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Structural, electrical and magnetic properties improvement of Bi1−xYxFe0.8Mn0.2O3 ultra-fine nanoparticles synthesized via reverse chemical co-precipitation technique
Author’s Accepted Manuscript Structural, electrical and magnetic properties improvement of Bi1-xYxFe0.8Mn0.2O3 ultra-fine nanoparticles synthesized via reverse chemical coprecipitation technique H. Sangian, O. Mirzaee, M. Tajally www.elsevier.com/locate/ceri
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S0272-8842(17)31772-8 http://dx.doi.org/10.1016/j.ceramint.2017.08.074 CERI16028
To appear in: Ceramics International Received date: 8 July 2017 Revised date: 9 August 2017 Accepted date: 10 August 2017 Cite this article as: H. Sangian, O. Mirzaee and M. Tajally, Structural, electrical and magnetic properties improvement of Bi1-xYxFe0.8Mn0.2O3 ultra-fine nanoparticles synthesized via reverse chemical co-precipitation technique, Ceramics International, http://dx.doi.org/10.1016/j.ceramint.2017.08.074 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Structural, electrical and magnetic properties improvement of Bi1-xYxFe0.8Mn0.2O3 ultra-fine nanoparticles synthesized via reverse chemical co-precipitation technique H. Sangian, O. Mirzaee*, M. Tajally Faculty of materials and metallurgical engineering, Semnan University, Semnan, Iran
Abstract Ultra-fine Bi1-xYxFe0.8Mn0.2O3 (BYFMO) nanopowders with x= 0, 0.05, 0.10, 0.15, 0.20 and 0.25 were successfully synthesized using reverse co-precipitation method. XRD graphs indicate the formation of the secondary phases such as YFeO3 and YMnO3 in synthesized powders with 25% of yttrium doping. Furthermore, the lattice parameter declined as yttrium doping grew. FESEM micrographs showed that, the particle size fell from 130 to 15 nm as yttrium doping rose from x=0 to x=0.25, respectively. Magnetic hysteresis loops illustrated a weak ferromagnetism for all samples at room temperature. Besides, Y and Mn co-doping improved magnetization from 0.298 emu/g for pure BFO to 1.518 emu/g for BYFM20 (x=0.20) because by raising the amount of dopants the particle size dropped, leading to a high surface-to-volume ratio and therefore more uncompensated surface spins. Also, spin cycloid was destroyed by Y-doping, thereby releasing the latent magnetization locked within cycloid. Electrical properties measurement reveals that ε′ and tanδ values climbed by an increase in co-doping ions. This enhancement may be related to various factors such as the formation of large dipole moments by more structural distortion and a much more increase in grain boundaries by adding extra amounts of dopant ions.
Keywords: Reverse co-precipitation; Bismuth ferrite; Magnetic properties; Dielectric properties
Highlights: Using a new reverse chemical co-precipitation technique, the ultra-fine Bi1-xYxFe0.8Mn0.2O3 (BYFMO) nanoparticles have been successfully prepared. The samples magnetization increased greatly by increasing dopants concentration due to more lattice distortion and uncompensated spins. Electrical properties measurement revealed that values of ε′ and tanδ increase by increasing codoping ions. 1. Introduction Multiferroic materials, which have at least two primary ferroic properties: ferroelectricity, ferromagneticity and ferroelasticity coupled to each other in the same phase [1], have received much attention because of their novel potential applications in storage devices [2], actuators [3], microelectronic device [4], non-volatile memories [5] and sensors [6]. Perovskite BiMO3 (M is Fe and Mn), mullite-type bismuth ferrite (Bi2Fe4O9), boracites family (BaMF4, M is divalent transition ions) and hexagonal RMnO3 (R is rare earths ions) are the important multiferroic materials studied rather extensively on the subject of magnetic properties, electrical properties and magnetoelectric coupling *
Corresponding author. Tel.: +98 233 1533336; fax: +98 2333654119. E-mail address: [email protected] (O. Mirzaee)
[7-9].Perovskite-type bismuth ferrite (BFO) which possesses high Néel and Curie temperatures ( and ) is the most important extensively effective single-phase multiferroic at room temperatures [10, 11], but owing to some weak properties such as electrical resistivity, leakage current density and low remnant polarization in the bulk form, the BFO industrial application in microelectronic devices has been limited [12-14]. To resolve these problems, several strategies such as thin film usage and doping in BFO have been studied [15-17]. For example, the bulk BFO has a remnant polarization of 6.1 but its thin films show large remnant polarization, 15 times larger than that of the BFO bulk form [18]. Also, many experiments have been carried out in the field of improvement of magnetic, electrical and multiferroic properties of BFO nanoparticles, thin films and bulk samples using A-site and B-site substitution by different ions [19]. BFO has a rhombohedrally distorted perovskite crystallographic structure which belongs to space group R3c, No.161 with lattice parameters of and ˚-89.4 However, BFO crystal structure can also be classified in hexagonal arrangement when is parallel to and [20].BFO has the G-type antiferromagnetic ordering with a long-period spin cycloid structure (62-64 nm) [12, 21]. Besides, BFO unit cell polar centrosymmetric distortion causes a spontaneous polarization along the [111]c pseudocubic (rhombohedral) rotation axis [22]. Early in 1967, Achenbach et al. [23] prepared single-phase polycrystalline BFO via and solid state reaction at temperatures over However, due to some disadvantages of their method like reaction high temperature, large particle size and impurities presence, new methods such as chemical co-precipitation [24, 25], hydrothermal [26], solvothermal [27], sonochemical [28], microemulsion [29], sol-gel [30], molten salt [31], and mechanochemical procedures [32] are currently being used for BFO nanopowders synthesis. As for chemical co-precipitation method advantages like simple processing, possibility of mass production and easy controlling of conditions, this method has found its place in the field of nanotechnology and wet chemical synthesis. This process has been applied efficiently for preparation of some electro-ceramic nanoparticles such as LiNbO3 (LN) [33], CoFe2O4 (CFO) [34] and Y3Al5O12 (YAG) [35]. So far, all the reports concerning BFO synthesis have focused on homogeneous co-precipitation in which the process is very sensitive to pH control [36-38]. The effects of Y and Mn-doping on electrical, optical and magnetic properties of BFO have been investigated separately. Among B-site ion substitutions, Mn doping improves BFO photoluminescent properties and exhibits a significantly reduced leakage current and an improved breakdown voltage, so that well-saturated ferroelectric hysteresis loops can be detected [39, 40]. Moreover, yttrium A-site substitution enhances the dielectric, leakage current density and magnetization in BFO nanoparticles [41, 42]. However, to the best of our knowledge, no work has been reported concerning BFO synthesis via reverse chemical co-precipitation. As compared to previous works, in this paper we synthesized yttrium and manganese co-doped BFO nanoparticles successfully via reverse co-precipitation methods at the pH value of This method “reverse co-precipitation” led to a much lower grain size of BYMFO nanoparticles by increasing yttrium content. Furthermore, formation of transient phases and structural transformation by raising Y content in BYMFO system were studied. At last the co-doping effect of on product purity and morphological features, as well as electrical and magnetic properties of synthesized samples were investigated in detail. 2. Materials and methods BYFMO nanoparticles were successfully synthesized by reverse chemical co-precipitation procedure. In a typical process, high-purity bismuth subnitrate Bi5H9N4O22(Merck kGaA 98.0%), iron nitrate nonahydrate (Merck KGaA 98.0 %), yttrium oxide (sigma-aldrich 99.9%) and manganese nitrate tetrahydrate Mn(NO3)2.4H2O (scharlau 98.0%) were dissolved in 2M nitric acid
