Geoscience Reference
In-Depth Information
8.0
MgO
7.6
direct beam
7.2
6.8
Experiments
Murakami
et al.,
2009
Sinogeikin & Bass, 2000
Zha
et
al
., 2000
6.4
Theory
Karki
et al
., 1999 (300 K)
6.0
Karki
et al
., 1997 (0 K)
0
20
40
60
80
100
120
diamond
Pressure (GPa)
107
GPa
Fig. 6.8
Shear wave velocities of MgO as a function of
pressure at 300 K from Murakami
et al
. (2009).
Third-order Eulerian finite strain fit is shown in black
line. Black circles, open circles and dashed line
indicate previous experimental results by Brillouin
scattering measurements (Zha
et al
., 2000; Sinogeikin
et al
., 2004; Murakami
et al
., 2009). Open upward and
downward pointing triangles indicate the results by
computational calculations at 0 K (Karki
et al
., 1997)
and 300 K (Karki
et al
., 1999).
(a)
data (Figure 6.7b) at high pressure condition
showed that the lattice parameter measured using
single lines exhibits a significantly small devi-
ation
107 GPa
0.00296), indi-
cating that nonhydrostatic stress at high-pressure
was in fact diminished by laser annealing process.
The aggregate shear properties of MgO are sum-
marized in Table 6.2. The
V
S
and
G
at ambient
pressure determined by (Murakami
et al
., 2009)
are in excellent agreement with the previous
measurements, which are indistinguishable
within the experimental uncertainties. On the
contrary, the pressure derivative of the shear
modulus,
G
0
of 1
.
92
(100
∗
(
a
(200)
−
a
fit
)
/a
fit
=−
Rayleigh peak
−
20
−
15
−
10
−
50
5 0 5 0
Frequency shift (GHz)
(b)
Fig. 6.7
2-dimensional X-ray diffraction image (a) and
high pressure Brillouin spectrum of polycrystalline
MgO at 107 GPa from Murakami
et al
. (2009).
Reproduced with permission of Elsevier.
48% lower
than previous results. As shown in Figure 6.8,
the shear wave velocity profile by (Zha
et al
.,
2000), with a maximum
G
0
±
0.04 is 15
−
aggregate shear velocities are shown in Figure 6.8.
In this experiment, the high-pressure series of
experiments was also once laser-annealed to
improve the pressure homogeneity and reduce
the deviatoric stress in the sample chamber. The
shear stress in the DAC can be related to the
difference in the lattice parameters form different
diffraction lines (Singh, 1993). X-ray diffraction
0.09
among the previous measurements, exhibits the
trend distinctly different from that by Murakami
et al
. (2009), and its trend also shows negative
correlation
value of 2
.
85
±
35 GPa. This anomalous
shear velocity behavior may be associated with
above
∼