High-pressure synthesis of lutetium hydrides from molecular hydrogen (H2) and lutetium (Lu) is systematically investigated using synchrotron X-ray diffraction, Raman spectroscopy, and visual observations. We demonstrate that the reaction pathway between H2 and Lu invariably follows the sequence Lu ⟶ LuH2 ⟶ LuH3 and exhibits a notable time dependence. A comprehensive diagram representing the formation and synthesis of lutetium hydrides as a function of pressure and time is constructed. Our findings indicate that the synthesis can be accelerated by elevated temperature and decelerated by increased pressure. Notably, two critical pressure thresholds at ambient temperature are identified: the synthesis of LuH2 from Lu commences at a minimum pressure of ∼3 GPa, while ∼28 GPa is the minimum pressure at which LuH2 fails to transform into LuH3 within a time scale of months. This underscores the significant impact of temporal factors on synthesis, with the reaction completion time increasing sub-linearly with rising pressure. Furthermore, the cubic phase of LuH3 can be obtained exclusively through compressing the trigonal LuH3 phase at ∼11.5 GPa. We also demonstrate that the bandgap of LuH3 slowly closes under pressure and is noticeably lower than that of LuH2.

Rare-earth metal (RE) hydrides exhibit a plethora of interesting properties under compression, such as unusual electronic states,1–3 novel crystalline structures,4–8 and a pressure-induced metal–insulator transition.9 In the quest for room-temperature superconductivity, extensive investigations have focused on binary rare-earth hydrides such as YH6,5,10 YH9,10,11 LaH10,6,12 CeH9,7,13 and CeH10,8 and a record high Tc of 250 K has been found in LaH10. Lutetium is the heaviest element among the rare-earth metals, and its structure is similar to that of lanthanum, which has led to a search for superconductivity in the lutetium hydride system. In 2023, the authors of Ref. 14 claimed to have discovered superconductivity in nitrogen-doped lutetium hydride with a superconducting transition temperature of 294 K at 10 kbar. Although this claim of room-temperature superconductivity14 was shown to be wrong15–17 and was subsequently retracted, it did focus attention to the physical properties of lutetium hydrides. Owing to the extraordinary nature of the claim, numerous theoretical18–36 and experimental15–17,37–45 studies were conducted within a very short period of time.

Two stoichiometric lutetium hydrogen binary compounds are known: LuH2 and LuH3.4 LuH2 has a cubic structure with Fm3̄m symmetry under ambient conditions and remains stable up 20 GPa. LuH3 is known to adopt two different structural configurations:2 a cubic phase Fm3̄m and a trigonal phase P3̄c1. The trigonal LuH3 phase is stable at ambient pressure and transforms to a cubic structure1 at ∼12 GPa and 300 K. This cubic LuH3 was reported to have a Tc of 12.4 K at 122 GPa.46 In Ref. 14 the near-ambient superconducting compound was claimed to be nonstoichiometric LuH3−δNɛ with the same cubic structure as LuH3. It was claimed14 that during the reaction between lutetium and hydrogen, the sample underwent a color change, with the initial sample being blue, then changing to pink at about 3 kbar and red at about 30 kbar. Subsequent investigations demonstrated the absence of room-temperature superconductivity15,16 and commented on the color of the claimed superconducting phase (LuH3−δNɛ-Fm3̄m) and its evolution with pressure. It was suggested that the color does undergo a sequential change from blue under ambient conditions to pink and then to red under compression. Additionally, it was suggested that nitrogen doping does not contribute to the superconductivity of lutetium hydrides, with comparisons of the resistance of nitrogen-doped LuH2 powders, pure LuH2 powders, and single-crystal LuH2 in nitrogen gas at high pressure42 revealing no significant differences between nitrogen-doped and undoped lutetium hydrides. Moreover, the same study confirmed that the near-ambient superconducting material in question is LuH2.42 However, none of the previous studies have explored the relationship between LuH2 and LuH3 or their interconversions.

Lutetium hydrides can be synthesized via two primary methods: the high-temperature/high pressure (HTHP) method15–17,42 and the Sievert method.47 The HTHP synthesis can be performed using a piston–cylinder apparatus, operating at around 2 GPa and 300–350 °C and resulting in the formation of LuH2 after 10 h. Alternatively, a diamond anvil cell (DAC) can be employed, covering the pressure range from 1 to 10 GPa and temperatures up to 1000 °C, allowing the synthesis of both LuH2 and LuH3. The Sievert method47 mainly relies on high temperatures, with the exposure of lutetium sheets to an H2 atmosphere at 200 °C and 4 MPa for 10 h leading to the synthesis of LuH3. These different synthesis methods predominantly produce LuH2, but reaching a higher hydrogen content could have a significant impact on the physical properties of lutetium hydrides, including an increased Tc. In the most recent publication on lutetium hydrides,33 the authors have emphasized the critical role that the specific experimental conditions play in defining the properties of the samples during the crystal growth process. The present study confirms this and offers new insights into the mechanisms of hydride synthesis.