HNO3 (scharlau 65.0%) at room temperature. Cation solutions were mixed and stirred for 30 minutes at the stoichiometric ratio (Table 1) to obtain a homogenous transparent mixture. 2M Sodium hydroxide (NaOH, scharlau 99.0%) was utilized as a precipitating agent. In the reverse coprecipitation process, the cations solution and precipitating agent were loaded into the separator funnel and glass beaker, respectively. Then the cations solution was vented drop by drop into the precipitating agent when the stirrer was working severely until the pH value of 9.5 was achieved. The chemical co-precipitation process lasted about 15 minutes and the final precipitate was washed with deionized water until the pH value of 7 was obtained. An electric drier at 80 ˚ for 24h was utilized to dry the precipitate. At last the dried chunks were crushed in a mortar to obtain amorphous powders. For crystallization and phase formation, powder samples were calcined at 550 ˚ for 1h. Calcined powders were pressed into pellets and sintered for 4 minute at 800±20 ˚ by microwave sintering furnace in air atmosphere. Calcination temperature was obtained via differential thermal analysis (DTA) at a heating rate of ˚ /min The sample pot was platinum and the reference material was alpha-alumina. Calcined powders phase structure was identified via an X-Ray diffractometer (XRD, - ay with uradiation and a scan rate of ˚/min in the scattering angular range of ourier transformed infrared (FT-IR) spectrum was recorded by a spectrometer (FT-IR SHIMADZU). BFO powders morphology and size distribution were attained by the field emission scanning electron microscope (FESEM, MIRA3-TSCAN) with 15 kV and transmission electron microscope (TEM, PHILIPS-CM3U) with 150 kV. The magnetic hysteresis loops with an external magnetic field of 1.0 T were measured at room temperature through a vibration sample magnetometer (VSM-AGFM). The electrical properties of sintered pellets were determined by inductance-capacitance-resistance (LCRmeter) within 1 KHz-to-1000 KHz frequency. 3. Results and discussion 3.1.Thermal behavior Fig. 1 shows DTA curves of un-calcined pure BFO and as-selected BYFMO15 powders synthesized by reverse co-precipitation with a pH value of 9.5. As clearly observed from thermograms, four various regions have been detected. The peaks located at 50˚ in DT curve correspond to decomposition or evaporation of possibly organic compounds, hydrates and nitrates, accompanied by a large weight loss at this stage [43] The exothermic peaks at ˚ are attributed to magnetic transitions from antiferromagnetic to paramagnetic state (Néel temperature) in BFO and BYFMO15 phases [44]. The exothermic peaks presented at 460˚ are related to crystallization of BFO and BYFMO15 powders utilized to select the appropriate calcination temperature of ˚ in this study As can be seen, crystallization temperature is raised by adding dopant ions, which is attributed to higher diffusion rate of Bi ions in comparison with Y ions [45]. When yttrium ions are added to system, it is more difficult for the diffusion process to cause higher crystallization temperature in BYFMO15 sample. The BFO formation in chemical co-precipitation is based on the following chemical reactions [36]. (1) (2) Usually, a ferroelectric-to-paraelectric phase transition in BFO can be observed by the low-intensity peak in DTA without any weight loss. This situation in DTA curves has been observed at 810˚ It can be observed that the temperature related to ferroelectric transition (Curie temperature) is slightly
increased by substitution of Y and Mn ions. Moreover, no significant change can detected at Neel temperature by adding dopant ions due to the fact that Bi-site and Fe-site are responsible for ferroelectric behavior and magnetic ordering in BFO systems, respectively. B-site substitution by Mn ions plays no remarkable role in BFO magnetic properties and therefore no noticeable change in magnetic transition temperature is measured [44]. 3.2.XRD analysis Fig. 2 shows XRD patterns of reversely co-precipitated samples with a pH value of 9.5 calcined at ˚ for all samples The Fig. 2a patterns indicate that single-phase formation of rhombohedral BiFeO3 with space group R3c No.161 and lattice parameters and angles of a=b=5.5876, c=13.8670, β and γ matched with the reference code of 01-071-2494 for the undoped-BFO sample. Single-phase formation of BFMO, BYFMO5, BYFMO10, BYFMO15 and BYFMO20 and the formation of YFeO3 and YMnO3 as impurities coexist with single-phase structure is clearly being seen for BYFMO25. The formation of single-phase BFMO and BYFMO samples confirms that the substitutions of Y in the A-site and Mn in the B-site were completely done. Because if the Y and Mn ions were not substituted properly (For example, if dopant ions were substituted on the contrary sites), the calculated stoichiometric ratios were broke up (see table 1) thereby a lot of impurities must be formed. Magnified X-ray patterns of two main peaks about and in range of ˚ to ˚ have been depicted in Fig. 2b. As compared to diffraction peaks of undoped-BFO and other samples, (006), (116) and (018) are attracted forward and disappear by Mn doping. Furthermore, increasing yttrium content reduces the intensity of all diffraction peaks. It can be concluded from Fig. 2b that diffraction main peaks of (104) and (110) incorporate into each other by adding the manganese dopant, proving structural phase transition from rhombohedral to orthorhombic. A similar phenomenon has also been previously reported [46, 47]. This phase transition is the characteristic feature for the orthorhombic BiFe0.8Mn0.2O3 single-phase structure, which is reported by M. Azuma et al. They have studied the effect of different amount of Mn doping in BiFe1-xMnxO3 (0
)
(3) (4)
(
)
(5)
Where is interplanar spacing in hexagonal system; h, k and l are Miller indices; a and c are the lattice parameters in hexagonal arrangement; λ is uwavelength of about Å; and is ragg’s angle Sharp peaks (012) and (110) have been employed for such calculations. The lattice parameters ahex and chex the ratio c/a of hexagonal unit cell and rhombohedral lattice angle rh have been listed in Table 2. The rhombohedral lattice angle is derived by rhombohedral-hexagonal transformation as follows (Equation 6) [49]: (
