Metallization and Superconductivity in the Hydrogen-Rich Ionic Salt BaReH9
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2015-07-20 |
| Journal | The Journal of Physical Chemistry C |
| Authors | Takaki Muramatsu, Wilson K. Wanene, Maddury Somayazulu, Eugene A Vinitsky, Dhanesh Chandra |
| Institutions | Carnegie Institution for Science, Geophysical Laboratory |
| Citations | 76 |
| Analysis | Full AI Review Included |
6CCVD Technical Documentation: Hydrogen-Rich Hydrides and Megabar Research
Section titled â6CCVD Technical Documentation: Hydrogen-Rich Hydrides and Megabar ResearchâExecutive Summary
Section titled âExecutive SummaryâThis documentation analyzes the high-pressure research on BaReH9, a hydrogen-rich ionic salt, highlighting the extreme material requirements for Diamond-Anvil Cell (DAC) studies in the megabar regime. The findings underscore the critical role of high-purity, engineering-grade diamond required for next-generation solid-state physics research.
- Discovery of Superconductivity: BaReH9, a candidate for dense hydrogen studies, transforms into a metallic superconductor above 100 GPa, exhibiting a maximum transition temperature (Tc) near 7 K.
- Extreme Pressure Demands: The study required specialized DACs capable of sustained operation up to 150 GPa, necessitating ultra-high strength, defect-free Single Crystal Diamond (SCD) anvils.
- Kinetics and Path Dependence: The insulator-to-metal transition is complex, showing sluggish kinetics, large pressure hysteresis, and dependence on the Pressure-Temperature (P-T) path. The transition was notably accelerated by red laser irradiation.
- Integrated Measurement Techniques: Experiments demanded precise in-situ electrical resistance measurements (using Pt electrodes) down to 1.8 K, combined with structural analysis via synchrotron X-ray diffraction and Raman spectroscopy.
- Optical Sensitivity: The use of red lasers (632 nm, 660 nm) was critical, as shorter wavelengths (488 nm, 532 nm) caused significant photo-induced sample damage above 20 GPa, demonstrating the need for precise optical handling through the diamond window.
- High Field Confirmation: Superconductivity was confirmed by the suppression of the resistance drop under applied magnetic fields, with an estimated upper critical field (Hc2) exceeding 5 T.
Technical Specifications
Section titled âTechnical SpecificationsâThe following parameters define the operational and physical boundaries established by the research:
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Maximum Applied Pressure | 150 | GPa | Pressure reached in Run 2, confirming SC persistence. |
| Superconducting Transition (Tc) | ~7 | K | Maximum critical temperature observed. |
| Zero Resistance Temperature | 2.2 | K | Extrapolated T for zero resistance at 139 GPa. |
| Metallic Phase Onset Pressure | 60 - 80 | GPa | Bracketed range for insulator-to-metal transition. |
| Magnetic Critical Field (Hc2) | > 5 | T | Required field to suppress superconductivity (Extrapolated). |
| Typical Diamond Anvil Tip Diameter | 100 | ”m | Flat top diameter, beveled from 300 ”m tips. |
| Minimum Diamond Tip Diameter Used | 60 | ”m | Used for highest pressure experiments (Run 3). |
| Recommended Laser Wavelength | 632, 660 | nm | Used for Raman/laser irradiation, minimizing damage. |
| Damaging Laser Wavelengths | 488, 532 | nm | Caused rapid sample damage above 20 GPa. |
| Minimum Measurement Temp. | 1.8 | K | Operational minimum for Quantum Design PPMS. |
Key Methodologies
Section titled âKey MethodologiesâThe following is an ordered list detailing the material and procedural requirements for achieving metallization and superconductivity measurements in BaReH9 under megabar pressure:
- Sample Synthesis and Handling: BaReH9 was synthesized via the reduction of perrhenate. Samples were extremely reactive and required careful loading into the DAC within an Argon (Ar) atmosphere glove box.
- Pressure Generation Components: High-pressure was generated using Diamond-Anvil Cells (DACs). Diamonds typically featured 300 ”m tips, beveled to create 100 ”m diameter flat tops for pressure stability.
- Electrode and Insulation Setup: Rhenium (Re) metal was used for gaskets, coated with an insulating mixture of cubic-Boron Nitride (c-BN) powder and epoxy. Platinum (Pt) electrodes were strategically placed for electrical measurements.
