{"id":"ecbefb7b-01e6-4912-a4bf-a31de658e64d","arxiv_id":"2507.08009","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":6.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":0,"one_line_summary":"LaH10 synthesized at 138 to 182 GPa retains its crystal structure and ~250 K superconducting transition for at least 66 months, contradicting a reported two-month decomposition.","lead":"This comment reports that lanthanum superhydride (LaH10) remains superconducting and structurally intact for over five years at high pressure. It directly challenges a recent Nature Communications claim that LaH10 decomposes within two months, using long-term X-ray diffraction and resistance measurements.","discovery_kind":"replication","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The 66-month stability evidence comes from LaH10 synthesized via La + H2 gas, not from Zhou et al.'s LaH3 + NH3BH3 route, so the claimed direct contradiction is not established.","rationale":"The paper provides substantial evidence that its own LaH10 samples, synthesized from La metal and H2 gas, retain a high superconducting transition temperature for up to 66 months, with X-ray diffraction confirming the lattice at 55 months for one sample. This is an independent and valuable experimental result. However, the paper's framing as a direct refutation of Zhou et al. depends on the assumption that the phase synthesized by Zhou from LaH3 and NH3BH3 is the same Fm-3m-LaH10 phase studied here. That equivalence is not demonstrated. The reader's weakest assumption focused on stoichiometry verification, and that concern is real; but even a direct hydrogen-content measurement on the present samples would not resolve the synthesis-route mismatch. The reader's rationale did mention the failure to replicate Zhou's exact synthesis conditions, so there is partial agreement. The correct verdict remains conditional: the paper's stability claim for its own samples is credible, but the contradictory force against Zhou et al. is not yet established without a replication study using the ammonia borane route.","tokens_in":6046,"tokens_out":5277,"duration_ms":63298,"concrete_test":"Replicate Zhou et al.'s synthesis exactly: laser-heat LaH3 with NH3BH3 at ~170 GPa, and monitor the same sample by X-ray diffraction, four-probe resistance, and 1H NMR over at least 60 days. If the Fm-3m-LaH10 phase and Tc ≈ 250 K persist while the NMR hydride signal remains constant, the contradiction is confirmed. If decomposition is observed, the present comment's samples are not comparable to Zhou's.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The central claim is that Fm-3m-LaH10 is thermodynamically stable under Zhou et al.'s formation conditions and that its long-term stability directly contradicts their observed decomposition. The load-bearing link is the assumed equivalence between the samples studied here and those in Ref. 14. Sample IV was made from a La piece and H2 gas by pulsed laser heating at 156/172 GPa (Fig. 2), and sample V from La + H2 at 151/182 GPa (Fig. 3). Zhou et al. instead laser-heated LaH3 with NH3BH3 at 170 GPa and reported LaHx with x = 10.2–11.1, a composition that may include higher hydrides such as Pm-3m-LaH11-12 (which appears as an impurity in the present sample V). The comment never reproduces the NH3BH3 synthesis, never characterizes Zhou's product by X-ray diffraction, and never shows that Zhou's NMR-observed phase is identical to Fm-3m-LaH10. Thermodynamic stability of Fm-3m-LaH10 relative to LaH3 + H2 (refs 1–3) does not rule out decomposition of a non-stoichiometric or differently synthesized hydride, nor does it address kinetic or impurity effects. Therefore the 66-month stability of LaH10 made from La + H2, while valuable, does not by itself contradict Zhou's observation; the contradiction hinges on an unverified sample equivalence.","agreement_with_reader":"partial"},"referee_report":{"model":"deepseek-v4-flash","summary":"This manuscript is a Comment on Zhou et al. (Nat. Commun. 