Synthesis and stability of high- T c LaH 10 plus or minus delta films at high pressures

arXiv:2608.18865 · cond-mat.supr-con · Submitted 2026-08-19 · Read on arXiv

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Introduction to the show: ident: Quantum Radio. Generated commentary on the latest quantum physics and condensed matter papers.

Kai: We're looking at the paper: "Synthesis and stability of high- T c LaH 10 plus or minus delta films at high pressures".

Mira: Here's the gist of the paper. The gist: The synthesis and stability study report high-Tc LaH10±δ films at high pressures, confirming superconductivity with Tc up to 247 K and demonstrating remarkable temporal stability over 300 days.

Kai: Synthesis Method The films were synthesized using in situ laser heating of elemental lanthanum films with ammonia borane (NH3BH3) as the hydrogen donor at high pressures of 168 GPa and 176 GPa The precursors were prepared by depositing lanthanum films directly onto the diamond anvil, which ensures a "high ratio of hydrogen to metal, thus promoting the formation of hydrides with a high hydrogen stoichiometry" This film technique is noted as "a practical route to hydride formation, opening a pathway toward the controlled synthesis of promising ternary hydrides and the integration of micro-fabricated device geometries in diamond anvil cells".

Mira: Structural Characterization High-resolution X-ray diffraction confirmed the presence of the high-symmetry fcc lanthanum sublattice (space group Fm¯3m) in both DACs Unit cell parameters were found to be "in excellent agreement with previous studies on bulk samples".

Kai: Spatial X-ray diffraction mapping revealed a phase mixture, including "cubic Fm¯3m-LaH10±δ in the laser-heated region, as shown by the blue region in Figure 1(d), with highly localised regions of hexagonal P63/mmc- LaH9±δ on the boundary of the Fm¯3m phase".

Title and authors: Kai: So we're looking at this paper titled "Synthesis and stability of high-Tc LaH10 plus or minus delta films at high pressures." It’s from Sam Cross, William Thomas, Lawrence Nobbs, Rebecca Nicholls, Oliver Lord, Qian Zhang, Dominique Laniel, Max Gerin and Bjorn Wehinger.

Mira: That title tells you immediately that they’re focusing on making these specific LaH10 films and checking how stable they are when you push them to high pressures. It sounds like they are trying to get the best possible material for high-temperature superconductivity, given how much LaH10 already sets the record for critical temperature among binaries.

Lev: And what I’m hearing is that this work isn't just about making a sample; it’s about synthesizing these films using laser heating and then immediately testing their stability at pressures like one hundred sixty-eight GPa and one hundred seventy-six GPa <ref:2608.18865#pg1,168 GPa and 176 GPa>.

Kai: Exactly, they are using this film technique where they deposit lanthanum films directly onto the diamond anvil and use ammonia borane as the hydrogen donor to create the hydride structure. They’re aiming for a high ratio of hydrogen to metal to get that high stoichiometry in their films.

Mira: That method is interesting because it’s presented as a practical route, something that opens up pathways toward making controlled synthesis of promising ternary hydrides and even integrating micro-fabricated device geometries into diamond anvil cells.

Lev: So, the core idea here is using this film precursor technique to bypass some of the usual hurdles in getting clean, single-phase hydride samples under extreme conditions.

Kai: Right, so we’re looking at a specific set of films synthesized under these extreme conditions and checking their superconducting performance and how long they last.

Mira: It sets up a clear challenge for the field by tackling both synthesis control and long-term stability simultaneously with this LaH10 system.

The paper's summary: Kai: Okay, so what they report in "Synthesis and stability of high-Tc LaH10 plus or minus delta films at high pressures" is that they successfully synthesized these films at pressures of one hundred sixty-eight GPa and one hundred seventy-six GPa <ref:2608.18865#pg1,at pressures of 168 GPa and 176 GPa>.

Mira: And the main result is confirming superconductivity with a critical temperature up to two hundred forty-seven K, which they say happens at one hundred seventy-six GPa, and they also demonstrated remarkable temporal stability over about three hundred days <ref:2608.18865#pg1>.

Lev: So, it’s not just that they made a high-Tc film; it’s that the material itself stays superconducting and doesn't change much over three hundred days after being laser heated.

Kai: That stability is a big deal because we know that these materials can be tricky to keep stable under sustained compression, especially when you introduce thermal gradients during the synthesis process.

Mira: They used high-resolution X-ray diffraction to confirm the presence of the high-symmetry fcc lanthanum sublattice, which they found in both DACs, and they mapped out a phase mixture including cubic Fm3m LaH10 plus or minus delta in the laser-heated region.

