Effect of Water on Lattice Thermal Conductivity of Ringwoodite and Its Implications for the Thermal Evolution of Descending Slabs

At a Glance

Metadata	Details
Publication Date	2020-05-25
Journal	Geophysical Research Letters
Authors	Enrico Marzotto, Wen‐Pin Hsieh, Takayuki Ishii, Keng‐Hsien Chao, Gregor Golabek
Institutions	Tohoku University, Institute of Earth Sciences, Academia Sinica
Citations	28
Analysis	Full AI Review Included

Technical Documentation & Analysis: MPCVD Diamond for High-Pressure Geophysics

Executive Summary

This research utilizes high-pressure diamond-anvil cell (DAC) experiments coupled with ultrafast Time Domain Thermoreflectance (TDTR) to determine the thermal properties of hydrous ringwoodite, a critical mineral in the Earth’s mantle transition zone (MTZ).

Core Achievement: Quantified the substantial reduction in lattice thermal conductivity ($\Lambda_{rw}$) of ringwoodite due to water incorporation under MTZ pressures (17-24 GPa).
Key Finding: The presence of $1.73 \text{ wt}%$ water reduces $\Lambda_{rw}$ by over $40%$ compared to dry ringwoodite at relevant MTZ pressures.
Methodology: DAC experiments utilized $400 \text{ µm}$ culet diamonds, requiring high-quality, optically transparent Single Crystal Diamond (SCD) for precise optical access and pressure stability.
Thermal Barrier Effect: The reduced thermal conductivity acts as a heat propagation barrier, significantly delaying the thermal decomposition of dense hydrous magnesium silicates (DHMS) by up to 27 Myr.
Geophysical Impact: This delay enables hydrous minerals to be transported to greater depths in the lower mantle (LM), fundamentally impacting the deep Earth water cycle.
6CCVD Relevance: The success of this high-P/T optical metrology relies directly on the quality and precision of the SCD anvils and the thin-film metalization (Al transducer), both of which are core 6CCVD capabilities.

Technical Specifications

The following hard data points were extracted from the research paper, focusing on experimental conditions and key results:

Parameter	Value	Unit	Context
Ringwoodite Stability Pressure	17 - 24	GPa	Mantle Transition Zone (MTZ) range
Maximum Water Content ($C_{H_2O}$)	1.73	wt%	Hydrous sample measurement
Thermal Conductivity Reduction	>40	%	Reduction due to $1.73 \text{ wt}%$ water at MTZ pressures
Dry $\Lambda_{rw}$ (Ambient Pressure)	4.84	W m^-1 K^-1	Calculated from empirical fit (0 wt% $C_{H_2O}$)
Dry $\Lambda_{rw}$ (20 GPa)	12.4	W m^-1 K^-1	Calculated from empirical fit (0 wt% $C_{H_2O}$)
Thermal Transducer Film	$\approx 90$	nm	Thickness of Al film deposited on sample
Sample Thickness (Polished)	$\approx 25$	µm	Thickness of ringwoodite crystal for TDTR
TDTR Modulation Frequency	8.7	MHz	Frequency used for pump beam synchronization
Critical Decomposition Temperature ($T_{crit}$)	1500	K	Temperature for DHMS breakdown
Maximum Thermal Delay Time ($t_{delay}$)	20 - 27	Myr	Observed for $C_{H_2O} = 1.5 \text{ wt}%$ and $D_{hyd} = 15-20 \text{ km}$
DAC Culet Size	400	µm	Diamond anvil size used in the experiment

Key Methodologies

The experiment combined high-pressure synthesis and advanced thermal measurement techniques, relying heavily on precision material preparation and high-quality diamond optics.

