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6CCVD Research

Vibrational Investigation of Pressure-Induced Phase Transitions of Hydroxycarbonate Malachite Cu2(CO3)(OH)2

At a Glance

Section titled “At a Glance”
MetadataDetails
Publication Date2020-03-19
JournalMinerals
AuthorsJing Gao, Xueyin Yuan
InstitutionsInstitute of Geology and Geophysics, Chinese Academy of Geological Sciences
Citations12
AnalysisFull AI Review Included

Executive Summary

Section titled “Executive Summary”
  • Phase Transition Discovery: Three distinct pressure-induced phase transitions were identified in malachite (Cu2(CO3)(OH)2) at room temperature, occurring sequentially at approximately 7 GPa, 15 GPa, and 23 GPa.
  • Structural Drivers: The initial transition (<7 GPa) is driven by the deformation and subsequent rotation of the [CuO6] octahedron, evidenced by varied shifting slopes of the Cu-O vibrational modes.
  • Hydrogen Bonding Dynamics: Compression up to 15 GPa significantly enhances hydrogen bonding (O-H redshift), shortening the O…O distance. Above 15 GPa, O-H modes exhibit hardening (reduced redshift slope), indicating reorientation or reordering of the hydrogen sites.
  • High-Pressure Stability Limit: The final transition (~23 GPa) is marked by O-H blueshift (weakening H-bonding due to enhanced Cu-H repulsion) and softening of O-C-O bending modes, suggesting malachite’s stability extends to pressures analogous to the Earth’s transition zone.
  • Synergistic Volatile Recycling: The results highlight the synergistic relationship between the stability of hydrogen bonding and the structural evolution of the coordinated [CO3]2- units, crucial for understanding water and carbon recycling in deep Earth systems.
  • Methodology: In-situ high-pressure behavior was monitored using complementary Raman and Fourier Transform Infrared (FTIR) spectroscopy in a Diamond Anvil Cell (DAC).

Technical Specifications

Section titled “Technical Specifications”
ParameterValueUnitContext
Material StudiedMalachite (Cu2(CO3)(OH)2)N/AHydroxycarbonate mineral.
Water Content (Initial)15.3wt%High water storage capacity.
Maximum Pressure (Raman)28.9GPaExperimental compression limit.
Maximum Pressure (FTIR)29.2GPaExperimental compression limit.
Phase Transition I (PT1)~7GPa[CuO6] rotation/deformation.
Phase Transition II (PT2)~15GPaO-H mode hardening; unit cell change.
Phase Transition III (PT3)~23GPaO-H blueshift; O-C-O softening.
Max O-H Redshift Slope (VOH-3)-12.58(4)cm-1.GPa-1Observed between 7 and 15 GPa (maximum H-bond strengthening).
O-H Blueshift Slope (VOH-1)1.61(4)cm-1.GPa-1Observed above 23 GPa (H-bond weakening).
Initial O…O Distance (Calculated)2.72ACorresponding to 3251.55 cm-1 band at 0.8 GPa.
Minimum O…O Distance (Calculated)2.66ACorresponding to 3251.55 cm-1 band at 15.8 GPa.
Raman Excitation Wavelength488nmSolid-state continuous-wave laser.
Raman Spectral Resolution1.105cm-1Achieved using 300 g/mm grating.

Key Methodologies

Section titled “Key Methodologies”
  1. Pressure Generation: A symmetrical-type Diamond Anvil Cell (DAC) was utilized, equipped with Type-II diamond anvils (300 µm culet size).
  2. Gasket and Sample Chamber: A Rhenium gasket was pre-indented to 50 µm, with a 150 µm diameter hole serving as the sample chamber.
  3. Pressure Mediums: Silicone oil was used as the pressure transmitting medium for Raman measurements. Dried KBr layers served as the infrared window and pressure medium for FTIR measurements.
  4. Pressure Calibration: Pressure was monitored in-situ using the shifts of ruby fluorescence lines.
  5. Raman Spectroscopy Setup: Experiments used a WITec alpha 300R system with a 488 nm laser (20 mW power). Spectra were collected in backscattering geometry with a 10x objective lens.
  6. FTIR Spectroscopy Setup: High-pressure FTIR was performed on a Bruker VERTEX 70V instrument coupled with a Hyperion 2000 microscope, utilizing a KBr beam-splitter and a liquid-nitrogen cooled MCT-A detector.
  7. Data Acquisition: FTIR spectra were recorded in the 650-5000 cm-1 region with a 4 cm-1 resolution, accumulating 640 scans per spectrum to ensure a high signal-to-noise ratio.
  8. Spectral Analysis: Peak fitting and manipulation were executed using Jandel Peakfit software (v4.12), employing a Voight function for reproducible results (R2 > 0.995).