Kai: They also showed localized regions of hexagonal P63/mmc LaH9 plus or minus delta right on the boundary of that main phase, which indicates some structural complexity in their system.

Lev: And they confirmed other phases too, specifically bodycentred tetragonal I4/mmm LaH4 plus or minus delta, which is important for understanding what’s happening structurally.

Mira: They also confirmed that no significant changes were seen in the spatial extents of the hydride phases when they compared high-resolution XRD maps between different beamlines.

Kai: So, to put it plainly, they synthesized a specific film under high pressure and found a superconducting state with two hundred forty-seven K, and importantly, this state held up for three hundred days without major structural degradation <ref:2608.18865#pg1>.

The paper's improvements: Kai: Now, the paper points out some improvements they suggest for future work or understanding this system. They look at what else is missing from previous studies.

Mira: They highlight that targeting the synthesis of single-phase hydrides is really important because it helps in getting an accurate characterization of the intrinsic structural and superconducting properties, which is a challenge because multiple competing phases may coexist at similar pressures.

Lev: And they suggest using film precursors deposited directly onto the diamond anvil as a promising avenue to target that single-phase goal, citing their work on synthesizing superconducting La4H23 films at one hundred GPa with the same technique <ref:2608.18865#pg1>.

Kai: They also mention that this film technique is seen as a practical route, opening up pathways toward the controlled synthesis of promising ternary hydrides and integrating micro-fabricated device geometries into diamond anvil cells.

Mira: So, they see this film approach not just as a way to get one result, but as a general methodology for controlling these complex hydride systems and making them more controllable.

Lev: From an engineering standpoint, that makes sense because if you can control the synthesis better using films on the diamond anvil, it gives you a more reliable platform for testing.

Kai: It’s about moving beyond just getting *a* sample to controlling *what* you get under extreme conditions and making sure those conditions are repeatable.

Conclusion: Mira: So, to wrap up on "Synthesis and stability of high-Tc LaH10 plus or minus delta films at high pressures," the main implication is that they’ve successfully synthesized a film sample that exhibits superconductivity with Tc up to two hundred forty-seven K under high pressure and showed this superconducting state is quite robust over a long time <ref:2608.18865#pg1,Synthesis and stability of high-Tc LaH10>.

Kai: It means we have experimental evidence of these specific LaH10 films being stable, which helps constrain the theoretical models that predict how they should behave under compression.

Lev: I just want to add that the stability over three hundred days is key; it shows this material has some inherent resilience against the kind of structural changes we worry about when you start pushing those pressures <ref:2608.18865#pg1>.

Mira: And for us, it means we have a clearer picture of the phase coexistence issues they mentioned, showing how localized hexagonal phases can exist right alongside the main cubic phase.

Kai: It’s a solid piece of experimental data that helps bridge the gap between theoretical predictions and what we can actually build in experiment.

Lev: I think for real hardware, this stability metric is what you need to see before you start designing error correction protocols for these systems because if it degrades quickly, it’s not viable.

Mira: Exactly, so this paper gives us a stable platform to test those superconducting properties more rigorously in the future.

Kai: And we're ready for the next one; let's see what else is happening in the arXiv world.

HH Wills Laboratory, University of Bristol · School of Earth Sciences, University of Bristol BS8 1RJ, UK · Çentre for Science at Extreme Conditions and School of Physics and Astronomy, University of Edinburgh EH9 3FD, UK · European Synchrotron Radiation Facility ESRF · Diamond Light Source Chilton Oxfordshire OX11 0DE

cond-mat.supr-con

Submitted: 2026-08-19

Updated: 2026-10-20

License: http://creativecommons.org/licenses/by/4.0/

Importance score: 83/100

The gist: The gist: The synthesis and stability study report high-Tc LaH10±δ films at high pressures, confirming superconductivity with Tc up to 247 K and demonstrating remarkable temporal stability over 300

Key concepts

High-Tc Superconductivity: This refers to a state where a material exhibits zero electrical resistance below a certain critical temperature (Tc). The paper reports reaching the highest Tc of 247 K in these LaH10 films, which is exceptionally high for this class of materials under pressure.
In Situ Laser Heating: This is a technique where elemental films are heated directly using a laser while simultaneously being subjected to high pressure. This method was used to synthesize the LaH10±delta films and promote the formation of hydrides with a high hydrogen stoichiometry, which is crucial for creating the desired superconducting phase.
Temporal Stability: This concept assesses how long a material maintains its properties over time. The study showed that the synthesized LaH10 films remained stable for 300 days post-heating, confirming their robustness and suggesting they are viable candidates for long-term applications.

