study of a newgamma camera [J]. IEEE. TranB. Nucl. Sci., 1987, 34(1): 272-276.
[20] Wojtowicz A J. Rare-earth-activated wide bandgap materials for scintillators [J].Nuclear Instruments and Methods in Physics Research A 2002,486(1-2):201-207.
[21] Wagner V, Kugler A, Paehr M, et al. Detection of Relativistic Neutrons by BaF2Seiotillators [J]. Nuel.lnstr.and Meth., 1997, A 394: 332-340.
[22] Klamra W, Kerek A, Moszynski M, et al. Response of BaF2and YAP:Ce toheavy ions [J]. Nucl. Instr.and Meth. A. 2000, 444, 626-630.
[23] Kim H ,Kim H S ,Lee B G, et al. [J ]. Effect of magnesium fluoride inchromium–magnesium catalysts on the fluorination reaction of1,1,1-trifluoro-2-chloroethane [J]. J. Chem. Soc. Chem. Commun., 1995,23:2383-2384.
[24]胥会祥，吕剑.镁基气相氟化催化剂的研究进展[J].工业催化，2002,11(6):43-47.
[25]胥会祥,吕剑. MgF2基催化剂合成CH2F2的研究[J].工业催化，2009,10(5):51-53.
[26] Xu H X, Lv J. Preparation and Performance of Cr3+/MgF2Catalyst for Synthesisof Difluoromethane [J]. Chinese Journal of Catalysis, 2003, 23(5):379-384.
[27] Quan H D, Tamura M, Gao R X, et al. Preparation and application of porouscalcium fluoride—a novel fluorinating reagent and support of catalyst [J].Journal of Fluorine Chemistry, 2002,116:65–69.
[28]周水琴，龙瑞强，黄亚萍等.甲烷氧化偶联CaF2/Sm2O3催化剂的研究[J].高等学校化学学报, 1995, 2:290-292.
[29]龙瑞强，陈明树，卢维奇等.碱土金属氟化物促进Eu2O3催化剂的甲烷氧化偶联剂[J].中国稀土学报，1997, 15: 197-201.
[30] Rog G, Kielski A, Kozlowska-Rog A, et al. Composite (CaF2+a-A12O3) SolidElectrolytes: Preparation, Properties and Application to the Solid Oxide GalvanicCell [J]. Ceramics Intenational, 1998, 24, 91-98.
[31] Ravi B G, Baskaran N, Ramasamy S et al. Preparation and a.c.ConductivityStudies of CaF2-LiF Composites [J]. Materials Science and Engineering:B, 1996,41(2):241-246.
[32] Rog G, Bueko M M, Kielski A et al. Conductivity of Composite CalciumFluoride-Silica Solid Eledtrlytes [J]. Ceramic International, 1999, 25:623-630.
[33] Sorokin N L, Breiter M W, Anionic Conductivity and Thermal Stability of SingleCrystal of Solid Solutions Based on Barium Fluoride [J]. Solid State Ionics, 1997,99: 241-250.
[34] Sorokin N I，Breiter M W, Anionic conductivity and thermal stability of singlecrystals of solid solutions based on calcium fluoride [J]. Solid State Ionics,1999,116:157-165.
[35] Sorokin N L, Breiter M W, Anionic Conductibity and Thermal Stability of SingleCrystal of Solid Solutions Based on Strontium Fluoride [J]. Solid State Ionic,1997, 104:325-333.
[36] Tang Q, Zhou W J, Shen J M, et al. A template-free aqueous route to Zn0nanorod arrays with high optical property [J]. Chem. Commun., 2004, 6:712-713.
[37] Nirmal M, Brus L. Luminescence photophysics in semiconductor nanocrystals[J]. Acc Chem Res, 1999, 32: 407-414.
[38] Alivisatos A P. Perspectives on the physical chemistry of semiconductornanocrystals [J]. J Phys Chem, 1996, 100: 13226-13239.
[39] Zhang J Z, Ultrafast studies of electron dynamics in semiconductor and metalcolloidal nanoparticles: Effects of size and surface [J]. Acc Chem Res, 1997, 30:423-429.