Commercial Applications

Section titled “Commercial Applications”

The fundamental understanding of mineral stability and volatile dynamics under extreme pressure conditions has relevance across several high-tech and industrial sectors:

  • High-Pressure Material Synthesis: The data on structural transitions (especially the role of [CuO6] octahedron deformation) informs the synthesis and stability prediction of novel copper-based functional materials (e.g., catalysts, pigments) designed for high-stress or high-temperature environments.
  • Carbon Capture and Storage (CCS): Malachite’s structural stability provides a proxy for other carbonate-bearing minerals. Understanding how the [CO3]2- unit evolves under pressure is crucial for modeling the long-term integrity and sequestration capacity of geological CO2 storage reservoirs.
  • Hydrogen Storage Technology: The detailed analysis of O-H bond shortening and reordering under pressure contributes to the knowledge base required for developing advanced solid-state materials capable of high-density hydrogen storage.
  • Deep Earth Resource Exploration: Geophysical models rely on accurate material properties (density, phase transitions) of minerals under mantle conditions. This data supports refining models for volatile (water and carbon) transport and recycling in subduction zones and the transition zone (~23 GPa).
  • Extreme Environment Engineering: Knowledge of mineral behavior under pressures up to 29 GPa is applicable to engineering design for deep-sea equipment, high-pressure chemical reactors, and components used in deep geothermal energy extraction.
View Original Abstract

Malachite Cu2(CO3)(OH)2 is a common hydroxycarbonate that contains about 15.3 wt % H2O. Its structural chemistry sheds light on other hydroxyl minerals that play a role in the water recycling of our planet. Here using Raman and infrared spectroscopy measurements, we studied the vibrational characteristics and structural evolution of malachite in a diamond anvil cell at room temperature (25 °C) up to ~29 GPa. Three types of vibrations were analyzed including Cu-O vibrations (300-600 cm−1), [CO3]2− vibrations (700-1600 cm−1), and O-H stretches (3200-3500 cm−1). We present novel observations of mode discontinuities at pressures of ~7, ~15, and ~23 GPa, suggesting three phase transitions, respectively. First, pressure has a great effect on the degree of deformation of the [CuO6] octahedron, as is manifested by the various shifting slopes of the Cu-O modes. [CuO6] deformation results in a rotation of the structural unit and accordingly a phase transition at ~7 GPa. Upon compression to ~15 GPa, the O-H bands redshift progressively with significant broadness, indicative of an enhancement of the hydrogen bonding, a shortening of the O···O distance, and possibly somewhat of a desymmetrization of the O-H···O bond. O-H mode hardening is identified above ~15 GPa coupled with a growth in the amplitude of the lower-energy bands. These observations can be interpreted as some reorientation or reordering of the hydrogen bonding. A further increment of pressure leads to a change in the overall compression mechanism of the structure at ~23 GPa, which is characterized by the blueshift of the O-H stretches and the softening of the O-C-O in-plane bending bands. The hydrogen bonding weakens due to a substantial enhancement of the Cu-H repulsion effect, and the O···O bond length shows no further shortening. In addition, the change in the local geometry of hydrogen is also induced by the softening of the [CO3]2− units. In this regard we may expect malachite and other analogous hydroxyl minerals as capable of transporting water downward towards the Earth’s transition zone (~23 GPa). Our results furnish our knowledge on the chemistry of hydrogen bonding at mantle conditions and open a new window in understanding the synergistic relations of water and carbon recycling in the deep Earth.

Tech Support

Section titled “Tech Support”

Original Source

Section titled “Original Source”

References

Section titled “References”
  1. 2012 - H2O storage capacity of olivine at 5-8 GPa and consequences for dehydration partial melting of the upper mantle [Crossref]
  2. 1994 - Seismic evidence for silicate melt atop the 410-km mantle discontinuity [Crossref]
  3. 2013 - Seismic evidence for subduction-transported water in the lower mantle. Earth’s Deep Water Cycle
  4. 1999 - The stability of dense hydrous magnesium silicates in Earth’s transition zone and lower mantle. Mantle Petrology: Field observations and high pressure experimentation: A tribute to francis R.(Joe) Boyd
  5. 2014 - Stability of hydrous silicate at high pressures and water transport to the deep lower mantle [Crossref]
  6. 2004 - Water transport into the deep mantle and formation of a hydrous transition zone [Crossref]
  7. 1967 - High-pressure reconnaissance investigations in the system Mg2SiO4-MgO-H2O [Crossref]
  8. 2014 - Melting of phase D in the lower mantle and implications for recycling and storage of H2O in the deep mantle [Crossref]
  9. 2001 - Stability field of new hydrous phase, δ-AlOOH, with implications for water transport into the deep mantle [Crossref]
  10. 2014 - Stability of a hydrous δ-phase, AlOOH-MgSiO2(OH)2, and a mechanism for water transport into the base of lower mantle [Crossref]

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