Correlated structural and electronic phase transformations in transition metal chalcogenide under high pressure

At a Glance

Metadata	Details
Publication Date	2016-04-04
Journal	Journal of Applied Physics
Authors	Chunyu Li, Feng Ke, Qingyang Hu, Zhenhai Yu, Jinggeng Zhao
Institutions	Carnegie Institution for Science, Geophysical Laboratory
Citations	7
Analysis	Full AI Review Included

6CCVD Technical Documentation: High-Pressure Semiconductor Physics

Executive Summary

This research investigates the structural and electronic properties of chromium sesquisulfide ($\text{Cr}_2\text{S}_3$), a key layered transition metal chalcogenide, under extreme pressure using Diamond Anvil Cell (DAC) methodologies. The findings are highly relevant to engineers optimizing thermoelectric and semiconductor materials for high-stress environments.

Application Focus: Comprehensive study of high-pressure structural (XRD) and electrical transport properties up to 36.3 GPa, supporting the development of advanced thermoelectric materials.
Core Achievement: Observation of a structural phase transition in rhombohedral $\text{Cr}_2\text{S}_3$ at approximately 16.5 GPa, confirmed via synchrotron angle dispersive X-ray diffraction (AD-XRD).
Electronic Transformation: Detection of a pressure-induced semiconductor-to-metal transition, characterized by a steep decrease in electrical resistance by an order of three across the 7 GPa to 15 GPa range.
Methodology: Utilized specialized DACs with 300 µm culets for pressure application and a custom four-electrode setup on the diamond surface for in-situ resistance measurements.
Material Implication: The necessity for highly stable, optically clear (for XRD), and electrically customized diamond anvils underscores the demand for 6CCVD’s Single Crystal (SCD) and Boron-Doped (BDD) diamond solutions.
DAC Engineering: The experiment required precision fabrication, including 300 µm culets and custom diamond surface modification for thin-film electrode integration.

Technical Specifications

The following hard data points were extracted from the experimental results and setup descriptions:

Parameter	Value	Unit	Context
Maximum Applied Pressure	36.3	GPa	Limit of high-pressure AD-XRD experiment
Structural Phase Transition Pressure	16.5	GPa	Observed onset of phase change via AD-XRD
Semiconductor-to-Metal Transition Range	14.4 to 17	GPa	Inferred from change in resistance temperature coefficient ($\text{dR}/\text{dT}$)
Electrical Resistance Reduction	Order of three (10³ factor)	N/A	Resistance drop observed between 7 GPa and 15 GPa
Isothermal Bulk Modulus ($\text{B}_0$)	59.8(6)	GPa	For the low-pressure (LP) phase of $\text{Cr}_2\text{S}_3$
Ambient Unit Cell Volume ($\text{V}_0$)	511.41(9)	Å³	Calculated from 3^rd-order Birch-Murnaghan fit
Resistance Measurement Temp Range	300 to 400	K	Used for characterizing temperature dependence of resistance
Diamond Anvil Culet Size	300	µm	Used for Symmetric DAC (XRD experiments)
Sample Chamber Diameter (XRD)	120	µm	Pre-indented stainless steel gasket size
Sample Chamber Diameter (Resistance)	150	µm	Hole diameter used for resistance measurement setup
Synchrotron Wavelength (X17C BNL)	0.4075	Å	Used for AD-XRD patterns

Key Methodologies

The experiment relied on high-precision DAC fabrication and specialized in-situ measurement techniques:

