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Electronic Topological Transition in Ag2Te at High-pressure.

Zhang Y, Li Y, Ma Y, Li Y, Li G, Shao X, Wang H, Cui T, Wang X, Zhu P - Sci Rep (2015)

Bottom Line: Here, a pressure-induced electronic topological transition (ETT) is firstly found in Ag2Te at 1.8 GPa.This result indicates that the best bulk insulating character and topological nature in Ag2Te can be obtained at this pressure.A pressure-induced metallization in Ag2Te is confirmed by the results of temperature-dependent resistivity measurements.

View Article: PubMed Central - PubMed

Affiliation: State Key Laboratory of Superhard Materials, College of Physics, Jilin University, Changchun 130012, China.

ABSTRACT
Recently, Ag2Te was experimentally confirmed to be a 3D topological insulator (TI) at ambient pressure. However, the high-pressure behaviors and properties of Ag2Te were rarely reported. Here, a pressure-induced electronic topological transition (ETT) is firstly found in Ag2Te at 1.8 GPa. Before ETT, the positive pressure coefficient of bulk band-gap, which is firstly found in TIs family, is found by both first-principle calculations and in situ high-pressure resistivity measurements. The electrical resistivity obtained at room temperature shows a maximum at 1.8 GPa, which is nearly 3.3 times to that at ambient pressure. This result indicates that the best bulk insulating character and topological nature in Ag2Te can be obtained at this pressure. Furthermore, the high-pressure structural behavior of Ag2Te has been investigated by in situ high-pressure synchrotron powder X-ray diffraction technique up to 33.0 GPa. The accurate pressure-induced phase transition sequence is firstly determined as P21/c → Cmca → Pnma. It is worth noting that the reported isostructural P21/c phase is not existed, and the reported structure of Cmca phase is corrected by CALYPSO methodology. The second high-pressure structure, a long puzzle to previous reports, is determined as Pnma phase. A pressure-induced metallization in Ag2Te is confirmed by the results of temperature-dependent resistivity measurements.

No MeSH data available.


Angle dispersive X-ray powder diffraction patterns of Ag2Te under high pressure at room temperature.Arrow and asterisk represent new diffraction peaks.
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f1: Angle dispersive X-ray powder diffraction patterns of Ag2Te under high pressure at room temperature.Arrow and asterisk represent new diffraction peaks.

Mentions: With increasing pressure, the first and the second pressure-induced structural transitions of Ag2Te occur at 2.2 and 11.3 GPa, respectively, which are illustrated in Fig. 1 by the onsets of new peaks. Based on the decompression data, all structural phase transitions are reversible. As can be seen in Supplementary Fig. S1(a,b), Rietveld refinement of ADXRD patterns indicate that the P21/c phase is retained up to 2.0 GPa. By comparing our Supplementary Fig. S2 with Fig. 1 and Supplementary Fig. S3 in ref. 24, it is clear that our ADXRD patterns of Cmca phase are distinct different with those of previous report in intensity sequence of peaks such as (202), (023), (204), and (221) in 3.2–9.5 GPa region. Moreover, a bad fitting result was obtained, when the previously proposed structure of Cmca phase was used to carry out Rietveld refinement. So, in order to determine the crystal structure of this phase, the structure prediction via CALYPSO methodology28 was performed and a corrected structure of Cmca phase was obtained. The corrected structure can result in a good Rietveld fitting (see Supplementary Fig. S3), and the detailed refinement result is shown in Supplementary Table S1. The distinct difference between the corrected structure and the reported structure is mainly in the internal coordinates of atoms. On the other hand, as shown in Supplementary Fig. S4(a), the pattern is well fitted by a combination of P21/c and Cmca phase at 2.2 GPa, and the inset indicates that the (023) characteristic peak of the Cmca phase can be observed at 2θ = 13.7°, which is ignored by Zhao et al. The detailed refinement result for 2.2 GPa are located in Table 1. From Supplementary Fig. S4(b) and the inset of it, it is clear that the first transition is not completed up to 2.6 GPa. Thus, the XRD pattern of 2.4 GPa, measured by previous report, in fact represents mixed structures of P21/c and Cmca phase rather than an isostructural P21/c phase24. When the pressure increase, the second structural transition emerged at 11.3 GPa with a new peak marked at 2θ = 14.3°, and the characteristic peak (marked by asterisk) of the second high-pressure phase become gradually stronger as the pressure increases to 19.2 GPa (see Supplementary Fig. S5(a,b)). By the known structures of A2B compounds23, the long-puzzling high-pressure phase has been assigned to an orthorhombic structure (space group Pnma, No.62). The diffraction data of 25.5 GPa can be well fitted by coexistence of Cmca and Pnma phase, as shown in Supplementary Fig. S6, and the detailed refinement result can be found in Table 2. The second high-pressure phase transition is not finished up to 33.0 GPa, the highest pressure measured here.