16, 1135, 2025), who reported that a lanthanum superhydride synthesized by laser heating LaH3 with NH3BH3 at 170 GPa decomposes into LaH3 and H2 over roughly two months. The present authors argue instead that metal superhydrides are thermodynamically stable under their formation conditions, and they present long-term experimental data on two Fm-3m-LaH10 samples made from La and H2: X-ray diffraction at 9 days and 55 months after synthesis for one sample, and four-probe resistance measurements showing Tc near 250 K at 2 days, 8 months, and 66 months for another sample. They also describe an earlier sample that survived decompression to 120 GPa without decomposing. On this basis they claim that their results directly contradict Zhou et al. and that Fm-3m-LaH10 remains stable for at least 66 months.","tokens_in":6319,"tokens_out":5933,"duration_ms":69955,"significance":"If the long-term data are taken at face value, the paper provides a valuable and rare longitudinal dataset: repeated electrical resistance measurements on a sample over 66 months and repeated synchrotron X-ray diffraction on another sample over 55 months, both consistently indicating the persistence of a phase with Tc near 247-250 K. The paper is also transparent about the use of two different pressure scales and makes source data available. However, the central claim that these observations directly contradict Zhou et al. is not supported, because the samples studied here were made by a different synthesis route (La + H2) and are not demonstrated to be equivalent to Zhou's LaHx (x = 10.2-11.1) product. In addition, no direct hydrogen-content measurement was performed on aged samples, so the inference of unchanged chemical composition rests on an assumption.","major_comments":[{"comment":"The paper's central assertion that its results 'directly contradict' Zhou et al. (Ref. 14) is not established because the samples are not shown to be equivalent. Zhou et al. synthesized LaH_x (x = 10.2-11.1) by laser heating LaH3 with NH3BH3 at 170 GPa, whereas the samples in Figures 2 and 3 were made from La + H2 and contain impurities of P63/mmc-LaH~10 and Pm-3m-LaH11-12; the manuscript neither reproduces the NH3BH3 route nor characterizes Zhou's product by X-ray diffraction. A concrete test of the contradiction would be to monitor a sample prepared exactly as in Ref. 14, and until then the 66-month stability of the La + H2 product does not, by itself, rule out decomposition of a differently synthesized, possibly non-stoichiometric hydride.","section":"Abstract and first section of the main text"},{"comment":"The inference that an unchanged diffraction pattern implies 'the same chemical composition' over 55 months is underdetermined. The observed <0.5% lattice-parameter decrease is attributed entirely to a slight pressure increase, but a comparable contraction could also result from a modest hydrogen loss, and no direct hydrogen-content measurement, Rietveld occupancy refinement, mass balance, or NMR analysis of the aged samples is reported. The paper should either supply quantitative hydrogen-content information or explicitly limit the conclusion to lattice stability rather than chemical stability.","section":"Figure 2 and its caption"},{"comment":"The statement that under the formation conditions 'metal superhydrides are thermodynamically more stable than metal trihydrides' is based on external calculations (Refs. 1-3) for ideal stoichiometric Fm-3m-LaH10 relative to LaH3 + H2, not on a free-energy analysis of the non-stoichiometric LaH10.2-11.1 phase or of the LaH3 + NH3BH3 reaction environment. Without applying the calculation to the exact composition and synthesis route of Ref. 14, the claim that Zhou's samples 'cannot spontaneously decompose' is not supported.","section":"Thermodynamic-stability paragraph"},{"comment":"The abstract states that the Fm-3m-LaH10 phase has been found to remain stable for at least 66 months 'as confirmed by X-ray diffraction and four-probe electrical resistance measurements,' but no X-ray diffraction pattern at the 66-month time point is presented. The X-ray diffraction evidence extends to 55 months in Sample IV, whereas the 66-month datum is a resistance measurement in Sample V without a contemporaneous structural characterization; the combined claim overstates what is shown for a single sample.","section":"Abstract and Figure 3"},{"comment":"The 66-month stability claim relies on R(T) transitions with Tc quoted only as 'approximately 250 K' and with no transition widths, onset criteria, or error bars, while pressures are reported on two different Raman scales that differ by roughly 20 GPa. Because the paper attributes minor Tc and lattice-parameter variations to pressure drift, it should provide simultaneous pressure determinations and quantify the uncertainty in Tc; otherwise the stability of Tc over time cannot be cleanly separated from pressure-calibration effects.","section":"Figure 3 and its caption"}],"minor_comments":[{"comment":"The title refers to 'metal superhydrides' generally, but the long-term stability data are for Fm-3m-LaH10 only; consider narrowing the title to reflect the actual scope.","section":"Title"},{"comment":"Pressures in the Raman spectra are presented using two scales (PH and PD) that differ by about 20 GPa; the