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Research Papers

Crystal Structure and Anomalous Sintering Behavior of (Sr0.7 La0.3 )1−x TiO3+δ Perovskites (0 ≤ x ≤ 0.12) Synthesized by the Pechini Method

[+] Author and Article Information
Masashi Mori1

 Central Research Institute of Electric Power Industry, 2-6-1 Nagasaka, Yokosuka, Kanagawa, 240-0196, Japan

Kaoru Nakamura

 Central Research Institute of Electric Power Industry, 2-6-1 Nagasaka, Yokosuka, Kanagawa, 240-0196, Japan

Takanori Itoh

 AGC Seimi Chemical Co. Ltd., 3-2-10 Chigasaki, Chigasaki-shi, Kanagawa, 253-8585, Japan

1

Corresponding author. e-mail: masashi@criepi.denken.or.jp

J. Fuel Cell Sci. Technol 9(2), 021007 (Mar 19, 2012) (8 pages) doi:10.1115/1.4005611 History: Received September 15, 2011; Revised October 06, 2011; Published March 07, 2012; Online March 19, 2012

The crystal structure, phase relationship and sintering characteristics of (Sr0.7 La0.3 )1−x TiO3+δ perovskites (0 ≤ x ≤ 0.12) have been studied using the Pechini method. High-temperature neutron diffraction analysis showed that (Sr0.7 La0.3 )TiO3+δ has an orthorhombic structure at room temperature and a cubic structure at 450 °C. (Sr0.7 La0.3 )0.88 TiO3+δ showed a single perovskite phase and other samples with an A-site deficiency of 0 ≤ x ≤ 0.08 included secondary Ruddlesden-Popper phases. Sintering characteristics improved as the A-site deficiency increased and it was found that during sintering, (Sr0.7 La0.3 )0.88 TiO3+δ expanded anomalously between 1400 °C and 1500 °C and for holding times between 0 h and 10 h at 1400 °C and 1500 °C. Additionally, observation of the samples by scanning electron microscopy showed that this expansion was caused by pore formation within the samples. All the samples showed a weight decrease at temperatures ≥1000 °C and the temperature at which oxygen release began rose as the A-site deficiency increased. The release of oxygen is likely to be related to pore formation.

Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

Observed, calculated and differential patterns of the Rietveld refinements of the neutron diffraction pattern of (Sr0.7 La0.3 )TiO3+δ . (a) At room temperature, in comparison with the orthorhombic model (space group Pmma, No.74), (b) at 450 °C, in comparison with the cubic model (space group Pm3¯m, No.221).

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Figure 2

Structure of orthorhombic perovskite phase

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Figure 3

XRD patterns of (Sr0.7 La0.3 )1−x TiO3+δ after firing at 1000 °C for 2 h; (a) x = 0, (b) x = 0.04, (c) x = 0.08, (d) x = 0.12. ×: SrCO3 , : Ruddlesden-Popper phase

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Figure 4

Cell volumes of (Sr0.7 La0.3 )1−x TiO3+δ after firing at 1000 °C for 2 h and 1600 °C for 5 h as a function of A-site deficiency. ○: 1000 °C for 2 h, Δ: 1600 °C for 5 h.

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Figure 5

SEM images of the ball-milled sample powders after firing at 1000 °C for 2 h. (a) (Sr0.7 La0.3 )TiO3+δ , (b) (Sr0.7 La0.3 )0.96 TiO3+δ , (c) (Sr0.7 La0.3 )0.92 TiO3+δ , (d) (Sr0.7 La0.3 )0.88 TiO3+δ .

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Figure 6

Surface-sectional SEM images of the samples after firing at 1500 °C for 10 h. (a) (Sr0.7 La0.3 )TiO3+δ , (b) (Sr0.7 La0.3 )0.96 TiO3+δ , (c) (Sr0.7 La0.3 )0.92 TiO3+δ , (d) (Sr0.7 La0.3 )0.88 TiO3+δ .

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Figure 7

Relative density of (Sr0.7 La0.3 )1−x TiO3+δ (a) as a function of firing temperature with a parameter of A-site deficiency. ○: x = 0, Δ: x = 0.04, □: x = 0.08, ●: x = 0.12.

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Figure 8

Relative density of (Sr0.7 La0.3 )1−x TiO3+δ as a function of holding time with a parameter of A-site deficiency. (a) At 1400 °C, (b) at 1500 °C. ○: x = 0, Δ: x = 0.04, □: x = 0.08, ●: x = 0.12.

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Figure 9

Volume of (Sr0.7 La0.3 )0.88 TiO3+δ as a function of holding time with a parameter of A-site deficiency. ○: x = 0, Δ: x = 0.04, □: x = 0.08, ●: x = 0.12.

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Figure 10

Cross-sectional SEM micrographs of (Sr0.7 La0.3 )0.88 TiO3+δ . (a) At 1400 °C with no holding time, (b) At 1400 °C for 10 h.

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Figure 11

Surface-sectional SEM micrographs of (Sr0.7 La0.3 )0.88 TiO3+δ . (a) At 1400 °C with no holding time, (b) At 1400 °C for 10 h.

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Figure 12

XRD patterns of (Sr0.7 La0.3 )0.88 TiO3+δ perovskite after firing at (a) 1400 °C with no holding time, (b) 1400 °C for 10 h, (c) 1500 °C with no holding time, and (d) 1500 °C for 10 h.

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Figure 13

Cell volumes of (Sr0.7 La0.3 )0.88 TiO3+δ perovskite as a function of temperature with a parameter of holding time. ○: x = 0, Δ: x = 0.12. The open and closed symbols show the samples fired at various temperatures with no holding time and 10 h, respectively.

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Figure 14

TG curves of (Sr0.7 La0.3 )0.88 TiO3+δ samples fired at 1000 °C for 2 h and at 1600 °C for 5 h. ○: x = 0, Δ: x = 0.12. The open and closed symbols show the samples fired at 1000 °C for 2 h and 1600 °C for 5 h, respectively.

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Figure 15

Cell volumes of (Sr0.7 La0.3 )1−x TiO3+δ before and after annealing at 1000 °C for 5 h in air as a function of A-site deficiency. The samples used were fired at 1600 °C for 5 h. The closed symbols show the samples annealed at 1000 °C for 5 h.

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Figure 16

(a) Cell volume changes induced by VO··, VSr″, VTi″″,  LaSr·, LaSr·-VSr″, LaSr·-VTi″″, and  LaSr·-VO·· as compared with the volume of a pristine SrTiO3 unit cell. Results of single defects are represented as black rods and that of LaSr· and vacancy complexes are represented as white rods. (b) Schematic illustration of bonding structure around  LaSr·.

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