Effect of heat treatments on superconducting properties and connectivity in K-doped BaFe2As2

Abstract Fe-based superconductors and in particular K-doped BaFe2As2 (K-Ba122) are materials of interest for possible future high-field applications. However the critical current density (J c ) in polycrystalline Ba122 is still quite low and connectivity issues are suspected to be responsible. In th...

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Autores principales:	Chiara Tarantini, Chongin Pak, Yi-Feng Su, Eric E. Hellstrom, David C. Larbalestier, Fumitake Kametani
Formato:	article
Lenguaje:	EN
Publicado:	Nature Portfolio 2021
Materias:	Medicine R Science Q
Acceso en línea:	https://doaj.org/article/b93ab901e05e4a3bbf3e77a8bb195235
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spelling	oai:doaj.org-article:b93ab901e05e4a3bbf3e77a8bb1952352021-12-02T14:06:56ZEffect of heat treatments on superconducting properties and connectivity in K-doped BaFe2As210.1038/s41598-021-82325-x2045-2322https://doaj.org/article/b93ab901e05e4a3bbf3e77a8bb1952352021-02-01T00:00:00Zhttps://doi.org/10.1038/s41598-021-82325-xhttps://doaj.org/toc/2045-2322Abstract Fe-based superconductors and in particular K-doped BaFe2As2 (K-Ba122) are materials of interest for possible future high-field applications. However the critical current density (J c ) in polycrystalline Ba122 is still quite low and connectivity issues are suspected to be responsible. In this work we investigated the properties of high-purity, carefully processed, K-Ba122 samples synthesized with two separate heat treatments at various temperatures between 600 and 825 °C. We performed specific heat characterization and T c -distribution analysis up to 16 T and we compared them with magnetic T c and J c characterizations, and transmission-electron-microscopy (TEM) microstructures. We found no direct correlation between the magnetic T c and J c , whereas the specific heat T c -distributions did provide valuable insights. In fact the best J c -performing sample, heat treated first at 750 °C and then at 600 °C, has the peak of the T c -distributions at the highest temperatures and the least field sensitivity, thus maximizing H c2 . We also observed that the magnetic T c onset was always significantly lower than the specific heat T c : although we partially ascribe the lower magnetization T c to the small grain size (< λ, the penetration depth) of the K-Ba122 phase, this behaviour also implies the presence of some grain-boundary barriers to current flow. Comparing the T c -distribution with J c , our systematic synthesis study reveals that increasing the first heat treatment above 750 °C or the second one above 600 °C significantly compromises the connectivity and suppresses the vortex pinning properties. We conclude that high-purity precursors and clean processing are not yet enough to overcome all J c limitations. However, our study suggests that a higher temperature T c -distribution, a larger H c2 and a better connectivity could be achieved by lowering the second heat treatment temperature below 600 °C thus enhancing, as a consequence, J c .Chiara TarantiniChongin PakYi-Feng SuEric E. HellstromDavid C. LarbalestierFumitake KametaniNature PortfolioarticleMedicineRScienceQENScientific Reports, Vol 11, Iss 1, Pp 1-11 (2021)
institution	DOAJ
collection	DOAJ
language	EN
topic	Medicine R Science Q
spellingShingle	Medicine R Science Q Chiara Tarantini Chongin Pak Yi-Feng Su Eric E. Hellstrom David C. Larbalestier Fumitake Kametani Effect of heat treatments on superconducting properties and connectivity in K-doped BaFe2As2
description	Abstract Fe-based superconductors and in particular K-doped BaFe2As2 (K-Ba122) are materials of interest for possible future high-field applications. However the critical current density (J c ) in polycrystalline Ba122 is still quite low and connectivity issues are suspected to be responsible. In this work we investigated the properties of high-purity, carefully processed, K-Ba122 samples synthesized with two separate heat treatments at various temperatures between 600 and 825 °C. We performed specific heat characterization and T c -distribution analysis up to 16 T and we compared them with magnetic T c and J c characterizations, and transmission-electron-microscopy (TEM) microstructures. We found no direct correlation between the magnetic T c and J c , whereas the specific heat T c -distributions did provide valuable insights. In fact the best J c -performing sample, heat treated first at 750 °C and then at 600 °C, has the peak of the T c -distributions at the highest temperatures and the least field sensitivity, thus maximizing H c2 . We also observed that the magnetic T c onset was always significantly lower than the specific heat T c : although we partially ascribe the lower magnetization T c to the small grain size (< λ, the penetration depth) of the K-Ba122 phase, this behaviour also implies the presence of some grain-boundary barriers to current flow. Comparing the T c -distribution with J c , our systematic synthesis study reveals that increasing the first heat treatment above 750 °C or the second one above 600 °C significantly compromises the connectivity and suppresses the vortex pinning properties. We conclude that high-purity precursors and clean processing are not yet enough to overcome all J c limitations. However, our study suggests that a higher temperature T c -distribution, a larger H c2 and a better connectivity could be achieved by lowering the second heat treatment temperature below 600 °C thus enhancing, as a consequence, J c .
format	article
author	Chiara Tarantini Chongin Pak Yi-Feng Su Eric E. Hellstrom David C. Larbalestier Fumitake Kametani
author_facet	Chiara Tarantini Chongin Pak Yi-Feng Su Eric E. Hellstrom David C. Larbalestier Fumitake Kametani
author_sort	Chiara Tarantini
title	Effect of heat treatments on superconducting properties and connectivity in K-doped BaFe2As2
title_short	Effect of heat treatments on superconducting properties and connectivity in K-doped BaFe2As2
title_full	Effect of heat treatments on superconducting properties and connectivity in K-doped BaFe2As2
title_fullStr	Effect of heat treatments on superconducting properties and connectivity in K-doped BaFe2As2
title_full_unstemmed	Effect of heat treatments on superconducting properties and connectivity in K-doped BaFe2As2
title_sort	effect of heat treatments on superconducting properties and connectivity in k-doped bafe2as2
publisher	Nature Portfolio
publishDate	2021
url	https://doaj.org/article/b93ab901e05e4a3bbf3e77a8bb195235
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Effect of heat treatments on superconducting properties and connectivity in K-doped BaFe2As2

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