Date of Approval 2017/6/21
Approver jun-ichi Suzuki
Date of Report 2017/5/16

Experimental Report
Project No.

Name of Instrument scientist

2015A0087

Jun-ichi Suzuki
Title of experiment

Name of Instrument/ BL No.

Small-angle neutron scattering of liquid Au-Si – investigation on
micro-inhomogeneity in homogeneous liquid in deep eutecticsystem

TAIKAN (BL15)
Date of ExperimentDecember 15 9:00 –17 9:00, 2016

Name of principal investigator
Yoshifumi Sakaguchi
Affiliation
CROSS

Please report your samples, experimental method and results, discussion and conclusions. Please add figures andtables for better explanation.
1.
Name of sample(s) and chemical formula, or compositions including physical form.
Au81.4Si18.6 (liquid in the quartz glass cell) (eutectic composition)

2.
Experimental method and results.

If you failed to conduct experiment as planned, please describe reasons.

Experimental method:
Fig.1 shows the phase diagram of Au-Si system. In this experiment, wemeasure small-angle neutron scattering (SANS) in the liquid phase of theeutectic composition, Au81.4Si18.6. To measure the SANS of the liquid phase,
we need a furnace and a sample container. Fig.2 show the high temperature
furnace, which was specially designed for SANS. Fig. 3 shows the quartz glass
cell with Au81.4Si18.6 (0.5mmthickness) in an alumina tube.
Such thin sample thickness wasFig. 2

required because of the large
absorption cross-section of gold.
Besidethethickness,

itisrequiredtoconsider

about“sealing” the liquid sample in acontainer because gold is easy to
be radio-activated. Usually, suchFig.1Fig. 3

a glass cell is broken when the sample solidifies due to an abrupt volume change at the solidification.

Experimental method and results (continued)

2.

Therefore, the sample was prepared as small as possible to just fill in the thin samples space with the thickness of
0.5 mm with a diameter of 8 mm. Also, the glass cell with the Au81.4Si18.6 sample was sealed in a larger quartz
glass tube again to prevent a leakage of the vapor when the glass cell is broken. The holes in the alumina tube do
not interrupt both the incident neutron beam and the scattered beam. The aluminum windows with the thicknessof 0.5mm minimize the absorption on the neutron beam paths. Prior to the SANS measurement of the sample, wemeasured the empty cell. The SANS measurements of the sample were performed from room temperature to800oC. The proton beam power in the measurements was 150kW.
Experimental results:
Fig. 4 shows the SANS profiles of crystalline (room temperature) and liquid (400, 600, and 800oC) Au81.4Si18.6.
At room temperature, the alloy is composed of separated two phases, Au and Si. The separated two phases form
“eutectic structure”, in which two types of lamellars alternatively align with the inter-lamellar spacing of several
micrometers.

The large SANS curve, which follows approximately Q-4, is considered to show a sharp interface

between the two phases. This large SANS intensity eventually decreases when the alloy melts by heating (Fig.
5). Usually, it is expected that such a SANS intensity completely disappears due to a formation of“homogeneous” liquid, which means that there is no orderwith nanometer-scale. However, an apparent SANS
intensity is observed in the liquid state in the Q-range lessthan 0.02 Å-1. Also, there could be a small hump (orshoulder) around 0.1 Å-1, although the influence of theanalytical procedure and the data processing should be
carefully considered. As of now, it is not easy to conclude
the physical origin of the SANS intensity in the liquid state.
One possibility is the compositional fluctuation, which isgenerally observed around “critical point” of a phaseseparation in liquid. In this case, the SANS intensity
follows so-called Orenstein-Zernike relationship, I (Q) = I(0) / (1+ 2Q2), whereis the correlation length, in theFig.4

Q-range, usually from 0.05 to 0.24 Å-1. Itami et al. pointed
out a presence of such type of compositional fluctuation toexplain the anomalous behavior in their experimental resultof the electrical resistivity measurement [1], and asserted
that the extremely low melting point at the eutectic
composition is related to the presence of the composition
fluctuation. However, we observe much larger SANS
intensity below Q= 0.03 Å-1, which is insensitive to thetemperature variation. Probably, there could be otherphysical origin to explain about the large SANS intensity.
[1] T. Itami et al., J. Non-Cryst. Solids 353 (2007) 3011.

Fig. 5