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In-plane chemical pressure essential for superconductivity in BiCh2-based (Ch: S, Se) layered structure.

Mizuguchi Y, Miura A, Kajitani J, Hiroi T, Miura O, Tadanaga K, Kumada N, Magome E, Moriyoshi C, Kuroiwa Y - Sci Rep (2015)

Bottom Line: BiCh2-based compounds (Ch: S, Se) are a new series of layered superconductors, and the mechanisms for the emergence of superconductivity in these materials have not yet been elucidated.We show that the structure parameter essential for the emergence of bulk superconductivity in both systems is the in-plane chemical pressure, rather than Bi-Ch bond lengths or in-plane Ch-Bi-Ch bond angle.Furthermore, we show that the superconducting transition temperature for all REO0.5F0.5BiCh2 superconductors can be determined from the in-plane chemical pressure.

View Article: PubMed Central - PubMed

Affiliation: Department of Electrical and Electronic Engineering, Tokyo Metropolitan University, 1-1, Minami-osawa, Hachioji 192-0397, Japan.

ABSTRACT
BiCh2-based compounds (Ch: S, Se) are a new series of layered superconductors, and the mechanisms for the emergence of superconductivity in these materials have not yet been elucidated. In this study, we investigate the relationship between crystal structure and superconducting properties of the BiCh2-based superconductor family, specifically, optimally doped Ce1-xNdxO0.5F0.5BiS2 and LaO0.5F0.5Bi(S1-ySey)2. We use powder synchrotron X-ray diffraction to determine the crystal structures. We show that the structure parameter essential for the emergence of bulk superconductivity in both systems is the in-plane chemical pressure, rather than Bi-Ch bond lengths or in-plane Ch-Bi-Ch bond angle. Furthermore, we show that the superconducting transition temperature for all REO0.5F0.5BiCh2 superconductors can be determined from the in-plane chemical pressure.

No MeSH data available.


Influence of in-plane chemical pressure to crystal structure and superconductivity in Ce1−xNdxO0.5F0.5BiS2 and LaO0.5F0.5Bi(S1−ySey)2.(a) Schematics of changes in crystal structure with increasing in-plane chemical pressure in Ce1−xNdxO0.5F0.5BiS2 and LaO0.5F0.5Bi(S1−ySey)2. In Ce1−xNdxO0.5F0.5BiS2, the volume of spacer layer decreases with increasing Nd concentration (x), and Bi-S plane is compressed; hence, in-plane chemical pressure is enhanced. In LaO0.5F0.5Bi(S1−ySey)2, the volume of superconducting Bi-Ch1 layer increases with increasing Se concentration (y). However, the expansion of Bi-Ch1 plane is smaller than that expected from the ionic radii of S2− and Se2− because the composition of the spacer layer (LaO layer) remains constant; hence, in-plane chemical pressure is enhanced as well as in Ce1−xNdxO0.5F0.5BiS2. (b) In-plane chemical pressure of Ce1−xNdxO0.5F0.5BiS2 and LaO0.5F0.5Bi(S1−ySey)2, calculated using equation (1), are plotted as a function of x (or y). In both systems, bulk SC is induced with increasing chemical pressure. The dashed line at an in-plane chemical pressure of ~1.011 is an estimated boundary of Bulk-SC and non-SC regions.
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f3: Influence of in-plane chemical pressure to crystal structure and superconductivity in Ce1−xNdxO0.5F0.5BiS2 and LaO0.5F0.5Bi(S1−ySey)2.(a) Schematics of changes in crystal structure with increasing in-plane chemical pressure in Ce1−xNdxO0.5F0.5BiS2 and LaO0.5F0.5Bi(S1−ySey)2. In Ce1−xNdxO0.5F0.5BiS2, the volume of spacer layer decreases with increasing Nd concentration (x), and Bi-S plane is compressed; hence, in-plane chemical pressure is enhanced. In LaO0.5F0.5Bi(S1−ySey)2, the volume of superconducting Bi-Ch1 layer increases with increasing Se concentration (y). However, the expansion of Bi-Ch1 plane is smaller than that expected from the ionic radii of S2− and Se2− because the composition of the spacer layer (LaO layer) remains constant; hence, in-plane chemical pressure is enhanced as well as in Ce1−xNdxO0.5F0.5BiS2. (b) In-plane chemical pressure of Ce1−xNdxO0.5F0.5BiS2 and LaO0.5F0.5Bi(S1−ySey)2, calculated using equation (1), are plotted as a function of x (or y). In both systems, bulk SC is induced with increasing chemical pressure. The dashed line at an in-plane chemical pressure of ~1.011 is an estimated boundary of Bulk-SC and non-SC regions.