text should state explicitly which scale is used for each pressure quoted in the main narrative.","section":"Figures 2d and 3e"},{"comment":"The argument that an increase in hydrogen content can also decrease Tc is logically fine but does not directly address the specific possibility of hydrogen loss in Zhou et al.; the example of lanthanum dihydride is not closely related to the superhydride regime and should be labeled as illustrative rather than as contrary evidence.","section":"Main text, discussion of Ref. 14"},{"comment":"The notation 'P63/mmc-LaH~10' is not defined; please clarify whether it denotes an off-stoichiometric LaH10-x phase or a distinct hexagonal structure.","section":"Main text, sample descriptions"},{"comment":"The claim that Zhou et al.'s broad low-Tc transitions indicate the absence of Fm-3m-LaH10 would be stronger if the manuscript provided quantitative transition widths and definitions of Tc for the comparison samples.","section":"Discussion of Ref. 14 electrical measurements"}],"recommendation":"major_revision","confidential_remarks":"The long-term stability data are a useful contribution in their own right, but the Comment format requires a direct contradiction with Ref. 14 that the present experiments cannot support because of the synthesis-route mismatch and the absence of hydrogen-content analysis on aged samples. A revised version that reframes the paper as a report of long-term stability of Fm-3m-LaH10 synthesized from La + H2, with the thermodynamic discussion as context rather than as a proof against Zhou et al.'s observations, would be more defensible."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"You'll want to know this: the new experimental data here are real and worth having, but the paper overreaches when it says it directly contradicts Zhou et al. The two parts need to be judged separately.\n\nWhat's good: sample IV shows the same X-ray diffraction pattern at 55 months as at one week, with only a <0.5% lattice parameter change attributed to pressure drift. Sample V shows Tc ≈ 250 K at 8 and 66 months. That is genuinely new longitudinal evidence that Fm-3m-LaH10 made from La + H2 gas is durable under megabar pressures. The paper also makes a fair point that Zhou et al. never did XRD on their NMR samples, and that their resistive transitions were broad with low Tc, so the phase identity in Zhou's study is not well established.\n\nThe soft spot is exactly what the stress-test flagged. Zhou used LaH3 + NH3BH3 at 170 GPa and reported LaHx with x = 10.2–11.1, which may include higher hydrides like Pm-3m-LaH11-12—and that phase actually appears as an impurity in the present sample V. The comment never reproduces the NH3BH3 synthesis, never characterizes Zhou's product, and never shows that the NMR-observed phase is the same Fm-3m-LaH10 studied here. So the 66-month stability of LaH10 made from La + H2 does not by itself contradict Zhou's observation of decomposition of a differently made, possibly non-stoichiometric hydride. The thermodynamic argument (superhydrides more stable than trihydrides) is generic and rests on DFT, not on direct free-energy measurements, so it cannot rule out kinetic or impurity effects in Zhou's samples.\n\nMinor issues: no direct hydrogen-content measurement on the aged samples, no error bars on Tc or pressure, and the pressure estimates differ by up to ~30 GPa depending on whether you use the H2 vibron or diamond edge Raman scale. These are addressable, not fatal.\n\nI'd send this to peer review. The long-term stability data deserve to be published; the commentary around them should be revised to drop or soften the direct-contradiction claim and explicitly acknowledge the unverified sample equivalence. For researchers in high-pressure superconductivity, this is a useful data point, and it sharpens the open question of whether Zhou's transient hydrogenation is specific to their synthesis route.","headline":"Solid multi-year stability data for LaH10, but the direct contradiction with Zhou et al. is weakened by the different synthesis route and unverified sample equivalence.","tokens_in":6898,"tokens_out":2314,"would_cite":true,"duration_ms":27006,"reading_group":"maybe","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":[],"model":"deepseek-v4-flash","headline":"The paper reports that the hydrogen-rich superconducting phase Fm-3m-LaH10 remained structurally intact and retained its ~250 K superconducting transition for at least 66 months after synthesis, directly contradicting a 2025 report that…","keywords":["lanthanum superhydride","LaH10","long-term stability","high-temperature superconductivity","diamond anvil