Structure and magnetization of lafe1-Xcoxo3 perovskite nanomaterials synthesized by co-precipitation method

JOURNAL OF SCIENCE OF HNUE DOI: 10.18173/2354-1059.2016-0058 Natural Sci. 2016, Vol. 61, No. 9, pp. 68-74 This paper is available online at 68 STRUCTURE AND MAGNETIZATION OF LaFe1-xCoxO3 PEROVSKITE NANOMATERIALS SYNTHESIZED BY CO-PRECIPITATION METHOD Nguyen Anh Tien and Nguyen Thi Truc Linh Faculty of Chemistry, Ho Chi Minh City University of Education Abstract. LaFe1-xCoxO3 (x = 0.1, 0.2, 0.3) perovskite nanomaterials have been synthesized by the hydrolysis of La(III), Co(II) and Fe(III) cations in boiling water with the presence of KOH 5% precipitating agent. The results show that when the ratio of Co(II)-doped in LaFeO3 crystals increases from 0.1 to 0.3 (%, wt.), the crystal sizes decrease from 29 nm to 16 nm; Ms values decrease from 0.787 emu/g to 0.254 emu/g; Mr values decrease from 0.149 emu/g to 0.016 emu/g and Hc values decrease from 294.746 Oe to 52.207 Oe. Keywords. Nanomaterial, LaFe1-xCoxO3, co-precipitation, magnetization, perovskite. 1. Introduction Nano-materials have been applied in a wide range of manufacture. Among them, the distorted-perovskite ABO3 (where A are rare earth-elements such as Y, La, etc. and B are the 3d transitional metals such as Mn, Fe, Co, Ni, Cr, etc.) has been attracted many studies because of its significant properties [1-3]. It is also used as the catalyst of oxidation-reduction reaction of hydrocarbon, CO, NOx, m-xylene. When Ca, Sr, Cd, Zn, Fe, Ni, La, Co, Ni, Ti elements are in the place of ion A or ion B or both of them, it leads to the mixture of valence number and distortion of precursor structure. As the result, the product prepared turns to have some interesting effects including: thermo-electric, thermo-magnetic phenomenon and giant resistance [1, 2, 4]. Therefore, this type of perovskite material has enabled many new applications in digital industry, information technology, petro-chemical process and catalyst. The perovskite material is prepared by traditional method such as the parent oxides, hydroxides or appropriate salts annealed at over 1200 ºC generally [1, 4]. At high temperature, the agglomeration results in an increasing size of grains and less homogeneity of obtained products. Nowadays, the alternative methods have been used to synthesize metal-dopped perosvkite material, for instance, co-precipitation, sol-gel, gel combustion, coordination [2]. In wet method, the precursor is calcinated at much lower temperature than that in traditional method and the produced nano-particles are more homogeneous and higher in purity. Received May 10, 2016. Accepted October 5, 2016. Contact Nguyen Anh Tien, e-mail address: anhtienhcmup@gmail.com Structure and magnetization of LaFe1-xCoxO3 perovskite nanomaterials synthesized 69 According to the studies [5-8], the researchers successfully synthesized LnFeO3 (Ln = La, Y) perovskite nanoparticles having replacements of Ca, Sr elements at Ln position by slow hydrolysis of metal cation in boiling water prior to their precipitation. However, the magnetic property of the materials were not investigated. In this study, we illustrate full data of synthesis, structural characteristic and magnetic property of Co(II)-dopped LaFe1-xCoxO3 (x = 0.1, 0.2, 0.3) perovskite nanoparticles by hydrolysis of La(III), Fe(III), Co(II) cations in boiling water, corresponding to precipitation of using solution of KOH 5% (w/w). 