[40] Colvin V L, Schlamp M C, Alivisatos A P. Light-emitting-diodes made fromcadmium selenide nanocrystals and a semiconducting polymer [J]. Nature, 1994,370: 354-357.
[41] Nirmal M, Dabbousi B O, Bawendi M G, et al. Fluorescence intermittency insingle cadmium selenide nanocrystals [J]. Nature, 1996, 383: 802-804.
[42] Bruchez M, Moronne M, Gin P, et al. Semiconductor nanocrystals as fluorescentbiological labels [J]. Science, 1998, 281: 2013-2016.
[43] Bensalaha A, Mortiera M, Patriarcheb, G et al. Synthesis and opticalcharacterizations of undoped and rare-earth-doped CaF2nanoparticles [J].Journal of Solid State Chemistry, 2006, 179:2636–2644.
[44] Pandurangappa C, Lakshminarasappa B N, Nagabhushana B M, Synthesis andcharacterization of CaF2nanocrystals [J]. Journal of Alloys and Compounds,2010, 489:592–595.
[45] Sun X M and Li Y D. Size-con trol lable luminescent single crystal CaF2nanocubes [J] . Chem Commun , 2003, 14: 1768-1769.
[46] Zhang C, Li C, Peng C, et al. Facile and Controllable Synthesis of MonodisperseCaF2and CaF2:Ce3+/Tb3+Hollow Spheres as Efficient Luminescent Materialsand Smart Drug Carriers [J]. Chem. Eur. J., 2010, 16: 5672-5680.
[47] Zhang C, Hou Z, Chai R, et al. Mesoporous SrF2and SrF2:Ln3+(Ln ) Ce, Tb, Yb,Er) Hierarchical Microspheres: Hydrothermal Synthesis, Growing Mechanism,and Luminescent Properties [J]. J. Phys. Chem. C., 2010, 114:6928-6936.
[48] Zhang X M, Quan Z W, Yang J, et al. Solvothermal synthesis of well-dispersedMF2(M = Ca, Sr, Ba) nanocrystal s and their optical properties [J].Nanotechnology, 2008, 19(1): 075603.
[49] Xie T , Li S, Peng Q, et al. Monodisperse BaF2nanocrystals: phases, sizetransitions, and self-assembly [J] . Angew Chem In t Ed, 2009, 48: 196-200.
[50] Feldmann C, Roming M, Trampert K. Polyol-Mediated Synthesis of NanoscaleCaF2and CaF2: Ce, Tb [J]. Small, 2006, 2(11): 1248- 1250.
[51] Cao M H, Hu C W, Wang E B. The First Fluoride One-DimensionalNanostructures: Microemulsion-Mediated Hydrothermal Synthesis of BaF2Whiskers [J]. J. Am. Chem. Soc., 2003, 125 (37): 11196-11197.
[52] Lian H Z, Liu J, Ye Z R, et al. Synthesis and photoluminescence properties oferbium-doped BaF2nanoparticles [J]. Chemical Physics Letters, 2004,386:291-294.
[53] Du Y P, Sun X, Zhang Y W, et al. Uniform Alkaline Earth Fluoride Nanocrystalswith Diverse Shapes Grown from Thermolysis of Metal Trifluoroacetates in HotSurfactant Solutions [J]. Crys. Growth. & Des., 2009, 9: 42013-42019.
[54] Mao Y, Zhang F, Wong S S. Ambient Template- Directed Synthesis of Single-Crystalline Alkaline- Earth Metal Fluoride Nanowires [J]. Adv. Mater., 2006,18:1895-1899.
[55] Kavner A. Radial diffraction strength and elastic behavior of CaF2in low-andhigh-pressure phases [J]. Phys. Rev. B, 2008, 77(22) 224102.
[56] Seifert K F and Bunsenges B. Strukturumwandlungen von Halogeniden desTypus AX2unter h heren Drücken [J]. Phys. Chem., 1966, 70(9-10):1041-1402.
