Materials may behave in non-expected ways when subject to unexpected conditions. For example, when Bi was turned into an amorphous phase (a-Bi) unexpectedly it became a superconductor at temperatures below 10 K. Using the superconductivity of the amorphous phase we provided an explanation as to why crystalline bismuth (c-Bi) had not been found to superconduct, and even predicted an upper limit for its superconducting transition temperature Tc. This was experimentally corroborated within the following year. We now decided to investigate what happens to the crystalline, Wyckoff structure, and amorphous Bi when pressures below the atmospheric are applied. Here it is shown that, within the BCS approach, under expansion the Wyckoff c-Bi increases its superconducting transition temperature minimally, whereas the amorphous phase decreases its Tc. The electron densities of states (eDoS), the vibrational densities of states (vDoS) and the Debye temperatures (θD) are calculated to perform this qualitative evaluation. Expansion can be obtained in the laboratory by chemically etching Bi-based alloys, for example, a process also known as dealloying.
Materials may behave in non-expected ways when subject to unexpected conditions. For example, when Bi was turned into an amorphous phase (a-Bi) unexpectedly it became a superconductor at temperatures below 10 K. We provided an explanation as to why a-Bi superconducts and the crystalline (c-Bi) had not been found to do so: we computer calculated their electronic properties and found that a-Bi has a larger electron density of states, eDoS, at the Fermi surface than c-Bi and this explained the phenomenon. We even predicted an upper limit for the superconducting Tc of the crystalline phase, which was experimentally corroborated within the following year. We now decided to investigate what happens to crystalline (Wyckoff structure) and amorphous Bi when pressures below the atmospheric are applied (expansion). Here we show that when expanded, c-Bi becomes more metallic, since the eDoS increases when the volume increases for the Wyckoff structure, while the amorphous eDoS decreases. If the crystalline structure is maintained its Tc would rise under expansion, whereas it would diminish for the a-Bi. Expansion can be obtained in the laboratory by chemically etching Bi-based alloys, a process also known as dealloying, for example.
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