Publish at : 31 Oct 2017
IJtech : IJtech
Vol 8, No 5 (2017)
DOI : https://doi.org/10.14716/ijtech.v8i5.871
Wisnu Ari Adi | Centre for Science and Technology of Advanced Materials, National Nuclear Energy Agency, Kawasan Puspiptek Serpong, Tangerang Selatan 15310, Banten, Indonesia |
Azwar Manaf | Department of Physics, Faculty of Mathematics and Natural Sciences, Universitas Indonesia, Kampus UI Salemba, Salemba Raya 4, Jakarta 10430, Indonesia |
Ridwan Ridwan | Centre for Technology of Nuclear Fuel, National Nuclear Energy Agency, Kawasan Puspiptek Serpong, Tangerang Selatan 15310, Banten, Indonesia |
This paper reports on the magnetic properties and electromagnetic characterization of La0.8Ba0.2FexMn½(1-x)Ti½(1-x)O3 (x = 0.1–0.8). The La0.8Ba0.2FexMn½(1-x)Ti½(1-x)O3 (x = 0.1–0.8) materials were prepared using a mechanical alloying method. All the materials were made of analytical grade precursors of BaCO3, Fe2O3, MnCO3, TiO2, and La2O3, which were blended and mechanically milled in a planetary ball mill for 10h. The milled powders were compacted and subsequently sintered at 1000°C for 5h. All the sintered samples showed a fully crystalline structure, as confirmed using an X-ray diffractometer. It is shown that all samples consisted of LaMnO3 based as the major phase with the highest mass fraction up to 99% found in samples with x < 0.3. The mass fraction of main phase in doped samples decreased in samples with x > 0.3. The hysteresis loop derived from magnetic properties measurement confirmed the present of hard magnetic BaFe12O19 phase in all La0.8Ba0.2FexMn½(1-x)Ti½(1-x)O3 (x = 0.1–0.8) samples. The results of the electromagnetic wave absorption indicated that there were three absorption peaks of ~9 dB, ~8 dB, and ~23.5 dB, respectively, at respective frequencies of 9.9 GHz, 12.0 GHz, and 14.1 GHz. After calculations of reflection loss formula, the electromagnetic wave absorption was found to reach 95% at the highest peak frequency of 14.1 GHz with a sample thickness of around 1.5 mm. Thus, this study successfully synthesized a single phase of La0.8Ba0.2FexMn½(1-x)Ti½(1-x)O3 (x = 0.1–0.8) for the electromagnetic waves absorber material application.
Absorber; Electromagnetic wave; Lanthanum manganite; Magnetic; Perovskite; Substitution; Structural
Most electronic devices that work at high frequency, such as
wireless telecommunication systems, local area networks, and other
communication equipment, often have noise problems due to electromagnetic wave
interference (EMI) (Wu & Li, 2011; Eswaraiah et al., 2011). EMI can reduce the performance of these
devices.
Not surprisingly, the demand to eliminate EMI has attracted increased interest as a research
topic
(Eswaraiah et al., 2011). Introducing materials that can absorb electromagnetic
waves is an alternative solution to eliminating EMI effects. Some materials,
such as radar absorbing materials (RAM) (Mohit et al., 2014), have been
reported to exhibit electromagnetic absorption characteristics (Song et al., 2010; Mohit et al., 2014; Sunny et al., 2010) even in the
microwave frequency range. To be used in this
capacity, electromagnetic wave absorbers must possess the following intrinsic
characteristics: permeability (magnetic loss properties) and permittivity
(dielectric loss properties). Other characteristics, such as microstructure,
thickness, and surface morphology, also determine the absorbing performance of
absorber materials. Some studies have reported on absorbers based on doped
ferrite magnetic materials (Adi & Manaf, 2012; Duggal & Aul, 2014; Kiani et al., 2014). Likewise,
absorbers based on doped dielectric properties have also been found to have
absorbing characteristics (Mohit et al., 2014), and tuneable electromagnetic
wave absorbers based on combined magnetic and dielectric properties through a
composite structure have also been developed (Sunny et al., 2010).
Manganite-based perovskite is another electromagnetic
wave absorbing material that has been also developed (Zhang &
Cao, 2012; Zhou et al.,
2009; Cheng et al., 2010). Manganite-based perovskite is one of the
potential candidate materials for microwave absorber applications due to its
high permittivity and permeability. Zhang & Cao (2012) succeeded in
synthesizing transition metal (TM)-doped La0.7Sr0.3Mn1?xTMxO3±? (TM: Fe, Co, or Ni) for microwave absorbing materials. La0.7Sr0.3Mn0.8Fe0.2O3±? has shown good properties for microwave absorption. The maximum
reflection loss was 27.67 dB at a 10.97 GHz frequency, which was obtained from
a sample thickness of 2mm. The absorption bandwidth was above 6 dB at a
frequency 6.80 GHz (Zhang & Cao, 2012).