[57] Gerward L, Olsen J S, Steenstrup S, et al. X-ray diffraction investigations ofCaF2at high pressure [J]. J. Appl. Crystallogr., 1992, 25:578-581.
[58] Dorfman S M, Jiang F, Mao Z, et al. Phase transitions and equations of state ofalkaline earth fluorides CaF2, SrF2, and BaF2to Mbar pressures [J]. Phys.Rev.B,2010, 81(17):174121.
[59] Kourouklis G A, Anastassakis E. Pressure-induced phase transition in SrF2: aRaman study [J]. Phys. Rev. B, 1986, 34 (2):1233-1237.
[60] Francisco E, Blanco M A, Sanjurjo G. Atomistic simulation of SrF2polymorphs[J]. Phys. Rev. B, 2001,63 (9):094107.
[61] Kanchana V, Vaitheeswaran G, Rajagopalan M, Structural phase stability ofCaF2and SrF2under pressure [J].Physica B, 2003,328 (3-4):283-290.
[62] Hao A M, Yang X C, Li J, et al. First-Principles Study of Structural Stabilities,Electronic and Optical Properties of SrF2under High Pressure [J]. Chin. Phys.Lett., 2009, 26 (7):077103.
[63] Smith J S, Desgreniers S, Tse J S, et al. High-pressure structures and vibrationalspectra of barium fluoride: Results obtained under nearly hydrostatic conditions[J]. Phys. Rev. B, 2009,79 (13):134104.
[64] Leger J M, Haines J, Atouf A, et al. High-pressure x-ray- and neutron-diffractionstudies of BaF2: An example of a coordination number of 11 in AX2compounds [J]. Phys. Rev. B, 1995, 52:13247–13256.
[65] Kanchana V, Vaitheeswaran G, Rajagopalan M. Pressure induced structuralphase transitions and metallization of BaF2[J]. Journal of Alloys andCompounds, 2003, 359:66-72.
[66] Kessler J R, Monberg E, Nichol M. Studies of fluorite and related divalentfluoride systems at high pressure by Raman spectroscopy [J]. J. Chem. Phys.,1974, 60:5057-5065.
[67] Ayala A P. Atomistic simulations of the pressure-induced phase transitions inBaF2crystals [J]. J. Phys.: Condens. Matter, 2001,13:11741-11749.
[68] Lin Y, Yang Y, Ma H, et al. Compressional Behavior of Bulk and NanorodLiMn2O4under Nonhydrostatic Stress [J]. J. Phys. Chem. C, 2011, 115(20):9844–9849.
[69] Biswas K, Muthu DVS, Sood A K, et al. Pressure-induced phase transitions innanocrystalline ReO3[J]. J. Phys.: Condens. Matter, 2007, 19 (43):436214.
[70] Wang Z, Wen X D, Hoffmann R, et al. Reconstructing a solid-solid phasetransformation pathway in CdSe nanosheets with associated soft ligands [J].PNAS, 2010, 107(40):17119-17124.
[71] Zhang H, Gilbert B, Huang F, et al. Water-driven structure transformation innanoparticles at room temperature [J]. Nature, 2003, 424:1025-1029.
[72] Wang Z W, Daemen L L, Zhao Y S, et al. Morphology-tuned wurtzite-type ZnSnanobelts [J]. Nat. Mater., 2005, 4: 922-927.
[73] Gilbert B, Huang F, Zhang H, et al. Nanoparticles: Strained and Stiff [J]. Science,2004, 305:651–654.
[74] Srivastava A, Tyagi N, Sharma U S, et al. Pressure induced phase transformationand electronic properties of AlAs [J]. Mater. Chem. Phys., 2011, 125(1-2):66–71.
[75] Tolbert S H, Alivisatos A P. Size dependence of a first order solid-solid phasetransition: the wurtzite to rock salt transformation in CdSe nanocrystals [J].Science, 1994, 265:373-376.
[76] Wang Z W, Guo Q X. Size-Dependent Structural Stability and TuningMechanism: A Case of Zinc Sulfide [J]. J. Phys. Chem. C, 2009, 113:4286–4295.