Here, we investigate the time-dependent evolution of the stoichiometric ratio in lutetium hydrides synthesized between 3 and 28.5 GPa and at about 300–400 K (see the supplementary material for details). The evolutionary process of the compounds was monitored in real time by visual observation of color changes, accompanied by Raman spectroscopy and synchrotron X-ray diffraction (XRD). Lutetium hydrides exhibit diverse structures and physical properties within a certain pressure range, as well as changing over time. The time evolution was found to consistently follow the same pathway: Lu → LuH2 → LuH3, leading to the synthesis of lutetium trihydride at room temperature at all pressures except the highest one of 28.5 GPa, at which LuH3 was not formed even after five months (see Fig. S7, supplementary material). Additionally, we observed a reversible phase transition at around 11.5 GPa between LuH3-P3̄c1 and LuH3-Fm3̄m and optically measured the bandgaps of LuH2 and LuH3 as functions of pressure up to 30 GPa.

Sixteen independent high-pressure experiments were conducted to synthesize lutetium hydrides using DACs (see Table S1, supplementary material). The DACs were equipped with anvils with culet diameters ranging from 200 to 800 μm. Rhenium was used as the gasket material to form the sample chamber.

The visual observations of the samples were supplemented by Raman spectroscopy. The confocal Raman setup used an excitation wavelength of 532 nm coupled with a 750 mm focal length single-stage imaging spectrometer (SP2750) equipped with an array of thermoelectrically cooled CCD detectors, providing spectral coverage up to 6000 cm−1. The vibrational bands of hydrogen and the R1 fluorescence peak of ruby were used for the pressure calibration. A lutetium foil (Alfa Aesar, stated purity 99.9%) was sealed inside the DAC sample chamber inside a glove box. Then, a gas mixture with an H2/N2 ratio of 99:1 at 180 MPa was loaded into the sample chamber using a gas loading system.48,49

Typically, within several hours of loading, the lutetium foil started to change color, which was accompanied by the appearance of novel Raman peaks. Additional warming (e.g., up to 65 °C) usually accelerated the reaction. In the compression experiments on LuH3, the synthesized LuH3 hydrides were transferred to another DAC with an NaCl pressure-transmitting medium, with the equation of state of gold being used to calibrate the pressure. Nine XRD measurements were conducted at both the Shanghai Synchrotron Radiation Facility (SSRF) and the SPring-850 synchrotron radiation facility in Japan. XRD data were collected at SPring-8’s BL10XU station and SSRF’s BL15U1 station. The X-ray wavelengths were 0.414 and 0.6199 Å, respectively, and the spot sizes were 3 × 2 and 3 × 3 μm2, respectively. The sample-to-detector distance and other geometric parameters were calibrated using a CeO2 standard. The Dioptas software package55 was used to integrate powder diffraction rings and convert the two-dimensional data to one-dimensional profiles. Full profile analyses of the diffraction patterns and Rietveld refinements were performed using GSAS-II51 and Jana202052 with the Le Bail method.

Figure 1 shows the synthesis phase diagram of the Lu + H2 system as a function of time and pressure. The combined effects of pressure and time caused molecular hydrogen to gradually penetrate the lutetium crystal lattice, resulting in the slow formation of metal hydrides with increasing hydrogen content. Visually, the loaded lutetium foil changed from silver–white to red and then to black. The transformation process from Lu-P63mmc → LuH2-Fm3̄m → LuH3-P3̄c1 was determined using Raman spectroscopy and XRD. Synthesis of the hydride was not observed below 3.0 GPa, which appears to be the minimum critical pressure. Above this pressure, the reaction occurred readily. However, as the pressure increased, the rate of lutetium hydride synthesis diminished. At 28.5 GPa, complete transformation could not occur, LuH2 failed to transform into LuH3 within a time scale of months, and only LuH2 was observed after 70 days.

FIG. 1.

Formation and synthesis diagram of the Lu + H2 system as function of time and pressure. The insets are images of different rounds of lutetium hydride synthesis, corresponding to Lu at 28.5 GPa, LuH2 at 5.0 GPa, and LuH3 at 3.0 GPa, respectively, with the Y-axis position corresponding to the time at which the inset photograph was taken. The hollow red, solid red, hollow black, and solid black symbols indicate the start of LuH2 generation, its completion, the start of LuH3 generation, and its full completion, respectively.

FIG. 1.

Formation and synthesis diagram of the Lu + H2 system as function of time and pressure. The insets are images of different rounds of lutetium hydride synthesis, corresponding to Lu at 28.5 GPa, LuH2 at 5.0 GPa, and LuH3 at 3.0 GPa, respectively, with the Y-axis position corresponding to the time at which the inset photograph was taken. The hollow red, solid red, hollow black, and solid black symbols indicate the start of LuH2 generation, its completion, the start of LuH3 generation, and its full completion, respectively.

Close modal

Figure 2 presents photographs and Raman spectra recorded during the reaction process at different pressures and room temperature over time (more details can be found in Table S1, supplementary material).

FIG. 2.

Photographs and Raman spectra of the Lu + H2 system as function of time after loading. (a)–(d) Images captured during the reaction process. The circles and the square in these photographs indicate where the corresponding Raman spectra were measured. The Raman spectrum detected at the position of the blue square corresponds to “H2-Rich” in (e), and the H2 rotons are marked with a black plus (+) symbol. The red and black components in the sample images correspond to LuH2, and LuH3, respectively. (e) Raman spectra of the Lu + H2 system as functions of time at 3.0 GPa and 298 K. The gray curve represents the spectrum of LuH3 from the literature.47 (f) Raman spectra of the Lu + H2 system as functions of time at 20.3 GPa and 298 K. The “growth” of lutetium hydrides occurs over a specific time scale, and “growth” can also be deduced from the sample size in the images. See the supplementary material for further details of the reaction conditions.

