Photon Factory Activity Report 2005 #23 Part B (2006)
Materials Science

4B2/2005G157, 2005G158, 2004G256, 2004G058

Crystal structure and Electron Density of La0.64(Ti0.92Nb0.08)O3 at 1000 °C and 1350 °C
Roushown Alia,b, *Masatomo Yashimab, Takahiro Wakitab, Takayuki Tsujib, Yoichi Kawaikeb,
Yoshiaki Andob and Fujio Izumia

aQuantum Beam Center, National Institute for Materials Science, 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan;
Department of Materials Science and Engineering, Interdisciplinary Graduate School of Science and Engineering,Tokyo Institute of Technology, 4259 Nagatsuta-cho, Midori-ku, Yokohama, 226-8502, Japan
calculations were done
Introduction
using PRIMA with the unit
Doped-La2/3TiO3 materials have an A-site deficient
divided into 64 × 64 ×
perovskite-type structure (ABO3) where A=La2/3±y,
La1 cell
128 pixels and wholeB=(Ti1-xMx) and M is dopant cation. These materials arepatternfitting
using
attractive owing to their high oxide-ion conductivities andRIETAN-2000.
Then,
thedielectric properties. Therefore, many researchers have
MEM-based pattern fitting
studied the unit-cell parameters, phase transition andwasappliedwhichstructural parameters of the compounds. To improve theirimproved the reliability
properties, it is important to understand the precisefactors(valuewithinchemical bonding nature. But no study has yet been
O2
parentheses in Table 1).
La2
reported on the bonding nature of La0.64(Ti0.92Nb0.08)O3.
Electron-density image isFurthermore, no crystal structure data above 500 °C isshown in Fig.2 to visualize
available in the literature. Here, we have determined thethe density derived fromTiNb
O3 the MEM calculations forcrystal structure and electron density distribution byO3
the data measured at 1350
combining a Rietveld method, a maximum-entropy
O3°C. The electron density
method (MEM) and whole pattern fitting using
map shows the covalentsynchrotron X-ray diffraction intensity measured at 1000
bonding between the O3°C and 1350 °C.
and TiNb atoms andExperimental
between Ti,Nb and O2
Fig.2 Equicontour surface of theatoms.
Synchrotron X-ray powder diffraction data were
electron-density distribution atcollected using the multi-detector system installed at theTable 1. Refined crystal
0.8 A on the (001) plane of SRbeam line BL-4B2 of Photon Factory, KEK, Tsukuba. TheXRD data of La (Ti Nb )Oparametersand reliability
wavelength was determined to be λ=1.20667(1) Å. A
measured at 1350 °C
1factors
ofthefurnace with MoSi2 heaters was used for the highLa0.64(Ti0.92Nb0.08)O3
temperature measurements.
Diffraction data were
Temperature1000 (°C)
1350 (°C)
collected at 1000 °C and 1350 °C in the 2θ range from 7°
Atomto 154° in the step interval of 0.005° in 2θ. Computera3.90047(1) 3.91930(1)programs RIETAN-20002, PRIMA3 and VENUS3 werec
7.90938(3) 7.92535(2)utilized for Rietveld analysis, MEM calculation and0.883(1)La1 g(La1) 0.911(1)visualization of the electron-density distribution,
0.0144(2)U (Å2) 0.0087(2)respectively.
0.369(1)0.397(1)La2g(La2)
Refined2
Results and discussion)
0.0371(7)0.0374(6)U(Åparameters
All the reflections in the synchrotron X-ray powder
TiNb z0.2663(2)0.2655(1)diffraction patterns measured at 1000 °C and 1350 °C
U (Å2) 0.0123(3)0.0160(3)were indexed on the basis of tetragonal symmetry withO1Ueq(Å2) 0.023
0.045
space group P4/mmm (a ≈ ap × b ≈ ap × c ≈ 2ap). The
0.031(2)O2
U (Å2) 0.016(2)calculated profiles fit well with that of observed one (Fig.
0.2496(4)0.2552(4)O3z(O3)
1). The final unit-cell and structural parameters and R0.041
Ueq(Å2) 0.035
factors for the two temperatures are summarized in Table I.
Rwp (%)
15.05(14.27) 13.43(11.69)
The MEM analyses were performed using the structure
10.88(10.20) 10.03(8.70)
factors obtained from the Rietveld analysis. The number
Reliability Rp (%)(%)
8.93(6.25)
10.46(5.54)
Rof structure factors was 92 for both the data. The MEM
I
factors
RF (%)
9.6294.86) 5.79(3.52)
S
2.18(2.06)
1.92(1.62)
b-3

Intensity (A.U.)

0.64

0.92

0.08

3

Tetragonal space group P4/mmm (No.123) Z=2. In the analyses the atom
positions were: La1 1a (0.0, 0.0, 0.0); La2 1b (0.0, 0.0, 1/2); TiAl 2h (1/2,1/2, z); O1 1c (1/2, 1/2, 0.0); O2 1d (1/2, 1/2, 1/2); O3 4i (1/2, 0.0, z).
Reliability factors shown in the parentheses are obtained after REMEDYcycles.

References2θ (deg.)

Fig.1 Rietveld fitting pattern measured at 1350 °C. Crosses(+ symbols) and line denote observed and calculated profile
intensities, respectively. Short vertical bars represent Braggreflection positions. A difference (observed-calculated) plotis shown bellow the profiles.

[1] M. Yashima et al, J. Appl. Cryst. 38, 854 (2005).
[2] F. Izumi and T. Ikeda, Mater. Sci. Forum 321-324, 198(2000).
[3] F. Izumi and R.A. Dilanian, “Recent Research Developmentsin Physics,” Transworld Res. Network, Trivandrum (2002), p.
699.

* yashima@materia.titech.ac.jp

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