Sample Synthesis: Ringwoodite was synthesized from San Carlos Olivine (SCO) powder using 1,000- and 1,200-t multianvil presses.
- Dry Synthesis: 22 GPa and 1900 K for 1.25 hr (Re foil capsule).
- Hydrous Synthesis: 20-22 GPa and 1600-1700 K for 3-8 hr (Pt₉₅Rh₅ capsule with distilled water).
Sample Preparation: Selected ringwoodite crystals were double-side polished to $\approx 25 \text{ µm}$ thickness.
Transducer Deposition: Samples were coated with an $\approx 90 \text{ nm}$ thick Aluminum (Al) film, which acts as the thermal transducer for the TDTR measurement.
High-Pressure Setup: Samples were loaded into a symmetric piston-cylinder Diamond-Anvil Cell (DAC) utilizing $400 \text{ µm}$ culet diamonds. Silicone oil was used as the pressure medium.
Pressure Calibration: Pressure inside the DAC was estimated using ruby fluorescence, providing an uncertainty typically less than $5%$.
Thermal Measurement (TDTR): Ultrafast optical pump-probe metrology was used to measure the lattice thermal conductivity ($\Lambda_{rw}$) by monitoring the temperature evolution of the Al film synchronized with the $8.7 \text{ MHz}$ pump beam modulation frequency.

6CCVD Solutions & Capabilities

The successful execution of high-P/T TDTR experiments, such as this study on ringwoodite, is fundamentally dependent on the quality and customization of the diamond components and thin-film deposition. 6CCVD is uniquely positioned to supply the necessary materials and engineering support to replicate and advance this research.

Applicable Materials and Services

Research Requirement	6CCVD Solution & Capability	Technical Advantage
High-Pressure Anvils (DAC)	Optical Grade Single Crystal Diamond (SCD)	6CCVD provides high-purity, low-defect SCD plates, ensuring maximum optical transparency for pump/probe access (TDTR) and superior mechanical stability required for pressures up to 25 GPa and beyond.
Thermal Transducer Coating	Custom Metalization Services (Au, Pt, Pd, Ti, W, Cu)	The TDTR method requires precise, uniform thin-film deposition. 6CCVD offers in-house metalization capabilities, including Al, Ti, Pt, and Au, tailored to specific thickness requirements (e.g., $90 \text{ nm}$ Al) for optimal thermal and electrical transducer performance.
Precision Polishing	Ultra-Low Roughness Polishing (Ra < 1nm SCD)	Precision polishing of SCD anvils and substrates is critical for maintaining optical flatness and ensuring uniform pressure distribution and accurate thermal contact, minimizing measurement uncertainty (Hsieh, 2015).
Custom Anvil Dimensions	Custom Dimensions & Laser Cutting	6CCVD can supply SCD or Polycrystalline Diamond (PCD) plates up to $125 \text{ mm}$ and provide custom laser cutting to produce anvils with specific culet sizes (e.g., $400 \text{ µm}$) or specialized geometries required for multi-anvil or DAC setups.
Extension to Electrical Studies	Boron-Doped Diamond (BDD)	To extend this research to the electrical properties of hydrous minerals (e.g., electrical conductivity), 6CCVD supplies highly conductive BDD substrates, stable under extreme P/T conditions, ideal for integrated electrical measurements in the DAC.

Engineering Support

6CCVD’s in-house team of PhD material scientists specializes in optimizing MPCVD diamond properties for extreme environments. We offer consultation services to assist researchers in selecting the optimal diamond grade (e.g., low-birefringence SCD for optical experiments, high-toughness PCD for large-volume presses) and designing custom metalization stacks for complex high-P/T metrology projects, such as TDTR or electrical conductivity measurements in geophysics.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

View Original Abstract

Abstract The presence of water in minerals generally alters their physical properties. Ringwoodite is the most abundant phase in the lowermost mantle transition zone and can host up to 1.5-2 wt% water. We studied high‐pressure lattice thermal conductivity of dry and hydrous ringwoodite by combining diamond‐anvil cell experiments with ultrafast optics. The incorporation of 1.73 wt% water substantially reduces the ringwoodite thermal conductivity by more than 40% at mantle transition zone pressures. We further parameterized the ringwoodite thermal conductivity as a function of pressure and water content to explore the large‐scale consequences of a reduced thermal conductivity on a slab’s thermal evolution. Using a simple 1‐D heat diffusion model, we showed that the presence of hydrous ringwoodite in the slab significantly delays decomposition of dense hydrous magnesium silicates, enabling them to reach the lower mantle. Our results impact the potential route and balance of water cycle in the lower mantle.

Tech Support

Original Source

DOI: https://doi.org/10.1029/2020gl087607