2. Content 2.1. Experiment * Chemicals La(NO3)3.6H2O, Fe(NO3)3.9H2O, Co(NO3)2.6H2O, KOH, de-ionized water, filtered paper are used. The salts are mixed up in the mole ratio of La 3+ :Fe 3+ :Co 2+ of 1:(1-x):x. Then, the solution is dissolved in water before precipitating. * Synthesis of LaFe1-xCoxO3 nanoparticles The mixture consisting of La(NO3)3: Fe(NO3)3: Co(NO3)2 of 1:(1-x):x is dropped into a flask of boiling water. The solution is stirred up till obtaining a change to a stable color of brown-red, at room temperature. Next, 5% KOH solution is dropped wisely into the solution, latter, stirred vigorously for 30 minutes. The precipitate is filtered and washed with water before drying at room temperature for 3 days. Finally, the precursor is milled and annealed in air atmosphere at different temperatures at the heating rate of 10 o C/minutes for investigation of crystallization and evaluation of phase components. * Instrumental analysis To determine the desired temperature of the formation of LaFe1-xCoxO3 phase, the sample is analyzed by Labsys Evo (TG-DSC 1600 ºC) in nitrogen atmosphere per heating steps of every 10 o C/minutes, from 35 o C to 1000 ºC. XRD patterns are resulted from D8-ADVANCE (Germany) with CuKα radiation, 2θ of 10 - 70º, step size of 0.03 º/min. The average size (nm) of crystal is calculated by using Scherrer equation. The micro-structure and morphological images are recorded by Scanning Electron Micro-scopy (SEM) in FESEM S4800 HITACHI (Japan) and Transmission Electron Micro-scopy (TEM) in JEOL-1400 (Japan). The magnetic properties of samples are studied by Vibrating Sample Magneto-meter (VSM) in MICROSENE EV11 (Japan). 2.2. Results and discussion 2.2.1. Thermogravimetric analysis The TG-DSC data of sample with x = 0.2 is shown in Figure 1. At overall view, the weight- loss process includes 2 steps: i) Starting from room temperature to 260 °C, the weight of sample decreases by 10.652% with an endothermic peak at 96.21 °C in DSC curve. It is assigned to the loss of water due to the physical absorption; ii) when the temperature goes up to 600 °C, a weight difference of 14.438% is recorded, corresponding to another endothermic peak at 352.2 °C because of the de-composition of hydroxides such as Fe(OH)3, Y(OH)3 and Co(OH)2. Next, an Nguyen Anh Tien and Nguyen Thi Truc Linh 70 exothermic peak of phase transformation at 576.35 °C is detected. The weight of residue is stable at over 600 o C, and the DSC curve is straight. Figure 1. TGA-DSC curves of LaFe0.8Co0.2O3 2.2.2. XRD and EDS data Figure 2a illustrates that XRD pattern of LaFe0.8Co0.2O3 sample annealed at 900 ºC matches well with i its standard pattern (No. 01-075-0439 - Lanthanum Iron Oxide – Cubic), and these of LaFe0.8Co0.2O3 samples annealed at the various temperatures have similar characteristics in comparison with each other’s, standard data as well. This evidence shows that the single phase exists in the products and Co(II) ions are in place of some positions in LaFeO3 crystals. However, increases of intensity, as well as the narrowness of peaks indicate that the crystallization at high temperature is better than that at low one. That is proved by a growth in the crystal size, according to Scherrer equation: d800 = 16.78 nm; d900 = 20.15 nm and d1000 = 21.64 nm. According to XRD analyses of LaFe0.8Co0.2O3, two precursors (x = 0.1 and 0.3) are calcinated at 900 ºC to determine their chemical composition. The results are shown in Figure. 