)
(6) √
( )
As it can be seen, by increasing the total amount of dopant ions, the ratio c/a decreases and subsequently extra distortion in crystal structure takes place. Furthermore, rhombohedral lattice angle rh increases as the total amount of dopants increases, causing more distortion in the rhombohedral lattice. The maximum value of rhombohedral angle change is 1.99% for BYFMO25 in comparison to pure BFO. Also, Y-doped BFO structural distortion has been studied by structure stability of perovskite compound quantified using tolerance factor (t) by M. Luo et al. [42]. They hold that smaller diameter of Y3+ in comparison to Bi3+ is the main reason for more distortion in crystal lattice by increasing Y content. As we will see, lattice distortion is a major cause of the samples magnetic properties enhancement. 3.3. FT-IR spectroscopy For characterization of fundamental absorption bands in BFO, BFMO and BYFMO systems, the FTIR spectrums of precursor and crystalline powders derived from reverse co-precipitation calcined at ˚ were taken in wave number range of 400-900 cm-1, as demonstrated in Fig 3. The first peak at 418 cm-1 is attributed to Fe3+ cations caused by internal vibration of FeO6 octahedra [50]. The sharp peak at 440 cm-1 and broad band at 550 cm-1 are characteristic of Fe-O bending and stretching vibration of FeO6 octahedral groups in perovskite structure, implying perovskite BFO phase formation [51]. Broad absorption at 550 cm-1 is due to overlapping of Fe-O and Bi-O of FeO6 and BiO6 octahedra group vibration [52]. As clearly seen from the comparison between pure BFO and doped-BFO samples, it is understood that after addition of Mn and Y doping, the small shift in peaks at 400-550 cm-1 towards lower-frequency side will occur. This shift in peak may arise from differences between bond lengths of Fe-O and Bi-O in BFMO and BYFMO samples due to A-site and B-site substitution by Y and Mn ions. When Mn ions are added to BFO system, a change in BiO and Fe-O bond length and O-Fe-O bond angle will take place. Furthermore, Y addition may change Fe-O-Fe angle in octahedral pairs, as well as Bi-O bond length of BiO6 octahedra [53]. 3.4. Morphological observations The transmission electron micrograph of the as-selected BYFMO15 specimen has been shown in Fig. 4. According to this micrograph, it is obvious that average particle size is about 40nm and that the agglomerated morphology due to the fast precipitation reaction and high surface energy of nanoparticles can clearly be observed. Morphology of powders, particle size and distribution have been observed using a field emission scanning electron microscopy (FESEM), equipped with energy dispersive X-ray spectroscopy (EDX). Fig. 5 represents FESEM micrographs of pure and doped BFO powders. Slight agglomeration and granular shape of particles is clearly seen. The fast (uncontrolled) precipitation and high surface energy of nanoparticles are the main reasons for agglomeration. The
average grain size of pure BFO is about 130 nm, while the Y-doped BFMO average grain size is about in range of 63 to 15 nm from BYFMO5 to BYFMO20, respectively. As depicted in these micrographs, by increasing the total amount of dopant ions, the average size of particles decreases and the distribution of as-synthesized particles is improved. In general, polycrystalline particles formation can be attributed to doping elements that distort crystal structure and restrict its normal growth [47]. Furthermore, dopant ions can be accumulated in grain boundaries and subsequently reduce grain growth. EDX analysis of a selected BYFMO15 sample has been depicted in Fig. 6. This pattern reveals that elements in the samples are limited to Bi, Y, Fe, Mn and O. The atomic percentages of elements have been listed in the inset table. The A-site/B-site ratio is 1.035, which is very close to the stoichiometric ratio for BFO pure phase synthesis. It is worth noting that the very small amount of Au has been measured by EDX, which is related to gold coat on the nonconductor sample in FESEM observation. 3.5. Magnetic evaluation Magnetic hysteresis loops of the BFMO and BYFMO calcined nanoparticles synthesized by reverse co-precipitation with an applied magnetic field in range of ± 1.0 T at room temperature were also measured in this research. BiFeO3 is G-type antiferromagnetic material and its magnetic ordering has been modulated by Fe3+ magnetic moments located in octahedral sites coupled ferromagnetically in (111) planes. Should ferromagnetically ordered Fe3+ magnetic moments be aligned parallel to (111) planes, canted antiferromagnetic sublattices can be created by symmetry and local magnetoelectric coupling, leading to increasing magnetization [54, 55]. However, spiral spin cycloid of BFO with a long period of 62 nm suppresses the total magnetization, causing a small saturation magnetization. I.Sosnowska et al. have reported structural transformation in Mn doped BFO using neutron diffraction. They noted that by adding Mn ions, BFO spiral spin modulation changes to a collinear canted antiferromagnetic structure with spins along c axis [56], thereby enhancing magnetization of BFMO versus undoped-BFO. Fig. 7 shows antiferromagnetic (weak ferromagnetic) behavior of all samples due to unsaturated magnetization even in the high magnetic field. Also, the as-prepared powders magnetic parameters have been depicted in Table 3. The BFO Néel temperature is thereby presents antiferromagnetic ordering in room temperature. But, nanoscale antiferromagnetic materials can represent weak ferromagnetic ordering due to their surface effects and creation of uncompensated surface spins. This matter has been reported in many antiferromagnetic materials such as BiFeO3 [57] and Bi2Fe4O9 [58]. As-synthesized powder samples magnetization increased by increasing yttrium concentration from 0.976 emu/g for pure BFMO to 1.518 emu/g for BYFM20 (x=0.20). Whereas Y3+ is the nonmagnetic ion, it cannot make a direct contribution to BYFMO system magnetization. Additionally, the YFeO3 has a very large coercivity, as compared with as-prepared BYFMO samples [59, 60]. Thus, possible contribution of YFeO3 as impurity phase can be excluded. Generally, raising magnetization by increasing yttrium concentration can be concluded as follows: i. Particle size of as-prepared powders with the reverse method is in range of 9 to 56 nm for all samples and declines by raising Y content. This means that all particles have a smaller diameter than spiral spin structure period, leading to destroying spiral spin cycloid, which leads to an increase in magnetization [12]. ii. Uncompensated spins from surface can improve BFO nanoparticle magnetization [61]. In the achieved BYFMO powders the particle size decreases as yttrium concentration increases. Thus, the large fraction of uncompensated spins from surface enhances magnetic properties due to high surface-to-volume ratio in the nanoparticles [57].