Mentions: Figure 3a shows schematics of compression or expansion of the Bi-Ch plane caused by Nd or Se substitution. In Ce1−xNdxO0.5F0.5BiS2, Bi-Ch1 planes are compressed owing to a decrease in the volume of spacer layers with increasing Nd concentration. The compression of the Bi-Ch1 plane results in an enhancement of the packing density of Bi2.5+ and S2− ions within the superconducting plane: this is the so-called in-plane chemical pressure. In LaO0.5F0.5Bi(S1−ySey)2, the in-plane Bi-Ch1 distance increases with increasing occupancy of Se at the Ch1 site. However, the increase of the in-plane Bi-Ch1 distance is smaller than that expected from the difference in the ionic radii of S2− and Se2− because the composition of the spacer layer (LaO) remains constant in LaO0.5F0.5Bi(S1−ySey)2. Therefore, the packing density of Bi2.5+ and Ch2− ions in the superconducting plane is enhanced. This situation is similar to the enhancement of in-plane chemical pressure in Ce1−xNdxO0.5F0.5BiS2. In order to compare the magnitude of in-plane chemical pressure in the two series, we define in-plane chemical pressure using equation (1).


In-plane chemical pressure essential for superconductivity in BiCh2-based (Ch: S, Se) layered structure.

Mizuguchi Y, Miura A, Kajitani J, Hiroi T, Miura O, Tadanaga K, Kumada N, Magome E, Moriyoshi C, Kuroiwa Y - Sci Rep (2015)

Influence of in-plane chemical pressure to crystal structure and superconductivity in Ce1−xNdxO0.5F0.5BiS2 and LaO0.5F0.5Bi(S1−ySey)2.(a) Schematics of changes in crystal structure with increasing in-plane chemical pressure in Ce1−xNdxO0.5F0.5BiS2 and LaO0.5F0.5Bi(S1−ySey)2. In Ce1−xNdxO0.5F0.5BiS2, the volume of spacer layer decreases with increasing Nd concentration (x), and Bi-S plane is compressed; hence, in-plane chemical pressure is enhanced. In LaO0.5F0.5Bi(S1−ySey)2, the volume of superconducting Bi-Ch1 layer increases with increasing Se concentration (y). However, the expansion of Bi-Ch1 plane is smaller than that expected from the ionic radii of S2− and Se2− because the composition of the spacer layer (LaO layer) remains constant; hence, in-plane chemical pressure is enhanced as well as in Ce1−xNdxO0.5F0.5BiS2. (b) In-plane chemical pressure of Ce1−xNdxO0.5F0.5BiS2 and LaO0.5F0.5Bi(S1−ySey)2, calculated using equation (1), are plotted as a function of x (or y). In both systems, bulk SC is induced with increasing chemical pressure. The dashed line at an in-plane chemical pressure of ~1.011 is an estimated boundary of Bulk-SC and non-SC regions.
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Related In: Results  -  Collection