FIG. 2.

Photographs and Raman spectra of the Lu + H2 system as function of time after loading. (a)–(d) Images captured during the reaction process. The circles and the square in these photographs indicate where the corresponding Raman spectra were measured. The Raman spectrum detected at the position of the blue square corresponds to “H2-Rich” in (e), and the H2 rotons are marked with a black plus (+) symbol. The red and black components in the sample images correspond to LuH2, and LuH3, respectively. (e) Raman spectra of the Lu + H2 system as functions of time at 3.0 GPa and 298 K. The gray curve represents the spectrum of LuH3 from the literature.47 (f) Raman spectra of the Lu + H2 system as functions of time at 20.3 GPa and 298 K. The “growth” of lutetium hydrides occurs over a specific time scale, and “growth” can also be deduced from the sample size in the images. See the supplementary material for further details of the reaction conditions.

Close modal

The thickness of the lutetium foil was nonuniform, with some areas of the foil being in direct contact with the culet of the diamond anvil, while others were not, leading to the formation of areas where signals of hydrogen could be detected. Notably, lutetium hydride initially formed at the edges where the lutetium foil was in contact with the culet of the diamond anvil, and it then “grew” to other locations. Before reaction, the hcp phonon of Lu emerged at a very low frequency of 74 cm−1, accompanied by a silver–white metallic appearance in the microscope images. After 24 h of reaction, new peaks appeared at 256 and 1225 cm−1, along with a low-frequency range peak, which can be assigned to an Lu–H compound. Theoretical calculations26 show that the peak at 1225 cm−1 corresponds to the Raman T2g mode. After nine days of reaction, as can be seen from the corresponding microscopic image in Fig. 2(a), the sample color changed to deep red and Raman peaks appeared at around 100 cm−1, which is consistent with previous work.14–16,42 The Raman peak of lutetium hydrides after nine days of synthesis was considerably more intense, since the more hydrides were produced during this period, as evidenced by the increasing dark red areas in the image, which suggests the formation of LuH2. After one month of reaction, the red portion in the image transformed to black [Fig. 2(b)], and the Raman peaks at 160 cm−1 became more pronounced. In addition, a peak appeared at 101 cm−1, as well as an intense band at 556 cm−1, which was resolved from one of the rotational modes of H2 located at 589 cm−1, indicating the formation of LuH3. Theoretical calculations20,26,47 reveal a total of 5A1g + 12Eg Raman modes in this LuH3 phase (see Table S2, supplementary material). In our spectra, we observe several Raman peaks that resemble the predicted pattern of 17 phonons. In the areas with a sufficient amount of hydrogen, the sample does not undergo further changes over a longer period of time, staying in the form of LuH3, which suggests that LuH3 is the most stable compound under these conditions. Figures 2(c) and 2(d) show images of LuH2 and LuH3, respectively, synthesized at 20.3 GPa and 298 K. The corresponding Raman spectra obtained at different times are shown in Fig. 2(f).

It has been shown previously15–17,37–42 that lutetium hydrides synthesized through various methods exhibit slightly different physical properties, such as different colors and resistance–temperature (RT) characteristics. This variation may be attributed to varying occupancy of hydrogen atoms in vacancies, despite the samples maintaining an identical crystal structure (Fm3̄m). Such occupancy variations lead to the formation of distinct nonstoichiometric compounds. Our experimental results revealed that following the nucleation stage, the crystal gradually expanded along the region containing H2. During this process, hydrogen atoms penetrated the tetrahedral and octahedral interstices of the lutetium lattice, progressively increasing the hydrogen content in the lutetium hydride. This increment in hydrogen content was marked by the emergence and growth of an initial red dot, signifying the formation of lutetium hydrides, and culminating in the production of black LuH3. Furthermore, varying the timing of pressure release yielded lutetium hydrides with differing hydrogen contents. This observation aligns with theoretical predictions,23,33 which indicate that variations in hydrogen content have a significant impact on the physical properties of lutetium hydrides.

We also optically investigated the pressure-dependent trends of the bandgaps for LuH2 and LuH3, which are presented in Fig. 3. The bandgaps were measured using a UV-Vis-NIR spectrophotometer and subsequently calculated through the Tauc equation, yielding values of 1.62 and 1.26 eV for LuH2 and LuH3, respectively, at room temperature (298 K) and atmospheric pressure (see Fig. S8, supplementary material). The bandgap of LuH3 is lower than that of LuH2 within the investigated pressure range of 0–30 GPa [Fig. 3(b)]. We also observe from Fig. 3(b) that the bandgap of LuH3 decreases linearly with increasing pressure, while that of LuH2 does not change noticeably. It is worth noting that above 12 GPa, the slope of the linear dependence appears to change, which might be related to the structural transition at 11.5 GPa (see also below). The observation of the decreasing bandgap of LuH3 is consistent with the claim that LuH3 becomes a superconductor at 122 GPa.46 On the basis of these findings, we hypothesize that an increase in hydrogen content in lutetium hydrides contributes to a reduction in the compound’s bandgap.

