Photon Factory Activity Report 2017 #35 (2018)

NE5C/2016G186

Pressure-Induced Liquid-to-Liquid Crossover in GeI4
Kazuhiro FUCHIZAKI1,* Hironori NISHIMURA1, Takaki HASE2 and Hiroyuki SAITOH3
1Department of Physics, Ehime University, Matsuyama, 790-8577, Japan
2
Technical Division, ANSYS JAPAN, Tokyo, 160-0023, Japan
3
Quantum Beam Science Research Directorate, National Institutes for Quantum and Radiological
Science and Technology, Hyogo 679-5148, Japan
1 Introduction
We could confirm in SnI4 the existence of the liquid—liquid critical point (LLCP) at around 1.5 GPa and 1000
K [1] and of the temperature of maximum density in theregion between 1100 K and 1400 K just below 1 GPa [2].
SnI4 thus allows us to enter the “no-man’s land”, whichcannot be accessed for bulk water
It should be emphasized that a melting maximum [3] is
not necessarily a condition for a liquid—liquid transition(LLT) to occur. The existence of a (seemingly) singularpoint on a melting curve may rather imply occurrence ofan LLT [4]. Indeed, the melting curve of SnI 4 does notexhibit an apparent maximum but has a breakpoint at ~1.5
GPa [4], which may be the triple point among the twoliquid phases and the crystalline phase (CP) [5].
The melting curve of a molecular crystalline GeI 4exhibits quite a similar shape (see Figure 1, in which themelting points are marked by open circles). The
breakpoint is shifted to ~3 GPa [6] reflecting a slight
reduction of molecular size. The aspect suggests us toexamine a possible LLT of liquid GeI4 in a pressure—temperature region close to the breakpoint.
2 Experiment
To this end, the energy-dispersive synchrotron x-ray
diffraction measurements were carried out employing
MAX-80, a cubic-type multianvil press, installed in thebeamline NE5C at KEK-AR. A new type of two-stagecompression method that was described previously in fullby [6] was employed. The compression was performed
using a set of anvils with a truncation edge length of 6mm to cover the relevant pressure range. NaCl was usedas the pressure standard The distributions of scattered xray intensities at various scattering angles, 3 through 20°,
were combined to construct a normalized structure factor,
which was then converted to the reduced radial
distribution function (RRDF) using the method by [7].
3 Results and Discussion
The characteristic feature of the RRDF was found to becompletely shared with that found for SnI4 [7]; theintramolecular I—I distance shrinks on compression
whereas the intramolecular Ge—I distance expands. Thislatter unusual feature enables us to judge the occurrenceof the LLT from the low-pressure liquid state (Liq-II) to
the high-pressure liquid state (Liq-I). The distribution ofstructure measurements at which Liq-II (blue circles) andLiq-I (pink circles) were identified is depicted in Figure 1.

Unlike the aspect observed for SnI4, the transition
between the two liquids is sluggish; transient states(purple circles) were indeed in the region near thebreakpoint. The LLCP for GeI4 might be located within
the CP field below the melting curve, making thetransition merely a crossover. The more complete
discussion was given in [8].

Fig. 1: Two liquid states of GeI4 and their coexistence.
Acknowledgement
This work was supported by JSPS KAKENHI (GrantNos. 26400398 and 17K05581). We thank theGeodyanimcs Research Center, Ehime University for theuse of facilities.
References[1] K. Fuchizaki et al., talk presented at StatPhys 26,Lyon, July 2016; to be published.
[2] K. Fuchizaki et al., talk prerented at EHPRG 2016,Bayreuth, September 2016; in preparation.
[3] E. Rapoport, J. Chem. Phys. 46, 2891 (1967).
[4] K. Fuchizaki, J. Chem. Phys. 139, 244503 (2013).
[5] K. Fuchizaki et al., J. Chem. Phys. 135, 091101(2011).
[6] K. Fuchizaki and N. Hamaya, J. Phys. Soc. Jpn. 83,074603 (2014).
[7] K. Fuchizaki et al., J. Chem. Phys. 130, 121101(2009).
[8] K. Fuchizaki et al., J. Phys.: Condens. Matter 30,045401 (2018).
* fuchizak@phys.sci.ehime-u.ac.jp