A15 Nb₃Si is, until now, the only ‘high’ temperature superconductor produced at high pressure (∼110GPa) that has been successfully brought back to room pressure conditions in a metastable condition. Based on the current great interest in trying to create metastable-at-room-pressure high temperature superconductors produced at high pressure, we have restudied explosively compressed A15 Nb₃Si and its production from tetragonal Nb₃Si. First, diamond anvil cell pressure measurements up to 88GPa were performed on explosively compressed A15 Nb₃Si material to trace T _c as a function of pressure. T _c is suppressed to ∼5.2K at 88GPa. Then, using these T _c (P) data for A15 Nb₃Si, pressures up to 92GPa were applied at room temperature (which increased to 120GPa at 5K) on tetragonal Nb₃Si. Measurements of the resistivity gave no indication of any A15 structure production, i.e. no indications of the superconductivity characteristic of A15 Nb₃Si. This is in contrast to the explosive compression (up to P ∼ 110GPa) of tetragonal Nb₃Si, which produced 50%–70% A15 material, T _c = 18K at ambient pressure, in a 1981 Los Alamos National Laboratory experiment. This implies that the accompanying high temperature (1000 C) caused by explosive compression is necessary to successfully drive the reaction kinetics of the tetragonal → A15 Nb₃Si structural transformation. Our theoretical calculations show that A15 Nb₃Si has an enthalpy vs the tetragonal structure that is 70 meV atom⁻¹ smaller at 100GPa, while at ambient pressure the tetragonal phase enthalpy is lower than that of the A15 phase by 90 meV atom⁻¹. The fact that ‘annealing’ the A15 explosively compressed material at room temperature for 39 years has no effect shows that slow kinetics can stabilize high pressure metastable phases at ambient conditions over long times even for large driving forces of 90 meV atom⁻¹.

迄今为止，A15 Nb ₃ Si 是唯一一种在高压 (~110GPa) 下生产的“高温”超导体，它已成功地在亚稳态下恢复到室温条件。基于目前对尝试制造在高压下生产的亚稳态高温超导体的极大兴趣，我们重新研究了爆炸压缩的 A15 Nb ₃ Si 及其从四方 Nb ₃ Si 的生产。首先，对爆炸压缩的 A15 Nb ₃ Si 材料进行高达 88GPa 的金刚石砧座单元压力测量，以追踪T _c作为压力的函数。T _c在 88GPa 下被抑制到~5.2K。然后，使用这些T _c ( P ) A15 Nb ₃ Si 的数据，在室温下对四方 Nb ₃ Si施加高达 92GPa 的压力（在 5K 时增加到 120GPa）。电阻率的测量没有给出任何 A15 结构产生的迹象，即没有迹象表明 A15 Nb ₃ Si的超导特性。这与四方 Nb ₃ Si的爆炸压缩（高达P ∼ 110GPa）形成对比，后者产生 50%–70% A15 材料，T _c = 18K 在环境压力下，在 1981 年洛斯阿拉莫斯国家实验室实验中。这意味着由爆炸压缩引起的伴随高温（1000℃）对于成功驱动四方→A15 Nb ₃ Si 结构转变的反应动力学是必要的。我们的理论计算表明，A15 Nb ₃ Si 的焓与四方结构相比，在 100GPa 时小70 meV 原子^-1 ，而在环境压力下，四方相的焓比 A15 相低 90 meV 原子^-1. 将 A15 爆炸性压缩材料在室温下“退火”39 年没有任何影响的事实表明，即使对于 90 meV 原子^{-1 的}大驱动力，慢动力学也可以在环境条件下长时间稳定高压亚稳态相。