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65Condensed Matter and Interphases. 2021;23(4): 600-606
Ig^^H ISSN 1606-867Х (Print)
ISSN 2687-0711 (Online)
¡нп Condensed Matter and Interphases
SC3Q Kondensirovannye Sredy i Mezhfaznye Granitsy
v'ilïïL J https://journals.vsu.ru/kcmf/
Original articles
Research article
https://doi.org/10.17308/kcmf.2021.23/3680
Optical and magnetic properties of orthoferrite NdFeO3 nanomaterials synthesized by simple co-precipitation method
Pham Thi Hong Duyen1, Nguyen Anh Tien2H
1Thu Dau Mot University,
Thu Dau Mot City, Binh Duong Province, 590000, Vietnam
2Ho Chi Minh City University of Education, Ho Chi Minh City 700000, Vietnam
Abstract
In this work, orthoferrite NdFeO3 nanomaterials with particle sizes 20-40 nm have been successfully synthesized via a simple co-precipitation method through the hydrolysis of Nd (III) and Fe (III) cations in hot water with 5% NaOH as a precipitating agent. Single-phase NdFeO3 was generated after calcination of the as-prepared powder at 700, 800, and 900 °C for 1 hour. The UV-Vis spectra at room temperature presented strong absorption in the UV-Vis regions (l = 200-400 nm and 400-600 nm) with small band gap energy (Eg = 2.2^2.5 eV). The obtained NdFeO3 nanomaterials exhibited a hard ferromagnetic behavior with high coercivity (Hc = 600-1600 Oe). Keywords: NdFeO3, Nanomaterial, Co-precipitation, Optical and Magnetic properties
For citation: Pham T. H. D., Nguyen A. T. Optical and magnetic properties of orthoferrite NdFeO3 nanomaterials synthesized by simple co-precipitation method. Kondensirovannye sredy i mezhfaznye granitsy = Condensed Matter and Interphases. 2021;23(4): 600-606. https://doi.org/10.17308/kcmf.2020.22/3680
Для цитирования: Оптические и магнитные свойства наноматериалов на основе ортоферрита NdFeO3, синтезированных методом совместного осаждения. Конденсированные среды и межфазные границы. 2021;23(4): 600-606. https://doi.org/10.17308/kcmf.2020.22/3680
И Nguyen Anh Tien, e-mail: tienna@hcmue.edu.vn © Pham T. H. D., Nguyen A. T., 2021
The content is available under Creative Commons Attribution 4.0 License.
Pham Thi Hong Duyen et al.
Optical and magnetic properties of orthoferrite NdFeO, nanomaterials...
1. Introduction
The characteristic structure and properties of nanomaterials in general, and RFeO3 rare-earth orthoferrite nanomaterials in particular, depend on several different factors such as particle size and morphology, crystal size, the distribution of the cations in the crystal lattice, the content of doping elements and also the preparation method [1-5]. Nano-sized rare earth orthoferrites RFeO3 (R = La, Y, Nd, Pr, Ho, ...) have been studied and applied in many fields such as photocatalysis for the decomposition of toxic organic waste [6-7], electrodes for solid oxide fuel cells [8], gas sensor materials [9], photomagnetic and electromagnetic devices [10-11], etc. The rare earth orthoferrites NdFeO3 is amongst the materials of interest to research. The structural and optical properties, magnetic properties or electrical properties of orthoferrite neodymium were previously studies [12-15], showing promising for application in As (V) adsorption [16].
NdFeO3 nanomaterials have been synthesized by various methods such as high-temperature mechanosynthesis [14-15], sol-gel or gel-combustion [16, 17-18], hydrothermal or co-precipitation with surfactants [12-13]. In our previous report [19], based on the thermal behavior of the hydroxides of Fe (III), Nd (III) and their mixture (molar ratio Fe3+/Nd3+ = 1/1), the appropriate annealing temperature for the formation of single phase perovskite was determined and NdFeO3 nano particles of < 50 nm were synthesized by co-precipitation method (without any surfactant). By this simple co-precipitation method, our group has successfully prepared a series of rare earth orthoferrite such as PrFeO3 [20], HoFeO3 [21-22], [LaFeO3 [23] or [YFeO3 [24-25] and studied their structural and optical, magnetic properties. However, in [19], the optical and magnetic properties of NdFeO3 nano materials have yet to be reported.
Follow-up to the work in [19], the aim of this paper is to study the characteristic optical and magnetic properties of NdFeO3 orthoferrite nanomaterial synthesized by simple co-precipitation method without any surfactants.
