High-pressure single-crystal X-ray diffraction
measurements of synthetic LiCrSi2O6 clinopyroxene (with
space group P21/c) were performed in a diamond-anvil cell up
to 7.970 GPa. No phase transition has been observed within the
pressure range investigated, but the elastic behavior at lower
pressures (up to 2.5 GPa) is affected by an anomalous
softening due to the proximity of the phase transition to the
HT-C2/c phase at 330 K and at ambient pressure. A third-order
Birch–Murnaghan equation of state fitted to the compression
data above 2.5 GPa yields a bulk modulus KT0 = 93(2) GPa
and its first derivative K0 = 8.8(6). The structural data measured
up to 7.970 GPa confirm that the space group P21/c is
maintained throughout the whole pressure range investigated.
The atomic parameters, obtained from the integrated diffraction
intensities, suggest that the Li coordination polyhedron
changes its coordination number from 5 to 6 at 6–7 GPa by
means of the approach of the bridging O atom, related to the
increased kinking of the B tetrahedral chain. Furthermore, at
higher pressures, the structural evolution of LiCrSi2O6 provides
evidence in the variation of kinking angles and bond
lengths of a potential phase transition above 8 GPa to the
HP-C2/c space group. A comparison of the Li-clinopyroxenes
(M1 = Cr, Al, Sc, Ga, Mg + Fe) previously investigated and
our sample shows that their elastic behavior and structural
mechanisms of compression are analogous.