Pressure-Induced Metallization of the Halide Perovskite (CH3NH3)PbI3

At a Glance

Metadata	Details
Publication Date	2017-03-14
Journal	Journal of the American Chemical Society
Authors	Adam Jaffe, Yu Lin, Wendy L. Mao, Hemamala I. Karunadasa
Institutions	SLAC National Accelerator Laboratory
Citations	199
Analysis	Full AI Review Included

Pressure-Induced Metallization of Halide Perovskite (CH₃NH₃)PbI₃: 6CCVD Technical Analysis & Documentation

Executive Summary

This study details the successful induction of a semiconductor-to-metal transition in the hybrid halide perovskite (MA)PbI₃ under extreme pressure using Diamond Anvil Cells (DACs). The results confirm the potential of high-pressure studies to unlock novel electronic properties in hybrid materials.

Critical Achievement: Metallization of (MA)PbI₃ confirmed above 60 GPa, evidenced by apparent bandgap closure (from 1.6 eV down to 0 eV).
Measurement Techniques: Metallic state verified independently using high-pressure IR reflectivity (observing Drude-like modes) and variable-temperature DC conductivity measurements.
Performance Metrics: DC conductivity increased over 10-fold, shifting from 0.57 S·cm⁻¹ (semiconducting at 50 GPa) to 6.6 S·cm⁻¹ (metallic at 62 GPa).
Key Insight: The transition onset is electronic, not driven by a first-order structural phase change, highlighting the highly tunable nature of the electronic bands under compression.
Material Necessity: This research relies critically on the exceptional mechanical strength and wide optical transparency of single crystal diamond (SCD) anvils, essential for generating GPa pressures while allowing optical and IR spectroscopic access.
6CCVD Relevance: 6CCVD is an expert provider of the high-purity, custom-metalized SCD required for complex, high-pressure electrical and optical measurements in DAC research.

Technical Specifications

Parameter	Value	Unit	Context
Initial Direct Bandgap (E_g)	1.6	eV	Ambient Pressure
Metallization Pressure (P_M)	> 60	GPa	Confirmed by Drude IR mode and T-dependent conductivity
Max Optical Measurement Pressure	64	GPa	IR Reflectivity
Max Structural Measurement Pressure	66	GPa	Powder X-ray Diffraction (PXRD)
Semiconducting Conductivity (σ)	0.57	S·cm⁻¹	Measured at 50 GPa
Metallic Conductivity (σ)	6.6	S·cm⁻¹	Measured at 62 GPa
Activation Energy (E_a)	19.2(3)	meV	Measured at 50 GPa (Semiconducting state)
Optical Confirmation (Metallic)	< 0.2	eV	Drude-like mode observed in IR reflectivity at 60 GPa
Phase at P > 3 GPa	Partially Amorphous	N/A	High-pressure γ phase

Key Methodologies

The following is an ordered list of the key experimental steps and techniques utilized, focusing on requirements for high-pressure material science:

Pressure Generation: High pressures (up to 66 GPa) were achieved using Diamond Anvil Cells (DACs), leveraging the rigidity and wide spectral window of the diamond anvils.
Pressure Calibration: Pressure values within the DAC were precisely measured using standard ruby fluorescence calibration techniques.
Bandgap Evolution Tracking: High-pressure absorption spectroscopy was performed across visible and IR wavelengths to monitor the redshift, blueshift, and eventual closure of the direct bandgap (E_g).
Metallic Confirmation (IR): High-pressure IR reflectivity measurements were conducted. The observation of a sharp increase in reflectivity at low frequency (below 0.2 eV) characterized as a Drude-like mode, confirmed the transition to the metallic state at 60 GPa.
Metallic Confirmation (Electrical Transport): Variable-temperature DC conductivity measurements were performed using a four-point electrode configuration to ensure accurate resistivity readings independent of contact resistance.
Structural Analysis: Powder X-ray Diffraction (PXRD) was used up to 66 GPa to verify the lack of a first-order structural phase transition associated with the metallization onset.

6CCVD Solutions & Capabilities

This research demonstrates a critical need for high-quality single crystal diamond (SCD) components capable of withstanding extreme mechanical load while enabling complex electrical and optical characterization. 6CCVD is uniquely positioned to supply the bespoke diamond material solutions necessary for replicating and advancing this type of high-pressure physics research.

Applicable Materials

To replicate and extend high-pressure DAC experiments involving optical transmission and electronic transport, 6CCVD recommends the following high-performance materials:

Optical Grade Single Crystal Diamond (SCD): Required for the anvils themselves. Our MPCVD-grown SCD offers exceptional purity, low birefringence, and superior mechanical robustness, ensuring reliable pressure generation and maximal transparency across the Visible and critical IR (Drude mode) spectrum.
Custom Metalized SCD: Essential for the four-point DC conductivity measurements performed in the DAC. Anvils can be customized with lithographically defined electrode structures to provide the necessary electrical contacts while maintaining high-pressure integrity.

Customization Potential

The success of DAC experiments hinges on highly precise material dimensions and tailored interfaces. 6CCVD provides end-to-end customization services:

Custom Specification	Research Requirement Addressed	6CCVD Capability
Custom Dimensions	Precise anvil plate dimensions, specific culet sizes, and high-aspect ratio substrates required for DAC stability.	We provide custom plates and wafers up to 125mm (PCD) and precise SCD components (thickness 0.1µm - 500µm) with custom laser cutting and shaping.
Metalization Services	Four-point probe configuration requires non-contaminating, highly conductive electrode deposition directly onto the anvil surface.	We offer internal metalization capabilities, including multilayer stacks of Au, Pt, Pd, Ti, W, and Cu, patterned to client specifications for electrical measurements.
Surface Finish	High-quality optical data (absorption, reflectivity) demands minimal surface scatter from the diamond window.	SCD polishing achieves Ra < 1 nm, ensuring ultra-smooth surfaces for high fidelity optical transmission and reflection measurements across wide spectral ranges.

Engineering Support

Pressure-induced electronic structure research, such as the induction of metallization in (MA)PbI₃, often requires integrating advanced electrode designs with specific diamond geometries.

6CCVD’s in-house PhD engineering team specializes in material selection and integration strategies for complex research setups, including high-pressure/high-temperature cells, quantum sensing, and electrical transport devices.
We offer consultation services for material selection, ensuring the optimal SCD type and metalization scheme are chosen for similar High-Pressure Electronic Transport projects.

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

View Original Abstract

We report the metallization of the hybrid perovskite semiconductor (MA)PbI3 (MA = CH3NH3+) with no apparent structural transition. We tracked its bandgap evolution during compression in diamond-anvil cells using absorption spectroscopy and observed strong absorption over both visible and IR wavelengths at pressures above ca. 56 GPa, suggesting the imminent closure of its optical bandgap. The metallic character of (MA)PbI3 above 60 GPa was confirmed using both IR reflectivity and variable-temperature dc conductivity measurements. The impressive semiconductor properties of halide perovskites have recently been exploited in a multitude of optoelectronic applications. Meanwhile, the study of metallic properties in oxide perovskites has revealed diverse electronic phenomena. Importantly, the mild synthetic routes to halide perovskites and the templating effects of the organic cations allow for fine structural control of the inorganic lattice. Pressure-induced closure of the 1.6 eV bandgap in (MA)PbI3 demonstrates the promise of the continued study of halide perovskites under a range of thermodynamic conditions, toward realizing wholly new electronic properties.

Tech Support

Original Source

DOI: https://doi.org/10.1021/jacs.7b01162