Polymorphism in Hydrogen Iodide

Mauer, F. A.; Keffer, Charles; Reeves, Raymond; Robinson, Dean W.

doi:10.1063/1.1696143

Cited by 9 publications

(2 citation statements)

References 8 publications

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“…HI is an aggressive toxic gas at room temperature, freezing as a clear solid at 222 K in an fee structure 4 with a zero-pressure molar volume of 34.9 cmVmole at r=5 K. 5 Two structural phase transitions take place at lower pressures and temperatures; although the structures are not known, they are probably similar to the other hydrogen halides. 6 The molar volume at which a MI transition takes place can be estimated by a simple model.…”

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confidence: 99%

Observation of Metal-insulator and Metal-Metal Transitions in Hydrogen Iodide under Pressure

Straaten

Silvera

1986

Phys. Rev. Lett.

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Hydrogen iodide has been studied up to pressures of 70 GPa at low temperatures in a diamondanvil cell. Electrical-conductivity and optical measurements have been used to observe pressureinduced phase transitions which are interpreted as follows: First a metal-insulator transition takes place in the molecular solid; with increased pressure a metal-metal molecular-to-atomic transition occurs. An additional transition due to intrinsic impurities has been observed. Implications for metallic hydrogen are discussed. PACS numbers: 71.30. + H, 62.50. + p, 64.70.Kb Metal-insulator (MI) transitions in solids are currently of great experimental and theoretical interest. H 2 is the prototype for molecular solids and is predicted to have transitions due to band-gap closure from molecular insulator to molecular metal to atomic metal 1 at very high pressure; such transitions have been observed in I 2 . 2 A second type of MI transition occurs in heterogeneous systems such as doped semiconductors when the density is such that the electrons in effective Bohr orbits of the impurity atoms overlap. 3 Our observations on HI under pressures up to 70 GPa indicate two transitions at pressures of 42.5 and 51 GPa. The first we interpret as a molecular-insulator to molecular-metal transition; the second as a molecularmetal to atomic-metal transition. In addition, light, pressure, and elevated temperatures stimulate the formation of intrinsic impurities that we believe are If anions in acceptor states. We have also observed MI transitions in doped HI at sufficiently high pressure or impurity density. Our experimental techniques have included optical and uv transmission, Raman scattering, four-terminal electrical conductivity, and photoconductivity in a diamond-anvil cell at temperatures down to 5 K.HI is an aggressive toxic gas at room temperature, freezing as a clear solid at 222 K in an fee structure 4 with a zero-pressure molar volume of 34.9 cmVmole at r=5 K. 5 Two structural phase transitions take place at lower pressures and temperatures; although the structures are not known, they are probably similar to the other hydrogen halides. 6 The molar volume at which a MI transition takes place can be estimated by a simple model. In the Herzfeld approach 7 the dielectric constant becomes infinite at the MI transition, or, by use of the Lorentz-Lorenz relationships, (/7 2 -l)/(/1 2 -+-2)=(€~l)/(€+2)=i?/K,which is equal to 1 at the MI transition. If the molar refraction, i?, is independent of pressure then R = V m , the metallization volume. The index of refraction of liquid HI is 1.466 8 at an estimated volume of 49.76 cmVmole, 9 which yields V m = 13.76 cmVmole.Although the equation of state of HI has not been measured, Stewart 10 has studied HC1 and HBr to 20 kbar. Assuming the equation of state of HI to be similar, with a zero-pressure volume V 0 of 34.9 cmVmole, 5 we find 11 for the metallization pressure corresponding to V m , P m = 51.4 GPa. We can check the result for V m by considering HI as one of a family of metal hydrides. 12 In ...

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Observation of Metal-insulator and Metal-Metal Transitions in Hydrogen Iodide under Pressure

Straaten

Silvera

1986

Phys. Rev. Lett.

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“…Such hydrogen-bonding is, however, relatively weak. At low temperatures hydrogen iodide differs from the chloride and bromide in adopting an ordered face-centred tetragonal lattice 451 . At higher temperatures, all the solids appear to assume disordered face-centred cubic lattices, again with four molecules per unit cell 426 » 451 » 452 .…”

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Chlorine, Bromine, Iodine and Astatine

Downs

Adams

1973

The Chemistry of Chlorine, Bromine, Iodine and Astatine

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Raman and infrared spectra of crystalline hydrogen iodide and deuterium iodide

Anderson

Torrie

Tse

1979

J Raman Spectroscopy

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I y 110-2 loo-? I-" -a) 9 0 -80 7 0Raman and infrared spectra of the three phases of crystalline HI and DI have been recorded, and mode frequencies corresponding to molecular vibrations, librations and translations are identified. A comparison with the spectra of solid HCI and HBr confirms that only the low temperature phase has an ordered structure. A simple force constant model is described which is used to assign the observed frequencies for this phase. ---

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Polymorphism in Hydrogen Iodide

Cited by 9 publications

References 8 publications

Observation of Metal-insulator and Metal-Metal Transitions in Hydrogen Iodide under Pressure

Observation of Metal-insulator and Metal-Metal Transitions in Hydrogen Iodide under Pressure

Chlorine, Bromine, Iodine and Astatine

Raman and infrared spectra of crystalline hydrogen iodide and deuterium iodide

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