2. Experimental and methods
NdFeO3 orthoferrite nano powder was prepared by co-precipitation method according
to [19]. 50 mL aqueous solution of the mixture of two salts Nd(NO3)3-6H2O and Fe(NO3)3-9H2O (molar ratio of 1/1) was added dropwise to 400 mL boiling water on a stirring hot plate (t° > 95 °C), resulting in a reddish-brown sol. Slowly adding the solution of Fe (III) and Nd (III) salts into water at high temperature helped speed up the hydrolysis of metal cations and restrict the particle size of resulting NdFeO3 particles, as proven previously for the synthesis of HoFeO3 and YFeO3 nano orthoferrite [22, 24]. Next, NaOH 5% solution was added dropwise to the system until all the cations Nd3+ and Fe3+ were completely precipitated (phenolphthalein paper turned pink). The obtained mixture was kept stirring for another 60 minutes, settled for 20 minutes, then vacuum filtered and washed with water until pH ~ 7.0. After drying at room temperature (for 5-7 days), the precipitate was ground with porcelain mortar and pestle into a yellowish-brown fine powder (precursor for NdFeO3). The precursor was then annealed at 700, 800 or 900 °C for 1h to study the formation of single phase orthorhombic NdFeO3.
Powder X-ray diffraction analysis (PXRD) of the NdFeO3 samples was carried out using a D8-ADVANCE X-ray diffractometer (Bruker, Bremen, Germany) with CuKa radiation, l = 0.154184 nm, angle range of 20 = 10-80°, and scan rate of 0.02 °/s. Average crystal size (Dxrd, nm) of the Nd1-xSrxFeO3 samples was calculated by Debye-Scherrer formula, lattice parameters (a, b, c, V) were calculated according to [13]. The morphology of the samples was determined by transmission electron microscopy (TEM) using a Joel JEM-1400 microscope (Jeol Ldt., Tokyo, Japan).
The UV-Vis absorption spectra of the NdFeO3 nanomaterials were studied on a UV-Visible spectrophotometer (UV-Vis, JASCO V-550, Japan). The optical energy gap (Eg, eV) of the samples was calculated according to [22]. Magnetic characteristics of nanopowders, including the coercive force (Hc, Oe), remanent magnetization (M, emu-g-1) and saturation magnetization (Ms, emu-g-1), were investigated at room temperature using a vibrating magnetometer (VSM, MICROSENE EV 11, Japan) with a maximum magnetic field of ± 20 kOe.
3. Results and discussion
Fig. 1 shows the PXRD patterns of the precursor for NdFeO3 nano orthoferrite after annealed at 700, 800 or 900 °C for 1 hour. All three samples exhibited single phase NdFeO3 orthoferrite with orthorhombic structure, Pbnm (62) space group.
The observable peaks match well with the standard pattern of NdFeO3 (JCPDS: 01-074-1473). When the annealing temperature increased, the degree of crystallinity (I, a.u), lattice cell volume (V, Â3) and average NdFeO3 crystal size according to Debye-Scherrer formula also increased (Table 1).
The morphology of the material NdFeO3 after annealing at 800 °C for 1h was studied
by transmission electron microscopy (Fig. 2), showing particles with the size varying from 20-40 nm and clear boundaries. However, the aggregation was significant because the attraction between those magnetic particles inhibited the scattering of the samples for TEM study.