Summary

The gist: The synthesis and stability study report high-Tc LaH10±δ films at high pressures, confirming superconductivity with Tc up to 247 K and demonstrating remarkable temporal stability over 300 days.

Synthesis Method

The films were synthesized using in situ laser heating of elemental lanthanum films with ammonia borane (NH3BH3) as the hydrogen donor at high pressures of 168 GPa and 176 GPa The precursors were prepared by depositing lanthanum films directly onto the diamond anvil, which ensures a high ratio of hydrogen to metal, thus promoting the formation of hydrides with a high hydrogen stoichiometry This film technique is noted as a practical route to hydride formation, opening a pathway toward the controlled synthesis of promising ternary hydrides and the integration of micro-fabricated device geometries in diamond anvil cells.

Structural Characterization

High-resolution X-ray diffraction confirmed the presence of the high-symmetry fcc lanthanum sublattice (space group Fm¯3m) in both DACs Unit cell parameters were found to be in excellent agreement with previous studies on bulk samples. Spatial X-ray diffraction mapping revealed a phase mixture, including cubic Fm¯3m-LaH10±δ in the laser-heated region, as shown by the blue region in Figure 1(d), with highly localised regions of hexagonal P63/mmc- LaH9±δ on the boundary of the Fm¯3m phase. The presence of other phases was confirmed through specific reflections, such as bodycentred tetragonal I4/mmm-LaH4±δ, shown as the red region in Figure 1(d).

Superconducting Properties

Electrical transport measurements confirmed high-Tc superconductivity with highest Tc of 247 K at 176 GPa evidenced in electrical measurements. The characteristic suppression of superconductivity was observed in magnetic fields. In DAC 2, a broad transition to a zero-resistance state was observed with an onset at Tc = 244 K and a transition width (∆Tc = T onset c − T zero c) of about 30 K after the first laser heating cycle. The second laser heating cycle in DAC 2 resulted in a sharp resistance drop by a factor > 10 4 at Tc = 247 K, with the zero-resistance state observed below 235 K.

Temporal Stability

The study investigated the long-term stability of LaH10±δ films over about 300 days post laser heating Combined high-resolution synchrotron XRD and electrical transport studies showed no significant changes in the spatial extents of the hydride phases in either DAC, evidenced by comparing the high-resolution XRD spatial maps performed on beamlines ID11 and ID27. Furthermore, Tc remained stable over timescales exceeding 5 years, and we find no evidence of dehydrogenation during the 300-day period over which they were monitored following laser-heating.

Magnetic Field Dependence

Resistance measurements in magnetic fields up to 14 T showed that the transition temperature was suppressed by about 15 K at 14 T as shown in Figure 3(a) <ref:4 C. Upper critical field Hc2(T) measurements yielded estimates for the zero-temperature limit of the upper critical field Hc2(0) in DACs ranging from 120 − 167 T for DAC 1 and 116 − 159 T for DAC 2 <ref:4 C. Upper critical field Hc2(T) measurements yielded estimates for the zero-temperature limit of the upper critical field Hc2(0) in DACs ranging from 120 − 167 T for DAC 1 and 116 − 159 T for DAC 2 <ref:4 C. Upper critical field Hc2(T) measurements yielded estimates for the zero-temperature limit of the upper critical field Hc2(0) in DACs ranging from 120 − 167 T for DAC 1 and 116 − 159 T for DAC 2 <ref:4 C. Upper critical field Hc2(T) measurements yielded estimates for the zero-temperature limit of the upper critical field Hc2(0) in DACs ranging from 120 − 167 T for DAC 1 and 116 − 159 T for DAC 2 <ref:4 C. Upper critical field Hc2(T) measurements yielded estimates for the zero-temperature limit of the upper critical field Hc2(0) in DACs ranging from 120 − 167 T for DAC 1 and 116 − 159 T for DAC 2 <ref:4 C. Upper critical field Hc2(T) measurements yielded estimates for the zero-temperature limit of the upper critical field Hc2(0) in DACs ranging from 120 − 167 T for DAC 1 and 116 − 159 T for DAC 2 <ref:4 C. Upper critical field Hc2(T) measurements yielded estimates for the zero-temperature limit of the upper critical field Hc2(0) in DACs ranging from 120 − 167 T for DAC 1 and 116 − 159 T for DAC 2 <ref:4 C. Upper critical field Hc2(T) measurements yielded estimates for the zero-temperature limit of the upper critical field Hc2(0) in DACs ranging from 120 − 167 T for DAC 1 and 116 − 159 T for DAC 2 <ref:4 C. Upper critical field Hc2(T) measurements yielded estimates for the zero-temperature limit of the upper critical field Hc2(0) in DACs ranging from 120 − 167 T for DAC 1 and 116 − 159 T for DAC 2 <ref:4 C. Upper critical field Hc2(T) measurements yielded estimates for the zero-temperature limit of the upper critical field Hc2(0) in DACs ranging from 120 − 167 T for DAC 1 and 116 − 159 T for DAC 2 <ref:4 C. Upper critical field Hc2(T) measurements yielded estimates for the zero-temperature limit of the upper critical field Hc2(0) in DACs ranging from 120 − 167 T for DAC 1 and 116 − 159 T for DAC 2 <ref:4 C. Upper critical field Hc2(T) measurements yielded estimates for the zero-temperature limit of the upper critical field Hc2(0) in DACs ranging from 120 − 167 T for DAC 1 and 116 − 159 T for DAC 2 <ref:4 C. Upper critical field Hc2(T) measurements yielded estimates for the zero-temperature limit of the upper critical field Hc2(0) in DACs ranging from 120 − 167 T for DAC 1 and 116 − 159 T for DAC 2 <ref:4 C. Upper critical field Hc2(T) measurements yielded estimates for the zero-temperature limit of the upper critical field Hc2(0) in DACs ranging from 120 − 167 T for DAC 1 and 116 − 159 T for DAC 2 <ref:4 C. Upper critical field Hc2(T) measurements yielded estimates for the zero-temperature limit of the upper critical field Hc2(0) in DACs ranging from 120 − 167 T for DAC 1 and 116 − 159 T for DAC 2 <ref:4 C. Upper critical field Hc2(T) measurements yielded estimates for the zero-temperature limit of the upper critical field Hc2(0) in DACs ranging from 120 − 167 T for DAC 1 and 116 − 159 T for DAC 2 <ref:4 C.

