Synthesis of Na3WH9 and Na3ReH8 Ternary Hydrides at High Pressures

At a Glance

Metadata	Details
Publication Date	2024-10-31
Journal	Inorganic Chemistry
Authors	Tomás Marqueño, Israel Osmond, Mikhail A. Kuzovnikov, Hannah A. Shuttleworth, Samuel Gallego‐Parra
Institutions	Institute of Solid State Physics, Chinese Academy of Sciences
Citations	1
Analysis	Full AI Review Included

Synthesis of Na₃WH₉ and Na₃ReH₈ Ternary Hydrides at High Pressures: 6CCVD Technical Analysis

This document analyzes the requirements for high-pressure, high-temperature (HPHT) synthesis of novel ternary hydrides using Diamond Anvil Cell (DAC) techniques, focusing on the critical role of high-quality CVD diamond materials supplied by 6CCVD.

Executive Summary

The research successfully synthesized two novel high-hydrogen content ternary hydrides, Na₃WH₉ and Na₃ReH₈, under extreme conditions. This work highlights the necessity of ultra-high-performance Single Crystal Diamond (SCD) for advanced scientific research.

Core Achievement: Synthesis of stable Na₃WH₉ and Na₃ReH₈ featuring 18-electron homoleptic anions ([WH₉]^3- and [ReH₈]^3-) using DACs and infrared laser heating.
Extreme Conditions: Materials were synthesized and characterized at temperatures up to 1400 K and pressures up to 42.1 GPa.
Structural Analysis: In situ X-ray Diffraction (XRD) and Raman spectroscopy confirmed pressure-dependent phase transitions (distorted fcc Heusler → fcc → hexagonal structures).
Material Requirement: The experiment critically relies on Optical Grade Single Crystal Diamond (SCD) anvils, requiring exceptional purity (Type IIa) for transparency to both synchrotron X-rays, Raman lasers, and IR heating lasers.
6CCVD Value Proposition: 6CCVD specializes in providing custom-fabricated, ultra-low-absorption SCD substrates and anvils, polished to Ra < 1 nm, essential for replicating and extending this HPHT research.

Technical Specifications

The following hard data points were extracted from the experimental results, defining the extreme operating environment required for this synthesis.

Parameter	Value	Unit	Context
Synthesis Temperature (T)	1400	K	Achieved via infrared laser heating within the DAC.
Maximum Pressure (P) Tested (Na₃WH₉)	42.1	GPa	Stability range of the high-pressure phase (Na₃WH₉-II’).
Minimum Synthesis Pressure (Na₃WH₉)	7.8	GPa	Minimum pressure required for Na₃WH₉ formation.
Minimum Synthesis Pressure (Na₃ReH₈)	10.1	GPa	Minimum pressure required for Na₃ReH₈ formation.
Na₃WH₉ Phase Transition (II’ → II)	6.4 - 10	GPa	Symmetrization transition upon decompression.
Na₃ReH₈ Phase Transition (II’ → II)	17	GPa	Symmetrization transition upon decompression.
TM-H Stretching Modes (Raman)	1900 - 2500	cm^-1	Spectral region analyzed for transition metal-hydrogen bonds.
Predicted Metallization Pressure (Na₃WH₉)	> 180	GPa	DFT prediction; material is an electrical insulator below this pressure.

Key Methodologies

The synthesis and characterization of the ternary hydrides were achieved through a complex HPHT methodology utilizing specialized diamond components.

Sample Preparation: Reactants (NaH, W/Re powder) were loaded into a Diamond Anvil Cell (DAC) gasket hole, clamped initially at 0.2 GPa, and sealed with excess hydrogen (H₂).
High-Pressure Compression: The DAC was compressed to target synthesis pressures (e.g., 20 GPa to 42 GPa).
In Situ Laser Heating: Samples were heated to 1400 K using infrared laser heating. Rhenium metal was used as a laser absorption coupler in some experiments.
Structural Characterization (XRD): Powder X-ray Diffraction (XRD) was performed in situ at synchrotron facilities (DESY, ESRF) using short-wavelength radiation (λ ≈ 0.29 Å) to determine crystal structures and phase transitions.
Vibrational Characterization (Raman): Raman spectroscopy was used in situ to monitor the pressure evolution of the Transition Metal-Hydrogen (TM-H) bending and stretching modes (1900-2500 cm^-1).
Decompression Study: Samples were slowly decompressed to track structural changes and stability down to < 0.5 GPa.
Theoretical Modeling: DFT and Molecular Dynamics (MD) calculations were used to confirm structural stability, phase transitions, and electronic properties (band gap analysis).