iii. By increasing the total amount of dopant ions the BFO structure should be further destroyed, resulting in magnetization enhancement as shown in Section 3.2 by calculating rhombohedral angle change value. The Fe-O-Fe super-exchange interaction is dependent on FeO6 octahedra structure. Recently, Yuan et al. have studied the effect of Y doping on FeO6 structural modification in LuFeO3. They hold that yttrium substitution can ameliorate magnetic properties by changing octahedral site structure in perovskite LuFeO3 [62]. 3.6. Electrical properties The variation of dielectric constant έ and loss factor tanδ) in frequency range of 1 KHz to 1000 KHz at room temperature has been shown in Fig. 8 and Fig. 9, respectively for BFO, BFMO and Y MO samples sintered in microwave furnace at ˚ at room temperature s shown in Fig. 8, a reduction in dielectric constant by enhancing frequency is clearly observed. This phenomenon is due to dielectric relaxation time which is directly related to polarization orientation [63]. This is the time when dielectric materials atoms need to align with the applied external electrical field, which is equal to 10-9 s. Also, at high frequencies, dielectric constant is negligible since dielectric materials atoms require a finite time to align with the applied electrical field. Furthermore, another important point is related to the exchanging of electrons from Fe2+ to Fe3+ ions, which consumes a large amount of energy [64]. At low frequencies, the electrical field could not secure this energy for the purpose of exchanging electrons. Yet by an increase in electrical field frequency, this energy is provided. Fig. 9 shows dielectric loss versus frequency at room temperature. This illustrates that dielectric loss is higher at low frequencies and then decreases at higher frequencies. Low frequency losses are related to polarization of the charged defects but at higher frequencies these defects could not follow ferroelectric switching [65]. As seen in Figs and values of ε′ and tanδ increase by increasing codoping. This may follow from the formation of large dipole moments by structural distortion [66]. Furthermore, as it is obvious in FESEM micrographs, the samples particle size falls from 130 to 15 nm as Yttrium doping increases, causing much more grain boundaries in sintered samples by increasing dopants concentration. Therefore, on the whole, the addition of Mn and Y ions to BFO system increases ε′ and tanδ of the samples 4. Conclusions The ultra-fine nanopowders in system of Bi1-xYxFe0.8Mn0.2O3 (BYFMO) with x= 0, 0.05, 0.10, 0.15, 0.20 and 0.25 were successfully synthesized using reverse chemical co-precipitation method. The DTA analysis revealed that crystallization temperature increases from to ˚ and the peaks at and ˚ correspond to the Curie point for BFO and BYFMO15, respectively. XRD patterns indicate the formation of YFeO3 and YMnO3 as impurities for the BYFMO25 sample. Moreover, crystallographic calculations showed more deviation in Hexagonal ratio (c/a), as well as rhombohedral lattice angle rh) by raising dopants content. The transmission electron micrograph of as-selected BYFMO15 specimen demonstrated that average particle size is about 40nm with an agglomerated morphology due to fast precipitation reaction and high surface energy of nanoparticles. The observation of samples with scanning electron microscopy indicated that particle size declines as dopants concentration grows from 130 to 15 nm for pure BFO to BYFMO25, respectively. Magnetic hysteresis loops confirmed an antiferromagnetic (weak ferromagnetic) behavior of BFO nanoparticles synthesized by reverse co-precipitation at room temperature. As-synthesized powder samples magnetization rose greatly by enhancing dopants concentration from 0.298 emu/g for pure BFO to 1.518 emu/g for BYFM20 due to increment of lattice distortion and a reduction in average particle
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Fig. 1. DTA curves of the reversely co-precipitated powders for BFO and BYFMO15.
Fig. 2. (a)X-ray diffraction patterns of un-doped, Mn doped and co-doped nanoparticles calcined at (104) and (110) diffraction peaks.
˚ ; (b) magnified patterns of
Fig. 3. FT-I spectra of the precursor and calcined powders at
˚ .
Fig. 4. Transmission electron micrograph of the as-selected BYFMO15 specimen.
Fig. 5. FESEM micrographs of reversely co-precipitated samples (a) un-doped BFO, (b) BMFO, (c) BYFMO5, (d) BYFMO10, (e) BYFMO15 and (d) BYFMO20.
Fig. 6. EDX analysis of the as-selected BYFMO15 sample.
Fig. 7. Magnetic hysteresis loops of all the samples synthesis via revers co-precipitation at pH value of 9.5.
Fig. 8. Dielectric constant of BYFMO with x=0.00, 0.05, 0.10, 0.15 and 0.20.
Fig. 9. Dielectric loss factor of BYFMO with x=0.00, 0.05, 0.10, 0.15 and 0.20.
Table 1. Abbreviated symbols of samples with different amount of dopants.
Sample abbreviation
X value
BFO
0.00
Stoichiometric molar ratio (Bi:Y:Fe:Mn) 1.00:0.00:1.00:0.00
Chemical formula BiFeO3
0.00 0.05 0.10 0.15 0.20 0.25
BFMO BYFMO5 BYFMO10 BYFMO15 BYFMO20 BYFMO25
1.00:0.00:0.80:0.20 0.95:0.05:0.80:0.20 0.90:0.10:0.80:0.20 0.85:0.15:0.80:0.20 0.80:0.20:0.80:0.20 0.75:0.25:0.80:0.20
BiFe0.8Mn0.2O3 Bi0.95Y0.05Fe0.8Mn0.2O3 Bi0.9Y0.1Fe0.8Mn0.2O3 Bi0.85Y0.15Fe0.8Mn0.2O3 Bi0.8Y0.2Fe0.8Mn0.2O3 Bi0.75Y0.25Fe0.8Mn0.2O3
Table 2. Crystallographic parameters of the samples. Sample
2θ of (012)
2θ of (110)
(Å)
(Å)
⁄
BFO
22.28
31.88
5.8232
14.0582
2.5000
59.1025
BFMO
22.42
32.04
5.5824
13.8296
2.4773
59.5026
BYFMO5
22.50
32.12
5.5678
13.7741
2.4738
59.5655
BYFMO10
22.64
32.30
5.5390
13.6118
2.4574
59.8581
BYFMO15
22.74
32.40
5.5211
13.5589
2.4558
59.8866
BYFMO20
22.80
32.48
5.5070
13.5066
2.4526
59.9559
BYFMO25
22.85
32.54
5.5070
13.4039
2.4339
60.2803
Table 3. Magnetic parameters of the as-prepared powders.
