Exploring High-Pressure Transformations in Low-Z (H2, Ne) Hydrates at Low Temperatures

The high pressure structural behavior of H2 and Ne clathrate hydrates with approximate composition H2/Ne·~4H2O and featuring cubic structure II (CS-II) was investigated by neutron powder diffraction using the deuterated analogues at ~95 K. CS-II hydrogen hydrate transforms gradually to isocompositional C1 phase (filled ice II) at around 1.1 GPa but may be metastably retained up to 2.2 GPa. Above 3 GPa a gradual decomposition into C2 phase (H2·H2O, filled ice Ic) and ice VIII’ takes place. Upon heating to 200 K the CS-II to C1 transition completes instantly whereas C1 decomposition appears sluggish also at 200 K. C1 was observed metastably up to 8 GPa. At 95 K C1 and C2 hydrogen hydrate can be retained below 1 GPa and yield ice II and ice Ic, respectively, upon complete release of pressure. In contrast, CS-II neon hydrate undergoes pressure-induced amorphization at 1.9 GPa, thus following the general trend for noble gas clathrate hydrates. Upon heating to 200 K amorphous Ne hydrate crystallizes as a mixture of previously unreported C2 hydrate and ice VIII’.

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First Experiments with a Newly Developed High-Pressure/High-Temperature Cell for Neutron Powder Diffraction

Materials Science Forum ◽

10.4028/www.scientific.net/msf.79-82.427 ◽

1991 ◽

Vol 79-82 ◽

pp. 427-432

Author(s):

K. Fütterer ◽

Wulf Depmeier ◽

J. Strobel ◽

T. Vogt

Keyword(s):

High Pressure ◽

High Temperature ◽

Powder Diffraction ◽

Neutron Powder Diffraction ◽

High Pressure High Temperature

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Isothermal equation of state and high-pressure phase transitions of synthetic meridianiite (MgSO4·11D2O) determined by neutron powder diffraction and quasielastic neutron spectroscopy

Acta Crystallographica Section B Structural Science Crystal Engineering and Materials ◽

10.1107/s2052520616018254 ◽

2017 ◽

Vol 73 (1) ◽

pp. 33-46 ◽

Cited By ~ 8

Author(s):

A. Dominic Fortes ◽

Felix Fernandez-Alonso ◽

Matthew Tucker ◽

Ian G. Wood

Keyword(s):

High Pressure ◽

Phase Transitions ◽

Equation Of State ◽

Powder Diffraction ◽

Diffraction Data ◽

Neutron Powder Diffraction ◽

Bulk Liquid ◽

Icy Satellites ◽

Neutron Spallation Source ◽

Quasielastic Neutron

We have collected neutron powder diffraction data from MgSO4·11D2O (the deuterated analogue of meridianiite), a highly hydrated sulfate salt that is thought to be a candidate rock-forming mineral in some icy satellites of the outer solar system. Our measurements, made using the PEARL/HiPr and OSIRIS instruments at the ISIS neutron spallation source, covered the range 0.1 < P < 800 MPa and 150 < T < 280 K. The refined unit-cell volumes as a function of P and T are parameterized in the form of a Murnaghan integrated linear equation of state having a zero-pressure volume V 0 = 706.23 (8) Å3, zero-pressure bulk modulus K 0 = 19.9 (4) GPa and its first pressure derivative, K′ = 9 (1). The structure's compressibility is highly anisotropic, as expected, with the three principal directions of the unit-strain tensor having compressibilities of 9.6 × 10−3, 3.4 × 10−2 and 3.4 × 10−3 GPa−1, the most compressible direction being perpendicular to the long axis of a discrete hexadecameric water cluster, (D2O)16. At high pressure we observed two different phase transitions. First, warming of MgSO4·11D2O at 545 MPa resulted in a change in the diffraction pattern at 275 K consistent with partial (peritectic) melting; quasielastic neutron spectra collected simultaneously evince the onset of the reorientational motion of D2O molecules with characteristic time-scales of 20–30 ps, longer than those found in bulk liquid water at the same temperature and commensurate with the lifetime of solvent-separated ion pairs in aqueous MgSO4. Second, at ∼ 0.9 GPa, 240 K, MgSO4·11D2O decomposed into high-pressure water ice phase VI and MgSO4·9D2O, a recently discovered phase that has hitherto only been formed at ambient pressure by quenching small droplets of MgSO4(aq) in liquid nitrogen. The fate of the high-pressure enneahydrate on further compression and warming is not clear from the neutron diffraction data, but its occurrence indicates that it may also be a rock-forming mineral in the deep mantles of large icy satellites.

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Neutron powder diffraction study of (ND4)2SeCl6 under high pressure

Physica B Condensed Matter ◽

10.1016/s0921-4526(97)00621-2 ◽

1997 ◽

Vol 241-243 ◽

pp. 466-468 ◽

Cited By ~ 3

Author(s):

O Yamamuro ◽

K Okishiro ◽

T Matsuo ◽

T Ohta ◽

Y Kume ◽

...

Keyword(s):

High Pressure ◽

Diffraction Study ◽

Powder Diffraction ◽

Neutron Powder Diffraction

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LOW TEMPERATURE NEUTRON DIFFRACTION ON CONGRUENT AND NEAR STOICHIOMETRIC LiNbO3

Modern Physics Letters B ◽

10.1142/s0217984912501424 ◽

2012 ◽

Vol 26 (22) ◽

pp. 1250142 ◽

Cited By ~ 1

Author(s):

SHUHUA YAO ◽

YUANHUA SANG ◽

DEHONG YU ◽

MAXIM AVDEEV ◽

HONG LIU ◽

...

Keyword(s):

Low Temperature ◽

Low Temperatures ◽

Structural Features ◽

Neutron Powder Diffraction ◽

Structural Behavior ◽

Li Isotope ◽

Anisotropic Displacement Parameters ◽

Li Content ◽

Large Disorder ◽

Mg Doped

Neutron powder diffraction has been carried out on a congruent LiNbO 3 sample containing 7 Li isotope ( C 7 LN ) and a near stoichiometric Mg doped LiNbO 3 sample ( Mg : NSLN ) in the temperature range of 4 K and 90 K. Large anisotropic displacement parameters (ADPs) of the Li ions have shown evidence of large disorder along the c-axis for both samples. The results have shown no evidence for the existence of anomalous structural behavior for both samples at low temperatures, although abnormal structural features at 55 K and 100 K for a LiNbO 3 crystal having different Li content as the samples used in the present studies have been observed by Fernandez-Ruiz et al. [Phys. Rev. B72 (2005) 184108].

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