Photon Factory Activity Report 2022 #40 (2023)

AR-NE5C/2020G048

Trial CAESAR Measurements using MAX80
Kazuhiro FUCHIZAKI1,* Akio SUZUKI2, Hiroki NARUTA1, Katsumi NAKAMURA1, andTomohiro OHUCHI3
1
Department of Physics, Ehime University, Matsuyama 790-8577, Japan2
Department of Earth Science, Tohoku University, Sendai 980-8578, Japan
3
Geodynamics Research Center, Ehime University, Matsuyama 790-8577, Japan
We succeeded in in situ combined angle- and energy-dispersive structural analysis and refinement (CAESAR)
measurements under high pressure and temperature using MAX80 installed at beamline NE5C, PF-AR, which must be
the first successful trial at that beamline to the authors.
1 Introduction
High-pressure experiments were often carried out using
a diamond anvil cell (DAC), which allows us to reach amegabar region relatively easily. In addition, the laser
heating technique, when combined, can elevate sample
temperature beyond several thousand Kelvin. This aspectconvinces us why a DAC is used in front-line research on
Earth science. However, a very intense, low-emittancebeam is required to measure a minimal amount of DAC
samples. Because of the limited number of such facilities,
the number of accessible researchers is also limited. Nonhydrostaticity realized in a sample space due to uniaxial
compression is another problem. We usually need to fill thesample chamber with a suitable pressure-transmitting
medium, which should not chemically react with a sample.
A multianvil press (MAP) is another crucial device togenerate high pressure. Recently, it can attain beyond 10
GPa, for example, in a 6–6 or 6–8 compression mode. Itcan still afford to give a sample hole of 1 mm in diametereven when using a truncated edge length (TEL) of 3 mmas the inner side of anvils. A larger sample can facilitate
obtaining valuable data even with synchrotron sources ofthe second generation. The non-hydrostaticity conditions
are undoubtedly reduced.
However, a high-pressure vessel with a MAP usually
restricts the diffraction geometry to the energy-dispersive
diffraction (EDD) mode. EDD data obtained with a fixed
scattering angle 2 can identify a unit cell when treating
crystalline materials but cannot provide reliable
crystallographic information such as atomic positions,bonding characteristics, and so forth. This unpleasantaspect may be improvable when measurements use an
imaging plate in an angle-dispersive diffraction (ADD)
mode. However, the pressure vessel mentioned above
often limits the 2 range to 15 degrees at most. Hence, theminimal d-spacing remains 0.95 A even for a typicalphoton energy of 50 keV.
Wang et al. overcame this situation by devising a newtechnique, combined angle- and energy-dispersive
structural analysis and refinement (CAESAR) [1]. The
technique can be briefly described as follows: For aninitially set 2, a standard EDD measurement is carried out
to obtain the intensity distribution as a function of photon
energy E. (In a solid-state detector (SSD) measurement,
photons are classified into multichannel bins according totheir scattered energies. The relation between channel andenergy is usually prescribed separately using characteristic
x-rays of multiple substances.) The scattering angle is thenchanged by an amount () and a measurement isrepeated until the final 2 that can cover the desired rangeof diffraction. We thus obtain the scattered intensity
distribution I(E,2) as a function of both energy andscattering angle. A cross-section at constant E yields theintensity distribution as a function of the scattering angle.
Wang et al. [1] demonstrated that the above prescription
worked using a MAP installed in synchrotron x-ray sourcesat APS and SPring-8. Indeed, ‘ADD’ data tolerable against
the Rietveld analysis were obtained from CAESAR
measurements for -Al2O3 at ambient conditions and for a
mixture of MgO and Au at high pressure.
MAX80, a MAP installed at NE5C in PF-AR, has beenoperated since the late 1980s. However, to the authors’knowledge, no CAESAR measurements have been tried.
Because they are exploring a region of about 15 GPa for
SnI4 to unveil its structural evolution upon pressureinduced amorphization, it is worth challenging CAESAR
measurements on this occasion. Because of the relative
ease of MAX80’s temperature control, the diffraction data
could complement the room-temperature measurements ofOhmura et al. using a DAC. The success of measurements
would enhance the appeal of MAX80.
2 Experiment
Before carrying out CAESAR measurements, we
simulated the distribution of major Bragg peaks of SnI 4 in
the ambient crystalline phase (CP-I) to assess the 2 range
with which to obtain meaningful ADD patterns. The upper
panel of Fig. 1 depicts the simulated intensity loci ofprimary Bragg reflections, 222, 400, 440, and 622, on the2–channel plane, where we used the recent calibration
result for the relation between the photon energy E andchannel number of the multichannel analyzer equippedwith an SSD installed in MAX80. For example, if wechoose the 600-channel section for the ADD pattern, it isappropriate to adopt an interval between 5 and 12 degrees
for the scattering angle. Let us assume it takes at least 2
minutes to measure the minimal scattered intensity at agiven angle. Then, if the measurement is made every 0.01
degrees of scattering angle, as was done by Wang et al. [1],