3. It is considered that there is no strange characteristic in XRD result in case of x = 0.1; 0.2, and 0.3 (as compared with standard patterns of LaFeO3). Moreover, the decrease of d-spacing values is observed when x rises from 0.1 to 0.3 (Table 1). Table 1 shows that the d-spacing values of LaFe1-xCoxO3 crystals decrease when the amount of Co(II)-doped increases. In this case, the replacement of Co(II) (r = 0,078 nm) into the position of Fe(III) (r = 0.067 nm) forms the mixture of oxidation states, namely (II) and (III). To get the balance of charge in the whole system, some of Fe(III) ions are oxidated to Fe(IV) (r = 0.058 nm) or some of Co(II) ions changes to Co(III), which lead to d-spacing values of LaFe1-xCoxO3 crystals decrease. The similar observation is also reported in the studies [2, 5, 6, 9]. The researchers shows Structure and magnetization of LaFe1-xCoxO3 perovskite nanomaterials synthesized 71 that the replacement of Sr(II), Cd(II) or Ca(II) cation into the position of Ln(III), as well as Sr(II) Bi(III), relatively, also leads to the decrease in the d-spacing values. EDS results of LaFe1-xCoxO3 products (x = 0.1, 0.2, 0.3) annealed at 900 o C illustrates of the exist of the peaks assigned to La, Fe, Co and O (Figure 4). The relative correlation between EDS results and the theoretical calculation in the percentage of the elements is also recorded considerably. Figure 2. XRD pattern of LaFe0.8Co0.2O3 product annealed at 900 o C (a) XRD patterns of LaFe0.8Co0.2O3 products annealed at the various temperature (b) Nguyen Anh Tien and Nguyen Thi Truc Linh 72 Figure 3. XRD patterns of LaFe1-xCoxO3 products with the different ratios of Co(II)-doped Figure 4. EDS results of the products a) LaFe0.8Co0.2O3 and b) LaFe0.7C0.3O3 Table 1. The d-spacing values of LaFe1-xCoxO3 (h, k, l)/d, Å LaFe0.9Co0.1O3 LaFe0.8Co0.2O3 LaFe0.7Co0.3O3 100 3.91165 3.90446 3.89354 110 2.76209 2.76094 2.75065 111 2.25788 2.25480 2.24693 200 1.95372 1.95281 1.94355 211 1.59585 1.59176 1.58623 220 1.37979 1.37574 1.37476 Structure and magnetization of LaFe1-xCoxO3 perovskite nanomaterials synthesized 73 2.2.3. TEM images TEM images of LaFe0.8Co0.2O3 and LaFe0.7Co0.3O3 products annealed at 900 ºC (t = 1h) are shown in Figure 5. The size of spherical grains with weak edges is in the range of 30 - 50 nm. Nevertheless, the grains agglomerate to clusters or prolonged crystals, which leads to the growth of grain size up to 100 nm. Figure 5. TEM images of the products: a) LaFe0.8Co0.2O3 and b) LaFe0.7C0.3O3 2.2.4. VSM invetigation The magnetic properties of La1-xCoxFeO3 (x = 0.1; 0.2; 0.3) perovskite nano-materials annealed at 900 o C for 1h are investigated. The VSM data indicate that the appearance of Co(II) ions in LaFeO3 crystals not only affects the grain size but also changes the magnetic properties of the perovskite nano-materials (Figure 6 and Table 2). For instance, at 15000 Oe, the values of magnetic coercivity (Hc), residual magnetism (Mr) and saturation magnetization (Ms) drop regularly when the x values rise. That can be attributed to the increase of the amount of Co(II)- doped in LaFeO3 crystals. Figure 6. The magnetic hysteresis curves of LaFe1-xCoxO3 products annealed at 900 ºC Nguyen Anh Tien and Nguyen Thi Truc Linh 74 Table 2. The magnetic properties of LaFe1-xCoxO3 samples annealed at 900 ºC (t = 1h) LaFe1-xCoxO3 D, nm Hc, Oe Mr, emu/g Ms, emu/g x = 0.1 29.34 294.746 0.149 0.787 x = 0.2 20.15 170.627 0.087 0.447 x = 0.3 16.78 52.207 0.016 0.254 3. Conclusion LaFe1-xCoxO3 (x = 0.1, 0.2, 0.3) perovskite nano-particles are prepared by the co-precipitation of La(III), Co(II) and Fe(III) ions in boiling water with the presence of KOH 5% precipitating agent. The increase in the amount of Co(II) doped in LaFeO3 crystals from 0.1 to 0.3 leads to the decrease of the grain size from 29.34 nm to 16.78 nm. Hc, Mr and Ms values from 0.787 emu/g to 0.254 emu/g; from 0.149 emu/g to 0.016 emu/g and from 294.746 Oe to 52.207 Oe, respectively. REFERENCES [1] Sania Maria de Lima, Jose Mansur Assaf, 2002. 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