Electronic Topological Transition in Ag2Te at High-pressure.

Zhang Y, Li Y, Ma Y, Li Y, Li G, Shao X, Wang H, Cui T, Wang X, Zhu P - Sci Rep (2015)

Angle dispersive X-ray powder diffraction patterns of Ag2Te under high pressure at room temperature.Arrow and asterisk represent new diffraction peaks.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4588579&req=5

f1: Angle dispersive X-ray powder diffraction patterns of Ag2Te under high pressure at room temperature.Arrow and asterisk represent new diffraction peaks.
Mentions: With increasing pressure, the first and the second pressure-induced structural transitions of Ag2Te occur at 2.2 and 11.3 GPa, respectively, which are illustrated in Fig. 1 by the onsets of new peaks. Based on the decompression data, all structural phase transitions are reversible. As can be seen in Supplementary Fig. S1(a,b), Rietveld refinement of ADXRD patterns indicate that the P21/c phase is retained up to 2.0 GPa. By comparing our Supplementary Fig. S2 with Fig. 1 and Supplementary Fig. S3 in ref. 24, it is clear that our ADXRD patterns of Cmca phase are distinct different with those of previous report in intensity sequence of peaks such as (202), (023), (204), and (221) in 3.2–9.5 GPa region. Moreover, a bad fitting result was obtained, when the previously proposed structure of Cmca phase was used to carry out Rietveld refinement. So, in order to determine the crystal structure of this phase, the structure prediction via CALYPSO methodology28 was performed and a corrected structure of Cmca phase was obtained. The corrected structure can result in a good Rietveld fitting (see Supplementary Fig. S3), and the detailed refinement result is shown in Supplementary Table S1. The distinct difference between the corrected structure and the reported structure is mainly in the internal coordinates of atoms. On the other hand, as shown in Supplementary Fig. S4(a), the pattern is well fitted by a combination of P21/c and Cmca phase at 2.2 GPa, and the inset indicates that the (023) characteristic peak of the Cmca phase can be observed at 2θ = 13.7°, which is ignored by Zhao et al. The detailed refinement result for 2.2 GPa are located in Table 1. From Supplementary Fig. S4(b) and the inset of it, it is clear that the first transition is not completed up to 2.6 GPa. Thus, the XRD pattern of 2.4 GPa, measured by previous report, in fact represents mixed structures of P21/c and Cmca phase rather than an isostructural P21/c phase24. When the pressure increase, the second structural transition emerged at 11.3 GPa with a new peak marked at 2θ = 14.3°, and the characteristic peak (marked by asterisk) of the second high-pressure phase become gradually stronger as the pressure increases to 19.2 GPa (see Supplementary Fig. S5(a,b)). By the known structures of A2B compounds23, the long-puzzling high-pressure phase has been assigned to an orthorhombic structure (space group Pnma, No.62). The diffraction data of 25.5 GPa can be well fitted by coexistence of Cmca and Pnma phase, as shown in Supplementary Fig. S6, and the detailed refinement result can be found in Table 2. The second high-pressure phase transition is not finished up to 33.0 GPa, the highest pressure measured here.

Bottom Line: Here, a pressure-induced electronic topological transition (ETT) is firstly found in Ag2Te at 1.8 GPa.This result indicates that the best bulk insulating character and topological nature in Ag2Te can be obtained at this pressure.A pressure-induced metallization in Ag2Te is confirmed by the results of temperature-dependent resistivity measurements.

View Article: PubMed Central - PubMed

Affiliation: State Key Laboratory of Superhard Materials, College of Physics, Jilin University, Changchun 130012, China.

ABSTRACT
Recently, Ag2Te was experimentally confirmed to be a 3D topological insulator (TI) at ambient pressure. However, the high-pressure behaviors and properties of Ag2Te were rarely reported. Here, a pressure-induced electronic topological transition (ETT) is firstly found in Ag2Te at 1.8 GPa. Before ETT, the positive pressure coefficient of bulk band-gap, which is firstly found in TIs family, is found by both first-principle calculations and in situ high-pressure resistivity measurements. The electrical resistivity obtained at room temperature shows a maximum at 1.8 GPa, which is nearly 3.3 times to that at ambient pressure. This result indicates that the best bulk insulating character and topological nature in Ag2Te can be obtained at this pressure. Furthermore, the high-pressure structural behavior of Ag2Te has been investigated by in situ high-pressure synchrotron powder X-ray diffraction technique up to 33.0 GPa. The accurate pressure-induced phase transition sequence is firstly determined as P21/c → Cmca → Pnma. It is worth noting that the reported isostructural P21/c phase is not existed, and the reported structure of Cmca phase is corrected by CALYPSO methodology. The second high-pressure structure, a long puzzle to previous reports, is determined as Pnma phase. A pressure-induced metallization in Ag2Te is confirmed by the results of temperature-dependent resistivity measurements.

No MeSH data available.