Magnetization at 9000Oe
Remnant Magnetization
Coercive Field
Ms (emu/g)
Mr (emu/g)
Hc (Oe)
Sample
BFO
0.298
0.0052
67
BFMO
0.976
0.0060
33
BYFMO5
1.140
0.0065
32
BYFMO10
1.200
0.0071
32
BYFMO15
1.255
0.0087
28
BYFMO20
1.518
0.0092
25
PII: DOI: Reference:
S0272-8842(17)31772-8 http://dx.doi.org/10.1016/j.ceramint.2017.08.074 CERI16028
To appear in: Ceramics International Received date: 8 July 2017 Revised date: 9 August 2017 Accepted date: 10 August 2017 Cite this article as: H. Sangian, O. Mirzaee and M. Tajally, Structural, electrical and magnetic properties improvement of Bi1-xYxFe0.8Mn0.2O3 ultra-fine nanoparticles synthesized via reverse chemical co-precipitation technique, Ceramics International, http://dx.doi.org/10.1016/j.ceramint.2017.08.074 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Structural, electrical and magnetic properties improvement of Bi1-xYxFe0.8Mn0.2O3 ultra-fine nanoparticles synthesized via reverse chemical co-precipitation technique H. Sangian, O. Mirzaee*, M. Tajally Faculty of materials and metallurgical engineering, Semnan University, Semnan, Iran
Abstract Ultra-fine Bi1-xYxFe0.8Mn0.2O3 (BYFMO) nanopowders with x= 0, 0.05, 0.10, 0.15, 0.20 and 0.25 were successfully synthesized using reverse co-precipitation method. XRD graphs indicate the formation of the secondary phases such as YFeO3 and YMnO3 in synthesized powders with 25% of yttrium doping. Furthermore, the lattice parameter declined as yttrium doping grew. FESEM micrographs showed that, the particle size fell from 130 to 15 nm as yttrium doping rose from x=0 to x=0.25, respectively. Magnetic hysteresis loops illustrated a weak ferromagnetism for all samples at room temperature. Besides, Y and Mn co-doping improved magnetization from 0.298 emu/g for pure BFO to 1.518 emu/g for BYFM20 (x=0.20) because by raising the amount of dopants the particle size dropped, leading to a high surface-to-volume ratio and therefore more uncompensated surface spins. Also, spin cycloid was destroyed by Y-doping, thereby releasing the latent magnetization locked within cycloid. Electrical properties measurement reveals that ε′ and tanδ values climbed by an increase in co-doping ions. This enhancement may be related to various factors such as the formation of large dipole moments by more structural distortion and a much more increase in grain boundaries by adding extra amounts of dopant ions.
Keywords: Reverse co-precipitation; Bismuth ferrite; Magnetic properties; Dielectric properties
Highlights: Using a new reverse chemical co-precipitation technique, the ultra-fine Bi1-xYxFe0.8Mn0.2O3 (BYFMO) nanoparticles have been successfully prepared. The samples magnetization increased greatly by increasing dopants concentration due to more lattice distortion and uncompensated spins. Electrical properties measurement revealed that values of ε′ and tanδ increase by increasing codoping ions. 1. Introduction Multiferroic materials, which have at least two primary ferroic properties: ferroelectricity, ferromagneticity and ferroelasticity coupled to each other in the same phase [1], have received much attention because of their novel potential applications in storage devices [2], actuators [3], microelectronic device [4], non-volatile memories [5] and sensors [6]. Perovskite BiMO3 (M is Fe and Mn), mullite-type bismuth ferrite (Bi2Fe4O9), boracites family (BaMF4, M is divalent transition ions) and hexagonal RMnO3 (R is rare earths ions) are the important multiferroic materials studied rather extensively on the subject of magnetic properties, electrical properties and magnetoelectric coupling *
Corresponding author. Tel.: +98 233 1533336; fax: +98 2333654119. E-mail address: [email protected] (O. Mirzaee)
[7-9].Perovskite-type bismuth ferrite (BFO) which possesses high Néel and Curie temperatures ( and ) is the most important extensively effective single-phase multiferroic at room temperatures [10, 11], but owing to some weak properties such as electrical resistivity, leakage current density and low remnant polarization in the bulk form, the BFO industrial application in microelectronic devices has been limited [12-14]. To resolve these problems, several strategies such as thin film usage and doping in BFO have been studied [15-17]. For example, the bulk BFO has a remnant polarization of 6.1 but its thin films show large remnant polarization, 15 times larger than that of the BFO bulk form [18]. Also, many experiments have been carried out in the field of improvement of magnetic, electrical and multiferroic properties of BFO nanoparticles, thin films and bulk samples using A-site and B-site substitution by different ions [19]. BFO has a rhombohedrally distorted perovskite crystallographic structure which belongs to space group R3c, No.161 with lattice parameters of and ˚-89.4 However, BFO crystal structure can also be classified in hexagonal arrangement when is parallel to and [20].BFO has the G-type antiferromagnetic ordering with a long-period spin cycloid structure (62-64 nm) [12, 21]. Besides, BFO unit cell polar centrosymmetric distortion causes a spontaneous polarization along the [111]c pseudocubic (rhombohedral) rotation axis [22]. Early in 1967, Achenbach et al. [23] prepared single-phase polycrystalline BFO via and solid state reaction at temperatures over However, due to some disadvantages of their method like reaction high temperature, large particle size and impurities presence, new methods such as chemical co-precipitation [24, 25], hydrothermal [26], solvothermal [27], sonochemical [28], microemulsion [29], sol-gel [30], molten salt [31], and mechanochemical procedures [32] are currently being used for BFO nanopowders synthesis. As for chemical co-precipitation method advantages like simple processing, possibility of mass production and easy controlling of conditions, this method has found its place in the field of nanotechnology and wet chemical synthesis. This process has been applied efficiently for preparation of some electro-ceramic nanoparticles such as LiNbO3 (LN) [33], CoFe2O4 (CFO) [34] and Y3Al5O12 (YAG) [35]. So far, all the reports concerning BFO synthesis have focused on homogeneous co-precipitation in which the process is very sensitive to pH control [36-38]. The effects of Y and Mn-doping on electrical, optical and magnetic properties of BFO have been investigated separately. Among B-site ion substitutions, Mn doping improves BFO photoluminescent properties and exhibits a significantly reduced leakage current and an improved breakdown voltage, so that well-saturated ferroelectric hysteresis loops can be detected [39, 40]. Moreover, yttrium A-site substitution enhances the dielectric, leakage current density and magnetization in BFO nanoparticles [41, 42]. However, to the best of our knowledge, no work has been reported concerning BFO synthesis via reverse chemical co-precipitation. As compared to previous works, in this paper we synthesized yttrium and manganese co-doped BFO nanoparticles successfully via reverse co-precipitation methods at the pH value of This method “reverse co-precipitation” led to a much lower grain size of BYMFO nanoparticles by increasing yttrium content. Furthermore, formation of transient phases and structural transformation by raising Y content in BYMFO system were studied. At last the co-doping effect of on product purity and morphological features, as well as electrical and magnetic properties of synthesized samples were investigated in detail. 2. Materials and methods BYFMO nanoparticles were successfully synthesized by reverse chemical co-precipitation procedure. In a typical process, high-purity bismuth subnitrate Bi5H9N4O22(Merck kGaA 98.0%), iron nitrate nonahydrate (Merck KGaA 98.0 %), yttrium oxide (sigma-aldrich 99.9%) and manganese nitrate tetrahydrate Mn(NO3)2.4H2O (scharlau 98.0%) were dissolved in 2M nitric acid
