Photon Factory Activity Report 2014 #32 (2015) B

BL-9C/2014G525

Local structure of perovskite type lanthanum titanium oxynitrides
Yuji Masubuchi1,* Daiki Habu1, Shinichi Kikkawa1,Takashi Takeda2, Kei-ichiro Murai3, and Akira Yoshiasa4
1
Hokkaido Univ., Sapporo 060-8628, Japan
2
NIMS, Tsukuba 305-0044, Japan
3
Tokushima Univ., Tokushima 770-8506, Japan
4
Kumamoto Univ., Kumamoto 860-8555, Japan
1 Introduction
Perovskite type oxynitrides, SrTaO2N and BaTaO2N
have attracted much attention because of a report of theirsuperior dielectric properties [1]. We have preparedhighly densified SrTaO2N ceramics by sintering withsintering additive and post-annealing in ammonia [2]. A
local ordering of nitride anions in the cis-configuration
was reported for TaO4N2 octahedra in SrTaO2N [3]. Thisordering may affect the dielectric properties of theperovskite oxynitrides.
LaTiO2N was reported to crystallize in triclinic
perovskite having a space group of I-1 [4]. Another reportsuggested an orthorhombic lattice with Imma [5]. Partial
anion ordering has been assumed on LaTiO2N in theformer crystal structure. Solid solution between LaTiO2Nand SrTiO3 changing the O/N ratio will affect the localanion ordering. Dielectric constants estimated frompowder mixtures between the oxynitrides and low melting
paraffin increased from LaTiO2N to La0.8Sr0.2TiO2.2N0.8.
In this study, the local structure around the Ti cationand oxidation state of Ti in the oxynitride solid solution
were investigated by using the X-ray absorption
measurement.
2 ExperimentLa1-xSrxTiO3.5-d (x = 0 or 0.2) oxide precursors obtainedby firing mixtures of La2O3, SrCO3 and TiO2 werenitrided under NH3 flow of 100 mL/min at 980~1100 °C.
Crystalline phase was characterized using powder X-ray
diffraction for the nitrided products. X-ray absorption
spectra of Ti K-edge were measured in transmittancemode at the beam line 9C in Photon Factory, in KEK. The
spectra were analyzed using the program REX2000 [6].
Neutron diffraction was performed in Super-HRPD in JPARC and analyzed by using the software Z-Rietveld.
3 Results and Discussion
The nitrided products were single phase of perovskite.
Their chemical composition was measured by using anO/N analysis to be LaTiO2.011(18)N1.017(3) for x=0 andLa0.8Sr0.2TiO2.19(1)N0.85(1) for x=0.2, which agreed with thenominal compositions. The lattice parameters of theLaTiO2N were almost comparable with the reported
values in Ref. [4] and which shrunk in the solid solution
La0.8Sr0.2TiO2.2N0.8. Structural analysis for the LaTiO2N
using the neutron diffraction data suggested theoxynitride crystallized in triclinic perovskite structure
having a space group of I-1. The absorption edge positionand pre-edge peaks of the Ti K-edge in the oxynitrides
did not change significantly by increasing the nitridation
temperature or by formation of the solid solution asshown in Fig. 1. Partial anion ordering of the LaTiO2N
may be maintained in the oxynitride solid solution.
Further studies on structural refinement and local
structure in the oxynitrides will lead to a better
understanding of the intrinsic crystal structure of theoxynitrides and their dielectric properties.

Fig. 1 XANES spectra of the Ti K-edge of the nitridedproducts LaTiO2N at 980 °C (a), 1050 °C (b), 1100 °C(c) and La0.8Sr0.2TiO2.2N0.8 nitrided at 980 °C (d).
References[1] Y. I. Kim, et al., Chem. Mater., 16 1267 (2004).
[2] S. K. Sun, et al., J. Am. Ceram. Soc., 97 1023 (2014).
[3] Y. R. Zhang, et al., J. Ceram. Soc. Jpn., 119 581(2011).
[4] D. Logvinovich, et al., Solid State Sci., 11 1513
(2009).
[5] M. Yashima, et al., Chem. Commun., 46 4704 (2010).
[6] T. Taguchi, et al., Phys. Scr., T115 205 (2005).
* yuji-mas@eng.hokudai.ac.jp