Photon Factory Activity Report 2016 #34 (2017)

BL-4B2/2016P009

Synchrotron X-ray Diffraction Study for High-Tc candidate Nd3.5Sm0.5Ni3O8
Masatomo Uehara*, Kai Kobayashi, Hiroki Yamamoto, Akitoshi Nakata,Kazuhei Wakiya and Izuru Umehara
Department of Physics, Yokohama National University, Yokohama, 240-8501, Japan
1 Introduction
Ln4Ni3O8 (Ln=La, Nd, Sm) contains 2-dimensional
NiO2 planes and its crystal structure is basically the samewith high-Tc cuprate as shown in fig.1. Moreover, theformal valence of Ni is +1.33 consisting of Ni+ 3d9 andNi2+ 3d8 states, being the same with high-Tc cuprate.
Therefore, Ln4Ni3O8 is a promising candidate for new
high-Tc material. Despite these similarities with cuprate,
Ln4Ni3O8 had showed neither metallic characteristic nor
superconductivity. [1-3]Recently, we found that the intercalation and subsequent
deintercalation treatment with sulfur induces the metallic
nature from 300 down to ~20 K in Nd3.5Sm0.5Ni3O8. [4]This is the first observation of the metallic state in thissystem. As the origin of this behavior, it can be guessedthat the additional oxygens at apical site of Ni is removed
by S-treatment, because a similar phenomenon has been
observed in T’-type high-Tc cuprate having similar
structure with present system.
In this study, synchrotron X-ray diffraction experiment
was performed to investigate what happens structurally
by S-intercalation and deintercalation.

to be the “S-deintercalated samples” hereafter. The assynthesized and S-deintercalated samples show thesemiconducting and the metallic behavior ( 300 - ~20 K ),respectively.
High-resolution synchrotron X-ray powder diffraction
data were collected at BL-4B2 beam line with an incident
beam wavelength of 1.19735 Å at room temperature.
3 Results and Discussion
Figure 2(a) and (b) show the synchrotron X-ray data foras-synthesized and S-deintercalated samples, respectively.
S-deintercalated sample contains very tiny amount of
impurity phase shown by asterisk marks. The electricalresistivity data for the samples used in synchrotron X-ray
experiments are displayed in the inset of the figures.
These data were analysed by Rietveld method by using
RIETAN program, [6] assuming I4mmm (No. 139) spacegroup. M(1) and M(2) are imaginary atoms of(Nd3.5Sm0.5). Blue solid and dotted lines are observed andcalculated data respectively. The difference between
observed and calculated data is displayed blow X-ray
profile. The vertical tick marks correspond to the Bragg
positions. For S-deintercalated sample, two-theta ranges
shown below where tiny amount of impurity phases aredetected were not used. 16.7-17.03 º, 20.0-20.76 º, 22.4723.18 º, 23.92-24.29 º, 28.5-29.5 º.
Rwp = 7.01 %, Re = 4.29 %Nd3.5Sm0.5Ni3O8
as-synthesized sample a = 3.9159(5) Å, c = 25.279(4) ÅO(3)
M(2)

O(1)

43
0S-deintercalated sample

100200T (K)300

Rwp = 10.9 %, Re = 3.67 %a = 3.9137(1) Å, c = 25.287(1) Å(b)6
 (10  cm)

Intensity (a. u.)

Ni(1)

O(2)
M(1)

(cm)

Ni(2)

5(a)

-2

5

Fig. 1. The crystal structure of Nd3.5Sm0.5Ni3O8. The
arrows show the displacement-directions of M(1), Ni(2)and O(2) atoms by S-treatment. The circles with brokenlines are possible additional apical oxygens.

2 Experiment
The detail of sample preparation was reported in ourprevious paper. [5] The intercalation and deintercalation
by sulfur is called as “S-treatment” hereafter.
Also, we call the sample without S-treatment to be the“as-synthesized sample” and the sample after S-treatment40* * **

20100

200
T(K)

300

*4060

2 (deg.)

80100

Fig. 2(a)(b). Synchrotron XRD patterns of assynthesized (a) and S-deintercalated (b) samples of
Nd3.5Sm0.5Ni3O8. Inset shows the temperaturedependence of electrical resistivity of the samples usedin synchrotron XRD experiments.

Photon Factory Activity Report 2016 #34 (2017)-2

position sift along c - axis (10 Å)

For isotropic atomic displacement parameters of oxygen,those determined by neutron diffraction experiment in ref.
[7] were used. For S-deintercalated sample, Rietveld
analysis was performed with the same isotropic atomic
displacement parameters with the values determined in
the analysis for as-synthesized sample. The occupation
factors for all ions were fixed to be 1.0 according to theprevious neutron diffraction result. [7] For as-synthesizedsample, the analysed crystal data is almost consistent topublished data by neutron diffraction experiments. [7]In order to see what was changed structurally by Streatment, figure 3 shows the displacement-length (Å)
along c - axis of Ni(2), O(2), M(1) and M(2) positions for
S-deintercalated sample, relative to those of assynthesized sample. O(2) atoms are being away fromNiO2 plane and close to block layer by S-treatment. Incontrast, Ni(2) atoms move with opposite way of O(2)atoms. This can be understood qualitatively by removal ofO2- ion at apical site (broken circles in Fig. 1) of Ni(2) byintuitive electrostatic consideration. The position of M(2)atoms is almost unchanged, while M(1) atoms moves
with the same direction of Ni(2) atoms. This might beunderstood by the Coulomb repulsion from Ni(2)1.33+ ionsovercoming the Coulomb attraction from O(2)2-. Thissituation is schematically shown in the picture of crystal
structure by using arrows (Fig.1).
108Ni(2) site
O(2) site
6420-286M(1) site
4M(2) site
20-2-4S-deintercalated
as-synthesizedsamplesample

Fig. 3. The position sift along c-axis of Ni(2), O(2),M(1) and M(2) sites for as-synthesized and Sdeintercalated samples of Nd3.5Sm0.5Ni3O8, comparing
to those of as-synthesized sample.

4 conclusion
We have performed synchrotron X-ray diffraction
experiment for “semiconductive” as-synthesized and“metallic” S-deintercalated Nd3.5Sm0.5Ni3O8 samples inorder to elucidate the origin of metallization by Streatment from a structural point of view. Synchrotron Xray diffraction study suggests that the appearance ofmetallic behavior for Nd3.5Sm0.5Ni3O8 by S-treatment isassociated with the removal of additional apical oxygen,similar to the situation of T’-type high-Tc cuprate.

Acknowledgement
We thank Dr. Kotaro Fujii, Mr. Haruki Sugiyama andKEK-PF user group for helpful support for synchrotron
X-ray diffraction experiments. This work was alsofinancially supported by Public interest Yokohamakogyokai Research aid Foundation.
References[1] V. V. Poltavets et al., Phys. Rev. Lett. 104, 206403(2010).
[2] Y. Sakurai et al., Physica C. 487, 27 (2013).
[3] Y. Sakurai et al., JPS Conf. Proc., 1, 012086-1-4(2014).
[4] A. Nakata et al., Advances in Condensed Matter
Physics, 5808029 (2016).
[5] K. Kobayashi et al., JJAP Conf. Proc. 6, 011106(2017).
[6] F. Izumi and T. Ikeda, Mater. Sci. Forum 321-324,
198 (2000).
[7] V. V. Poltavets et al., Inorg. Chem. 46, 10887(2007)* uehara-masatomo-cf@ynu.ac.jp