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
May 4, 2013

課題番号 Project No.

装置責任者 Name of responsible person

2012B0247

Takashi Kamiyama

実験課題名 Title of experiment

装置名 Name of Instrument/（BL No.）

Detailed crystal structural study on highly hole doped R2−xSrxNiO4 with x > 1/2

SuperHRPD/(BL08)

実験責任者名 Name of principal investigator

実施日 Date of Experiment

Ryoichi Kajimoto

9:00 on Feb. 7 – 9:00 on Feb. 13, 2013

所属 Affiliation
J-PARC Center, Japan Atomic Energy Agency
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.
Powder samples of Pr2−xSrxNiO4 with x = 0.5, 0.7, and 0.9

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.

Layered perovskite nickel oxide, R2−xSrxNiO4 (R = La, Pr, Nd, etc.) shows charge and spin orderings uponhole doping. The holes enter the x2−y2 orbitals of Ni ions when the hole concentration per nickel site x is lessthan 1/2, which results in a so-called stripe ordering of charges and spins in the NiO2 planes. On the other hand,when x > 1/2, the holes also enter the 3z2−r2 orbitals, and the x2−y2 character in eg orbitals of the Ni3+ ionsbecomes dominant [1]. In order to clarify structural changes caused by the change of orbital character as well as
the charge and spin ordering in R2−xSrxNiO4 with x > 1/2, we performed high-resolution powder neutron
diffraction measurements on Pr2−xSrxNiO4 with x = 0.7, 0.8, and 0.9. We utilized a 4–5 g powder sample for eachcomposition, and measured the powder diffraction patterns with changing the temperature from 10 K to 310 K in
20 K step. Unfortunately, observed data were contaminated by the diffraction profile from an unused time-framedue to a failure of synchronization of the frame-overlap choppers. Therefore, we could not obtain high-quality
data of x = 0.5 and x = 0.7 for a precise analysis. Though the contamination of the x = 0.9 data is less severe, thedata contains small spurious peaks caused by this contamination. We are now trying to get rid of thecontamination from the data by manipulating the raw event data.
12. 実験方法及び結果（つづき） Experimental method and results (continued)
Figure 1 shows the powder diffraction pattern of x = 0.9 measured at 10 K and the result of its Rietveld
analysis. The Rietveld analysis was performed using the software package Z-Rietveld (ver. 0.9.36). We removed
the spurious peaks described above in the analysis as much as possible, fixed the site occupancies to theirnominal values, and assumed the isotropic temperature factor for each atom. Though the observed peak positions
are describable in the space group I4/mmm, the goodness of the fit (R-factor) is not satisfactory, partly because
the profile shapes of several peaks are not reproduced by the refinement. A previous neutron powder diffraction
work on LaSrNiO4 (x = 1) reported that multiple phases and anisotropic strain broadening were required to reacha satisfactory refinement due to a distribution of La/Sr ratios throughout the sample [2]. We should also try toincorporate these effects to improve the refinement.

Fig. 1. Powder diffraction pattern of Pr1.1Sr0.9NiO4 at 10 K as a function of time-of-flight. Red marks show the observed data. Light
blue line, green vertical bars, and dark blue line show the calculated diffraction pattern, peak positions, and difference between theobserved and calculated patterns obtained by the Rietveld analysis.

Figure 2 shows temperature dependence of the ratio of theRatio of Ni-O bond lengths
1.099

axial [Ni-O(1)] to equatorial [Ni-O(2)] Ni-O bond length, whichwere obtained by the Rietveld refinement of each temperaturekink around 100 K. This temperature corresponds to the one
where the sign of the Hall coefficient changes [1]. Since the ratioof the Ni-O bond lengths reflects the character of eg orbitals of Niions, the change of the temperature dependence may indicate thechange of the orbital character concomitant with the change ofthe character of carriers. Though it is an interesting
interpretation, we need further analysis and comparison of thedata of the other compositions to conclude.
References[1] M. Uchida et al., Phys. Rev. B 86, 165126 (2012).
[2] J. E. Millburn et al., J. Solid State Chem 145, 401 (1999).

2

Ni-O(1)/Ni-O(2)data. The ratio decreases as temperature decreases, but it shows a

1.098

1.097

1.096

1.095
050 100 150 200 250 300 350
Temperature (K)Fig. 2. Temperature dependence of the ratio of
the axial to equatorial Ni-O bond lengths in
Pr1.1Sr0.9NiO4.