RESUMO
This corrects the article DOI: 10.1103/PhysRevLett.107.025501.
RESUMO
Europium hydride EuH(x), when exposed to high-pressure H2, has been found to exhibit the following structural and valence changes: Pnma(x = 2, divalent) â P63/mmc(x = 2, 7.2-8.7 GPa) â I4/m(x > 2, 8.7-9.7 GPa) â I4/mmm(x > 2, 9.7 GPa-,trivalent). With a trivalent character and a distorted cubic fcc structure, the I4/mmm structure is the ß phase commonly observed for other rare-earth metal hydrides. Our study clearly demonstrates that EuH(x) is no longer an irregular member of the rare-earth metal hydrides.
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Near ambient pressures, molecular diffusion dominates protonic diffusion in ice. Theoretical studies have predicted that protonic diffusion will dominate at high pressures in ice. We measured the protonic diffusion coefficient for the highest temperature molecular phase of ice VII at 400 kelvin over its entire stable pressure region. The values ranged from 10(-17) to 10(-15) square meters per second at pressures of 10 to 63 gigapascals. The diffusion coefficients extrapolated to high temperatures close to the ice VII melting curve were less by a factor of 10(2) to 10(3) than a superionic criterion of approximately 10(-8) square meters per second, at which protons would diffuse freely.
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The "devil's staircase"-type phase transition in the quarter-filled spin-ladder compound NaV2O5 has been discovered at low temperature and high pressure by synchrotron radiation x-ray diffraction. A large number of transitions are found to successively take place among higher-order commensurate phases with 2a x 2b x zc type superstructures. The observed temperature and pressure dependence of modulation wave number q(c), defined by 1/z, is well reproduced by the axial next nearest neighbor Ising model. The q(c) is suggested to reflect atomic displacements presumably coupled with charge ordering in this system.