| dc.description.abstract-en | Structure deformations induced by pressure and temperature in synthetic "Cs-tetra-ferriannite"
1M [Cs1.78(Fe21
5.93Fe31
0.07)(Si6.15 Fe31
1.80Al0.05)O20(OH)4], space group C2/m, were analyzed
to investigate the capability of the mica structure to store the radiogenic isotopes
135Cs and 137Cs. ‘‘Cs-tetra-ferri-annite’’ is not a mineral name, but for the sake of brevity
is used here to designate a synthetic analog of the mineral tetra-ferri-annite. The bulk
modulus and its pressure derivative determined by fitting the unit-cell volumes between 0
and 47 kbar to a third-order Birch-Murnaghan equation of state are K0 5 257(8) kbar and
K09 5 21(1), respectively. Between 23 8C and 582 8C, the a and b lattice parameters remain
essentially unchanged, but the thermal expansion coefficient of the c axis is ac 5 3.12(9)
3 1025 8C21. High pressure (P) and high temperature (T) produce limited internal strain
in the structure. The tetrahedral rotation angle, a, is very small and does not change
significantly throughout the P and T range investigated. Above 450 8C in air, ‘‘Cs-tetraferri-
annite’’ underwent an oxidation of octahedral iron in the M2cis site, balanced by the
loss of H and shown by a decrease of the unit-cell volume.
Independent isobaric data on thermal expansion and isothermal compressibility data
define the ‘‘geometric’’ equation of state for ‘‘Cs-tetra-ferri-annite’’: V/V0 5 1 1 3.0(1)
1025 T 2 2.68(9) 1023 P 1 2.0(2) 3 1025 P2 where T is in degrees Celsius, P is in kilobars.
The a/b ratio of about 12 bar/8C indicate that the cell volume of ‘‘Cs-tetra-ferri-annite’’
remains unchanged under geothermal gradients of ;23 8C/km. On the whole, the data
confirm that the structure of ‘‘Cs-tetra-ferri-annite’’ may be a suitable candidate for the
storage of large ions, such as Cs in the interlayer and should be considered as a potential
Synroc component. | en |