実験報告書様式（一般利用課題・成果公開利用）
提出日 Date of Report

MLF Experimental ReportAug. 15, 2017

課題番号 Project No.

装置責任者 Name of responsible person

2017A0256

Toshiya Otomo

実験課題名 Title of experiment

装置名 Name of Instrument/（BL No.）

Investigation

into

thenanoscale

fluctuation

oftheNOVA(BL-21)

atomic-displacement-type ice state by the PDF analysis

実施日 Date of Experiment

実験責任者名 Name of principal investigator

May 25-29, 2017

Noriaki Hanasaki
所属 Affiliation
Osaka University
試料、実験方法、利用の結果得られた主なデータ、考察、結論等を、記述して下さい。（適宜、図表添付のこと）
Please report your samples, experimental method and results, discussion and conclusions. Please add figures andtables for better explanation.
1. 試料 Name of sample(s) and chemical formula, or compositions including physical form.

*Spinel-type Titanate Oxides Mg1+xTi2-xO4(x=0, 0.01, 0.06, 0.125, 0.25, 0.32, and 0.4)

*Powder sample

2. 実験方法及び結果 （実験がうまくいかなかった場合、その理由を記述してください。）
Experimental method and results.

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

Experimental method
The sample (Mg1+xTi2-xO4) was put in V-Ni cell (6mmφ-13cm). The neutron powder diffraction was measured
in BL21 (NOVA) . In each sample of the composition x, we measured the neutron diffraction at 150K. In x=0.01
and 0.06, we also measured the neutron diffraction at the bottom temperature (BT, 20K) and the room
temperature (RT). In these measurements, we used the machine changing the sample automatically. We
succeeded in obtaining the diffraction data in all the samples. On the basis of the measured diffraction pattern,
we calculated the atomic Pair Distribution Function (PDF). In order to analyze the PDF, we performed thesimulation of the PDF by use of the software PDFgui, and obtained the local positions of the Ti, Mg, and Oatoms.
Experimental results
According to the previous reports, the MgTi2O4 undergoes the structural transition from the cubic phase to thetetragonal phase at 260K, which is associated with the Ti-Ti dimerization [1,2]. Figure 1 shows the experimental1

2. 実験方法及び結果（つづき） Experimental method and results (continued)
results of the PDF at 150K and 300K in Mg1.01Ti1.99O4.
The dip at the distance r = 2.1A is ascribed to the atomic
correlation of the Ti-O pair.

The peak at r = 3.0A

corresponds to the correlation of the Ti-Ti and O-O pairs.
The x-ray diffraction measurement suggests that thestructuraltransition

occursat220K-230K

in

Mg1.01Ti1.99O4. One kind of the distance in the Ti-O pair,
Ti-Ti pair, and O-O pair exist in the cubic phase, while there
are several kinds of the distances in the these pairs in thetetragonal phase. In the low-temperature tetragonal phase,the peak at r = 3.0A becomes more sharp than thehigh-temperature cubic phase.

This is attributed to thesmaller U values of the Debye Waller factors in the Ti and Oions, which accompanies the Ti-Ti dimerization, ascompared to the cubic phase.

Though there are several

kinds of the Ti-O pairs around r = 2.1A, the depth of the dip
at r = 2.1A hardly changes owing to the smaller U value ofthe Ti and O ions.
Figure 2 shows the experimental results of the PDF in
Mg1+xTi2-xO4 (x = 0, 0.01, 0.06, 0.125, 0.25, 0.32, and 0.4) at
150K. Around x = 0.02, the x-ray diffraction suggests thephase transition between the tetragonal phase and the cubic
phase. In x=0-0.06, however, the dip at r = 2.1A and thepeak at r = 3.0A still remain sharp. No clear change wasobserved in the PDF in this x range. This suggests thetetragonal short range order exists in x>0.02 in the cubic
phase. In x>0.125, the depth of the dip decreases clearly.
The height of peak at r = 3.0A also is reduced. The neutron
scattering lengths of the Mg and O atoms have a positivesign, while that of the Ti atom has a negative one. Thus, thesubstitution of the Ti ion with the Mg ion reduces the depthof the dip at r = 2.1A and the height of the peak at r = 3.0A.
The detailed PDF analysis reveals the tetragonal local order,
which is associated with the ice-type Ti displacement, still
exists in x<0.32.
Reference[1] M.Isobe et al., J.Phys.Soc.Jpn. 71, 1848 (2002).
[2] M.Schmidt et al., Phys.Rev.Lett. 92, 056402 (2004).
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