実験報告書様式（一般利用課題・成果公開利用）（ ※本報告書は英語で記述してください。ただし、産業利用課題として採択されている方は日本語で記述していただいても結構です。 ）MLF Experimental Report

提出日 Date of Report
March 11, 2013

課題番号 Project No.

装置責任者 Name of responsible person

2012B0182

Dr. K.Ikeda and Dr. Ohtomo

実験課題名 Title of experiment

装置名 Name of Instrument/（BL No.）

Investigation of the charge ice state by the PDF analysis

BL-21 NOVA

実験責任者名 Name of principal investigator

実施日 Date of Experiment

Noriaki Hanasaki

From Dec.23, 2012 to Dec.25, 2012

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.
Pyrochlore Niobates YCaNb2O7

PowderPyrochlore Niobates NdCaNb2O7 Powder
Pyrochlore Niobates Y2Nb2O7

PowderPyrochlore Niobates Pb1.5Nb2O6.5 Powder
Pyrochlore Niobates Cd2Nb2O7

Powder2. 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.

The sample powder (the pyrochlore niobates) and the helium gas were put into the vanadium tube, throughwhich the neutron beam can go. This vanadium tube was set in the bottom of the cryostat. In BL-21(NOVA),
the sample powder was irradiated by the pulsed neutron beam during the several hours. The neutron
diffraction was observed by use of the detector set in the 90 (degree) bank. In YCaNb2O7, the diffraction wasobtained at 50K, 300K, and 450K. In NdCaNb2O7, the diffraction was measured at 300K and 450K. In thereference sample of Y2Nb2O7, Cd2Nb2O7, and Pb1.5Nb2O6.5, the diffraction was measured at room temperature.
The neutron-diffraction intensity is obtained as a function of the wave number Q. By the Fouriertransformation of these data, we get the neutron PDF (pair distribution function). Since the neutron absorptionof Cd is very strong in Cd2Nb2O7, the diffraction intensity is too weak to analyze the PDF.
In the neutron PDF, one can see the peak around r = 2(A), r = 2.6(A) and r = 3.7(A) in all the samples except
Cd2Nb2O7. The peak around r = 2(A) is ascribed to the correlation between the niobium atom and the nearest12. 実験方法及び結果（つづき） Experimental method and results (continued)
neighbor oxygen atoms, which is consistent with the single crystal analysis by the X-ray diffraction, indicating
the reliability of these PDF data.
We investigate the temperature dependence of the PDF data in YCaNb2O7 and NdCaNb2O7. As thetemperature decreases, the peak becomes sharp. Besides this, the striking change of the peak shape cannot
be seen. Since the diffuse scattering, that originates from the Nb displacement, is observed below 500℃ in
the X-ray diffraction, we should compare the PDF data measured below and above 500℃. However, we cannot
measure neutron diffraction above 500℃, since there is a possibility that the cryostat, which is used thesample holder, can be damaged under the high temperatures. The PDF measurement above 500℃ will benecessary and left for the further study.
We examine the peak around r = 2(A) in YCaNb2O7, NdCaNb2O7, Y2Nb2O7, and Pb1.5Nb2O6.5. There is atendency about the peak position ( r ) around 2(A) that r(Pb1.5Nb2O6.5) < r(YCaNb2O7 and NdCaNb2O7) <r(Y2Nb2O7). This suggests that the distance between the niobium ion and the nearest-neighbor oxygen ion
decreases, as the valence of the niobium ion increases. The striking splitting or the broading of the peakaround r = 2 (A), which are suggestive of the large charge disproportionation in the Nb site, are not observed.
In order to examine the possibility of the two-in or two-out Nb configuration and two-in-two-out Nb
configuration, we try to simulate the neutron PDF on the assumption of these models. The conclusion has notbeen drawn yet.

Fig. Neutron PDF of the pyrochlore niobates measured in BL-21 (NOVA).

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