- Electrical Measurement Technique: Electrical resistance measurements predominantly employed the quasi-four-electrode technique (Runs 2 and 3) to accurately determine resistivity.
- Laser Use and Kinematic Control: Laser irradiation using low-power red lasers (632 nm, 660 nm) was used not just for Raman measurements, but also to accelerate the sluggish insulator-to-metal transition, demonstrating a kinetic dependence.
- Pressure Determination: Pressure was calibrated in situ using either the frequency shifts of ruby fluorescence or the first-order Raman band of the diamond anvils.
- Structural Confirmation: In-situ synchrotron x-ray diffraction (XRD) was utilized at beamline 16-BM-D of HPCAT to confirm structural changes and the preservation of the Ba-Re sublattice up to 120 GPa.
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & CapabilitiesâThis research relies heavily on materials science expertise to deliver reliable performance under extreme conditions (high pressure, low temperature, sensitive optics). 6CCVD provides the custom SCD and engineering solutions necessary to replicate or advance this foundational research into novel high-Tc hydrides.
| Research Requirement | 6CCVD Material/Capability | Value Proposition |
|---|---|---|
| Ultra-High Pressure Containment | High-Purity Single Crystal Diamond (SCD) Wafers & Substrates | Our SCD is manufactured via MPCVD, offering exceptional material purity and low defect density crucial for minimizing failure (cracking) under megabar forces, as noted in Run 3. We supply substrates up to 10mm thickness. |
| Electrical Interface & Contact | Custom Metalization (Pt, Au, Ti, W) | The use of Pt electrodes requires precise contact geometry. 6CCVD provides in-house metalization services, offering Pt or Ti/Pt/Au stack deposition directly onto prepared SCD plates, ensuring robust, low-resistance ohmic contacts essential for quasi-four-electrode setup. |
| Optical Access & Imaging | Optical Grade SCD (Low Birefringence) | For in-situ Raman scattering, ruby fluorescence, and minimized photo-induced damage (requiring 632 nm / 660 nm lasers), 6CCVD delivers highly transparent, low-birefringence SCD material. This ensures clean optical paths and reduced thermal distortion. |
| Precision Anvil Geometry | Custom Laser Cutting and Polishing | The experiment demanded extremely small flat tops (60 ”m - 100 ”m) and beveling. We offer precision diamond shaping services, including laser cutting for complex geometries and ultra-smooth polishing (Ra < 1nm for SCD) required for mating surfaces in DACs. |
| Advanced Gasket/Insulation Design | Polycrystalline Diamond (PCD) Plates (Up to 125mm) | For scaling experiments or developing integrated sensor platforms (like Rhenium gaskets combined with c-BN insulation), our large-area PCD plates (up to 125mm) provide stable, durable templates for high-pressure apparatus development. |
Engineering Support: 6CCVDâs in-house PhD team can assist researchers with material selection, geometry optimization, and metalization schemes tailored specifically for extreme High-Pressure/Low-Temperature (HP/LT) superconductivity projects. We ensure that diamond components meet the precise requirements to manage the kinetic and P-T path dependencies observed in hydride materials.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
BaReH<sub>9</sub> is an exceedingly high hydrogen content metal hydride that is predicted to exhibit interesting behavior under pressure. The high-pressure electronic properties of this material were investigated using diamond-anvil cell electrical conductivity techniques to megabar (100 GPa) pressures. The measurements show that BeReH<sub>9</sub> transforms to a metal and then superconductor above 100 GPa with a maximum T<sub>c</sub> near 7 K. The occurrence of superconductivity is confirmed by the suppression of the resistance drop on application of magnetic fields. The transition to the metallic phase is sluggish, but is accelerated by laser irradiation. Raman scattering and x-ray diffraction measurements, used to supplement the electrical measurements, indicate that the Ba-Re sublattice is largely preserved on compression at the conditions explored, but there is a possibility that hydrogen atoms are gradually disordered under pressure. This is suggested from sharpening of peaks of Raman spectroscopy and x-ray diffraction by heat treatment as well as temperature dependence of resistance under pressure. The data suggest that the transition to the superconducting state is first order. Furthermore, the possibility that the transition is associated with the breakdown of BeReH<sub>9</sub> is discussed.