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Calcium fluoride as an internal pressure standard in high‐pressure crystallography
Author(s) -
Hazen R. M.,
Finger L. W.
Publication year - 1981
Publication title -
journal of applied crystallography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.429
H-Index - 162
ISSN - 1600-5767
DOI - 10.1107/s0021889881009266
Subject(s) - fluorite , volume (thermodynamics) , diffraction , chemistry , analytical chemistry (journal) , thermocouple , atmospheric temperature range , single crystal , crystal (programming language) , thermodynamics , materials science , crystallography , optics , composite material , physics , programming language , organic chemistry , chromatography , computer science
Cleavage plates of fluorite, CaF 2 , provide a simple and sensitive pressure calibration based on variation of the cubic unit‐cell volume in high‐pressure/high‐temperature ( PT ) single‐crystal diffraction experiments, when temperature is measured independently by thermocouple. Over the range 0 ≤ T ≤ 500°C and P ≤ 0.04 Mbar (4 GPa), the temperature–pressure–volume equation of state for CaF 2 is approximately, where ΔV / V o is the fractional change in cubic unit‐cell volume from T = 0°C and P = 0 Mbar, T is temperature in °C, and P is pressure in Mbar. Crystal structures of CaF 2 determined at several PT conditions are evidence of reversibility of single‐crystal unit‐cell parameters with heating and compression. Nonreversible changes occurred in observed temperature factors and extinction parameter.