Research ArticleSUPERCONDUCTORS

Block copolymer self-assembly–directed synthesis of mesoporous gyroidal superconductors

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Science Advances  29 Jan 2016:
Vol. 2, no. 1, e1501119
DOI: 10.1126/sciadv.1501119
  • Fig. 1 GA structure and sample/structure evolution from initial compounds to final NbN superconductors.

    (A) GA before and after processing, with the unit cell indicated by the black cube. (B) (Top) Chemical structures of compounds and (bottom) schematic of synthesis and processing steps with photographs of the final materials. Block terpolymers (ISO) are combined with the Nb2O5 sol-gel precursors in a common solvent. Hybrid block copolymer/Nb2O5 GA structures are generated by solvent evaporation–induced self-assembly. After calcination in air, the mesoporous Nb2O5 GAs are transformed to NbN GAs in a two-step nitriding process. Scale bars in all photographs represent 1 cm. NH3, ammonia.

  • Fig. 2 Materials characterization by x-ray scattering.

    (A and B) SAXS patterns of samples derived from ISO-64k (A) and ISO-86k (B) at various processing stages. From bottom to top: ISO/oxide hybrids; samples calcined at 450°C in air; samples nitrided at 700°C; and sample nitrided at 850°/865°C. Observed (solid) and expected (dashed) peak positions for the GA structure are indicated by ticks above each curve. Curves for the ISO-86k–derived samples were integrated using a selected angular range as a result of the significant orientation of the mesostructure. (C) Powder XRD patterns of samples at various processing stages. From bottom to top: Sample calcined at 450°C in air; sample nitrided at 700°C; sample nitrided at 850°C; and sample nitrided at 865°C. All patterns are from samples derived from ISO-64k, except for the top trace, which is from a sample derived from ISO-86k. Bottom tick marks indicate expected peak positions and relative intensities for a cubic rock salt NbN pattern (Powder Diffraction File card 04-008-5125).

  • Fig. 3 Materials characterization by N2 sorption and SEM.

    (A) Pore size distributions from N2 sorption measurements for ISO-64k–derived samples at various processing stages. (B to F) SEM images of mesoporous samples at different processing stages. ISO-64k–derived gyroidal NbN (B) after nitriding at 700°C and (C) after nitriding at 850°C. (D) ISO-86k–derived gyroidal Nb2O5 after calcination at 450°C in air. ISO-86k–derived gyroidal NbN (E) after nitriding at700°C and (F) after nitriding at 865°C.

  • Fig. 4 Magnetization and electrical resistance of superconducting gyroids.

    (A) Temperature-dependent magnetization from 2.5 to 10 K for ISO-64k–derived NbN films in an applied field of 200 Oe, with their long axis oriented either parallel (top; ||) or perpendicular (bottom; ┴) to the applied field (see insets for the different geometries tested). (B) Temperature-dependent magnetization from 2.5 to 10 K for ISO-86k–derived NbN films in an applied field of 100 Oe, with their long axis oriented perpendicular to the field. (C) Temperature-dependent four-point electrical resistance of ISO-86k–derived NbN films showing a drop beginning at approximately 7 K.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/2/1/e1501119/DC1

    Fig. S1. Cross-sectional SEM images of ISO-64k–derived material nitrided in one step at 1050°C.

    Fig. S2. Two-dimensional SAXS patterns of ISO-64k–derived samples at various processing stages.

    Fig. S3. Two-dimensional SAXS patterns of ISO-86k–derived samples at various processing stages.

    Fig. S4. SEM images of ISO-64k–derived mesoporous samples at different processing stages.

    Fig. S5. Cross-sectional SEM images of an ISO-64k–derived monolith after final nitriding at 850°C.

    Fig. S6. Cross-sectional SEM images of an ISO-86k–derived monolith after final nitriding at 865ºC.

    Fig. S7. N2 adsorption/desorption isotherms for ISO-64k–derived powder samples calcined at 450ºC, nitrided at 700ºC, and nitrided at 850ºC.