FIG. 3.

Bandgaps of LuH2 and LuH3 under high pressure. (a) Plots of the transformed Kubelka–Munk function vs photon energy for LuH2 and LuH3 at high pressures. (b) Pressure-dependent bandgaps of LuH2 and LuH3 under compression. The bandgap at ambient pressure is shown in Fig. S8 (supplementary material).

FIG. 3.

Bandgaps of LuH2 and LuH3 under high pressure. (a) Plots of the transformed Kubelka–Munk function vs photon energy for LuH2 and LuH3 at high pressures. (b) Pressure-dependent bandgaps of LuH2 and LuH3 under compression. The bandgap at ambient pressure is shown in Fig. S8 (supplementary material).

Close modal

Figure 4 presents the synchrotron radiation XRD patterns of the lutetium–hydrogen system as a function of time, demonstrating an evolution process consistent with the results of Raman spectroscopy. Specifically, the two elements underwent the transformation sequence from Lu → LuH2 → LuH3 at 3.0 GPa over a span of 30 days. Initially, the XRD patterns of the reactant metal demonstrated a hexagonal Lu structure characterized by P63mmc symmetry. As time progressed, a combination of hexagonal Lu and cubic (Fm3̄m) LuH2 was detected. Over the subsequent weeks, the remaining unreacted Lu metal gradually transformed into LuH2, while the initial LuH2 concurrently reacted to form trigonal (P3̄c1) LuH3. Consequently, a mixture of LuH2-Fm3̄m and LuH3-P3̄c1 was observed, as shown in Fig. 4(c). The final XRD patterns identified the product as pure trigonal LuH3, thereby confirming the time-evolution process. Specifically, we propose that the “LuH2” discussed in our study is more accurately characterized as LuHx, derived from an Fm3̄m parent structure. This characterization implies the potential presence of H vacancies within the structure, which may explain why the vibrational modes observed in our Raman spectra exceed those predicted for pure LuH2 in theoretical calculations. Notably, no evidence of nitrogen doping was detected in the XRD patterns, despite the introduction of 1% nitrogen in some samples during the loading process.

FIG. 4.

XRD spectra of the Lu + H2 system as functions of time after loading at 3.0 GPa and 300 K: (a) Lu-P63mmc (day 0); (b) Lu-P63mmc + LuH2-Fm3̄m (day 5); (c) LuH2-Fm3̄m + LuH3-P3̄c1 (day 20); (d) LuH3-P3̄c1 (>30 days). In (d), Re and NaCl are from the gasket and pressure-transmitting medium, respectively.

FIG. 4.

XRD spectra of the Lu + H2 system as functions of time after loading at 3.0 GPa and 300 K: (a) Lu-P63mmc (day 0); (b) Lu-P63mmc + LuH2-Fm3̄m (day 5); (c) LuH2-Fm3̄m + LuH3-P3̄c1 (day 20); (d) LuH3-P3̄c1 (>30 days). In (d), Re and NaCl are from the gasket and pressure-transmitting medium, respectively.

Close modal

The synchrotron radiation XRD patterns of LuH3 during compression up to 41.4 GPa and subsequent decompression are shown in Fig. 5(a). A phase transition from a trigonal (P3̄c1) structure to a cubic (Fm3̄m) structure of LuH3 is revealed at ∼11.5 GPa. This suggests that LuH3 becomes better packed under pressure. The occurrence of this phase transition is further substantiated by the molecular volume–pressure diagram in Fig. 5(c). Notably, this phase transition is reversible upon decompression.

FIG. 5.

Phase transition of lutetium trihydride under high pressure. (a) XRD spectra of LuH3 during both compression and decompression runs. The asterisk indicates the diffraction peak of NaCl. The spectra in orange, purple, and cyan correspond to LuH3-P3̄c1, the intermediate state, and LuH3-Fm3̄m, respectively. (b) Rietveld refinement of the Fm3̄m spectrum at 41.4 GPa. The experimental data, fitted line, and residues are shown in black, red, and gray, respectively. (c) Pressure dependence of the primitive cell volume. The solid orange circles represent the primitive cell volume of P3̄c1 and the solid blue circles the primitive cell volume of Fm3̄m. The theoretical predictions of Dangic et al.26 and experimental data from Palasyuk and Tkacz1 and Moulding et al.47 are also shown for comparison.

FIG. 5.

Phase transition of lutetium trihydride under high pressure. (a) XRD spectra of LuH3 during both compression and decompression runs. The asterisk indicates the diffraction peak of NaCl. The spectra in orange, purple, and cyan correspond to LuH3-P3̄c1, the intermediate state, and LuH3-Fm3̄m, respectively. (b) Rietveld refinement of the Fm3̄m spectrum at 41.4 GPa. The experimental data, fitted line, and residues are shown in black, red, and gray, respectively. (c) Pressure dependence of the primitive cell volume. The solid orange circles represent the primitive cell volume of P3̄c1 and the solid blue circles the primitive cell volume of Fm3̄m. The theoretical predictions of Dangic et al.26 and experimental data from Palasyuk and Tkacz1 and Moulding et al.47 are also shown for comparison.