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f3: Influence of in-plane chemical pressure to crystal structure and superconductivity in Ce1−xNdxO0.5F0.5BiS2 and LaO0.5F0.5Bi(S1−ySey)2.(a) Schematics of changes in crystal structure with increasing in-plane chemical pressure in Ce1−xNdxO0.5F0.5BiS2 and LaO0.5F0.5Bi(S1−ySey)2. In Ce1−xNdxO0.5F0.5BiS2, the volume of spacer layer decreases with increasing Nd concentration (x), and Bi-S plane is compressed; hence, in-plane chemical pressure is enhanced. In LaO0.5F0.5Bi(S1−ySey)2, the volume of superconducting Bi-Ch1 layer increases with increasing Se concentration (y). However, the expansion of Bi-Ch1 plane is smaller than that expected from the ionic radii of S2− and Se2− because the composition of the spacer layer (LaO layer) remains constant; hence, in-plane chemical pressure is enhanced as well as in Ce1−xNdxO0.5F0.5BiS2. (b) In-plane chemical pressure of Ce1−xNdxO0.5F0.5BiS2 and LaO0.5F0.5Bi(S1−ySey)2, calculated using equation (1), are plotted as a function of x (or y). In both systems, bulk SC is induced with increasing chemical pressure. The dashed line at an in-plane chemical pressure of ~1.011 is an estimated boundary of Bulk-SC and non-SC regions.
Mentions: Figure 3a shows schematics of compression or expansion of the Bi-Ch plane caused by Nd or Se substitution. In Ce1−xNdxO0.5F0.5BiS2, Bi-Ch1 planes are compressed owing to a decrease in the volume of spacer layers with increasing Nd concentration. The compression of the Bi-Ch1 plane results in an enhancement of the packing density of Bi2.5+ and S2− ions within the superconducting plane: this is the so-called in-plane chemical pressure. In LaO0.5F0.5Bi(S1−ySey)2, the in-plane Bi-Ch1 distance increases with increasing occupancy of Se at the Ch1 site. However, the increase of the in-plane Bi-Ch1 distance is smaller than that expected from the difference in the ionic radii of S2− and Se2− because the composition of the spacer layer (LaO) remains constant in LaO0.5F0.5Bi(S1−ySey)2. Therefore, the packing density of Bi2.5+ and Ch2− ions in the superconducting plane is enhanced. This situation is similar to the enhancement of in-plane chemical pressure in Ce1−xNdxO0.5F0.5BiS2. In order to compare the magnitude of in-plane chemical pressure in the two series, we define in-plane chemical pressure using equation (1).

Bottom Line: BiCh2-based compounds (Ch: S, Se) are a new series of layered superconductors, and the mechanisms for the emergence of superconductivity in these materials have not yet been elucidated.We show that the structure parameter essential for the emergence of bulk superconductivity in both systems is the in-plane chemical pressure, rather than Bi-Ch bond lengths or in-plane Ch-Bi-Ch bond angle.Furthermore, we show that the superconducting transition temperature for all REO0.5F0.5BiCh2 superconductors can be determined from the in-plane chemical pressure.

View Article: PubMed Central - PubMed

Affiliation: Department of Electrical and Electronic Engineering, Tokyo Metropolitan University, 1-1, Minami-osawa, Hachioji 192-0397, Japan.

ABSTRACT
BiCh2-based compounds (Ch: S, Se) are a new series of layered superconductors, and the mechanisms for the emergence of superconductivity in these materials have not yet been elucidated. In this study, we investigate the relationship between crystal structure and superconducting properties of the BiCh2-based superconductor family, specifically, optimally doped Ce1-xNdxO0.5F0.5BiS2 and LaO0.5F0.5Bi(S1-ySey)2. We use powder synchrotron X-ray diffraction to determine the crystal structures. We show that the structure parameter essential for the emergence of bulk superconductivity in both systems is the in-plane chemical pressure, rather than Bi-Ch bond lengths or in-plane Ch-Bi-Ch bond angle. Furthermore, we show that the superconducting transition temperature for all REO0.5F0.5BiCh2 superconductors can be determined from the in-plane chemical pressure.

No MeSH data available.