High-Pressure X-Ray Diffraction (AD-XRD):
- Symmetric DACs utilized single crystal diamond anvils with a 300 µm culet size to achieve pressures up to 36.3 GPa.
- Sample chambers (120 µm diameter) were formed in pre-indented 45 µm thick stainless steel gaskets.
- Silicone oil was employed as the pressure transmitting medium for XRD, calibrated using ruby fluorescence.
- AD-XRD patterns were collected using focused synchrotron beams ($\lambda = 0.4075$ Å).
In-situ Electrical Resistance Measurement:
- Performed using a four-electrode method, requiring highly customized diamond anvils where electrodes were set up directly on the diamond surface.
- A 150 µm sample chamber was drilled into the gasket.
- Insulation for the electrodes was achieved by filling the chamber with compacted cubic Boron Nitride (c-BN) powder and covering the remaining gasket area with insulating gel.
- Measurements were conducted on a temperature-controlled hot plate (300 K to 400 K) without a pressure transmitting medium, introducing deviatoric stress (noted as a cause for differing transition pressures compared to XRD).
First-Principles Calculations:
- Density Functional Theory (DFT) utilized the VASP package, employing the generalized gradient approximation (GGA) plus Hubbard U ($\text{U} = 3.2$ eV) method.
- Calculations confirmed the transition nature and predicted structural changes by applying hydrostatic pressure (Pulay stress) to fully optimize the unit cell.

6CCVD Solutions & Capabilities

The successful replication and extension of high-pressure studies like this rely fundamentally on the quality, customizability, and electrical properties of the diamond anvils. 6CCVD provides the specialized CVD diamond products required for next-generation DAC experiments.

Applicable Materials & Customization

Research Requirement	6CCVD Recommended Solution	Key Capability Alignment
High Purity/High Stress Anvils	Optical Grade Single Crystal Diamond (SCD)	Provides maximum mechanical strength and optical transmission necessary for synchrotron XRD and high-pressure stability (>36 GPa). 6CCVD supplies SCD up to 500 µm thick.
Robust Electrical Pathways	Boron-Doped Diamond (BDD) Substrates	For high-P transport studies, BDD offers stable, known conductivity, essential for eliminating signal noise associated with c-BN insulation. Available in SCD or PCD formats.
Electrode Fabrication	Custom Metalization Services	Required for the four-electrode setup. 6CCVD offers in-house deposition of thin films including Ti, Pt, Au, W, or Cu onto polished diamond surfaces, enabling precise electrical contacting on small culet sizes (300 µm).
Precision Anvil Shaping	Custom Laser Cutting Services	Necessary for producing highly symmetric diamond anvils and precise culet sizes (300 µm) critical for achieving homogeneous pressure distribution.
Surface Quality	Precision Polishing	Ensures optimal surface contact between the metal electrodes and the sample. 6CCVD guarantees ultra-low roughness: $\text{Ra} < 1$ nm for SCD, and $\text{Ra} < 5$ nm for inch-size PCD.

Engineering Support

The observed differences in transition pressures between the XRD (hydrostatic/quasi-hydrostatic) and resistance (non-hydrostatic, no PCM) experiments highlight the complexity of material behavior under deviatoric stress.

6CCVD’s in-house PhD engineering team specializes in the fabrication and selection of diamond materials optimized for complex high-pressure research. We can assist researchers in selecting the ideal material (e.g., optical SCD vs. heavy BDD) and configuring custom metalization patterns for transport studies in similar semiconductor or thermoelectric phase transformation projects.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly. We offer global shipping (DDU default, DDP available) to ensure reliable delivery of highly customized diamond components.

View Original Abstract

Here, we report comprehensive studies on the high-pressure structural and electrical transport properties of the layered transition metal chalcogenide (Cr2S3) up to 36.3 GPa. A structural phase transition was observed in the rhombohedral Cr2S3 near 16.5 GPa by the synchrotron angle dispersive X-ray diffraction measurement using a diamond anvil cell. Through in situ resistance measurement, the electric resistance value was detected to decrease by an order of three over the pressure range of 7-15 GPa coincided with the structural phase transition. Measurements on the temperature dependence of resistivity indicate that it is a semiconductor-to-metal transition in nature. The results were also confirmed by the electronic energy band calculations. Above results may shed a light on optimizing the performance of Cr2S3 based applications under extreme conditions.

Tech Support

Original Source

DOI: https://doi.org/10.1063/1.4945323