http://www.revistadechimie.ro REV.CHIM.(Bucharest)♦68♦No. 3 ♦2017 504 Impact of Cations Nature of Double Perovskite Ca 2 BWO 6 on Structure and Magnetic Properties IOANA A. GORODEA 1 , NICOLETA CORNEI 1 *, ION SANDU 2 * 1 Alexandru I. Cuza University of Iasi, Department of Chemistry, 11 Carol I Blvd, 700506 Iasi, Romania 2 Alexandru I. Cuza University of Iasi, ARHEOINVEST Interdisciplinary Platform, Laboratory of Scientific Investigation and Conservation of Cultural Heritage, 22 Carol I Blvd., Corp G, 700506 Iasi, Romania The aim of this work is to study the perovskite-type oxide Ca 2 BWO 6 materials, where B = Cr, La and Sm, obtained by the sol–gel citrate-combustion method. The nature of the B-site cations influences the structure and properties of these compound. The synthesis progress was evaluated using X-ray diffraction and the structure of the samples was characterized by the Fourier transform infrared spectroscopy. In our case, the tolerance factor decrease with increasing of the ionic radius B leads to the structural distortion different from the cubic one. The magnetic properties were evaluated by a SQUID magnetometer and they are discussed in relationship with their compositions. From experimental data, it was noticed that all compound are ferromagnetic. Keywords: double-perovskite, sol–gel citrate, FT-IR spectroscopy, X-ray diffraction, magnetic properties The general formula for oxides type perovskite is ABO 3 , where A represents an electropositive cation and B represents a transition metal ion [1]. They have some flexibility in the chemical composition and the crystal structure; the control of their crystal structure and properties are possible with the combination of many cations. The modification of structural and magnetic properties by changing the A, B’ and/or B” site cations has gained interest in recent years in order to better understand the mechanism of colossal magnetoresistance [2]. In general, the size of A ion influences the crystal symmetry significantly while that of the B ion does not change the symmetry, but changes the lattice volume proportionally [3, 4]. Depending on the valences and relative ionic radii of all the ions involved, the B’ and B’’ ions are either random or in an ordered arrangement. The crystal system of double perovskite is cubic, orthorhombic, or monoclinic, because the B (B’) - cation arrangement is limited to be a random type. Since the B cation generally determines the physical properties of perovskites, different kinds of B’ and B’’ ions should show a variety of the electronic and magnetic properties of these double perovskites [5, 6] . In order to improve the properties of double perovskites and to obtain the appropriate products for different applications, various synthesis techniques such as sol–gel [7] have been developed. The sol–gel and its variants, including sol–gel autocombustion, has been shown to have great potential in the preparation of metal oxides with the perovskite structure for advanced applications [8]. The objective of this investigation was to prepare by citrate combustion method a series of double perovskite oxides Ca 2 BWO 6 (B = Cr, La and Sm) for the first time. Also, we presented the variation of the structural characteristics and magnetic properties with the size of this three trivalent in the B-site cations. Experimental part Synthesis We have prepared our samples of Ca 2 BWO 6 using the sol–gel autocombustion method. The starting materials * email; ncornei@uaic.ro; ion.sandu@uaic.ro were Ca(NO 3 ) 2 . 4H 2 O, Cr(NO 3 ) 3 . 9H 2 O, La(NO 3 ) 3, Sm(NO 3 ) 3 . 6H 2 O, (NH 4 ) 6 W 7 O 24 . 4H 2 O and citric acid as the combustion agent. The metallic precursors and citric acid were dissolved in distilled water and the mixtures were gradually heated up to 80°C under continuous stirring in a water bath in order to obtain a viscous gel. The resulting mixtures were stirred for the 4 h at 80°C for concentrating solutions by slow evaporation The gels was then dried in the air up to 220 o C, until that occurs autocombustion. The powders obtained from autocombustion were then heated in air at 350 o C/7h and 500 o C/7h. After that, the compounds were slowly cooled, then ground, shaped by uniaxial pressing at 150 kPa into pellets. Presintering was done in air at 750 o C/ 7h and 900 o C/7h. The samples were slowly cooled, ground, pressed with radial gradient into pellets of 10 mm diameter and 2 mm thickness. The samples were sintered in the air, with a heating rate of 5°C/ min at 1100 o C/24 h and 1200 o C/24 h. After repeating this procedure with grinding, pelletizing and firing, only single-phase perovskite was obtained. The phase formation of the double perovskite Ca 2 BWO 6 and analysis of crystalline structure was monitored by using a Fourier transform infrared (FTIR) spectra and X-ray diffraction technique. Characterization X-ray diffraction (XRD) patterns of the sample were recorded with a SHIMADZU LabX6000 diffractometer equipped with a graphite monochromator and CuKα radiation ( λ= 1.5406 A) with a scan step of 0.02° and a counting time of 1 s/step, for 2θ ∈ (20-80)°. FT-IR spectra were obtained with wave number range 4000-400 cm -1 using a JASCO 660 PLUS spectro- photometer on the KBr pellets. The magnetic properties were studied using a Quantum Design MPMS-XL superconducting quantum interference device (SQUID) magnetometer. The sample was packed into teflon tape packet and field and zero field cooled magnetizations were measured on a Quantum Design SQUID magnetometer.