(48g) Synthesis and Characterization of Submicron Multiferroic Complex Oxides

The multiferroic materials having a magnetic-ferroelectric coupling are of great interest for potential application as a new type of memory storage devices, magneto-electric hard drive materials, miniaturized sensors and digital pigments. We report a novel approach to produce crystalline multiferroic submicron particles such as HoMnO3, Fe doped BaTiO3, and BaTiO3-CoFe2O4 by self-sustaining one step process, named Carbon Combustion Synthesis of Oxides (CCSO). It produces complex oxide much faster (order of minute) than the common calcination process (order of hours) without any external power consumption and using rather inexpensive raw materials. In CCSO the exothermic oxidation of carbon (-393.5 kJ/mol) generates a thermal reaction wave with temperature up to 1200 °C that propagates at a velocity of 0.1-3 mm/s through the solid reactant mixture converting it to the desired oxide. The carbon used in the CCSO is not incorporated in the product and is emitted as a gas from the sample. The major parameters affecting the synthesis and properties of the multifferoic materials were the carbon concentration in the reactant mixture, type of precursors, oxygen flow rate and density/porosity of sample, which controls the ability of the oxygen infiltration to the reaction zone. Solid state interactions between the precursors and crystal growth of the products started in the early period of the combustion and continued in the post-combustion zone. The release of carbon dioxide (CO2) generates many pores and the synthesized powders were friable and loosely agglomerated. The product particle size increased with increasing carbon content in the reactants mixture and oxygen concentrations. The grain size of as-synthesized powders was varied from 80 to 900 nm with a surface area up to 10 m2/g. XRD, Raman spectroscopy and electron probe microanalysis of as-synthesized powders show that essentially complete conversion to single-phase products was accomplished during the synthesis. Low angle XRD patterns did not include any "amorphous hump" and had a flat background, indicating that no amorphous phases were present. Carbon analysis of products indicated that the concentration of the residual carbon was less than 0.06 wt %. Magnetic and dielectric behavior of as-synthesized powders in the temperature range of 2-400 K has been measured and analyzed.