The UV-Vis spectra at room temperature of the NdFeO3 materials annealed at different temperatures (700, 800 or 900 °C for 1h) show strong absorption in the UV (~ 200-400 nm) and visible regions (~ 400-600 nm) (Fig. 3a). In the UV range, the absorption of the materials tends to decrease when rising the annealing temperature (increment of crystal size). However, there were no remarkable variations in the absorption in
Fig. 1. XRD patterns of NdFeO3 formed at 700, 800 and 900 °С for 1h
Table 1. Structural characteristics of crystalline NdFeO3 nanoparticles annealed at 700, 800 and 900 °C for 1 h
NdFeO3 I, (a.u.) d, (A) D, (nm) Lattice constants, (A) V, A3
a b c
700 °C 120.29 2.75320 24.41 5.4417 5.6747 7.7727 240.02
800 °C 157.82 2.75322 25.37 5.4522 5.6827 7.7967 241.57
900 °C 269.33 2.75210 29.13 5.4573 5.6963 7.8154 242.95
the visible region for NdFeO3 nanomaterials with different annealing temperature, thus showing the stability of the absorption of the materials at the wave length of l ~ 750 nm. This can be originated from the minor amount of NdFeO3 hexagonal phase (h-NdFeO3) which has very indistinguishable PXRD peaks from those of orthorhombic phase (o-NdFeO3). The increase in the absorption of the hexagonal phase in the visible region was also reported previously for the materials containing the o-YbFeO3/h-YbFeO3 mixture [26]. The existence of o-NdFeO3 and h-NdFeO3 in the samples is in good consistence with the band gap values (Eg, eV) showing in Fig. 3b. The band gap of NdFeO3 nanomaterials varied from 2.2 eV to 2.5 eV (Table 2), remarkably lower than that of NdFeO3 orthoferrite in earlier work [26] with Eg = 4.3 eV and HoFeO3 with Eg = 3.39 eV) [11] prepared by solid-state reaction method. The Eg value of NdFeO3 nanomaterials in this work is comparable with HoFeO3 orthoferrite (Eg = 2.1-2.6 eV) in our previous study [22]. This low band gap of NdFeO3 nanomaterials is
Fig. 2. TEM image of the NdFeO3 nanoparticles annealed at 800 °C for 1 h
favorable for the application as photocatalysts to decompose toxic organic substances for environmental remediation [6-7, 21, 27].
From the M-H curves at room temperature (300 K) of the YFeO3 samples annealed at 700, 800 and 900 °C, saturation magnetization
Fig. 3. (A) Room-temperature optical absorbance spectrum of the NdFeO3 samples; (B) Tauc plot of (Ahv)2 as a function of photon energy for NdFeO3 nanoparticles annealed at 700, 800 and 900 °C for 1 h
Table 2. Optical and magnetic characteristics of NdFeO3 nanoparticles annealed at 700, 800 and 900 °C for 1 h
Samples Eg, (eV) H,, (Oe) Mr, emu-g-1 Ms, emu-g-1
NdFeO3, 700 °C 2.2130-2.4729 1620.66 7.7-10-2 0.81
NdFeO3, 800 °C 2.2130-2.4147 1453.30 7.5-10-2 1.01
NdFeO3, 900 °C 2.2130-2.3417 590.17 4.9-10-2 1.47
(Ms) continued increasing in the magnetic field H = ± 20000 Oe (the saturation was not reached). When the annealing temperature increased, the coercivity (Hc, Oe) and remanent magnetization (Mr, emu-g-1) decreased, while he saturation magnetization (Ms, emu-g-1) increased (Table 2). As the annealing temperature rose, the crystallinity of the materials also increased, the crystals became more stable, and thus the crystal anisotropy decrease, resulting in a drop in the value of Mr and Hc and an increment in Ms [28-29]. With a high coercivity (Hc >> 100 Oe), the obtained NdFeO3 orthoferrite nanomaterials can be classified as hard magnetic materials that can be applied for the manufacture of permanent magnet or magnetic tape.
4. Conclusions
NdFeO3 orthoferrite nanomaterials were successfully synthesized by simple co-precipitation method via the hydrolysis of neodymium (III) and iron (III) cations in boiling water. Single-phase NdFeO3 can be obtained after annealing the precursor at 700, 800 or 900 °C for 1h, having the crystal size of 25-30 nm, particle size of 20-40 nm and lattice cell volume of 240243 Â3. The synthesized NdFeO3 nanomaterials exhibited low band gap value (2.2-2.5 eV), and hard magnetic properties with high coercivity (Hc >> 100 Oe), thus have great potential in photocatalysis for the decomposition of toxic organic waste and can be recovered easily by rare-earth magnetics.
Contribution of the authors
The authors contributed equally to this article.
Conflict of interests
The authors maintain that they have no conflict of interest to be described in this communication.
Fig. 4. Room-temperature magnetic hysteresis loops of as-prepared NdFeO3 nanoparticles annealed at 700, 800 and 900 °C for 1h
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Information about the authors
Pham Thi Hong Duyen, Master in Chemistry, Lecturer of Institute of Applied Technology, Thu Dau Mot University, Binh Duong Province, Vietnam; e-mail: duyenpth@tdmu.edu.vn. ORCID iD: https:// orcid.org/0000-0002-7350-0634
Anh Tien Nguyen, PhD in Chemistry, Chief of Inorganic Chemistry Department, Ho Chi Minh City University of Education, Vietnam; e-mail: tienna@ hcmue.edu.vn. ORCID iD: https://orcid.org/0000-0002-4396-0349
Received September8,2021; approved after reviewing October 10,2021; accepted November 15,2021; published online December 25, 2021.
