Center for Superconducting and Magnetic Materials, Department of Materials Science and Engineering, the Ohio State University, Columbus, OH, USA.
Sci Rep. 2016 Jul 13;6:29306. doi: 10.1038/srep29306.
High temperatures and under pressure (HTP) processing has been used to study the effects of chemical doping in MgB2. ZrB2, TiB2 and NbB2 were selected as additives since, like MgB2, they have an AlB2-type structure and similar lattice parameters. Dy2O3 was selected as it has been reported to generate nanoscale, secondary intragrain phases in MgB2. While C is known to enter the B-sublattice readily, attempts to dope Zr and other elements onto the Mg site have been less successful due to slow bulk diffusion, low solubility in MgB2, or both. We have used high-temperature, solid-state sintering (1500 °C), as well as excursions through the peritectic temperature (up to 1700 °C), to investigate both of these limitations. Bulk MgB2 samples doped with MB2 (M = Zr, Ti and Nb) and Dy2O3 additions were synthesized and then characterized. Lattice distortion and high densities of crystal defects were observed in the MgB2 grains around nano-sized MB2 inclusions, this highly defected band contributed to a large increase in Bc2 but was not large enough to increase the irreversibility field. In contrast, distributed intragrain precipitates were formed by Dy2O3 additions which did not change the lattice parameters, Tc, Tc distribution or Bc2 of MgB2, but modified the flux pinning.
高温高压（HTP）处理已被用于研究化学掺杂对 MgB2 的影响。ZrB2、TiB2 和 NbB2 被选为添加剂，因为它们与 MgB2 一样具有 AlB2 型结构和相似的晶格参数。选择 Dy2O3 是因为它已被报道在 MgB2 中产生纳米级的二次晶内相。虽然 C 很容易进入 B 亚晶格，但由于体扩散缓慢、在 MgB2 中的溶解度低或两者兼而有之，尝试将 Zr 和其他元素掺杂到 Mg 位上的效果并不理想。我们使用高温固态烧结（1500°C）以及过包晶温度（高达 1700°C）来研究这两个限制。合成了掺杂 MB2（M = Zr、Ti 和 Nb）和 Dy2O3 添加剂的大块 MgB2 样品，并对其进行了表征。在纳米级 MB2 夹杂物周围的 MgB2 晶粒中观察到晶格畸变和高密度的晶体缺陷，这一高度缺陷带导致 Bc2 大幅增加，但不足以增加不可逆场。相比之下，通过 Dy2O3 添加剂形成了弥散的晶内沉淀物，它不改变晶格参数、Tc、Tc 分布或 MgB2 的 Bc2，但改变了磁通钉扎。
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