Pressure-Induced Hydrogen-dominant metallic state in Aluminum Hydride HAGIHARA Toshiya Shimizu-group...
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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, 04550 4 (2008)
Pressure-Induced Hydrogen-dominant metallic state in Aluminum Hydride HAGIHARA Toshiya Shimizu-group Igor Goncharenko et al., Phy. Rev. Lett. 100, 045504
Pressure-Induced Hydrogen-dominant metallic state in Aluminum
Hydride HAGIHARA Toshiya Shimizu-group Igor Goncharenko et al.,
Phy. Rev. Lett. 100, 045504 (2008)
Slide 2
Contents Introduction theoretical prediction of hydrogen under
high pressure why hydrides previous studies on AlH 3 Experimental
method Result & discussion Summary
Slide 3
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
Slide 4
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.
Slide 5
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.
Slide 6
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
Slide 7
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)
Slide 8
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.
Slide 9
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
Slide 10
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
Slide 11
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
Slide 12
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
Slide 13
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
Slide 14
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