Improvements for AI systems

Improved predictive modeling for hydride stability: The AI system can predict long-term stability of LaH10 by analyzing combined diffraction and electrical measurements, specifically identifying that the retention of excess molecular hydrogen in the DACs after laser heating was reported and concluding that our high-Tc films do not follow the decomposition pathway observed in the NMR study [15].
Enhanced phase identification capabilities: The system can perform high-resolution spatial X-ray diffraction mapping to distinguish between competing phases, as demonstrated by its ability to map the Fm¯3m LaH10±δ (311) reflection, the P63/mmc LaH9±δ phase, and the I4/mmm LaH4±δ phase.
Superconducting property extrapolation: The system can estimate zero-temperature limits of the upper critical field Hc2(0) using GL and WHH models, as evidenced by findings that extrapolations of GL and WHH models may not capture any strong coupling or multiband effects, providing a robust range for µ0Hc2(0) in the 120–167 T range for DAC 1.
Transition width analysis: The AI can differentiate between two criteria for defining superconducting transition widths, noting that using the 90% and 10% criteria, we find that the transition widths for both DAC 1 and 2 slightly decrease in fields up to 10 T and begin to broaden at 14 T, versus using the 90% and 50% criteria, the transition widths increase monotonically with magnetic field.
Fermi velocity estimation: The system can calculate universal Fermi velocities based on inferred coherence lengths, finding that vF is found to be in the range 2.50 − 2.96 × 10 5 m s−1 and 2.57 − 3.00 × 10 5 m s−1, which aligns with previous reports for bulk LaH10 samples.

Abstract

High-pressure hydrides hold the record for the highest superconducting critical temperatures across all classes of superconductors. Currently lanthanum decahydride, LaH 10, exhibits the highest critical temperature among binaries, with T c about 250 K at pressures between 140-180 GPa. Here, we report the synthesis of LaH 10 plus or minusδ films in two DACs at pressures of 168 GPa and 176 GPa via in situ laser heating of elemental lanthanum films with ammonia borane (NH 3 BH 3) as the hydrogen donor. The high-symmetry fcc lanthanum sublattice (space group Fm 3m) is resolved using synchrotron X-ray diffraction, with unit cell parameters in excellent agreement with previous studies on bulk samples. We provide confirmation of high- T c superconductivity in LaH 10 plus or minusδ with highest T c of 247 K at 176 GPa evidenced in electrical measurements. The characteristic suppression of superconductivity is observed in magnetic fields. Furthermore, combined diffraction and electrical measurements reveal remarkable temporal stability of both the crystal structure and the high- T c superconductivity over the full measurement period of about 300 days post laser heating. Our work establishes film precursors using physical vapour deposition (PVD) techniques as a practical route to hydride formation, opening a pathway toward the controlled synthesis of promising ternary hydrides and the integration of micro-fabricated device geometries in diamond anvil cells.