Close modal

In the cubic phase, the molecular volume of LuH3 exceeds 31 Å3, which decreases to 28 Å3 following the phase transition. Previous computational models have detailed the phase transition of lanthanide hydrides under high pressure.53 However, our experimental results indicate that the observed phase transition pressure is significantly lower than the calculated value. Additionally, an XRD data point at 13.9 GPa suggests the presence of an intermediate phase, and subsequent Raman spectroscopy data indicate that this may be similar to that of DyH3.54 

Figure 6(a) illustrates the alterations in the Raman spectra of LuH3 under different pressures, highlighting the intensity variations of each Raman peak. With increasing pressure, the spectra reveal a weakening of the strongest Raman modes around 560 cm−1 and enhancement of the modes at 310 and 750 cm−1, indicating a transition from a trigonal to a cubic phase. Throughout the compression process, the disappearance, emergence, and merging of several Raman peaks suggest that the structure of LuH3 undergoes two structural transitions: from the trigonal phase to an intermediate phase, and subsequently from this intermediate phase to the cubic phase. Figure 6(b) provides a more detailed illustration of the variations of Raman frequency with pressure, in close alignment with the results of the study of DyH354 mentioned above. Both of these elements, of course, belong to the lanthanide series. Our findings delineate a distinct transition region between the trigonal and cubic phases, underscoring the complexity of the phase transition process. Interestingly, the cubic phase of LuH3 can be exclusively obtained by compressing the trigonal LuH3 phase to ∼11.5 GPa. This implies that even when the lutetium foil and H2 were subjected to pressures up to 20.3 GPa, only the trigonal LuH3 phase was formed.

FIG. 6.

Raman spectra of the phase transition of lutetium trihydride under high pressure. (a) Raman spectra of LuH3 during compression. (b) Pressure dependence of the vibrational frequencies of LuH3 obtained upon compression. Different colors correspond to different phases, and the white region represents the coexisting phases.

FIG. 6.

Raman spectra of the phase transition of lutetium trihydride under high pressure. (a) Raman spectra of LuH3 during compression. (b) Pressure dependence of the vibrational frequencies of LuH3 obtained upon compression. Different colors correspond to different phases, and the white region represents the coexisting phases.

Close modal

Rare-earth metal hydrides exhibit distinctive physical and chemical properties under high pressure, and this study has delved into the evolution of these properties over time and under different pressures. Under the combined influence of pressure and time, molecular hydrogen gradually permeates the lutetium lattice, leading to the formation of a metal hydride with a low hydrogen content. This reaction constitutes a chemical transformation distinct from the molecular confinement. Over extended time scales, we have observed the eventual formation of a stable trigonal phase, specifically lutetium trihydride. This work has revealed the structural transformation of a lutetium hydrogen system over time, progressing through the sequence Lu-P63mmc → LuH2-Fm3̄m → LuH3-P3̄c1 from ∼3.0 to 30.0 GPa. Such kinetic growth processes warrant further investigation and could potentially represent a pivotal aspect of high-pressure chemistry in the future research.

We have also examined the phase transition of LuH3 under compression, identifying a phase transition from LuH3-P3̄c1 to a higher-symmetry structure LuH3-Fm3̄m. This phase is maintained to at least 122 GPa.46 Our research underscores the significance of time in chemical reactions, thereby suggesting a novel approach to the synthesis of superhydrides. The results of this study enrich our understanding of materials science and high-pressure physics.

Details of the experiments and data processing are provided in the supplementary material.

This work was supported by research grants of the Youth Innovation Promotion Association of CAS (Grant No. 2021446), the National Science Foundation of China (Grant Nos. 12204484, 51672279, 12174398 and 11874361), the Anhui Key Research and Development Program (Grant No. 2022h11020007), and the HFIPS Director’s Fund of the Chinese Academy of Sciences (Grant Nos. BJPY2022B02, YZJJ202102, YZJJ-GGZX-2022-01, and 2021YZGH03). We thank the BL10XU station of Spring-8 Synchrotron Radiation Facility and the BL15U1 station and Raman Auxiliary Laboratory of Shanghai Synchrotron Radiation Facility (SSFR) for the synchrotron XRD measurements. We thank the National Synchrotron Radiation Laboratory and the Instruments Center for Physical Science of USTC for providing the conditions to determine the bandgaps of lutetium hydrides. Part of the bandgap measurement was performed in the National Synchrotron Radiation Laboratory and the Instruments Center for Physical Science of USTC.

The authors have no conflicts to disclose.

Yuan-Ao Peng: Data curation (equal). Han-Yu Wang: Data curation (equal). Fu-Hai Su: Data curation (equal). Pu Wang: Data curation (equal). Hai-An Xu: Data curation (equal). Lin Liu: Data curation (equal). Lun-Xuan Yu: Data curation (equal). Ross T. Howie: Data curation (equal). Wan Xu: Data curation (equal); Formal analysis (equal); Writing – original draft (equal); Writing – review & editing (equal). Eugene Gregoryanz: Writing – review & editing (equal). Xiao-Di Liu: Conceptualization (equal); Formal analysis (equal); Project administration (equal); Resources (equal); Supervision (equal); Writing – review & editing (equal).

The data that support the findings of this study are available within the article and its supplementary material and from the corresponding authors upon reasonable request.