[77] He Y, Liu J F, Chen W, et al. High-pressure behavior of SnO2nanocrystals [J].Physical Review B, 2005, 72:212102.
[78] Qadri S B, Yang J, Ratna B R, et al. Pressure induced structural transitions innanometer size particles of PbS [J]. Appl. Phys. Lett. 1996, 69 (15):2205.
[79] Tolbert H S, Alivisatos P A. The wurtzite to rock salt structural transformation inCdSe nanocrystals under high pressure [J]. J. Chem. Phys., 1995, 102:4642.
[80] Jiang J Z, Olsen J S, Gerward L. Structural stability in nanocrystalline ZnO [J].Europhys. Lett., 2000, 50 (1):48-53.
[81] Jiang J Z, Olsen J S, Gerward L, et al. Enhanced bulk modulus and reducedtransition pressure inγ-Fe2O3nanocrystals [J]. Europhys. Lett., 1998, 44:620.
[82] Wang Z W, Tait K, Zhao Y S, et al. Size-Induced Reduction of TransitionPressure and Enhancement of Bulk Modulus of AlN Nanocrystals [J]. J. Phys.Chem. B, 2004, 108:11506.
[83] Wang Z W, Saxena S K, Pischedda V et al. In situ x-ray diffraction study ofpressure-induced phase transformation in nanocrystalline CeO2[J]. Phys. Rev. B,2001，64: 012102-1-4.
[84] Zhang F X, Lang M, Ewing R C, et al. High pressureresponse of zirconiananoparticles with an alumina shell [J]. Journal of Physical Chemistry C, 2009,113:14658-14662.
[85] Swamy V, Kuznetsov A, Kubrovinsky L S, et al. Size dependent pressureinduced amorphization in nanoscale TiO2[J]. Physical Review Letters, 2006,96:135702.
[86] Wang L, Yang W G, Ding Y, et al. Size-Dependent Amorphization of NanoscaleY2O3at High Pressure [J]. Phys. Rev. Lett., 2010, 105:095701.
[87] Quan Z W, Wang Y X, Bae I T, et al. Reversal of Hall–Petch Effect in StructuralStability of PbTe Nanocrystals and Associated Variation of Phase Transformation[J].Nano Lett., 2011, 11 (12), 5531-5536.
[88] Li Z P, Liu B B, Yu S D, et al. The Study of Structural Transition of ZnSNanorods under High Pressure [J]. J. Phys. Chem. C, 2011, 115:357-361.
[89] Liu B, Yao M G, Liu B B, et al. High-Pressure Studies on CeO2Nano-Octahedrons with a (111) - Terminated Surface [J]. J. Phys. Chem. C, 2011,115: 4546-4551.
[90] Guo Q, Zhao Y, Mao W L, et al. Cubic to Tetragonal Phase Transformation inCold-Compressed Pd Nanocubes [J]. Nano Lett. 2008, 8:972.
[91] Shen L H, Li X F, Ma Y M, et al.Pressure-induced structural transition in AlNnanowires [J]. Appl. Phys. Lett., 2006, 89:141903.
[92] Park S W, Jang J T, Cheon J, et al. Shape-Dependent Compressibility of TiO2Anatase Nanoparticles [J]. J. Phys. Chem. C, 2008, 112: 9627-9631.
[93] Dong Z H, Song Y, Pressure-induced morphology-dependent phasetransformations of nanostructured tin dioxide [J], Chemical Physics Letters, 2009,480:90-95.
[94] Su F, Wu X J, Qin X Y, et al. Ionic conduction of nanophase Ca1-xLaxF2+x[J].Chinese Science Bulletin, 1993, 38:1518-1522.
[95] Jun X, Su W F, Qin X Y. Synthesis and ionic conductivity of nanophaseCa1-xLaxF2+x[J]. Mater. Res. Soc. Symp. Proc., 1993, 286:27-32.
[96] Puin W, Heitjans P. Frequency Dependent Ionic Conductivity in NanocrystallineCaF2Studied by Impedance Spectroscopy [J]. Nanostructured Materials, 1995,6:885-888.
