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condition, it is typically
∼
60-80
μ
mindiameter
1
2
at the sample in the DAC.
Laser heated in situ high-pressure Brillouin
scattering experiments were first applied for the
pure H
2
O system in its liquid state, demonstrat-
ing the huge potential of this combined measure-
ment system (Murakami
et al
., 2009). As shown
in Figure 6.3a, the melting of ice in a DAC under
pressure was easily recognized by the sample
image, and the visible thermal emission from the
center of the melting spot with increasing temper-
ature is easily observed. The focused probe laser
beam for Brillouin scattering measurements is
also appropriately located in the center of heating
spot from heating infrared laser, which ensures
that the Brillouin spectra were obtained from the
sample exactly at the hot spot. The molten por-
tions during heating were surrounded by the solid
ice, indicating that the direct interaction between
the H
2
O fluid and metal gasket did not occur.
As shown in Figure 6.3b, simultaneously high-
temperature and high-pressure Brillouin spectra
during laser heating were successfully obtained
up to 2200 K. While significantly higher back-
ground noise for the spectrum at 2200 K was
observed, the peak intensity from the sample is
much high than that from background, showing
the potential feasibility of higher temperature
sound velocity measurements. With this sys-
tem, (Murakami
et al
., 2009) further showed
the preliminary result on shear wave velocity of
polycrystalline MgO under simultaneously high-
temperature and high-temperature conditions at
mid-lower mantle (at 49 GPa and
3
4
(a)
Ice VII Vp
Ice VII Vp
before heating
Water Vp
Water Vp
at melting T
Water Vp
Water Vp
at 2200 K
Ice VII Vp
Ice VII Vp
2300 K), which
also demonstrated the potential ability of this
combined measurement system for the sound
velocity measurements under
P-T
condition that
covers whole lower mantle.
∼
after quenching
−
20
−
15
−
10
5 0
Frequencu shift (GHz)
−
5
10
15
20
(b)
Fig. 6.3
(a) Photomicrographs of the H
2
OinaDACat
5.5 GPa at room temperature (1), at melting
temperature (2), at 2200 K (3) and during Brillouin
scattering measurement (4) from Murakami
et al
.
(2009). The sample chamber is
6.3 Representative Recent
Experimentnal Results
The major elastic properties of the lower mantle
can be described, to a first approximation, by
using two principle phases of magnesium silicate
perovskite (pv) and ferropericlase (fp) to construct
100
μ
m in size.
(b) Brillouin spectrum of H
2
O before heating, during
heating and after heating. Reproduced with permission
of Elsevier.
∼
