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首页> 外文OA文献 >The cause of ‘weak-link’ grain boundary behaviour in polycrystalline Bi2Sr2CaCu2O8 and Bi2Sr2Ca2Cu3O10 superconductors.
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The cause of ‘weak-link’ grain boundary behaviour in polycrystalline Bi2Sr2CaCu2O8 and Bi2Sr2Ca2Cu3O10 superconductors.

机译：多晶Bi2Sr2CaCu2O8和Bi2Sr2Ca2Cu3O10超导体中“弱链接”晶界行为的原因。

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The detrimental effects of grain boundaries have long been considered responsible for the low critical current densities (J_c) in high temperature superconductors. In this paper, we apply the quantitative approach used to identify the cause of the 'weak-link' grain boundary behaviour in YBa2Cu3O7 [1], to the Bi2Sr2CaCu2O8 and Bi2Sr2Ca2Cu3O10 materials that we have fabricated. Magnetic and transport measurements are used to characterise the grain and grain boundary properties of micro- and nanocrystalline material. Magnetisation measurements on all nanocrystalline materials show non-Bean-like behaviour and are consistent with surface pinning. ud Bi2Sr2CaCu2O8: Our microcrystalline material has very low grain boundary resistivity (ρ_GB), which is similar to that of the grains (ρ_G) such that ρ_GB≈ρ_G=2×〖10〗^(-5) Ωm (assuming a grain boundary thickness (d) of 1 nm) equivalent to an areal resistivity of ρ_G=2×〖10〗^(-14) Ωm^2. The transport J_c values are consistent with well-connected grains and very weak grain boundary pinning. However, unlike low temperature superconductors in which decreasing grain size increases the pinning along the grain boundary channels, any increase in pinning produced by making the grains in our Bi2Sr2CaCu2O8 materials nanocrystalline was completely offset by a decrease in the depairing current density of the grain boundaries caused by their high resistivity. We suggest a different approach to increasing J_c from that used in LTS materials, namely incorporating additional strong grain and grain boundary pinning sites in microcrystalline materials to produce high J_c values.ud Bi2Sr2Ca2Cu3O10: Both our micro- and nanocrystalline samples have ρ_GB/ρ_G of at least 10^3. This causes strong suppression of J_c across the grain boundaries, which explains the low transport J_c values we find experimentally. Our calculations show that low J_c in untextured polycrystalline Bi2Sr2Ca2Cu3O10 material is to be expected and the significant effort in the community in texturing samples and removing grain boundaries altogether is well-founded.
机译：长期以来，人们一直认为晶界的有害影响是造成高温超导体中低临界电流密度（J_c）的原因。在本文中，我们将用于确定YBa2Cu3O7 [1]中“弱链接”晶界行为原因的定量方法应用于我们制造的Bi2Sr2CaCu2O8和Bi2Sr2Ca2Cu3O10材料。磁和输运测量用于表征微晶和纳米晶材料的晶粒和晶界特性。对所有纳米晶体材料的磁化测量显示出非豆类行为，并且与表面钉扎一致。 ud Bi2Sr2CaCu2O8：我们的微晶材料的晶界电阻率（ρ_GB）非常低，类似于晶粒（ρ_G）的晶界电阻率，使得ρ_GB≈ρ_G= 2×〖10〗^（-5）Ωm（假设晶界）厚度（d）为1 nm）等于ρ_G= 2×〖10〗^（-14）Ωm^ 2的面电阻率。传输J_c值与晶粒连接良好且晶粒边界钉扎非常弱一致。但是，与低温超导体不同，在低温超导体中，减小晶粒尺寸会增加沿晶界通道的钉扎，而通过将Bi2Sr2CaCu2O8材料中的纳米颗粒制成纳米晶而产生的钉扎的任何增加，都将被所引起的晶界去配对电流密度的降低所完全抵消。由于它们的高电阻率。我们建议采用与LTS材料不同的方法来增加J_c，即在微晶材料中引入额外的强晶粒和晶界钉扎位点以产生高J_c值。 ud Bi2Sr2Ca2Cu3O10：我们的微晶和纳米晶样品的ρ_GB/ρ_G为至少10 ^ 3。这会导致J_c跨晶界的强烈抑制，这解释了我们通过实验发现的低传输J_c值。我们的计算表明，无织构的多晶Bi2Sr2Ca2Cu3O10材料中的J_c较低，这是可以预料的，并且在社区中对织构化样品和完全消除晶界的巨大努力是有充分根据的。

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