[97] Puin W, Rodewald S, Ramlau R, et al. Local and overall ionic conductivity innanocrystalline CaF2[J], Solid State Ionics, 2000, 131:159-164.
[98] Beecroft L L, Ober C K. Nanocornposite Materials for Optical Applications [J],Chem. Mater., 1997, 9:1302-1317.
[99] Wang L, Liu B B, Liu D D, et al. Synthesis and high pressure inducedamorphization of C60 nanosheets [J]. Appl. Phys. Lett., 2007, 91:103112.
[100] Wang L, Liu B, Liu D, et al. Synthesis of Thin, Rectangular C60 NanorodsUsing m-Xylene as a Shape Controller [J]. Adv. Mater., 2006, 18:1883.
[101] Wang X, Zhuang J, Peng Q, et al. A general strategy for nanocrystal synthesis[J].Nature, 2005, 437(7055): 121-124.
[102] Ge J P, Chen W, Liu L P, et al. Formation of disperse nanoparticles at theoil/water interface in normal microemulsions [J]. Chem Eur J, 2006, 12(55):6552-6558.
[103] Huo Z Y, Chen C, Liu X W, et al. One-pot synthesis of monodisperse CeO2nanocrystals and superlattices [J]. Chem Commun, 2008, 32:3741-3743.
[104] Ge J P, Xu S, Zhuang J, et al. Synthesis of CdSe, ZnSe, and Znx Cd1 xSenanocrystals and their silica sheather core/shell structures [J]. Inorg Chem, 2006,45(13): 4922-4927.
[105] Wang X, Peng Q, Li Y D. Interface-mediated growth of monodispersednanostructures [J]. Acc. Chem. Res., 2007, 40: 635-643.
[106] Ge J P, Xu S, Liu L P, et al. A positive-microemulsion method for preparingnearly uniform Ag2Se nanoparticles at low temperature [J]. Chem Eur J, 2006,12(13): 3672-3677.
[107] Wang X, Zhuang J, Peng Q, et al. Synthesis and characterization of sulfide andselenide colloidal semiconductor nanocrystals [J]. Langmuir, 2006,22:7364-7368.
[108] Zhang J T, Liu J F, Peng Q, et al. Nearly monodisperse Cu2O and CuOnanospheres: preparation and applications for sensitive gas sensors [J]. ChemMater, 2006, 18(4): 867-871.
[109] Wang X, Li Y D. Monodisperse nanocrystals: General synthesis, assembly, andtheir applications [J]. Chem. Commum., 2007, (28): 2901-2910.
[110] Liang X, Wang X, Zhuang J, et al. Synthesis of nearly monodisperse iron oxideand oxyhydroxide nanocrystals [J]. Adv. Funct. Mater., 2006, 16: 1805-1813.
[111] Wang X, Zhuang J, Peng Q, et al. Liquid-solid-solution synthesis of biomedicalhydroxyapatite nanorods [J]. Adv Mater., 2006, 18: 2031-2034.
[112] Wang L Y, Li Y D. Na(Y1.5Na0.5)F6single crystal nanorods as multicolorluminescent materials [J]. Nano Lett, 2006, 6:1645-1649.
[113] Wang X, Zhuang J, Peng Q, et al. Hydrothermal synthesis of rare earth fluoridenanocrystals [J]. Inorg Chem, 2006, 45: 6661-6665.
[114] Wang L Y, Li Y D. Controlled synthesis and luminescence of lanthanide dopedNaYF4nanocrystals [J].Chem. Mater., 2007, 19:727-734.
[115] Huo Z Y, Chen C, Li Y D. Self-assembly of uniform hexagonal yttriumphosphate nanocrystals [J].Chem Commun, 2006, 33:3522-3524.
[116] Liu J F, Li Y D. Synthesis and self-assembly of luminescent Ln3+-dopedLaVO4 uniform nanocrystals [J].Adv. Mater., 2007, 19:1118-1122.
[117] Srivastava R, Lauer Jr H V, Chase L L, et al. Raman frequencies of fluoritecrystals [J].Physics Letters A, 1971, 36(4):333-334.
