Synchrotron X-ray Diffraction Study of BaFe2As2 and CaFe2As2 at High Pressures up to 56 GPa: Ambient and Low-Temperatures Down to 33 K
msra(2010)
摘要
We report high pressure powder synchrotron x-ray diffraction studies on
MFe2As2 (M=Ba, Ca) over a range of temperatures and pressures up to about 56
GPa using a membrane diamond anvil cell. A phase transition to a collapsed
tetragonal phase is observed in both compounds upon compression. However, at
300 (33) K in the Ba-compound the transition occurs at 26 (29) GPa, which is a
much higher pressure than 1.7 (0.3) GPa at 300 (40) K in the Ca-compound, due
to its larger volume. It is important to note that the transition in both
compounds occurs when they are compressed to almost the same value of the unit
cell volume and attain similar ct/at ratios. We also show that the FeAs4
tetrahedra are much less compressible and more distorted in the collapsed
tetragonal phase than their nearly regular shape in the ambient pressure phase.
We present a detailed analysis of the pressure dependence of the structures as
well as equation of states in these important BaFe2As2 and CaFe2As2 compounds.
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关键词
phase transition,equation of state,high pressure,diamond anvil cell
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