HNO3 (scharlau 65.0%) at room temperature. Cation solutions were mixed and stirred for 30 minutes at the stoichiometric ratio (Table 1) to obtain a homogenous transparent mixture. 2M Sodium hydroxide (NaOH, scharlau 99.0%) was utilized as a precipitating agent. In the reverse coprecipitation process, the cations solution and precipitating agent were loaded into the separator funnel and glass beaker, respectively. Then the cations solution was vented drop by drop into the precipitating agent when the stirrer was working severely until the pH value of 9.5 was achieved. The chemical co-precipitation process lasted about 15 minutes and the final precipitate was washed with deionized water until the pH value of 7 was obtained. An electric drier at 80 ˚ for 24h was utilized to dry the precipitate. At last the dried chunks were crushed in a mortar to obtain amorphous powders. For crystallization and phase formation, powder samples were calcined at 550 ˚ for 1h. Calcined powders were pressed into pellets and sintered for 4 minute at 800±20 ˚ by microwave sintering furnace in air atmosphere. Calcination temperature was obtained via differential thermal analysis (DTA) at a heating rate of ˚ /min The sample pot was platinum and the reference material was alpha-alumina. Calcined powders phase structure was identified via an X-Ray diffractometer (XRD, - ay with uradiation and a scan rate of ˚/min in the scattering angular range of ourier transformed infrared (FT-IR) spectrum was recorded by a spectrometer (FT-IR SHIMADZU). BFO powders morphology and size distribution were attained by the field emission scanning electron microscope (FESEM, MIRA3-TSCAN) with 15 kV and transmission electron microscope (TEM, PHILIPS-CM3U) with 150 kV. The magnetic hysteresis loops with an external magnetic field of 1.0 T were measured at room temperature through a vibration sample magnetometer (VSM-AGFM). The electrical properties of sintered pellets were determined by inductance-capacitance-resistance (LCRmeter) within 1 KHz-to-1000 KHz frequency. 3. Results and discussion 3.1.Thermal behavior Fig. 1 shows DTA curves of un-calcined pure BFO and as-selected BYFMO15 powders synthesized by reverse co-precipitation with a pH value of 9.5. As clearly observed from thermograms, four various regions have been detected. The peaks located at 50˚ in DT curve correspond to decomposition or evaporation of possibly organic compounds, hydrates and nitrates, accompanied by a large weight loss at this stage [43] The exothermic peaks at ˚ are attributed to magnetic transitions from antiferromagnetic to paramagnetic state (Néel temperature) in BFO and BYFMO15 phases [44]. The exothermic peaks presented at 460˚ are related to crystallization of BFO and BYFMO15 powders utilized to select the appropriate calcination temperature of ˚ in this study As can be seen, crystallization temperature is raised by adding dopant ions, which is attributed to higher diffusion rate of Bi ions in comparison with Y ions [45]. When yttrium ions are added to system, it is more difficult for the diffusion process to cause higher crystallization temperature in BYFMO15 sample. The BFO formation in chemical co-precipitation is based on the following chemical reactions [36]. (1) (2) Usually, a ferroelectric-to-paraelectric phase transition in BFO can be observed by the low-intensity peak in DTA without any weight loss. This situation in DTA curves has been observed at 810˚ It can be observed that the temperature related to ferroelectric transition (Curie temperature) is slightly
increased by substitution of Y and Mn ions. Moreover, no significant change can detected at Neel temperature by adding dopant ions due to the fact that Bi-site and Fe-site are responsible for ferroelectric behavior and magnetic ordering in BFO systems, respectively. B-site substitution by Mn ions plays no remarkable role in BFO magnetic properties and therefore no noticeable change in magnetic transition temperature is measured [44]. 3.2.XRD analysis Fig. 2 shows XRD patterns of reversely co-precipitated samples with a pH value of 9.5 calcined at ˚ for all samples The Fig. 2a patterns indicate that single-phase formation of rhombohedral BiFeO3 with space group R3c No.161 and lattice parameters and angles of a=b=5.5876, c=13.8670, β and γ matched with the reference code of 01-071-2494 for the undoped-BFO sample. Single-phase formation of BFMO, BYFMO5, BYFMO10, BYFMO15 and BYFMO20 and the formation of YFeO3 and YMnO3 as impurities coexist with single-phase structure is clearly being seen for BYFMO25. The formation of single-phase BFMO and BYFMO samples confirms that the substitutions of Y in the A-site and Mn in the B-site were completely done. Because if the Y and Mn ions were not substituted properly (For example, if dopant ions were substituted on the contrary sites), the calculated stoichiometric ratios were broke up (see table 1) thereby a lot of impurities must be formed. Magnified X-ray patterns of two main peaks about and in range of ˚ to ˚ have been depicted in Fig. 2b. As compared to diffraction peaks of undoped-BFO and other samples, (006), (116) and (018) are attracted forward and disappear by Mn doping. Furthermore, increasing yttrium content reduces the intensity of all diffraction peaks. It can be concluded from Fig. 2b that diffraction main peaks of (104) and (110) incorporate into each other by adding the manganese dopant, proving structural phase transition from rhombohedral to orthorhombic. A similar phenomenon has also been previously reported [46, 47]. This phase transition is the characteristic feature for the orthorhombic BiFe0.8Mn0.2O3 single-phase structure, which is reported by M. Azuma et al. They have studied the effect of different amount of Mn doping in BiFe1-xMnxO3 (0
)
(3) (4)
(
)
(5)
Where is interplanar spacing in hexagonal system; h, k and l are Miller indices; a and c are the lattice parameters in hexagonal arrangement; λ is uwavelength of about Å; and is ragg’s angle Sharp peaks (012) and (110) have been employed for such calculations. The lattice parameters ahex and chex the ratio c/a of hexagonal unit cell and rhombohedral lattice angle rh have been listed in Table 2. The rhombohedral lattice angle is derived by rhombohedral-hexagonal transformation as follows (Equation 6) [49]: (