cell","X-ray diffraction","four-probe electrical resistance","superhydride decomposition"],"falsifier":"A decisive observation would be a hydrogen-sensitive measurement on a sample that has been aged for years under pressure: quantify the free H2 inside the diamond anvil cell and the hydrogen content of the solid phase, for example by NMR, neutron diffraction, or mass balance upon decompression. If the aged sample has measurably lost hydrogen or accumulated H2 gas while the ~250 K transition persists, then the unchanged XRD and Tc are indeed insufficient and the stability claim fails; if hydrogen content is unchanged, the claim is confirmed.","tokens_in":5839,"feed_emoji":"⚡","tokens_out":10195,"duration_ms":101702,"temperature":0.7,"pith_summary":"This paper directly challenges a 2025 claim that the near-room-temperature superconductor LaH10 breaks down into LaH3 and hydrogen gas within two months of being synthesized. The authors report that in their own diamond-anvil-cell samples, the Fm-3m-LaH10 phase kept its crystal lattice for at least 55 months and its superconducting transition near 247–250 K for at least 66 months, as judged by X-ray diffraction and four-probe electrical resistance measurements. They argue this is direct experimental evidence that metal superhydrides are thermodynamically more stable than metal trihydrides under the pressures where they form, consistent with earlier theoretical predictions. The disagreement matters because hydride superconductors could only anchor the field's claims of near-room-temperature superconductivity if the phase is durable enough to study and confirm.","feed_headline":"LaH10 superconductor stays stable and superconducting for 66 months","feed_subtitle":"X-ray and resistance data contradict claims that LaH10 decomposes within two months.","key_machinery":"The central object is the Fm-3m-LaH10 phase, a face-centered cubic lanthanum superhydride whose high hydrogen content is responsible for its high superconducting transition temperature. The load-bearing mechanism is the long-baseline comparison of two complementary measurements on the same diamond-anvil-cell sample: X-ray powder diffraction with Le Bail refinement to track the crystal lattice, and four-probe electrical resistance to track the superconducting transition. Because Tc in these hydrides is highly sensitive to hydrogen content, the reproducible ~250 K transition across 8, 34, and 66 months serves as an indirect stoichiometry check, while the diffraction pattern rules out a large-scale phase change. Pressure is tracked independently by the diamond Raman edge and the hydrogen vibron, so pressure drift can be separated from chemical change.","core_discovery":"On its own terms, the paper's central claim is that Fm-3m-LaH10 — the hydrogen-rich lanthanum superhydride with a face-centered cubic structure that superconducts near 250 K — does not decompose on a timescale of months or years under the conditions used to synthesize it. The evidence is longitudinal: for one sample, X-ray diffraction one week and 55 months after synthesis shows the same Fm-3m phase with lattice parameters within 0.5%, and resistance at 34 months gives a superconducting transition near 247 K; for a second sample, resistance measurements 2 days, 8 months, and 66 months after synthesis all show a transition near 250 K, with X-ray diffraction about one month after synthesis confirming the Fm-3m phase. A sample decompressed to 120 GPa distorted structurally and lost its high Tc, but recompression to 136 GPa restored Tc around 241 K, showing that the phase is robust over a pressure range rather than being a transient product. The paper further argues that the earlier NMR-based decomposition study never structurally characterized its samples and that its resistance data show transitions well below the ~250 K signature of Fm-3m-LaH10, so the proposed decomposition scenario likely refers to a different material.","pith_inferences":["A step beyond the paper's evidence would be a hydrogen-sensitive measurement on the aged samples, such as quantitative NMR of the cell contents, neutron diffraction, or mass balance upon decompression; if those confirmed full stoichiometry, the decomposition claim would be closed rather than merely contradicted.","If long-term stability is generic across superhydrides, it would change experimental planning: beam time, transport, and multi-technique campaigns could be scheduled around months-old samples, making these materials much more practical to study.","The disagreement between the two groups could be resolved by exchanging samples or protocols: if a structurally confirmed LaH10 sample