1.
T.
Palasyuk
and
M.
Tkacz
, “
Pressure-induced structural phase transition in rare-earth trihydrides. Part I. (GdH3, HoH3, LuH3)
,”
Solid State Commun.
133
,
481
486
(
2005
).
2.
T.
Palasyuk
and
M.
Tkacz
, “
Pressure-induced structural phase transition in rare-earth trihydrides. Part II. SmH3 and compressibility systematics
,”
Solid State Commun.
141
,
302
305
(
2007
).
3.
T.
Palasyuk
and
M.
Tkacz
, “
Pressure-induced structural phase transition in rare-earth trihydrides. Part III. Systematics: General and geometric approach
,”
Solid State Commun.
141
,
354
358
(
2007
).
4.
C. E.
Holley
,
R. N. R.
Mulford
,
F. H.
Ellinger
,
W. C.
Koehier
, and
W. H.
Zachariasen
, “
The crystal structure of some rare earth hydrides
,”
J. Phys. Chem.
59
,
1226
1228
(
2002
).
5.
I. A.
Troyan
,
D. V.
Semenok
,
A. G.
Kvashnin
,
A. V.
Sadakov
,
O. A.
Sobolevskiy
et al, “
Anomalous high-temperature superconductivity in YH6
,”
Adv. Mater.
33
,
e2006832
(
2021
).
6.
M.
Somayazulu
,
M.
Ahart
,
A. K.
Mishra
,
Z. M.
Geballe
,
M.
Baldini
et al, “
Evidence for superconductivity above 260 K in lanthanum superhydride at megabar pressures
,”
Phys. Rev. Lett.
122
,
027001
(
2019
).
7.
N. P.
Salke
,
M. M.
Davari Esfahani
,
Y.
Zhang
,
I. A.
Kruglov
,
J.
Zhou
et al, “
Synthesis of clathrate cerium superhydride CeH9 at 80–100 GPa with atomic hydrogen sublattice
,”
Nat. Commun.
10
,
4453
(
2019
).
8.
P.
Tsuppayakorn-aek
,
U.
Pinsook
,
W.
Luo
,
R.
Ahuja
, and
T.
Bovornratanaraks
, “
Superconductivity of superhydride CeH10 under high pressure
,”
Mater. Res. Express
7
,
086001
(
2020
).
9.
R.
Griessen
,
J. N.
Huiberts
,
M.
Kremers
,
A. T. M.
van Gogh
,
N. J.
Koeman
et al, “
Yttrium and lanthanum hydride films with switchable optical properties
,”
J. Alloys Compd.
253–254
,
44
50
(
1997
).
10.
Y.
Li
,
J.
Hao
,
H.
Liu
,
J. S.
Tse
,
Y.
Wang
et al, “
Pressure-stabilized superconductive yttrium hydrides
,”
Sci. Rep.
5
,
9948
(
2015
).
11.
P.
Kong
,
V. S.
Minkov
,
M. A.
Kuzovnikov
,
A. P.
Drozdov
,
S. P.
Besedin
et al, “
Superconductivity up to 243 K in the yttrium-hydrogen system under high pressure
,”
Nat. Commun.
12
,
5075
(
2021
).
12.
A. P.
Drozdov
,
P. P.
Kong
,
V. S.
Minkov
,
S. P.
Besedin
,
M. A.
Kuzovnikov
et al, “
Superconductivity at 250 K in lanthanum hydride under high pressures
,”
Nature
569
,
528
531
(
2019
).
13.
W.
Chen
,
D. V.
Semenok
,
X.
Huang
,
H.
Shu
,
X.
Li
et al, “
High-temperature superconducting phases in cerium superhydride with a Tc up to 115 K below a pressure of 1 megabar
,”
Phys. Rev. Lett.
127
,
117001
(
2021
).
14.
N.
Dasenbrock-Gammon
,
E.
Snider
,
R.
McBride
,
H.
Pasan
,
D.
Durkee
et al, “
Retracted article: Evidence of near-ambient superconductivity in a N-doped lutetium hydride
,”
Nature
615
,
244
250
(
2023
).
15.
X.
Ming
,
Y. J.
Zhang
,
X.
Zhu
,
Q.
Li
,
C.
He
et al, “
Absence of near-ambient superconductivity in LuH(2+/−x)Ny
,”
Nature
620
,
72
(
2023
).
16.
X.
Xing
,
C.
Wang
,
L.
Yu
,
J.
Xu
,
C.
Zhang
et al, “
Observation of non-superconducting phase changes in nitrogen doped lutetium hydrides
,”
Nat. Commun.
14
,
5991
(
2023
).
17.
D.
Peng
,
Q.
Zeng
,
F.
Lan
,
Z.
Xing
,
Y.
Ding
et al, “
The near-room-temperature upsurge of electrical resistivity in Lu–H–N is not superconductivity, but a metal-to-poor-conductor transition
,”
Matter Radiat. Extremes
8
,
058401
(
2023
).
18.
F.
Xie
,
T.
Lu
,
Z.
Yu
,
Y.
Wang
,
Z.
Wang
et al, “
Lu–H–N phase diagram from first-principles calculations
,”
Chin. Phys. Lett.
40
,
057401
(
2023
).
19.
M.
Liu
,
X.
Liu
,
J.
Li
,
J.
Liu
,
Y.
Sun
et al, “
Parent structures of near-ambient nitrogen-doped lutetium hydride superconductor