)
(6) √
( )
As it can be seen, by increasing the total amount of dopant ions, the ratio c/a decreases and subsequently extra distortion in crystal structure takes place. Furthermore, rhombohedral lattice angle rh increases as the total amount of dopants increases, causing more distortion in the rhombohedral lattice. The maximum value of rhombohedral angle change is 1.99% for BYFMO25 in comparison to pure BFO. Also, Y-doped BFO structural distortion has been studied by structure stability of perovskite compound quantified using tolerance factor (t) by M. Luo et al. [42]. They hold that smaller diameter of Y3+ in comparison to Bi3+ is the main reason for more distortion in crystal lattice by increasing Y content. As we will see, lattice distortion is a major cause of the samples magnetic properties enhancement. 3.3. FT-IR spectroscopy For characterization of fundamental absorption bands in BFO, BFMO and BYFMO systems, the FTIR spectrums of precursor and crystalline powders derived from reverse co-precipitation calcined at ˚ were taken in wave number range of 400-900 cm-1, as demonstrated in Fig 3. The first peak at 418 cm-1 is attributed to Fe3+ cations caused by internal vibration of FeO6 octahedra [50]. The sharp peak at 440 cm-1 and broad band at 550 cm-1 are characteristic of Fe-O bending and stretching vibration of FeO6 octahedral groups in perovskite structure, implying perovskite BFO phase formation [51]. Broad absorption at 550 cm-1 is due to overlapping of Fe-O and Bi-O of FeO6 and BiO6 octahedra group vibration [52]. As clearly seen from the comparison between pure BFO and doped-BFO samples, it is understood that after addition of Mn and Y doping, the small shift in peaks at 400-550 cm-1 towards lower-frequency side will occur. This shift in peak may arise from differences between bond lengths of Fe-O and Bi-O in BFMO and BYFMO samples due to A-site and B-site substitution by Y and Mn ions. When Mn ions are added to BFO system, a change in BiO and Fe-O bond length and O-Fe-O bond angle will take place. Furthermore, Y addition may change Fe-O-Fe angle in octahedral pairs, as well as Bi-O bond length of BiO6 octahedra [53]. 3.4. Morphological observations The transmission electron micrograph of the as-selected BYFMO15 specimen has been shown in Fig. 4. According to this micrograph, it is obvious that average particle size is about 40nm and that the agglomerated morphology due to the fast precipitation reaction and high surface energy of nanoparticles can clearly be observed. Morphology of powders, particle size and distribution have been observed using a field emission scanning electron microscopy (FESEM), equipped with energy dispersive X-ray spectroscopy (EDX). Fig. 5 represents FESEM micrographs of pure and doped BFO powders. Slight agglomeration and granular shape of particles is clearly seen. The fast (uncontrolled) precipitation and high surface energy of nanoparticles are the main reasons for agglomeration. The
average grain size of pure BFO is about 130 nm, while the Y-doped BFMO average grain size is about in range of 63 to 15 nm from BYFMO5 to BYFMO20, respectively. As depicted in these micrographs, by increasing the total amount of dopant ions, the average size of particles decreases and the distribution of as-synthesized particles is improved. In general, polycrystalline particles formation can be attributed to doping elements that distort crystal structure and restrict its normal growth [47]. Furthermore, dopant ions can be accumulated in grain boundaries and subsequently reduce grain growth. EDX analysis of a selected BYFMO15 sample has been depicted in Fig. 6. This pattern reveals that elements in the samples are limited to Bi, Y, Fe, Mn and O. The atomic percentages of elements have been listed in the inset table. The A-site/B-site ratio is 1.035, which is very close to the stoichiometric ratio for BFO pure phase synthesis. It is worth noting that the very small amount of Au has been measured by EDX, which is related to gold coat on the nonconductor sample in FESEM observation. 3.5. Magnetic evaluation Magnetic hysteresis loops of the BFMO and BYFMO calcined nanoparticles synthesized by reverse co-precipitation with an applied magnetic field in range of ± 1.0 T at room temperature were also measured in this research. BiFeO3 is G-type antiferromagnetic material and its magnetic ordering has been modulated by Fe3+ magnetic moments located in octahedral sites coupled ferromagnetically in (111) planes. Should ferromagnetically ordered Fe3+ magnetic moments be aligned parallel to (111) planes, canted antiferromagnetic sublattices can be created by symmetry and local magnetoelectric coupling, leading to increasing magnetization [54, 55]. However, spiral spin cycloid of BFO with a long period of 62 nm suppresses the total magnetization, causing a small saturation magnetization. I.Sosnowska et al. have reported structural transformation in Mn doped BFO using neutron diffraction. They noted that by adding Mn ions, BFO spiral spin modulation changes to a collinear canted antiferromagnetic structure with spins along c axis [56], thereby enhancing magnetization of BFMO versus undoped-BFO. Fig. 7 shows antiferromagnetic (weak ferromagnetic) behavior of all samples due to unsaturated magnetization even in the high magnetic field. Also, the as-prepared powders magnetic parameters have been depicted in Table 3. The BFO Néel temperature is thereby presents antiferromagnetic ordering in room temperature. But, nanoscale antiferromagnetic materials can represent weak ferromagnetic ordering due to their surface effects and creation of uncompensated surface spins. This matter has been reported in many antiferromagnetic materials such as BiFeO3 [57] and Bi2Fe4O9 [58]. As-synthesized powder samples magnetization increased by increasing yttrium concentration from 0.976 emu/g for pure BFMO to 1.518 emu/g for BYFM20 (x=0.20). Whereas Y3+ is the nonmagnetic ion, it cannot make a direct contribution to BYFMO system magnetization. Additionally, the YFeO3 has a very large coercivity, as compared with as-prepared BYFMO samples [59, 60]. Thus, possible contribution of YFeO3 as impurity phase can be excluded. Generally, raising magnetization by increasing yttrium concentration can be concluded as follows: i. Particle size of as-prepared powders with the reverse method is in range of 9 to 56 nm for all samples and declines by raising Y content. This means that all particles have a smaller diameter than spiral spin structure period, leading to destroying spiral spin cycloid, which leads to an increase in magnetization [12]. ii. Uncompensated spins from surface can improve BFO nanoparticle magnetization [61]. In the achieved BYFMO powders the particle size decreases as yttrium concentration increases. Thus, the large fraction of uncompensated spins from surface enhances magnetic properties due to high surface-to-volume ratio in the nanoparticles [57].
