Synthesis and characterization of nanoparticles of Ba 2 EuZrO 5.5 : A new complex perovskite ceramic oxide
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R. Divakar Physical Metallurgy Section, Indira Gandhi Centre for Atomic Research, Kalpakkam, India, 603 102
J. Koshya Regional Research Laboratory, Council of Scientific and Industrial Research, Trivandrum, India, 695 019 (Received 22 December 1999; accepted 10 July 2000)
Nanoparticles of barium europium zirconate, a complex perovskite oxide, were synthesized using a modified self-propagating combustion synthesis. The solid combustion products thus obtained were characterized by x-ray and electron diffraction, differential thermal analysis, thermogravimetric analysis, infrared spectroscopy, particle-size analysis, surface area determination, gas adsorption studies, and high-resolution transmission electron microscopy. According to the results of the x-ray and electron diffraction, as-prepared powder showed the single phase of barium europium zirconate (Ba2EuZrO5.5) without another phase and had a complex cubic perovskite (A2BB⬘O6) structure. The transmission electron microscopic investigation showed a mean grain size of 38 nm with a standard deviation of 12 nm. High-resolution lattice imaging of the nanoparticles indicated the possibility of finer crystallite in the particle having the same orientation. The nanoparticles of Ba2EuZrO5.5 obtained by the present method could be sintered to 97% theoretical density at a relatively low temperature of 1525 °C. I. INTRODUCTION
Synthesis of advanced ceramics and specialty materials as nanoparticles is one of the major fields in materials-processing technology.1–3 The specific advantages of nanocrystalline materials are superior phase homogeneity, sinterability, and microstructure leading to unique mechanical, electrical, dielectric, magnetic, optical, and catalytic properties.2–6 The coarse-grained powder synthesized through the conventional solid-state reaction route has the disadvantages of poor powder characteristics, high temperature of processing, and lower purity.7 Recently, a new perovskite oxide material, barium europium zirconium oxide (Ba2EuZrO5.5), was synthesized by conventional solid-state reaction method for its potential use as substrate for high–Tc superconductors.8 This material is found to be chemically nonreacting with both YBa2Cu3O7–␦ (YBCO) and Bi(2223) superconductors at extreme processing conditions and has attractive dielectric properties for its use as substrate for these hightemperature superconductors at microwave frequencies.9 a)
Address all correspondence to this author. e-mail: [email protected] J. Mater. Res., Vol. 15, No. 10, Oct 2000
To synthesize this material as phase-pure powder by solid-state route, very prolonged heating (approximately 100 h) at temperatures above 1350 °C was required. The particle size of the powder thus obtained was of the order of a few tens of microns. To obtain a sintered density of about 96%, it was essential that the compacted powder should be sintered at temperatures above 1625 °C for at least 10 h. In order to improve the characteristics of the powder, especially its sinterability and phase purity,
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