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1 Raman spectra and X-ray diffraction of Boron Triiodide at high pressure SHIMIZU Group ONODA Suzue Ref: A. Anderson and L. Lettress J. Raman Spectrosc.

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Presentation on theme: "1 Raman spectra and X-ray diffraction of Boron Triiodide at high pressure SHIMIZU Group ONODA Suzue Ref: A. Anderson and L. Lettress J. Raman Spectrosc."— Presentation transcript:

1 1 Raman spectra and X-ray diffraction of Boron Triiodide at high pressure SHIMIZU Group ONODA Suzue Ref: A. Anderson and L. Lettress J. Raman Spectrosc. 2002; 33: 173

2 2 Contents Introduction ・ Structure of boron triiodide ・ Pressure effect Experiment Results and discussions Summary

3 3 B I Structure of BI 3 molecule: planar triangle structure ( 平面三角形分子) unit cell molecules are layered to c-axis crystal structure: hexagonal (space group P6 3 /m)

4 4 Pressure effect The decrease in volume or atomic distance change of atomic orbital and energy band structure pressure van der Waals bond molecular orbital covalent bond molecular crystal / insulator monatomic metal molecular dissociation (分子解離) diatomic molecular crystal

5 5 Motivation linear fcc 21 fcc-like tetrahedral I SnSn amorphous orthorhombic cubic pressure (GPa) 22 superconductor I2I2 SnI ・ structural transition ・ metallization ・ molecular dissociation … etc. ? B I BI 3 triangular metallization molecular dissociation

6 6 Experiment 1 ・ Sample were loaded into a diamond anvil cell (DAC) of the piston-cylinder type using a glove-bag with an argon atmosphere. ・ A few grain of ruby powder were included for pressure measurements. ruby gasket sample (inconel) 120μm 300μm Raman spectroscopy

7 7 Raman scattering ν 0 ±ν R :Raman scattering (ν R ›0) ν R :Raman shift Raman shift (cm -1 ) Intensity (arb.units) S.Sugai., J. Phys. C: Solid State Phys., 18, 799 (1985) νRνR ν0ν0 (Rayleigh scattering) ν0+νRν0+νR ν0ν0 ν 0 -ν R 1 atm 1.6 GPa 5.3 GPa (×30) 11.3 GPa (×200) 24.7 GPa (×400)

8 8 Raman spectra (a)1.3 GPa (b)2.3 GPa (c)4.1 GPa ν 4 : degenerate in-plane bend mode ν 1 : symmetric B-I stretch mode L xy : libration about in-plane axes T xy : in-plane translation intramolecular mode intermolecular mode ν1ν1 ν4ν4 L xy T xy Intensity (arb.units) Raman shift (cm -1)

9 9 Pressure dependence of Raman shift *The data points for all modes have been fitted to linear function. The spectra evolve smoothly, with no obvious discontinuities. ・ no evidence of any structural phase transitions ・ no indication of any major distortion of BI 3 molecules ν1ν1 ν4ν4 L xy T xy Raman shift (cm -1 ) Pressure (GPa) The intermolecular forces are greatly affected by external pressure intramolecular modes : modest increase ν1ν4ν1ν4 L xy T xy intermolecular modes: dramatic increase

10 10 Experiment 2 gasket rubysample 600μm 60μm (stainless steel) lever-arm diamond anvil cell X-ray diffraction at SPring-8 BL04B2 (my work)

11 11 X-ray diffraction d hkl d h’k’l’ Bragg’s law 2d hkl sinθ=λ d hkl : spacing of lattice planes θ λ

12 12 X-ray diffraction pattern 2θ(degrees) Intensity (arb.units) (a)3.16 GPa (b)5.74 GPa (c)6.96 GPa (d)9.14 GPa (e)15.3 GPa :new peak From diffraction pattern ・・・ ・ (a) and (b) :typical diffraction patterns for hexagonal (phase Ⅰ ) ・ (c): two phases (phase Ⅰ and Ⅱ) coexist ・ Above 9 GPa, the peaks of phase Ⅰ disappear and there is single phase( Ⅱ ) indexed with the fcc (face centered cubic). (λ= Å ) hexagonal fcc

13 13 Pressure dependence of atomic distance Pressure (GPa) Distance between iodine atoms ( Å ) ’ 3’ r(1-2): constant r(fcc) : shorten by compression molecular dissociation r(fcc) : most nearest I-I distance continuously r(fcc) discontinuously intralayer I-I interlayer I-I ( 層内 ) ( 層間 ) *assumption: molecules are rigid

14 14 Discussion Distance between iodine atoms/ Å Pressure/GPa ・ In case of iodine, the nearest interatomic distance r I-I (I 2 ) is 3.6 Å at 16 GPa. ・ r I-I ( SnI 4 ) is also 3.6 Å at 7 GPa. Metallization of BI 3 may occur at about 11GPa. ref. 高圧力の科学と技術 15, 120 (2005) At metallization ・・・

15 15 fcc fcc-like tetrahedral I SnSn orthorhombic cubic pressure (GPa) linear I2I2 SnI metallization molecular dissociation B I BI 3 triangular 7 GPa hexagonal ~ 11 GPa fcc Discussion

16 16 Summary From Raman spectra ・・・ ・ The original crystal structure appears to be stable over the pressure range 0-5 GPa. ・ The molecular identity is retained and no major distortions occur. From X-ray diffraction ・・・ ・ Structural transition to fcc phase appears at 6.9 GPa. ・ In phase Ⅱ (fcc), molecular dissociation occurs. ・ Metallization may occur about 11 GPa. In future ・・・ I will measure electric resistivity to confirm metallization.


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