,”
Phys. Rev. B
108
,
L020102
(
2023
).
20.
Y.
Sun
,
F.
Zhang
,
S.
Wu
,
V.
Antropov
, and
K. M.
Ho
, “
Effect of nitrogen doping and pressure on the stability of LuH3
,”
Phys. Rev. B
108
,
L020101
(
2023
).
21.
Z.
Huo
,
D.
Duan
,
T.
Ma
,
Z.
Zhang
,
Q.
Jiang
et al, “
First-principles study on the conventional superconductivity of N-doped fcc-LuH3
,”
Matter Radiat. Extremes
8
,
038402
(
2023
).
22.
W.
Wu
,
Z.
Zeng
, and
X.
Wang
, “
Investigations of pressurized Lu–N–H materials by using the hybrid functional
,”
J. Phys. Chem. C
127
,
20121
20127
(
2023
).
23.
S. W.
Kim
,
L. J.
Conway
,
C. J.
Pickard
,
G. L.
Pascut
, and
B.
Monserrat
, “
Microscopic theory of colour in lutetium hydride
,”
Nat. Commun.
14
,
7360
(
2023
).
24.
K. P.
Hilleke
,
X. Y.
Wang
,
D. B.
Luo
,
N. S.
Geng
,
B. S.
Wang
et al, “
Structure, stability, and superconductivity of N-doped lutetium hydrides at kbar pressures
,”
Phys. Rev. B
108
,
014511
(
2023
).
25.
J.
Du
,
W.
Sun
,
X.
Li
, and
F.
Peng
, “
Pressure-induced stability and superconductivity in LuH12 polyhydrides
,”
Phys. Chem. Chem. Phys.
25
,
13320
13324
(
2023
).
26.
D.
Dangić
,
P.
Garcia-Goiricelaya
,
Y.-W.
Fang
,
J.
Ibañez Azpiroz
, and
I.
Errea
, “
Ab initio study of the structural, vibrational, and optical properties of potential parent structures of nitrogen-doped lutetium hydride
,”
Phys. Rev. B
108
,
064517
(
2023
).
27.
A.
Denchfield
,
F.
Belli
,
E.
Zurek
,
H.
Park
, and
R. J.
Hemley
, “
Quantum stabilization and flat hydrogen-based bands of nitrogen-doped lutetium hydride
,”
Phys. Rev. B
110
,
174110
(
2024
).
28.
Y.-W.
Fang
,
D.
Dangić
, and
I.
Errea
, “
Assessing the feasibility of near-ambient conditions superconductivity in the Lu–N–H system
,”
Commun. Mater.
5
,
61
(
2024
).
29.
R.
Lv
,
W.
Tu
,
D.
Shao
,
Y.
Sun
, and
W.
Lu
, “
Physical origin of color changes in lutetium hydride under pressure
,”
Chin. Phys. Lett.
40
,
117401
(
2023
).
30.
N. S.
Pavlov
,
I. R.
Shein
,
K. S.
Pervakov
,
V. M.
Pudalov
, and
I. A.
Nekrasov
, “
Anatomy of the band structure of the newest apparent near-ambient superconductor LuH3−xNx
,”
JETP Lett.
118
,
693
699
(
2023
).
31.
X.
Liang
,
Z.
Lin
,
J.
Zhang
,
J.
Zhao
,
S.
Feng
et al, “
Observation of flat band and van Hove singularity in non-superconducting nitrogen-doped lutetium hydride
,” arXiv:2308.16420 [cond-mat.supr-con] (
2023
).
32.
R.
Lucrezi
,
P. P.
Ferreira
,
M.
Aichhorn
, and
C.
Heil
, “
Temperature and quantum anharmonic lattice effects on stability and superconductivity in lutetium trihydride
,”
Nat. Commun.
15
,
441
(
2024
).
33.
C.
Tresca
,
P. M.
Forcella
,
A.
Angeletti
,
L.
Ranalli
,
C.
Franchini
et al, “
Molecular hydrogen in the N-doped LuH3 system as a possible path to superconductivity
,”
Nat. Commun.
15
,
7283
(
2024
).
34.
X.
Tao
,
A.
Yang
,
S.
Yang
,
Y.
Quan
, and
P.
Zhang
, “
Leading components and pressure-induced color changes in N-doped lutetium hydride
,”
Sci. Bull.
68
,
1372
1378
(
2023
).
35.
B.
Li
,
Y. Q.
Yang
,
Y. X.
Fan
,
C.
Zhu
,
S. L.
Liu
et al, “
Theoretical predictions on superconducting phase above room temperature in lutetium-beryllium hydrides at high pressures
,”
Chin. Phys. Lett.
40
,
097402
(
2023
).
36.
P. P.
Ferreira
,
L. J.
Conway
,
A.
Cucciari
,
S.
Di Cataldo
,
F.
Giannessi
et al, “
Search for ambient superconductivity in the Lu–N–H system
,”
Nat. Commun.
14
,
5367
(
2023
).
37.
S.
Cai
,
J.
Guo
,
H. Y.
Shu
,
L. X.
Yang
,
P. Y.
Wang
et al, “
No evidence of superconductivity in a compressed sample prepared from lutetium foil and H2/N2 gas mixture
,”
Matter Radiat. Extremes
8
,
048001
(
2023
).