    Fig. S8. XRD-derived lattice spacing as a function of nitriding temperature for NbN fibers [(17); black circles and fit] and our materials (red squares).

    Fig. S9. TEM micrographs of nitrides derived from (A) ISO-64k and (B) ISO-86k after final heat treatments.

    Fig. S10. High-resolution TEM micrograph of ISO-64k–derived nitride after final heat treatment.

    Fig. S11. High-resolution TEM micrograph of ISO-86k–derived nitride after final heat treatment.

    Fig. S12. Magnetization behavior of ISO-64k–derived 850ºC gyroidal NbN material from 2.5 to 30 K, measured in a perpendicular orientation with an applied field of 70 Oe.

    Fig. S13. Field-cooled magnetization behavior of ISO-86k–derived 865ºC gyroidal NbN material from 2 to 30 K, measured in a perpendicular orientation with an applied field of 50 Oe.

    Fig. S14. Field-sweeping magnetization behavior at 2.5 K of ISO-64k–derived NbN material heat-treated to 850°C.

    Fig. S15. High-field magnetization behavior at 2.5 K of ISO-86k–derived NbN material heat-treated to 865ºC.

    Fig. S16. Two-dimensional (A) and integrated (B) SAXS patterns of ISO-86k–derived material processed in the same batch as that in fig. S3.

    Fig. S17. Photograph of the four-point conductivity measurement apparatus.

    Table S1. Surface area and pore volume (as measured by N2 sorption) of ISO-64k–derived materials at different stages of thermal processing.

  • Supplementary Materials

    This PDF file includes:

    • Fig. S1. Cross-sectional SEM images of ISO-64k–derived material nitrided in one step at 1050°C.
    • Fig. S2. Two-dimensional SAXS patterns of ISO-64k–derived samples at various processing stages.
    • Fig. S3. Two-dimensional SAXS patterns of ISO-86k–derived samples at various processing stages.
    • Fig. S4. SEM images of ISO-64k–derived mesoporous samples at different processing stages.
    • Fig. S5. Cross-sectional SEM images of an ISO-64k–derived monolith after final nitriding at 850°C.
    • Fig. S6. Cross-sectional SEM images of an ISO-86k–derived monolith after final nitriding at 865ºC.
    • Fig. S7. N2 adsorption/desorption isotherms for ISO-64k–derived powder samples calcined at 450ºC, nitrided at 700ºC, and nitrided at 850ºC.
    • Fig. S8. XRD-derived lattice spacing as a function of nitriding temperature for NbN fibers (17); black circles and fit and our materials (red squares).
    • Fig. S9. TEM micrographs of nitrides derived from (A) ISO-64k and (B) ISO-86k after final heat treatments.
    • Fig. S10. High-resolution TEM micrograph of ISO-64k–derived nitride after final heat treatment.
    • Fig. S11. High-resolution TEM micrograph of ISO-86k–derived nitride after final heat treatment.
    • Fig. S12. Magnetization behavior of ISO-64k–derived 850ºC gyroidal NbN material from 2.5 to 30 K, measured in a perpendicular orientation with an applied field of 70 Oe.
    • Fig. S13. Field-cooled magnetization behavior of ISO-86k–derived 865ºC gyroidal NbN material from 2 to 30 K, measured in a perpendicular orientation with an applied field of 50 Oe.
    • Fig. S14. Field-sweeping magnetization behavior at 2.5 K of ISO-64k–derived NbN material heat-treated to 850°C.
    • Fig. S15. High-field magnetization behavior at 2.5 K of ISO-86k–derived NbN material heat-treated to 865ºC.
    • Fig. S16. Two-dimensional (A) and integrated (B) SAXS patterns of ISO-86k–derived material processed in the same batch as that in fig. S3.
    • Fig. S17. Photograph of the four-point conductivity measurement apparatus.
    • Table S1. Surface area and pore volume (as measured by N2 sorption) of ISO-64k–derived materials at different stages of thermal processing.

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