pressure-induced hydrogen-dominant metallic state in aluminum hydride hagihara toshiya shimizu-group...
TRANSCRIPT
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- Pressure-Induced Hydrogen-dominant metallic state in Aluminum Hydride HAGIHARA Toshiya Shimizu-group Igor Goncharenko et al., Phy. Rev. Lett. 100, 045504 (2008)
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- Contents Introduction theoretical prediction of hydrogen under high pressure why hydrides previous studies on AlH 3 Experimental method Result & discussion Summary
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- Hydrogen Interesting physical properties Metallic conductivity High-temperature superconductivity T c ~ room temperature Molecular hydrogenHydrogen dense state experimentally difficult. Theoretical prediction More than 400~500 GPa is required. under high pressure
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- hydrides Interstitial hydrides Covalent hydrides M: rare earth metalM: Al, Si. The M-H bonding is covalent. Insulator at ambient pressure Hydrogen atoms are in the interstitial site of metal lattice. For the model of dense metallic hydrogen, hydrides (for example MH x ) are paid attention.
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- hydrides MH x ; YH 3, AlH 3 Hydrogen molecular is contained 1.5 mol per 1.0 mol of M. Hydrogen in MH x is precompressed at ambient pressure. The partial hydrogen volume in MH x < That volume in H 2. At much lower pressure, hydrogen dense metallic state could be observed. Hydrogen atomic volume in MHx from subtraction of atomic volume of M.
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- AlH 3 R-3c structure Two AlH 6 -units share this H atom. AlH 6 octahedrons linked by Al-H-Al bridges The partial hydrogen volume per H atom in AlH 3 (5.5 A 3 ) is smaller than that in H 2 (7.5 A 3 ). Hydrogen in AlH 3 is precompressed ! P ~ ambient pressure H H Al-H distance: 1.7 A H-H distance: 2.5 A Volume per formula unit in AlH 3 : 33 A 3
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- Previous studies on AlH 3 P < 35 GPa, there is no structural transition. Insulator is stable at about 100 GPa. Band gap decreases by the pressure. X-ray diffraction measurement Electrical property Electrical density of states at 0, 50 and 100 GPa were calculated. Insulator to metal transition? (P > 100 GPa)
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- Purpose of this experiment the insulator to metal transition in AlH 3 To observe the crystal structure under high pressure X-ray diffraction measurement electrical resistance measurement were performed under high pressure.
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- Experimental method X-ray diffraction measurement ( at European Synchrotron Radiation Facility) ( P < 110 GPa, T = 300 K) Electrical resistance measurement ( P < 164 GPa, 4 K < T < 300 K) quasi-four-probe measurements pressure gauge : ruby fluorescence Raman pressure medium : no use pressure medium : hydrogen wavelength is 0.412 Sample : AlH 3 Pressure generator : DAC The image of DAC
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- Result (X-ray diffraction) X-ray diffraction patterns of AlH 3 The structure is simple. Aluminum atoms forms bcc. Structural transition occurs At 63 GPa, Phase to Phase (P1 structure) At 100 GPa, Phase to Phase Hydrogen atom ? Experimental diffraction pattern Pattern of P1
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- Discussion Phase Crystal structure or P > 100 GPa Al-H distance: 1.72 H-H distance: 1.54 At 110 GPa, Calculated enthalpy in the R-3C, Im-3m, Pm-3n
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- Discussion Phase Partial hydrogen volume per H atom in AlH 3 at 100 GPa Partial hydrogen volume per H atom in molecular hydrogen at 300 GPa. Phase is a hydrogen dense phase ! Equal to
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- Result (electrical resistance) Sample becomes dark. Electrical resistance sharply drops. At 100 GPa At 120, 164 GPa, on cooling Electrical resistance shows typical metallic behavior. insulator to metal transition
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- Summary Crystal structure Electrical property R-3c 63100 insulatormetal P1P1Pm-3n 0 P (GPa) At over 100 GPa, Pressure-Induced Hydrogen- Dominant metallic state was observed in AlH 3. Hydrogen dense state
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- Thats all. Thank you for your attention.
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- Al-H distance: 1.7 H-H distance: 2.5
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