The crystal structure and bonding environment of K2Ca(CO3)2bütschliite were probed under isothermal compression via Raman spectroscopy to 95 GPa and single crystal and powder X-ray diffraction to 12 and 68 GPa, respectively. A second order Birch-Murnaghan equation of state fit to the X-ray data yields a bulk modulus,
- Award ID(s):
- 1916941
- NSF-PAR ID:
- 10317878
- Date Published:
- Journal Name:
- American Mineralogist
- Volume:
- 107
- Issue:
- 1
- ISSN:
- 0003-004X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract GPa with an imposed value of$${K}_{0}=46.9$$ for the ambient pressure phase. Compression of bütschliite is highly anisotropic, with contraction along the$${K}_{0}^{\prime}= 4$$ c -axis accounting for most of the volume change. Bütschliite undergoes a phase transition to a monoclinicC 2/m structure at around 6 GPa, mirroring polymorphism within isostructural borates. A fit to the compression data of the monoclinic phase yields Å3$${V}_{0}=322.2$$ $$,$$ GPa and$${K}_{0}=24.8$$ using a third order fit; the ability to access different compression mechanisms gives rise to a more compressible material than the low-pressure phase. In particular, compression of the$${K}_{0}^{\prime}=4.0$$ C 2/m phase involves interlayer displacement and twisting of the [CO3] units, and an increase in coordination number of the K+ion. Three more phase transitions, at ~ 28, 34, and 37 GPa occur based on the Raman spectra and powder diffraction data: these give rise to new [CO3] bonding environments within the structure. -
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