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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.


The average structure of the high-Tc superconductor HBCO, drawn using the coordinates published by Bertinotti et al. (1996 ▸). (a) A projection down [010], showing how the planar HgOδ layer is sandwiched between two Ba2CuO4 layers. (b) The HgOδ layer shown in projection down [001], showing the O3 interstitial site surrounded by four Hg atoms and sandwiched between Ba atoms in the layers below and above (not shown). The O3 site has an occupancy of δ.
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fig2: The average structure of the high-Tc superconductor HBCO, drawn using the coordinates published by Bertinotti et al. (1996 ▸). (a) A projection down [010], showing how the planar HgOδ layer is sandwiched between two Ba2CuO4 layers. (b) The HgOδ layer shown in projection down [001], showing the O3 interstitial site surrounded by four Hg atoms and sandwiched between Ba atoms in the layers below and above (not shown). The O3 site has an occupancy of δ.

Mentions: To understand these materials it is not sufficient to know their average unit-cell structure as revealed by Bragg scattering. It requires additionally knowledge of their local or nanoscale structure – information that can only be obtained from the diffuse scattering component of the total scattering. Considering the above examples, it is perhaps quite surprising that, while there have been many studies of single-crystal diffuse scattering for alloys and ferroelectric materials, there have been very few for high-Tc superconductors. The reasons for this are not apparent, since the experiments reported by Izquierdo et al. (2011 ▸) for the high-Tc superconductor HgBa2CuO4+δ (hereinafter referred to as HBCO) showed that very detailed single-crystal diffuse scattering (SCDS) patterns are readily obtainable using synchrotron radiation. An example section of data obtained by these authors is shown in Fig. 1 ▸(a) for reference. A diagram of the average structure of HBCO is shown in Fig. 2 ▸.


Interpretation of diffuse scattering in the high- T c superconductor HgBa 2 CuO 4+ δ
The average structure of the high-Tc superconductor HBCO, drawn using the coordinates published by Bertinotti et al. (1996 ▸). (a) A projection down [010], showing how the planar HgOδ layer is sandwiched between two Ba2CuO4 layers. (b) The HgOδ layer shown in projection down [001], showing the O3 interstitial site surrounded by four Hg atoms and sandwiched between Ba atoms in the layers below and above (not shown). The O3 site has an occupancy of δ.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

fig2: The average structure of the high-Tc superconductor HBCO, drawn using the coordinates published by Bertinotti et al. (1996 ▸). (a) A projection down [010], showing how the planar HgOδ layer is sandwiched between two Ba2CuO4 layers. (b) The HgOδ layer shown in projection down [001], showing the O3 interstitial site surrounded by four Hg atoms and sandwiched between Ba atoms in the layers below and above (not shown). The O3 site has an occupancy of δ.
Mentions: To understand these materials it is not sufficient to know their average unit-cell structure as revealed by Bragg scattering. It requires additionally knowledge of their local or nanoscale structure – information that can only be obtained from the diffuse scattering component of the total scattering. Considering the above examples, it is perhaps quite surprising that, while there have been many studies of single-crystal diffuse scattering for alloys and ferroelectric materials, there have been very few for high-Tc superconductors. The reasons for this are not apparent, since the experiments reported by Izquierdo et al. (2011 ▸) for the high-Tc superconductor HgBa2CuO4+δ (hereinafter referred to as HBCO) showed that very detailed single-crystal diffuse scattering (SCDS) patterns are readily obtainable using synchrotron radiation. An example section of data obtained by these authors is shown in Fig. 1 ▸(a) for reference. A diagram of the average structure of HBCO is shown in Fig. 2 ▸.

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.