TY - JOUR
T1 - High pressure behavior and structural transition of beryl-type johnkoivulaite, Cs(Be2B)Mg2Si6O18
AU - Gatta, G. Diego
AU - Ende, Martin
AU - Miloš, Sofija
AU - Rotiroti, Nicola
AU - Palke, Aaron
AU - Miletich, Ronald
PY - 2024/1/2
Y1 - 2024/1/2
N2 - The beryl-group mineral johnkoivulaite, Cs(Be2B)Mg2Si6O18,
was compressed hydrostatically in a diamond-anvil cell up to 10.2 GPa.
In situ Raman spectroscopy and X-ray crystallography revealed a P6/mcc-to-P3c1 (second-order) phase transition on isothermal compression at the critical transition pressure Pc
= 4.13 ± 0.07 GPa. The elastic parameters determined for the volume
elasticity of the two polymorphs correspond to a Birch-Murnaghan
equation of state with K0 = 148 ± 2 GPa and K′ = 0 for P < Pc and K0 = 75.5 ± 0.9 GPa with K′ = 4 for P > Pc. The low-P
polymorph shows anomalously linear compression behavior, as reported
for several other beryl-derived framework structures. The high-P polymorph, which was found to follow a a′ = a·√3, c′ = c superstructure according to P3c1, is almost twice as compressible as its low-P
form. This is unique for any beryl-derived structure and can be
attributed to the high degree of freedom for atomic displacements in the
superstructure. The reduced symmetry can also be understood as the
effect of the driving mechanism of the transformation. The
extra-framework Cs channel components counteract any lateral deformation
of the channels parallel to [0001] within the microporous framework
and, similar to pezzottaite, are responsible for maintaining the
trigonal/hexagonal lattice metrics.
AB - The beryl-group mineral johnkoivulaite, Cs(Be2B)Mg2Si6O18,
was compressed hydrostatically in a diamond-anvil cell up to 10.2 GPa.
In situ Raman spectroscopy and X-ray crystallography revealed a P6/mcc-to-P3c1 (second-order) phase transition on isothermal compression at the critical transition pressure Pc
= 4.13 ± 0.07 GPa. The elastic parameters determined for the volume
elasticity of the two polymorphs correspond to a Birch-Murnaghan
equation of state with K0 = 148 ± 2 GPa and K′ = 0 for P < Pc and K0 = 75.5 ± 0.9 GPa with K′ = 4 for P > Pc. The low-P
polymorph shows anomalously linear compression behavior, as reported
for several other beryl-derived framework structures. The high-P polymorph, which was found to follow a a′ = a·√3, c′ = c superstructure according to P3c1, is almost twice as compressible as its low-P
form. This is unique for any beryl-derived structure and can be
attributed to the high degree of freedom for atomic displacements in the
superstructure. The reduced symmetry can also be understood as the
effect of the driving mechanism of the transformation. The
extra-framework Cs channel components counteract any lateral deformation
of the channels parallel to [0001] within the microporous framework
and, similar to pezzottaite, are responsible for maintaining the
trigonal/hexagonal lattice metrics.
UR - http://doi.org/10.2138/am-2022-8908
M3 - Article
VL - 109
SP - 15
EP - 23
JO - American Mineralogist: an international journal of earth and planetary materials
JF - American Mineralogist: an international journal of earth and planetary materials
SN - 0003-004X
IS - 1
ER -