is tracked by NMR under the criticized study's conditions and shows no hydrogen buildup, the earlier conclusion would be attributed to sample identity, not to intrinsic instability.","One extension beyond the paper is to apply the same multi-year tracking to other superhydrides such as CeH9, YH9, or ternary hydrides, which would reveal whether thermodynamic stability is a general property of superhydrides or specific to the lanthanum-hydrogen system."],"forward_implications":["If LaH10 is stable for five years, the near-room-temperature superconducting transition can be reproduced and studied by multiple techniques on the same sample, removing the need to race against decomposition.","The two-month decomposition scenario proposed by the criticized study would not apply to genuinely Fm-3m-LaH10 samples; the NMR-observed loss of proton signal likely needs an alternative explanation.","The phase remains intact even when pressure drops to about 120 GPa, where it distorts structurally; recompression restores the high Tc, so pressure excursions do not destroy the material.","The experimental stability data align with the theoretical prediction that Fm-3m-LaH10 is the thermodynamically stable phase above roughly 150 GPa, strengthening the case that high-Tc hydride phases are equilibrium phases rather than metastable transient products."],"supporting_citations":[{"why":"The report this paper rebuts: it claims LaH10 decomposes into LaH3 and H2 within two months, the scenario the paper argues against.","marker":"14"},{"why":"Original report of superconductivity at 250 K in Fm-3m-LaH10; supplies the synthesis route and the baseline Tc the paper re-measures years later.","marker":"10"},{"why":"Report of yttrium superhydrides with X-ray Rietveld refinement; provides parallel evidence that superhydrides form and persist under pressure.","marker":"5"},{"why":"Theoretical prediction that Fm-3m-LaH10 is thermodynamically stable above 150 GPa; the quantum-chemistry anchor for the stability claim.","marker":"3"},{"why":"Synthesis and stability study of lanthanum superhydrides; supports the phase identity and the persistence of LaH10 at lower pressures.","marker":"13"},{"why":"Study of LaH10 near a structural instability; shows decompression and recompression change Tc but do not decompose the sample.","marker":"9"},{"why":"Evidence that H3S retains its ~200 K superconductivity for years; used as precedent that hydride superconductors can be stable over long periods.","marker":"18"}],"fun_headline_variants":["LaH10 superconductor stable for 66 months, contradicts decomposition claim","Five-year stability shown for high-Tc LaH10 superhydride","X-ray and resistance data: LaH10 survives years, not months","LaH10 superconducting phase persists over 5 years, new evidence","Long-lived LaH10: stability and superconductivity endure for years"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The load-bearing premise is that an unchanged crystal structure and a superconducting transition near 250 K seen years after synthesis prove the sample is still the hydrogen-rich LaH10 phase with essentially full hydrogen content, a link the paper does not verify with a direct hydrogen-content measurement.","fun_headline_variants_meta":{"raw":{"variants":["LaH10 superconductor stable for 66 months, contradicts decomposition claim","Five-year stability shown for high-Tc LaH10 superhydride","X-ray and resistance data: LaH10 survives years, not months","LaH10 superconducting phase persists over 5 years, new evidence","Long-lived LaH10: stability and superconductivity endure for years"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000656,"raw_usage":{"total_tokens":3044,"prompt_tokens":1026,"completion_tokens":2018,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":642,"completion_tokens_details":{"reasoning_tokens":1923}},"tokens_in":642,"tokens_out":2018,"duration_ms":15152,"temperature":1.0,"reasoning_tokens":1923,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-06T20:27:42.833019+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"A decisive observation would be a hydrogen-sensitive measurement on a sample that has been aged for years under pressure: quantify the free H2 inside the diamond anvil cell and the hydrogen content of the solid phase, for example by NMR, neutron diffraction, or mass balance upon decompression. If the aged sample has measurably lost hydrogen or accumulated H2 gas while the ~250 K transition persists, then the unchanged XRD and Tc are indeed insufficient and the stability claim fails; if hydrogen content is unchanged, the claim is confirmed.","supporting_citations":[],"review_version":1}