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Interpretation of diffuse scattering in the high- T c superconductor HgBa 2 CuO 4+ δ

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ABSTRACT

Published diffuse X-ray scattering from the high-Tc superconductor HgBa2CuO4+δ has been reexamined with a view to developing a model that more satisfactorily accounts for the observed patterns. The present work agrees with the previous conclusion that the doping oxygen atoms form long and isolated interstitial chains that run in both tetragonal directions. However, a distinctly different model is proposed for the accompanying displacement patterns of the atoms surrounding these linear defects. In this new model it is proposed that it is the correlated shifts of the Ba atoms along the length of the defect chains that are the primary source of the observed scattering, and that the variations of intensity in the generated diffuse streaks of scattering originate from lateral shifts of both Hg and Ba atoms away from defects. The new model yields diffraction patterns that are in much more convincing agreement with the observations than the original model.

No MeSH data available.


Model 2 simulation results. (a) A region in the simulation array showing a chain comprising displaced O3 atoms (red) and displaced Ba ions (brown). Blue circles are Hg ions. Parts (b) to (f) are hk0 diffraction patterns calculated with different values of the Ba shift δBa and the size-effect shifts ξBa and ξHg. (b) δBa = 0.3, ξBa = ξHg = 0. (c) δBa = 0.3, ξBa = −0.04. (d) δBa = 0.3, ξBa = 0.04. (e) δBa = 0.3, ξHg = −0.04. (f) δBa = 0.3, ξHg = 0.04.
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fig7: Model 2 simulation results. (a) A region in the simulation array showing a chain comprising displaced O3 atoms (red) and displaced Ba ions (brown). Blue circles are Hg ions. Parts (b) to (f) are hk0 diffraction patterns calculated with different values of the Ba shift δBa and the size-effect shifts ξBa and ξHg. (b) δBa = 0.3, ξBa = ξHg = 0. (c) δBa = 0.3, ξBa = −0.04. (d) δBa = 0.3, ξBa = 0.04. (e) δBa = 0.3, ξHg = −0.04. (f) δBa = 0.3, ξHg = 0.04.

Mentions: Fig. 7 ▸(a) shows schematically the arrangement of ions around a defect for this system. The red O3 atoms are shown to identify the defect but, as for the previous example, they contribute very little to the scattering compared with the displacement scattering of the heavy metal ions (Ba in this case). The brown circles represent Ba ions and the blue circles the Hg ions. The displaced Ba ions are drawn rather larger than the undisplaced ones in order to be able to see them behind the O atoms. Fig. 7 ▸(b) shows the corresponding diffraction pattern obtained for a Ba displacement of δBa = 0.3, with all other ions fixed to their average site positions. The scattering in this picture comes almost entirely from the Ba atoms. As for the case of Model 1, varying the magnitude of this shift affects the relative magnitude of the different orders of diffuse line.


Interpretation of diffuse scattering in the high- T c superconductor HgBa 2 CuO 4+ δ
Model 2 simulation results. (a) A region in the simulation array showing a chain comprising displaced O3 atoms (red) and displaced Ba ions (brown). Blue circles are Hg ions. Parts (b) to (f) are hk0 diffraction patterns calculated with different values of the Ba shift δBa and the size-effect shifts ξBa and ξHg. (b) δBa = 0.3, ξBa = ξHg = 0. (c) δBa = 0.3, ξBa = −0.04. (d) δBa = 0.3, ξBa = 0.04. (e) δBa = 0.3, ξHg = −0.04. (f) δBa = 0.3, ξHg = 0.04.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5391853&req=5

fig7: Model 2 simulation results. (a) A region in the simulation array showing a chain comprising displaced O3 atoms (red) and displaced Ba ions (brown). Blue circles are Hg ions. Parts (b) to (f) are hk0 diffraction patterns calculated with different values of the Ba shift δBa and the size-effect shifts ξBa and ξHg. (b) δBa = 0.3, ξBa = ξHg = 0. (c) δBa = 0.3, ξBa = −0.04. (d) δBa = 0.3, ξBa = 0.04. (e) δBa = 0.3, ξHg = −0.04. (f) δBa = 0.3, ξHg = 0.04.
Mentions: Fig. 7 ▸(a) shows schematically the arrangement of ions around a defect for this system. The red O3 atoms are shown to identify the defect but, as for the previous example, they contribute very little to the scattering compared with the displacement scattering of the heavy metal ions (Ba in this case). The brown circles represent Ba ions and the blue circles the Hg ions. The displaced Ba ions are drawn rather larger than the undisplaced ones in order to be able to see them behind the O atoms. Fig. 7 ▸(b) shows the corresponding diffraction pattern obtained for a Ba displacement of δBa = 0.3, with all other ions fixed to their average site positions. The scattering in this picture comes almost entirely from the Ba atoms. As for the case of Model 1, varying the magnitude of this shift affects the relative magnitude of the different orders of diffuse line.

View Article: PubMed Central - HTML - PubMed

ABSTRACT

Published diffuse X-ray scattering from the high-Tc superconductor HgBa2CuO4+δ has been reexamined with a view to developing a model that more satisfactorily accounts for the observed patterns. The present work agrees with the previous conclusion that the doping oxygen atoms form long and isolated interstitial chains that run in both tetragonal directions. However, a distinctly different model is proposed for the accompanying displacement patterns of the atoms surrounding these linear defects. In this new model it is proposed that it is the correlated shifts of the Ba atoms along the length of the defect chains that are the primary source of the observed scattering, and that the variations of intensity in the generated diffuse streaks of scattering originate from lateral shifts of both Hg and Ba atoms away from defects. The new model yields diffraction patterns that are in much more convincing agreement with the observations than the original model.

No MeSH data available.