Photon Factory Activity Report 2014 #32 (2015) B
BL-9A, BL-12C/ 2013G154

Local distortion in a Ni-doped TiO2 semiconductor
Ikuo Nakai1,* Yuhji Yamao,1 Toshimasa Inoue,1 Takahiro Ishii,1 Masaaki Chikaraishi,1Ryouhei Hisamatsu,1 Makio Kurisu,2
1Tottori Univ., Tottori 680-8552, Japan
2Ehime Univ., Matsuyama 790-8557, Japan
We report the x-ray diffraction, x-ray absorption fine structure and magnetization study for Ni-doped TiO2 magneticsemiconductors. We have observed the local distortion around the impurity atom in the diluted magnetic semiconductor.

3. Results and Discussion
Any other peaks than those of the rutile-type phase(space group P42/mnm) are not observed in x-ray
diffraction patterns. We determine the lattice constantsfrom the Rietveld analysis of x-ray diffraction, which
decreases with increasing the Ni content. The
magnetization measurement shows that they are
ferromagnetic at room temperature.
Figure 1 shows the radial structural function around Ti
atoms for TiO2. A peak around 1.5 Å corresponds to Ti-Opairs, the second one around 2.5 Å is for the Ti-Ti bondand the third peak around 3.0 Å consists of Ti-O and TiTi pairs. These peaks are characteristic of the rutile-typestructure.
Figure 2 represents the radial structural function aroundNi atoms for 5%Ni-doped TiO2, which shows that thedoped Ni atom is substituted for the Ti site of the rutile
type TiO2 matrix. The x-ray absorption near edge
structure measurement shows the valence of thesubstituted Ni to be 2+. The interatomic distance between
Ni and O is by about 0.05 Å larger than that of the Ti-Obond in the Ni-doped TiO2, which is as same as that ofthe TiO2 matrix. That is, the O neighbor keeps away fromthe Ni atom. This may relate both of the Ni valence of 2+and the charge neutrality.

12Radial structure function |  |2. Experiment
The Ni-doped TiO2 was synthesized by the solid state
reaction from the mixture of rutile-type TiO2 (99.99%)
and NiO (99.97%). They were milled and annealed at 800oC for 20 h in air.
We measured XAFS of Ni-doped TiO2 and rutile-typeTiO2 at the Photon Factory to investigate the electronicstates and the local structure. X-ray diffraction andmagnetic hysteresis measurements were also carried out
at room temperature.

In conclusion, we have observed the local distortion
around the impurity atom in the diluted magnetic
semiconductor, which is much different from the average
lattice structure measured by x-ray diffraction.

rutile type TiO 2
8Ti K edge
300 K
4O00

Ti

24
Distance R / Å6Fig. 1: The radial structure function of a rutyle-type TiO2
for the Ti K edge at 300 K.
12
Radial structure function |  |1. Introduction
Dilute magnetic semiconductor oxides with aferromagnetic behavior above room temperature areinvestigated extensively for applying to spintronics
devices [1]. Some models have been proposed forferromagnetism of the oxides in which defects, especiallyoxygen vacancies, play an important role [2]. We havedetected the oxygen vacancies in the room temperature
ferromagnet Co-doped TiO2 by XAFS measurements [3].
We here report on XAFS for a Ni-doped TiO2.

(Ti0.95 Ni0.05 )O28
Ni K edge
300 K4O00Ti

24Distance R / Å6Fig. 2: The radial structure function of (Ti0.95Ni0.05)O2 for
the Ni K edge at 300 K.
References[1] Y. Matsumoto et al., Science 291, 854 (2001).
[2] J. M. D. Coey et al., Nature Mater. 5, 173 (2005).
[3] I. Nakai el al., J. Korean Phys. Soc. 63, 532 (2013).
* nakai@ele.tottori-u.ac.jp