Additionally, Zhou et al. (2009)
reported the successful synthesis of a modified of manganite-based compound.
The Mn substituted lanthanum manganite compound composed of La0.8Sr0.2Mn1-yFeyO3
(0
An LaMnO3 system has high
permittivity, but low permeability (Mondal et al., 2006). In a previous report
(Sardjono & Adi, 2014), barium substituted La0.8Ba0.2MnO3was
shown to have ferromagnetic behavior in which the permeability of the material
increased. However, the increase in the absorption bandwidth was still
relatively low; it only ranged from ~6.5 dB to ~3 dB at a frequency of 14.2
GHz. In this paper, we report on the results of manganite-based materials with
La0.8Ba0.2FexMn½(1-x)Ti½(1-x) O3
(x = 0.1.–0.8) compositions, which were synthesized using a mechanical alloying
process. The presence of Ba, Fe, and Ti in the
compound should affect the amount of Mn3+/Mn4+ coupling;
these significantly contribute to the material’s magnetic properties thereby
increasing its permeability. Therefore, the present study aimed to investigate
the nature of the coupling-order parameters and the magnetic properties that
are exhibited by this manganite-based compound. The results and discussion
focused on the synthesis and characterization of Mn-Ti-doped lanthanum
manganite of the perovskite system. This paper discusses the changes in the
parameters of the crystal structure, microstructure, magnetic properties, and
microwave characterization of this material.
The La0.8Ba0.2FexMn½(1-x)Ti½(1-x)O3
(x = 0.1–0.8) materials were synthesized by a solid reaction method using a
mechanical milling technique. This material consisted of a mixture of La2O3,
BaCO3, Fe2O3, MnCO3, and TiO2,
obtained from Merck, with purity (> 99%). The mixture was milled using a
high-energy milling (HEM) SPEX 8000 mixer for 10h. The mixture was compacted
into pellet shape using 5000 psi of pressure, and then it was sintered in the
furnace at 1000°C in the air for 5h and cooled naturally in the furnace.
The phases were identified using the Rigaku
MiniFlex X-ray diffractometer (XRD) with an X-ray tube of CuKa. The radiation wave length (CuKa) was 1.5406 Å. The diffraction angles,
ranging from 20° to 80°, were measured using continuous scan mode
and a step size of 0.02o. The Rietveld analysis was performed using
General Structure Analysis System (GSAS) software. The pseudo-Voigt function
was used to describe the diffraction line profiles at refinement of the
geometry profile (Idris & Osman, 2013). The surface morphology and
elemental identification of the sample were analyzed, respectively, using a scanning
electron microscope (
The phase identification results for the La0.8Ba0.2FexMn½(1-x)Ti½(1-x)O3
(x = 0.1–0.8) samples, measured using XRD, are shown in Figure 1.
Figure 1 XRD patterns of theLa0.8Ba0.2FexMn½(1-x)Ti½(1-x)O3
(x = 0.1–0.8) samples
The qualitative analysis of the XRD patterns refers to
the crystallography open database (COD) with card numbers (COD: 1001820), (COD:
2002196), (COD: 1008841), and (COD: 5910030), respectively, for the phases of
LaMnO3, La2Ti2O7, BaFe12O19,
and BaO (Figure 1). As seen,
the sample with the doping concentration compositions of x = 0.2 and x = 0.3
formed peaks that are believed to be a single phase of LaMnO3.
However, some foreign peaks were observed in the samples with the doping
concentration compositions of x < 0.2 and x > 0.3, which means that the
samples contain multi-phases. The composition of the x <
0.2 doping concentrationsample consisted of two phases: LaMnO3 and La2Ti2O7.
The composition of the x >
0.3 doping concentration sample
consisted of three phases: LaMnO3, BaFe12O19, and
BaO.
|
(a) x = 0.1 |
|
(b) x = 0.3 |
|
(c) x = 0.4 |
|
(d) x = 0.8 |
Figure 2 XRD pattern
refinement results fortheLa0.8Ba0.2FexMn½(1-x)Ti½(1-x)O3 (x = 0.1, 0.3, 0.4, and 0.8) samples
The calculation resulting from the Goldschmidt’s
tolerance factor showed that the maximum doping concentration of the Ti and Fe substituted
into the Mn atom are only around x~0.4 and x~0.3, respectively. Thus, the rest
of the components can alter the crystal structure of the material. The crystal structure analysis conducted using
GSAS software was required to determine changes in the crystal structure
parameters, the amount of mass fraction formed, and the cationic distribution
resulting from the substitution of Fe and Ti into the Mn atom, as shown in
Figure 2. Figure 2 shows the refinement X-ray diffraction (XRD) pattern on the
samples of La0.8Ba0.2FexMn½(1-x)Ti½(1-x)O3 (x = 0.1, 0.3, 0.4, and 0.8).