Photon Factory Activity Report 2022 #40 (2023)

more than one day is necessary for a whole measurement,
including the time required for driving the SSD. Therefore,in our CAESAR measurements, setting the minimum 2
steps to be 0.1 degrees is practical, considering the usual
beamtime given. The interval of 0.1 degrees is too coarse
for a diffraction pattern to be analyzed adequately. We hopethe intensity interpolation from neighboring channels
could equally work, as illustrated by Wang et al [1].
Compression was made in a 6–6 mode with an inner setof anvils of a truncated edge length (TEL) of 3 mm.
Applying such a TEL of anvils was pioneered by Kawazoe
et al. [2], and we fully utilized their developed techniqueto reach a pressure region of about 15 GPa. A finepowdered sample of high-purity SnI4 was loaded in acontainer made of hBN enclosed by a TiB2 sleeve, to which
an electric current was applied to heat the sample. The
relationship between the power supplied and thetemperature generated was well-calibrated to read thetemperature at the sample position.
3 Results and Discussion
A CAESAR measurement conducted at ambientconditions is presented here as a preliminary report; a total
result, including measurements at elevated temperatures
under ~15 GPa, will be reported shortly.
The lower panel of Fig. 1 shows a contour map of theraw intensity distribution I(2q, channel) measured withthe magnitude of intensity illustrated as a heat map on theright. The spectra below 500 channels, consisting ofcharacteristic lines of Sn and I, were unavailable fortransforming to an ADD pattern and were removed fromthe map. Comparing the map thus measured with the one
simulated (the upper panel), it is apparent that the brighter
loci originate from the primary peaks.

We chose the 600-channel data to obtain an ADD pattern
in which the data on the adjacent channels complement
intervening intensities. Figure 2 shows the pattern thus
obtained after making intensity corrections regarding
diffracting volume. Although we measured the intensities
every 0.1 degrees, the complement works well as judged
from the close resemblance to the ADD intensity
distribution resulting from a DAC experiment. Indeed, theintensity distribution, representing an extra bump between
320 and 321 due to diffraction from a container, depictedin the inset proves the perfection of the interpolation.
Although the background intensity is nonuniform andrelatively high, the pattern may allow us to analyze withthe Rietveld method. The result will be included in the fullreport mentioned above.

Fig. 2: An ADD pattern converted from the present
CAESAR measurement for SnI4 at ambient conditions.
We could perform four CAESAR measurements in asingle compression–decompression cycle. However, each
CAESAR measurement was done entirely manually; wechanged the scattering angle as one measurement at anangle was over by issuing instructions through a PC
controlling the measuring system. We could have been
freed from the restriction for more than 12 hours if theprocess had been automated.
3 Conclusion
We could thus prove that EDD data obtained throughMAX80 can be transformed into ADD patterns. Beamline
NE5C, in which MAX80 is installed, can use white andmonochromatized x-rays, whose switching can beperformed in a moment. The facility thus allows
simultaneous diffraction and XAFS measurements.
MAX80, set up in PF-AR, a synchrotron radiation facilityof the second generation, appeals to last a long time. This
aspect encourages researchers in high-pressurecommunities. They must welcome the measurement
automation mentioned in the last paragraph.

Fig. 1: Simulated (upper panel) and measured (lowerpanel) loci of the primary Bragg peaks for SnI4’s CP-I.

Acknowledgement
This work was partly supported by JSPS KEKENHI(grant no. 20K03790). Furthermore, the Geodynamics

Photon Factory Activity Report 2022 #40 (2023)

Research Center, Ehime University, kindly allowed us touse a facility when producing and assembling the parts
required for the experiments.
References[1] Y. Wang et al., J. Appl. Cryst. 37, 947 (2004).
[2] T. Kawazoe et al., High Pressure Research 30, 167(2010).
* fuchizak@phys.sci.ehime-u.ac.jp