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Title: High pressure raman spectroscopy and X-ray diffraction of K2Ca(CO3)2 bütschliite: multiple pressure-induced phase transitions in a double carbonate

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,$${K}_{0}=46.9$$K0=46.9GPa with an imposed value of$${K}_{0}^{\prime}= 4$$K0=4for the ambient pressure phase. Compression of bütschliite is highly anisotropic, with contraction along thec-axis accounting for most of the volume change. Bütschliite undergoes a phase transition to a monoclinicC2/mstructure at around 6 GPa, mirroring polymorphism within isostructural borates. A fit to the compression data of the monoclinic phase yields$${V}_{0}=322.2$$V0=322.2 Å3$$,$$,$${K}_{0}=24.8$$K0=24.8GPa and$${K}_{0}^{\prime}=4.0$$K0=4.0using 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 theC2/mphase 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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Author(s) / Creator(s):
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Publisher / Repository:
Springer Science + Business Media
Date Published:
Journal Name:
Physics and Chemistry of Minerals
Medium: X
Sponsoring Org:
National Science Foundation
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