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Title: Defect studies of molecular and rare gas crystals down to 50 mK and up to 150 MPa using X-ray diffraction

Abstract

Special challenges face the scientist interested in structural transformations in molecular crystals under unusual conditions of temperature and specimen volatility especially when the materials have either very small or very large scattering amplitudes. Techniques have been developed to prepare single crystals of condensed gases of mm or larger size, to ascertain their degree of crystalline perfection and fix their orientation, to measure Bragg spacings, changes in Bragg spacings and intensities. For precise work at higher temperatures and pressures a Be specimen cell attached to a heat exchanger is used at the focus of a large orientable back-reflection camera. Phase transitions arising from changes in molecular rotational ordering in solid CH/sub 4/ and CD/sub 4/ and lattice parameters during sublimation and melting of solid Ar, Kr, and Xe have thus been studied. For lower temperatures, the x-ray scattering specimen cell is fixed to a helium dilution refrigerator. In case 1), the known fcc form of solid hydrogen, stable below about 2 K for ortho-rich material, was determined by J. V. Gates and coworkers to transform to hcp form at lower concentrations and temperatures. The transformation temperatures and compositions could be followed, despite internal specimen heating due to spontaneous ortho- to para-conversion,more » below 200 mK. In case 2), x-ray studies of isotopic phase separation in /sup 3/He--/sup 4/He bcc solids were carried out by B. A. Fraass.« less

Authors:
Publication Date:
Research Org.:
Department of Physics and Materials Research Laboratory, University of Illinois at Urbana-Champaign, 1110 West Green, Urbana, Illinois 61801
OSTI Identifier:
5830593
Resource Type:
Journal Article
Journal Name:
Trans. Am. Crystallogr. Assoc.; (United States)
Additional Journal Information:
Journal Volume: 17:1
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; ARGON; EQUATIONS OF STATE; LATTICE PARAMETERS; X-RAY DIFFRACTION; HELIUM; CRYSTAL-PHASE TRANSFORMATIONS; HYDROGEN; KRYPTON; METHANE; XENON; CRYSTAL STRUCTURE; HIGH PRESSURE; MOLECULAR CRYSTALS; ORDER-DISORDER TRANSFORMATIONS; ULTRALOW TEMPERATURE; ALKANES; COHERENT SCATTERING; CRYSTALS; DIFFRACTION; ELEMENTS; EQUATIONS; FLUIDS; GASES; HYDROCARBONS; NONMETALS; ORGANIC COMPOUNDS; PHASE TRANSFORMATIONS; RARE GASES; SCATTERING; 360602* - Other Materials- Structure & Phase Studies

Citation Formats

Simmons, R O. Defect studies of molecular and rare gas crystals down to 50 mK and up to 150 MPa using X-ray diffraction. United States: N. p., 1981. Web.
Simmons, R O. Defect studies of molecular and rare gas crystals down to 50 mK and up to 150 MPa using X-ray diffraction. United States.
Simmons, R O. 1981. "Defect studies of molecular and rare gas crystals down to 50 mK and up to 150 MPa using X-ray diffraction". United States.
@article{osti_5830593,
title = {Defect studies of molecular and rare gas crystals down to 50 mK and up to 150 MPa using X-ray diffraction},
author = {Simmons, R O},
abstractNote = {Special challenges face the scientist interested in structural transformations in molecular crystals under unusual conditions of temperature and specimen volatility especially when the materials have either very small or very large scattering amplitudes. Techniques have been developed to prepare single crystals of condensed gases of mm or larger size, to ascertain their degree of crystalline perfection and fix their orientation, to measure Bragg spacings, changes in Bragg spacings and intensities. For precise work at higher temperatures and pressures a Be specimen cell attached to a heat exchanger is used at the focus of a large orientable back-reflection camera. Phase transitions arising from changes in molecular rotational ordering in solid CH/sub 4/ and CD/sub 4/ and lattice parameters during sublimation and melting of solid Ar, Kr, and Xe have thus been studied. For lower temperatures, the x-ray scattering specimen cell is fixed to a helium dilution refrigerator. In case 1), the known fcc form of solid hydrogen, stable below about 2 K for ortho-rich material, was determined by J. V. Gates and coworkers to transform to hcp form at lower concentrations and temperatures. The transformation temperatures and compositions could be followed, despite internal specimen heating due to spontaneous ortho- to para-conversion, below 200 mK. In case 2), x-ray studies of isotopic phase separation in /sup 3/He--/sup 4/He bcc solids were carried out by B. A. Fraass.},
doi = {},
url = {https://www.osti.gov/biblio/5830593}, journal = {Trans. Am. Crystallogr. Assoc.; (United States)},
number = ,
volume = 17:1,
place = {United States},
year = {1981},
month = {10}
}