Journal of Radioanalytical and Nuclear Chemistry, Vol. 261, No. 3 (2004) 569576 02365731/2004/USD 20.00 AkadØmiai Kiad, Budapest ' 2004 AkadØmiai Kiad, Budapest Kluwer Academic Publishers, Dordrecht Preparation of magnesium and calcium ferrites from the thermolysis of M 3 [Fe(cit) 2 ] 2 . xH 2 O precursors B. S. Randhawa,* Kaur Manpreet Department of Chemistry, Guru Nanak Dev University, Amritsar 143 005, Punjab, India (Received January 20, 2004) Magnesium and calcium ferrites have been prepared from the thermolysis of M 3 [Fe(C 6 H 5 O 7 ) 2 ] 2 . xH 2 0 (M=Mg, Ca) precursors. Thermal decomposition of the precursors has been studied employing various physico-chemical techniques, i.e., TG-DSC, XRD, IR and Mssbauer spectroscopy. After dehydration the anhydrous precursors undergo an abrupt oxidative pyrolysis to yield -Fe 2 O 3 and a metastable acetone- dicarboxylate intermediate. A subsequent exothermic decomposition leads to the formation of MgO and CaCO 3 from the respective intermediates. Finally ferrite is formed as a result of solid state reaction between MO/MCO 3 and -Fe 2 O 3 . Nanosized ferrites of the stoichiometry MgFe 2 O 4 and Ca 2 Fe 2 O 5 have been obtained from magnesium and calcium bis(citrato) ferrates(III). The temperature of ferrite formation is much lower than possible in conventional ceramic method. The results have been compared with the respective oxalate and maleate precursors. Introduction Ferrites have attracted a considerable attention owing to their potential application as magnetic materials in the various electronic, magnetic and microwave devices, satellite communication, ferrofluids and ferroseals. 13 Magnesium ferrite is especially used in transformer cores and magnetic recording devices. 4 The ceramic method which is the most common technique for bulk preparation of ferrites involves high temperature sintering of reactant oxides coupled with frequent milling. Since high sintering temperature results in particle coarsening and aggregation, nanoparticle ferrites cannot be obtained by this method. 5,6 Thermal decomposition of metal ferricarboxylate precursors (precursor technique) provides better route for the obtention of nanosized ferrites at lower temperature and in shorter time. 7,8 This technique does not require any milling of the starting materials which introduces lattice defects in ferrites obtained, thus affecting their permanent magnetic properties. Ferricitrate precursors have proven to be the pioneers for the obtention of ferrites because of their direct rapid oxidative pyrolysis into oxide phase and subsequent atomic scale mixing of the cations lowers the temperature of ferrite formation. The ferrites, thus obtained, have reduced particle size and have greater homogeneity than possible by the conventional ceramic method. Experimental The metal ferricitrate precursors, M 3 [Fe(C 6 H 5 O 7 ) 2 ] 2 . . xH 2 O (M=Mg, Ca) were prepared by mixing equimolar quantities of aqueous solutions of ferric citrate, citric acid and respective metal nitrate. The reaction mixture was refluxed at 100 C for 10 hours and then concentrated on water bath. The fluffy concentrated * Author for correspondence. precursor, thus obtained, was kept in oven at 60 C for 2 hours. The resultant precursor powder obtained was then washed with ethanol, dried and stored in vacuum desiccator. The identity of the precursors was established by chemical analysis. The iron content was determined by 110 phenenthroline method. 9 Magnesium and calcium contents were determined by atomic absorption spectroscopy (Table 1). The infrared spectra of the precursors and the thermolysis products were recorded on a Pye-Unicam SP3-300 IR spectrophotometer in the range 4000 200 cm 1 using KBr matrix. Simultaneous TG-DSC curves were recorded on a Pyris Diamond Model (Perkin Elmer) at a heating rate of 10 C . min 1 in flowing air atmosphere. Mssbauer measurements were performed at UniversitØ de LiLge, Belgium. Isomer shift values are reported with respect to pure iron absorber. XRD powder patterns were recorded at the Soils Department, PAU, Ludhiana. SEM micrographs were recorded by using JEOL-6100 (Tokyo, Japan) microscope. Magnetic studies were performed by using VSM. For identification of intermediates and products, the precursors were also calcined isothermally in silica crucibles. Results and discussion The IR spectrum of magnesium ferricitrate precursor exhibits a broad band centred at 3500 cm 1 due to (O-H) of lattice water and hydroxy group of citrate ligand. A shoulder at 2960 cm 1 is assigned to (C-H) of the citrate ligand. A strong band at 1680 cm 1 is attributed to asy (C=O) and a band at 1410 cm 1 indicates sym (C=O) of coordinated citrate group. Some weak bands in the range 850920 cm 1 are ascribed to (C-C), (C-O) and (O-H) bending modes. A small but distinct band at 520 cm 1 due to (Fe-O) indicates Fe-O