Time: July 26, 2017, 9:30-10:30 am
Venue: Room 201, No.5 Basic Energy Building
Lecturer: Prof. Mira Risti？, Ru？er Bo？kovi？ Institute, Zagreb, Croatia
Abstract:
In this presentation the magnetic behaviour of two different iron containing compounds, Fe(IO3)3 and CoFe2O4, will be shown.
Generally, most metal iodates show pyroelectric, piezoelectric and non-linear (NLO) properties which can be utilized for advanced technological applications. One of the most interesting metal iodates is Fe(IO3)3 which is characterized with noncentrosymmetric crystal structure. Fe(IO3)3 particles in the form of nanorods were synthesized following the procedure by von Endrédy and characterized with XRD, FT-IR, DTA, UV/Vis, FE-SEM/EDS, magnetometric and 57-Fe M？ssbauer measurements. The RT M？ssbauer spectrum of Fe(IO3)3 was characterized by single line whereas hyperfine magnetic splitting was completely developed at ~ 4.3 K. DTA analysis showed that Fe(IO3)3 particles are thermally stable up to ~ 370 oC. Heating of 1D Fe(IO3)3 particles at 520 oC produced α-Fe2O3 particles with preserved original morphology of Fe(IO3)3, while 1Dα-Fe2O3 particles produced at 800 oC were decreased in length and increased in width.
CoFe2O4 is ferrite of spinel crystal structure and its cation distribution can be described by a general formula (Fe1-xCox)A(Fe1+xCo1-x)BO4 where A and B denote tetrahedral and octahedral sites, respectively. Cation distribution in CoFe2O4 is almost completely inverse (x~0) with Co2+ ions mainly at B sites and Fe3+ ions distributed equally at A and B sites. Cobalt ferrite samples were prepared (a) by combining coprecipitation, Co(OH)2/2Fe(OH)3 using NaOH at two different pH values: 5.2 and 11.4, and autoclaving and (b) by autoclaving the Co(OH)2/2Fe(OH)3 coprecipitate in a very strong alkaline medium. Cobalt ferrite precipitated at pH 7.2 and at pH 11.4 contained a very small fraction of α-Fe2O3, whereas in the samples precipitated at pH 11.4 traces of α-FeOOH were also detected with FT-IR. M？ssbauer measurements suggested the structural migration of cobalt and iron ions in CoFe2O4 with the prolonged time of autoclaving. Magnetic measurements showed the magnetic behaviour typical for spinel ferrite nanoparticles.
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