[118] Kourouklis G A, Anastassakis E. Pressure-induced phase transition in SrF2: Araman study [J]. Physical Review B, 1986, 34(2):1233-1237.
[119] Smith J S, Desgreniers S, John S T, et al. High-pressure structures andvibrational spectra of barium fluoride: Results obtained under nearly hydrostaticconditions [J]. Physical Review B, 2009, 79:134104.
[120] Dressler L, Rauch R, Reimann R. On the Inhomogeneity of Refractive Index ofCaF2Crystals for High Performance Optics [J]. Crystal Research Technology,1992, 27(3):413-420.
[121] Wu X, Qin S, Wu Z Y. First-principles study of structural stabilities, andelectronic and optical properties of CaF2under high pressure [J]. Phys. Rev. B,2006, 73:134103.
[122] Cui S X, Feng W X, Hua H Q. Structural stabilities, electronic and opticalproperties of CaF2under high pressure: A first-principles study [J]. Comput.Mater. Sci, 2009, 47:41-45.
[123] Morris E, Groy T, Leinenweber K. Crystal structure and bonding in thehigh-pressure form of fluorite (CaF2) [J]. J. Phys. Chem. Solids, 2001, 62(6):1117-1122.
[124] Boulfelfel S E, Zahn D, Hochrein O, et al. Low-dimensional sublattice meltingby pressure: Superionic conduction in the phase interfaces of thefluorite-to-cotunnite transition of CaF2[J]. Phys. Rev. B, 2006, 74: 094106.
[125] Yel’kin F S, Tsiok O B, Brazhkin V V, et al. High-precision in situ investigationof the kinetics of the high-pressure phase transition in CaF2including the initialtransformation stages [J]. Phys. Rev. B, 2006, 73:094113.
[126] Speziale S, Duffy T S. Single-crystal elastic constants of fluorite (CaF2) to 9.3GPa [J]. Phys. Chem. Miner., 2002, 29(7):465-472.
[127] Rekhi A, Saxena S K, Lazor P, High-pressure Raman study on nanocrystallineCeO2[J]. J. Appl. Phys., 2001, 89:2968.
[128] Wang Z W, Tait K, Zhao Y S, et al. Size-induced reduction of transition pressureand enhancement of bulk modulus of AlN nanocrystals [J]. J. Phys. Chem. B,2004, 108:11506.
[129] Hao J, Zou B, Zhu P, et al. In situ X-ray observation of phase transitions inMg2Si under high pressure [J]. Solid State Communications, 2009,149:689-692.
[130] Hao J, Li Y, Zhou Q, et al. Structural Phase Transformations of Mg3N2at HighPressure: Experimental and Theoretical Studies [J]. Inorg. Chem., 2009,48:9737-9741.
[131] Chen D, Yu Y, Huang F, et al. Modifying the size and shape of monodispersebifunctional alkaline-earth fluoride nanocrystals through lanthanide doping [J].J. Am. Chem. Soc., 2010, 132 (29):9976–9978.
[132] Samara G A. Temperature and pressure dependences of the dielectric propertiesof PbF2and the alkaline- earth fluorides [J]. Phys. Rev. B, 1976, 13:4529.
[133] Dandekar D P, Jamieson J C. Some high-pressure phases of RX2fluorides [J].Trans. Am. Crystallogr., 1969, 5:19-27.
[134] Shen Y, Kumar R S, Pravica M, et al. Characteristics of silicone fluid as apressure transmitting medium in diamond anvil cells [J]. Rev. Sci. Instrum.,2004,75:4450-4454.
[135] Z. L. Wang. Transmission electron microscopy of shape-controlled nanocrystalsand their assemblies [J]. J. Phys. Chem. B, 2000, 104:1153-1173.
[136] Jiang H, Pandey R, Darrigan C, et al. First-principles study of structural,electronic and optical properties of BaF2in its cubic, orthorhombic andhexagonal phases [J]. J. Phys.: Condens. Matter, 2003, 15:709-718.