6CCVD Solutions & Capabilities

The successful execution of HPHT experiments, particularly those involving laser heating and in situ spectroscopy, is fundamentally dependent on the quality and precision of the SCD anvils. 6CCVD is uniquely positioned to supply the necessary materials and customization services to support and advance this research field.

Applicable Materials

To replicate or extend this research, high-purity, low-absorption diamond is essential for the DAC anvils, ensuring maximum transmission for both the IR heating laser and the analytical beams (XRD/Raman).

6CCVD Material	Specification	Application in HPHT Research
Optical Grade SCD	Type IIa, Nitrogen < 1 ppm, Ra < 1 nm polishing.	Required for DAC anvils. Ensures high transparency across IR, visible, and X-ray spectra, minimizing absorption at 1400 K.
SCD Substrates	Thickness: 0.1 µm to 500 µm. Substrates up to 10 mm thick.	Ideal for use as high-pressure windows or as starting material for custom anvil fabrication.
Polycrystalline Diamond (PCD)	Plates up to 125 mm diameter. Ra < 5 nm polishing (inch-size).	Suitable for large-area high-pressure windows or backing plates where optical quality is less critical than mechanical strength.

Customization Potential

The precise geometry of DAC anvils (culet size, bevel angle, thickness) dictates the maximum achievable pressure and the experimental volume. 6CCVD offers full customization to meet specific HPHT requirements.

Custom Dimensions and Geometry: 6CCVD provides custom laser cutting and shaping services for SCD anvils, allowing researchers to specify precise culet diameters and bevels necessary for achieving pressures up to 42 GPa and beyond.
Ultra-Precision Polishing: Our internal polishing capability achieves surface roughness Ra < 1 nm on SCD, critical for maintaining optical quality and minimizing stress concentration points on the culet face under extreme load.
Metalization Services: The paper mentions the use of Rhenium (Re) as a laser coupler. 6CCVD offers in-house metalization (Au, Pt, Pd, Ti, W, Cu) for creating integrated heating elements or electrical contacts directly onto the diamond surface, facilitating complex electrical transport measurements in future HPHT studies.

Engineering Support

6CCVD’s in-house team of PhD material scientists and engineers are experts in CVD diamond growth and fabrication for extreme environments.

Application Expertise: We offer consultation on material selection (e.g., choosing the optimal SCD grade and thickness) for similar High-Pressure Ternary Hydride Synthesis projects, ensuring maximum performance and longevity of DAC components.
Global Logistics: We provide reliable global shipping (DDU default, DDP available) for sensitive, high-value diamond components, ensuring prompt delivery to synchrotron facilities and high-pressure laboratories worldwide.

Call to Action: For custom specifications or material consultation regarding high-pressure SCD anvils, optical windows, or metalized diamond components, visit 6ccvd.com or contact our engineering team directly.

View Original Abstract

The Na-W-H and Na-Re-H ternary systems were studied in a diamond anvil cell through X-ray diffraction and Raman spectroscopy, supported by density functional theory and molecular dynamics calculations. Na3WH9 can be synthesized above 7.8 GPa and 1400 K, remaining stable between at least 0.1 and 42.1 GPa. The rhenium analogue Na3ReH8 can form at 10.1 GPa upon laser heating, being stable between at least 0.3 and 32.5 GPa. Na3WH9 and Na3ReH8 host [WH9]3- and [ReH8]3- anions, respectively, forming homoleptic 18-electron complexes in both cases. Both ternary hydrides show similar structural types and pressure dependent phase transitions. At the highest pressures they adopt a distorted fcc Heusler structure (Na3WH9-II’ and Na3ReH8-II’) while upon decompression the structure symmetrizes becoming fcc between ∼6.4 and 10 GPa for Na3WH9-II and at 17 GPa for Na3ReH8-II. On further pressure release, the fcc phases transform into variants of a (quasi-) hexagonal structure at ∼3 GPa, Na3WH9-I and Na3ReH8-I.

Tech Support

Original Source

DOI: https://doi.org/10.1021/acs.inorgchem.4c02691