iii. By increasing the total amount of dopant ions the BFO structure should be further destroyed, resulting in magnetization enhancement as shown in Section 3.2 by calculating rhombohedral angle change value. The Fe-O-Fe super-exchange interaction is dependent on FeO6 octahedra structure. Recently, Yuan et al. have studied the effect of Y doping on FeO6 structural modification in LuFeO3. They hold that yttrium substitution can ameliorate magnetic properties by changing octahedral site structure in perovskite LuFeO3 [62]. 3.6. Electrical properties The variation of dielectric constant έ and loss factor tanδ) in frequency range of 1 KHz to 1000 KHz at room temperature has been shown in Fig. 8 and Fig. 9, respectively for BFO, BFMO and Y MO samples sintered in microwave furnace at ˚ at room temperature s shown in Fig. 8, a reduction in dielectric constant by enhancing frequency is clearly observed. This phenomenon is due to dielectric relaxation time which is directly related to polarization orientation [63]. This is the time when dielectric materials atoms need to align with the applied external electrical field, which is equal to 10-9 s. Also, at high frequencies, dielectric constant is negligible since dielectric materials atoms require a finite time to align with the applied electrical field. Furthermore, another important point is related to the exchanging of electrons from Fe2+ to Fe3+ ions, which consumes a large amount of energy [64]. At low frequencies, the electrical field could not secure this energy for the purpose of exchanging electrons. Yet by an increase in electrical field frequency, this energy is provided. Fig. 9 shows dielectric loss versus frequency at room temperature. This illustrates that dielectric loss is higher at low frequencies and then decreases at higher frequencies. Low frequency losses are related to polarization of the charged defects but at higher frequencies these defects could not follow ferroelectric switching [65]. As seen in Figs and values of ε′ and tanδ increase by increasing codoping. This may follow from the formation of large dipole moments by structural distortion [66]. Furthermore, as it is obvious in FESEM micrographs, the samples particle size falls from 130 to 15 nm as Yttrium doping increases, causing much more grain boundaries in sintered samples by increasing dopants concentration. Therefore, on the whole, the addition of Mn and Y ions to BFO system increases ε′ and tanδ of the samples 4. Conclusions The ultra-fine nanopowders in system of Bi1-xYxFe0.8Mn0.2O3 (BYFMO) with x= 0, 0.05, 0.10, 0.15, 0.20 and 0.25 were successfully synthesized using reverse chemical co-precipitation method. The DTA analysis revealed that crystallization temperature increases from to ˚ and the peaks at and ˚ correspond to the Curie point for BFO and BYFMO15, respectively. XRD patterns indicate the formation of YFeO3 and YMnO3 as impurities for the BYFMO25 sample. Moreover, crystallographic calculations showed more deviation in Hexagonal ratio (c/a), as well as rhombohedral lattice angle rh) by raising dopants content. The transmission electron micrograph of as-selected BYFMO15 specimen demonstrated that average particle size is about 40nm with an agglomerated morphology due to fast precipitation reaction and high surface energy of nanoparticles. The observation of samples with scanning electron microscopy indicated that particle size declines as dopants concentration grows from 130 to 15 nm for pure BFO to BYFMO25, respectively. Magnetic hysteresis loops confirmed an antiferromagnetic (weak ferromagnetic) behavior of BFO nanoparticles synthesized by reverse co-precipitation at room temperature. As-synthesized powder samples magnetization rose greatly by enhancing dopants concentration from 0.298 emu/g for pure BFO to 1.518 emu/g for BYFM20 due to increment of lattice distortion and a reduction in average particle
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Fig. 1. DTA curves of the reversely co-precipitated powders for BFO and BYFMO15.
Fig. 2. (a)X-ray diffraction patterns of un-doped, Mn doped and co-doped nanoparticles calcined at (104) and (110) diffraction peaks.
˚ ; (b) magnified patterns of
Fig. 3. FT-I spectra of the precursor and calcined powders at
˚ .
Fig. 4. Transmission electron micrograph of the as-selected BYFMO15 specimen.
Fig. 5. FESEM micrographs of reversely co-precipitated samples (a) un-doped BFO, (b) BMFO, (c) BYFMO5, (d) BYFMO10, (e) BYFMO15 and (d) BYFMO20.
Fig. 6. EDX analysis of the as-selected BYFMO15 sample.
Fig. 7. Magnetic hysteresis loops of all the samples synthesis via revers co-precipitation at pH value of 9.5.
Fig. 8. Dielectric constant of BYFMO with x=0.00, 0.05, 0.10, 0.15 and 0.20.
Fig. 9. Dielectric loss factor of BYFMO with x=0.00, 0.05, 0.10, 0.15 and 0.20.
Table 1. Abbreviated symbols of samples with different amount of dopants.
Sample abbreviation
X value
BFO
0.00
Stoichiometric molar ratio (Bi:Y:Fe:Mn) 1.00:0.00:1.00:0.00
Chemical formula BiFeO3
0.00 0.05 0.10 0.15 0.20 0.25
BFMO BYFMO5 BYFMO10 BYFMO15 BYFMO20 BYFMO25
1.00:0.00:0.80:0.20 0.95:0.05:0.80:0.20 0.90:0.10:0.80:0.20 0.85:0.15:0.80:0.20 0.80:0.20:0.80:0.20 0.75:0.25:0.80:0.20
BiFe0.8Mn0.2O3 Bi0.95Y0.05Fe0.8Mn0.2O3 Bi0.9Y0.1Fe0.8Mn0.2O3 Bi0.85Y0.15Fe0.8Mn0.2O3 Bi0.8Y0.2Fe0.8Mn0.2O3 Bi0.75Y0.25Fe0.8Mn0.2O3
Table 2. Crystallographic parameters of the samples. Sample
2θ of (012)
2θ of (110)
(Å)
(Å)
⁄
BFO
22.28
31.88
5.8232
14.0582
2.5000
59.1025
BFMO
22.42
32.04
5.5824
13.8296
2.4773
59.5026
BYFMO5
22.50
32.12
5.5678
13.7741
2.4738
59.5655
BYFMO10
22.64
32.30
5.5390
13.6118
2.4574
59.8581
BYFMO15
22.74
32.40
5.5211
13.5589
2.4558
59.8866
BYFMO20
22.80
32.48
5.5070
13.5066
2.4526
59.9559
BYFMO25
22.85
32.54
5.5070
13.4039
2.4339
60.2803
Table 3. Magnetic parameters of the as-prepared powders.
Magnetization at 9000Oe
Remnant Magnetization
Coercive Field
Ms (emu/g)
Mr (emu/g)
Hc (Oe)
Sample
BFO
0.298
0.0052
67
BFMO
0.976
0.0060
33
BYFMO5
1.140
0.0065
32
BYFMO10
1.200
0.0071
32
BYFMO15
1.255
0.0087
28
BYFMO20
1.518
0.0092
25