38.
Y. J.
Zhang
,
X.
Ming
,
Q.
Li
,
X.
Zhu
,
B.
Zheng
et al, “
Pressure induced color change and evolution of metallic behavior in nitrogen-doped lutetium hydride
,”
Sci. China: Phys., Mech. Astron.
66
,
287411
(
2023
).
39.
X.
Zhao
,
P.
Shan
,
N.
Wang
,
Y.
Li
,
Y.
Xu
et al, “
Pressure tuning of optical reflectivity in LuH2
,”
Sci. Bull.
68
,
883
886
(
2023
).
40.
X. P.
Ma
,
N. N.
Wang
,
W. T.
Wang
,
J. Z.
Nie
,
W. L.
Gao
et al, “
Microstructure and structural modulation of lutetium dihydride LuH2 as seen via transmission electron microscopy
,”
Scr. Mater.
245
,
116022
(
2024
).
41.
J.
Guo
,
S.
Cai
,
D.
Wang
,
H.
Shu
,
L.
Yang
et al, “
Robust magnetism against pressure in non-superconducting samples prepared from lutetium foil and H2/N2 gas mixture
,”
Chin. Phys. Lett.
40
,
097401
(
2023
).
42.
D.
Wang
,
N. N.
Wang
,
C. S.
Zhang
,
C. S.
Xia
,
W. C.
Guo
et al, “
Unveiling a novel metal-to-metal transition in LuH2: Critically challenging superconductivity claims in lutetium hydrides
,”
Matter Radiat. Extremes
9
,
037401
(
2024
).
43.
X.
Li
,
Y.
Wang
,
Y.
Fu
,
S. A. T.
Redfern
,
S.
Jiang
et al, “
Stabilization of high-pressure phase of face-centered cubic lutetium trihydride at ambient conditions
,”
Adv. Sci.
11
,
e2401642
(
2024
).
44.
D.
Peng
,
Q. S.
Zeng
,
F. J.
Lan
,
Z. F.
Xing
,
Z. D.
Zeng
et al, “
Origin of the near-room temperature resistance transition in lutetium with H2/N2 gas mixture under high pressure
,”
Natl. Sci. Rev.
11
,
nwad337
(
2023
).
45.
P.
Li
,
J.
Bi
,
S.
Zhang
,
R.
Cai
,
G.
Su
et al, “
Transformation of hexagonal Lu to cubic LuH2+x single-crystalline films
,”
Chin. Phys. Lett.
40
,
087401
(
2023
).
46.
M.
Shao
,
S.
Chen
,
W.
Chen
,
K.
Zhang
,
X.
Huang
et al, “
Superconducting ScH3 and LuH3 at megabar pressures
,”
Inorg. Chem.
60
,
15330
15335
(
2021
).
47.
O.
Moulding
,
S.
Gallego Parra
,
Y.
Gao
,
P.
Toulemonde
,
G.
Garbarino
et al, “
Pressure-induced formation of cubic lutetium hydrides derived from trigonal LuH3
,”
Phys. Rev. B
108
,
214505
(
2023
).
48.
T.
Scheler
,
M.
Marques
,
Z.
Konopkova
,
C. L.
Guillaume
,
R. T.
Howie
et al, “
High-pressure synthesis and characterization of iridium trihydride
,”
Phys. Rev. Lett.
111
,
215503
(
2013
).
49.
R. T.
Howie
,
C. L.
Guillaume
,
T.
Scheler
,
A. F.
Goncharov
, and
E.
Gregoryanz
, “
Mixed molecular and atomic phase of dense hydrogen
,”
Phys. Rev. Lett.
108
,
125501
(
2012
).
50.
N.
Hirao
,
S. I.
Kawaguchi
,
K.
Hirose
,
K.
Shimizu
,
E.
Ohtani
et al, “
New developments in high-pressure X-ray diffraction beamline for diamond anvil cell at SPring-8
,”
Matter Radiat. Extremes
5
,
018403
(
2020
).
51.
B. H.
Toby
and
R. B.
Von Dreele
, “
GSAS-II: The genesis of a modern open-source all purpose crystallography software package
,”
J. Appl. Crystallogr.
46
,
544
549
(
2013
).
52.
V.
Petříček
,
L.
Palatinus
,
J.
Plášil
, and
M.
Dušek
, “
JANA2020—A new version of the crystallographic computing system JANA
,”
Z. Kristallogr. Cryst. Mater.
238
,
271
282
(
2023
).
53.
B.
Kong
,
L.
Zhang
,
X. R.
Chen
,
T. X.
Zeng
, and
L. C.
Cai
, “
Structural relative stabilities and pressure-induced phase transitions for lanthanide trihydrides REH3 (RE = Sm, Gd, Tb, Dy, Ho, Er, Tm, and Lu)
,”
Physica B
407
,
2050
2057
(
2012
).
54.
H.
Meng
,
T.
Palasyuk
,
V.
Drozd
, and
M.
Tkacz
, “
Study of phase stability and isotope effect in dysprosium trihydride at high pressure
,”
J. Alloys Compd.
722
,
946
952
(
2017
).
55.
C.
Prescher
and
V. B.
Prakapenka
, “
DIOPTAS: A program for reduction of two-dimensional X-ray diffraction data and data exploration
,”
High Pressure Res.
35
,
223
230
(
2015
).