Effect of Zn on dielectric properties of Mn-Zn spinel ferrite synthesized by coprecipitation
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- Điều hướng trang này:
- 3. Results and discussion
| 2. Experimental details
Mn 1-x Zn x Fe 2 O 4 spinel ferrite (x = 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8) was prepared by coprecipitation method. The materials used were FeCl 3 .6H 2 O, ZnSO 4 .7H 2 O, MnCl 2 .H 2 O, NaOH, HCl. All chemicals were of analytical grade (Merck Emsure). The chemical reaction is showed by (1-x)MnCl 2 + xZnSO 4 + 2FeCl 3 + 8NaOH→ Mn 1-x Zn x Fe 2 O 4 + xNa 2 SO 4 + (8-2x) NaCl + 4H 2 O (1) For x = 0.5 the stoichiometry of Mn:Zn:Fe has ratio =1:1:4. Then the ratio serves as references for others concentration. For dielectric properties, the powder was pressed by applying a force of 50.000 N to get circular pellets with dimensions 12.5 mm in diameter and 4.3 mm in thickness. X-ray diffraction (XRD) analysis has been carried out by using X-Ray diffractometer Shimadzu XD using monochromic Cu-Kα radiation (λ = 1.5406 Ǻ) and the recorded angle (2 ) is in the range 20-80 ° . The morphology and selected area diffraction (SAED) pattern were investigated by Transmission electron microscope (TEM) Jeol Jem- 1400. The room temperature dielectric measurements were conducted using a RC impedance spectroscopy analyzer in the frequency range 5 -120 kHz. 3. Results and discussion XRD patterns are shown in Fig. 1a. The patterns confirmed that the formation of cubic spinel structures and all of the observed diffraction peaks are indexed based on JCPDS (10-0467). The XRD patterns show all the characteristic reflections of ferrite material having most intense (311) peak. For x = 0.2, 0.4, 0.5, 0.6, 0.7, 0.8 the second phase was observed additional peaks indicating non-spinel phase. There are two peaks non spinel phase observed which are indicating related to Zn(OH) 2 (JCPDS no.01-0360) and MnO(OH) (JCPDS no.24-0713). The variations of lattice constant and crystallite sizes with Zn concentration are shown in Fig. 1b. The size of crystallites was calculated by Scherer’s equation. The calculated sizes of the crystallites are found to be ranging 15- 30 nm and decrease by increasing Zn concentration due to the replacement of larger ionic Mn 2+ . The values for lattice constant have been calculated from main diffraction peak of each sample using d-spacing values and the respective (h k l) parameters by using the classical Nelson-Riley formula [7]. The lattice constant reduces to minimun at x = 0.5 and reachs maximum at x = 0.6. The increasing lattice constant with increasing Zn concentration at x = 0.6 may be attributed the smaller ionic Zn 2+ (0.57Å) ions compared to Mn 2+ (0.66Å) ions. A. Yusmar et al./ Materials Today: Proceedings 5 (2018) 14955–14959 14957 Fig. 1. (a) X-ray diffraction pattern of Mn 1-x Zn x Fe 2 O 4 ferrite synthesized by coprecipitation method (a) x = 0.2, (b) x = 0.3, (c) x = 0.4, (d) x = 0.5, (e) x = 0.6, (f) x = 0.7, and (g) x = 0.8, (b) Variation of average crystal sizes (■) and lattice constant (▼) as a function of Zn concentration. The morphology of Mn 1-x Zn x Fe 2 O 4 spinel ferrite was observed by TEM analysis. TEM image of Mn 1-x Zn x Fe 2 O 4 spinel ferrite is shown in Fig. 2. TEM image shows Mn 1-x Zn x Fe 2 O 4 as prepared experience agglomeration due to small particle size producing high surface energy and surface tension of ferrites. The SEAD pattern confirms that Mn 1-x Zn x Fe 2 O 4 spinel ferrite was polycrystalline materials. Fig. 2 (a) TEM image of Mn 1-x Zn x Fe 2 O 4 (b).SAED image of Mn 1-x Zn x Fe 2 O 4 . Figure 3 shows the variation of real dielectric constant (ε’) and imaginary dielectric constant ( ”) as a function of frequency for the all samples Mn 1-x Zn x Fe 2 O 4 spinel ferrite at room temperature in the frequency range from 5-120 kHz. For all samples, the value of ε’ and ε” is high at low frequency and then it decreases as the frequency increases, and finally becomes saturated at high frequency. This is a normal behavior observed in most of the ferrite material [3]. The frequency dependent behaviors of dielectric constants in ferrite follow the Maxwell-Wagner’s interfacial polarization is in agreement with Koop’s theory [8]. The high values of dielectric constant at low frequency are caused by the predominance of species like Fe 2+ ions, interfacial dislocation pile-ups, oxygen vacancies, grain boundaries and different kind of polarizations (electronic, atomic, interfacial, and ionic etc.) [9]. In the other hand at high frequency, the dielectric constant decreases due to the electronic exchange between the ferrous and ferric ions a b tải về 0.64 Mb. Chia sẻ với bạn bè của bạn:
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