Observation of non-superconducting phase changes in nitrogen doped lutetium hydrides

Abstract

The recent report of near-ambient superconductivity and associated color changes in pressurized nitrogen doped lutetium hydride has triggered worldwide interest and raised major questions about the nature and underlying physics of these latest claims. Here we report synthesis and characterization of high-purity nitrogen doped lutetium hydride LuH2±xNy. We find that pressure conditions have notable effects on Lu-N and Lu-NH chemical bonding and the color changes likely stem from pressure-induced electron redistribution of nitrogen/vacancies and interaction with the LuH2 framework. No superconducting transition is found in all the phases at temperatures 1.8-300 K and pressures 0-38 GPa. Instead, we identify a notable temperature-induced resistance anomaly of electronic origin in LuH2±xNy, which is most pronounced in the pink phase and may have been erroneously interpreted as a sign of superconducting transition. This work establishes key benchmarks for nitrogen doped lutetium hydrides, allowing an in-depth understanding of its novel pressure-induced phase changes.

Temperature and quantum anharmonic lattice effects on stability and superconductivity in lutetium trihydride

“…The two phases of LuH 2 and LuH 3 , even though the latter is supposedly dynamically unstable, are of significant importance. On the one hand, recent studies argue that the actual composition observed in Dasenbrock-Gammon et al’s work 1 is, in fact, N-doped or pure fcc LuH 2 14 , 16 – 18 , 20 . The differentiation here is quite tricky, as LuH 2 and LuH 3 share the same structural framework with H atoms occupying only tetrahedral sites or tetrahedral + octahedral sites, respectively.…”

Unraveling the electronic structure of LuH, LuN, and LuNH: building blocks of new materials

“…4 The authors found the same color change from dark blue to violet and then pink/red, however superconductivity was not observed above 2 K. Peng et al , have also performed a quantitative temperature-dependent resistance comparison of Lu–N–H and pure lutetium before reaction and concluded that the change is resistance mentioned by Dasenbrock-Gammon et al , is likely caused by a metal-to-poor conductor transition. 5 Xingzhou et al also reported that they could not find evidence of a superconducting transition in all phases from temperatures ranging from 1.8 to 300 K. 6 The aforementioned and several other studies have also shown, that the superconductivity properties described by Dasenbrock-Gammon et al 3 cannot be reproduced, hence the original manuscript was retracted. 4,5,7–28 However, the electronic properties of the building blocks of these materials have not been explained or understood.…”

“…As Xingzhou et al mentioned in their work: “…we identify a notable temperature-induced resistance anomaly of electronic origin in LuH 2± x N y , which is most pronounced in the pink phase and may have been erroneously interpreted as a sign of superconducting transition”. 6 In addition, the electronic structure of the lattice building blocks has not been detailed properly.…”

Investigations of Pressurized Lu–N–H Materials by Using the Hybrid Functional

“…A large number of H-rich compounds with ultrahigh T c have been predicted and synthesized. − In 2019, the clathrate-like structure LaH 10 , which is a rare-earth hydride, was reported to have a T c of 250 K at 130–220 GPa. , Very recently, an experimental study has discovered superconductivity in the Lu–N–H systems under near-ambient pressure (approximately 1 GPa), with an exceptional T c of 294 K . This study pointed out that the room-temperature superconductor observed in the Lu–N–H systems can likely be attributed to the presence of cubic LuH 3−δ N ε in the space group of Fm m , which is LuH 3 doped with N. This work has attracted widespread attention. − …”