Since the discovery of YBa2Cu3O7−x (Y123) by Wu et al. in 1987 [1, 2], the applications of high-Tc ceramic superconductors in scientific and engineering fields have been increasing continuously [3–5]. The conventional method of preparing Y123 powders is by the solid-state reaction of oxides and carbonates [1, 2, 6]. These starting materials are stoichiometrically mixed, and then calcined in air or oxygen at atmospheric pressure and a temperature of 900–980 ◦C for 20–50 hr. Intermittent grinding is required to obtain phase-pure and homogeneous Y123 powders. Although the method is relatively simple, and alternative processes exist which decrease the total reaction time [7], all of the conventional solid reaction processes are, in general, timeconsuming and energy-intensive. Recently, a variety of wet-chemical synthesis methods have also been reported to be effective in generating ultrafine and more homogeneous powders of ceramic oxides [8–10]. Relatively complex schedules and low production rates are the common problems of the wet-chemical methods. Fortunately, the drawbacks of these methods as mentioned above could be partially eliminated by the combustion synthesis method, which has been applied to the synthesis of various high performance materials including ceramics, intermetallics, and composites [11, 12]. Among its many advantages are low processing cost, and high energy efficiency and production rates [13]. However, the lack of homogeneity and relatively lower purity of the synthesized product are two potential disadvantages. Recently, several researchers have used a sol–gel combustion method to synthesize ferrite and perovskite powders [14–16]. This is a novel and unique technique that combines the chemical sol–gel process and the combustion synthesis process. The advantages of this technique include inexpensive precursors, simple preparation process, and a resulting submicron-sized powder with high homogeneity. Although there have
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Jul 13, 2017
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