Energy-efficient synthesis of ferrite powders and films
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Energy-efficient synthesis of ferrite powders and films Ranajit Sai1,2, Suresh D. Kulkarni1,2, K. J. Vinoy3, Navakanta Bhat1,3, S. A. Shivashankar1,2 1
Centre for Nano Science and Engineering, Indian Institute of Science, Bangalore, India. Materials Research Centre, Indian Institute of Science, Bangalore, India. 3 Electrical Communication Engineering, Indian Institute of Science, Bangalore, India. 2
ABSTRACT In recent years, there has been significant effort in the synthesis of nanocrystalline spinel ferrites due to their unique properties. Among them, zinc ferrite has been widely investigated for countless applications. As traditional ferrite synthesis methods are energy- and time-intensive, there is need for a resource-effective process that can prepare ferrites quickly and efficiently without compromising material quality. We report on a novel microwave-assisted soft-chemical synthesis technique in the liquid medium for synthesis of ZnFe2O4 powder below 100 °C, within 5 min. The use of β-diketonate precursors, featuring direct metal-to-oxygen bonds in their molecular structure, not only reduces process temperature and duration sharply, but also leads to water-soluble and non-toxic by-products. As synthesized powder is annealed at 300 °C for 2 hrs in a conventional anneal (CA) schedule. An alternative procedure, a 2-min rapid anneal at 300 °C (RA) is shown to be sufficient to crystallize the ferrite particles, which show a saturation magnetization (MS) of 38 emu/g, compared with 39 emu/g for a 2-hr CA. This signifies that our process is efficient enough to reduce energy consumption by ~85% just by altering the anneal scheme. Recognizing the criticality of anneal process to the energy budget, a more energyefficient variation of the reaction process was developed, which obviates the need for postsynthesis annealing altogether. It is shown that the process also can be employed to deposit crystalline thin films of ferrites. INTRODUCTION Advanced material preparation and processing are essential to address current microelectronics challenges. Commercialization calls for the need for economical, simple and effective methods for the fabrication of nanomaterials. Of late, spinel ferrite nano-particles have generated lot of interest and a variety of methods of their synthesis have been reported, such as sol-gel [1], combustion [2], coprecipitation [3], sonochemical [4], etc., apart from traditional ceramic synthesis processes [5]. These syntheses typically take several hours of preparation, followed by annealing at high temperatures for hours, making them very energy-intensive, contrary to modern industrial and environmental requirements. Further, the methods do not all provide control of grain size, or a narrow size distribution at the nanometric level, or homogeneity at the micrometer level. On the top of these high throughput and low energy consumption are two important factors to be met by any process so as to be a green process. Modern synthesis routes have to be energy-efficient, i.e., higher yields and higher puri
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