The composition-dependent crystal and defect structures, and superconducting properties of NbSe (0 ≤ ≤ 0.09) polycrystalline samples were revealed by x-ray diffraction, electrical resistivity, magnetization and specific-heat measurements. Stacking-disordered structures were characterized by gradually broadened and weakened (0) reflections: disordered 2H structure for ≤ 0.04 and 2H + 3R mixed-layer structure for ≥ 0.05. Superconducting transition temperature () is 7.3 K in pristine NbSe, which decreases with increasing the content of interstitial-Nb (Nb), down to below 2 K in = 0.09. The lowered originates from the decreased electron-phonon coupling and density of states at the Fermi level . Upper critical field of all samples evidently exceed the Pauli limit except for pristine NbSe. , irreversible field and critical current density are all raised in slight-Nb samples compared with NbSe. The enhancements are due to the increase in charge carrier scattering and vortex pinning by Nb impurity and stacking disorders. These results indicate that minor nonmagnetic impurity doping could improve the current-carrying capacity under the premise of small impact on , which thus is a promising strategy to develop high-field superconducting magnets.

中文翻译：

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非化学计量Nb1+xSe2的结构和超导性能

通过 X 射线衍射、电阻率、磁化强度和比热测量揭示了 NbSe (0 ≤ ≤ 0.09) 多晶样品的成分相关晶体和缺陷结构以及超导性能。堆垛无序结构的特征是逐渐变宽和减弱(0)反射：≤0.04为无序2H结构，≥0.05为2H+3R混合层结构。原始 NbSe 的超导转变温度 () 为 7.3 K，随着间隙铌 (Nb) 含量的增加而降低，在 = 0.09 时降至 2 K 以下。降低源于电子-声子耦合和费米能级态密度的降低。除原始 NbSe 外，所有样品的上临界场均明显超过泡利极限。与NbSe相比，微铌样品的不可逆场和临界电流密度均有所提高。这种增强是由于铌杂质和堆积紊乱导致电荷载流子散射和涡旋钉扎的增加。这些结果表明，少量非磁性杂质掺杂可以在对 影响较小的前提下提高载流能力，是开发高场超导磁体的一种有前景的策略。