The XRD pattern refinement results forthe La0.8Ba0.2FexMn½(1-x)Ti½(1-x)O3
(x = 0.1–0.8) sampleshave a very good
quality and meet the criteria of fit Rwp (Rwp< 10%)
and the goodness of fit ?2 (chi-squared of 1 < ?2<
1.3) (Idris & Osman, 2013). Analysis of the crystal structure was only
conducted on the sample with the x = 0.1 doping composition, which represents x
< 0.2 and x = 0.3, and the samples with thex = 0.4 and x = 0.8 compositions,
which represents x > 0.3. The analysis results for the other compositions
are summarized in detail in Table 1.
Results in Table 1 show that La0.8Ba0.2FexMn½(1-x)Ti½(1-x)O3
(x = 0.1–0.8) samples with La0.8Ba0.2MnO3;
x=0.2 or La0.8Ba0.2Fe0.2Mn0.4Ti0.4O3
and x=0.3 or La0.8Ba0.2Fe0.3Mn0.35Ti0.35O3
are a single phase materials. A single phase sample with La0.8Ba0.2Fe0.2Mn0.4Ti0.4O3
composition was also previously reported
(Manaf
& Adi,
2014). Hence, Mn ion in La0.8Ba0.2MnO3 has
been successfully substituted partially by Fe and Ti ions. However, it is noted
that sample with x > 0 exhibited the increase in unit cell volume over that
of non doped LaMnO3 (239.68 Å3). When x = 0.1 a steep
increase in the unit cell volume of doped LaMnO3 phase ( 243.13 Å3)
occured before a continuous decrease along with an increase in x up to 0.8 (
240.57 Å3). Based on the analysis of changes in the volume of the
unit cell, it appears that expansion of the unit cell volume for the LaMnO3
phase occurred in the doping concentrations ranging from x = 0.1 to x = 0.3.
Thus, the Mn atom was succesfully
substituted by Fe and Ti. The expansion of the unit cell volume for the LaMnO3
phase looks very large because, for the doping concentration of x = 0.1, the
biggest substitution is Ti, which has a
radii (r = 2.0 Å) larger than the radii of the Mn atom (r = 1.79 Å). The
volume of the unit cell of this LaMnO3 phase gradually decreases
with increasing doping concentration, which means the content of Ti decreased
and the content of Fe increased. The addition of the doping concentration (x
> 0.3) results in an imbalance inthe reaction; thus there is anexcess of Fe,
so Fe prefers to bind to Ba to form barium hexaferrite. Because the composition
of these compounds is relatively stable, no change in the unit cell volume is
seen forthe BaFe12O19 phase.
Table 1 Detail summary of the refinement results for the crystal
structure parameters of the La0.8Ba0.2FexMn½(1-x)Ti½(1-x)O3
(x = 0.1–0.8)
Sample |
Phase |
Space |
Lattice
parameters |
V |
Fraction |
Rwp
(%) |
?2 |
||
(x) |
Group |
a |
b |
c |
(Å 3) |
wt% |
|||
0.1 |
LaMnO3 |
I12/a1 |
5.527(1) |
5.572(1) |
7.8605(1) |
243.13(7) |
97.39 |
7.98 |
1.297 |
La2Ti2O7 |
Pna21 |
25.76(1) |
7.85(1) |
5.57(1) |
1125.5(1) |
2.61 |
|||
0.2 |
LaMnO3 |
I12/a1 |
5.5315(9) |
5.575(1) |
7.8608(1) |
243.12(7) |
100.00 |
7.75 |
1.262 |
0.3 |
LaMnO3 |
I12/a1 |
5.5386(9) |
5.577(1) |
7.8465(1) |
242.88(7) |
100.00 |
7.33 |
1.221 |
0.4 |
LaMnO3 |
I12/a1 |
5.5363(1) |
5.5822(1) |
7.831(1) |
242.57(8) |
97.76 |
7.89 |
1.288 |
BaFe12O19 |
P63/mmc |
5.856(5) |
5.856(5) |
23.15(4) |
687.9(1) |
1.07 |
|||
La2O3 |
P63/mmc |
3.863(2) |
3.863(2) |
6.052(4) |
78.2(1) |
1.16 |
|||
BaO |
Fm-3m |
5.512(5) |
Materials with designated La0.8Ba0.2FexMn½(1-x)Ti½(1-x)O3
(x=0.1–0.8) composition were successfully synthesized through the mechanical
alloying process. The LaMnO3 based phase is being the major phase in
all samples with the highest mass fraction up to 99 % found in samples with x
< 0.3. All samples contained hard magnetic BaFe12O19
phase. The microwave absorbing properties of sample with x= 0.3 is the highest
among the samples. The electromagnetic wave absorption reaches 95% at the highest
peak frequency 14.1 GHz in the sample of x = 0.3 having sample thickness of
relatively thin about 1.5 mm.
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