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Sol-gel synthesis and the investigation of the properties of nanocrystalline holmium orthoferrite
A. T. Nguyen1, H. L. T. Tran1, Ph. U. T. Nguyen1, I. Ya. Mittova2, V. O. Mittova3, E. L. Viryutina2, V. H. Nguyen4, X. V. Bui5, T. L. Nguyen6,7
1Ho Chi Minh City University of Education, Ho Chi Minh City 700000, Vietnam 2 Voronezh State University, Universitetskaya pl. 1, Voronezh, 394018, Russia 3Burdenko Voronezh State Medical University, Voronezh, 394036, Russia 4Dong Thap University, Cao Lanh City 81000, Vietnam 5Sai Gon University, Ho Chi Minh City, 700000, Vietnam 6Institute of Fundamental and Applied Sciences, Duy Tan University, Ho Chi Minh City, 700000, Vietnam 7Faculty of Environmental and Chemical Engineering, Duy Tan University, Da Nang, 550000, Vietnam
tienna@hcmue.edu.vn, tran.hongle86@gmail.com, nguyenphuonguyen0110@gmail.com, imittova@mail.ru, vmittova@mail.ru, viryutina.helena@yandex.ru, nguyenvanhung@dthu.edu.vn, buixuanvuongsgu@gmail.com, nguyentuanloi@duytan.edu.vn
DOI 10.17586/2220-8054-2020-11-6-698-704
Holmium orthoferrite nanocrystals (HoFeO3) were synthesized from an aqueous solution by the sol-gel method, using polyvinyl alcohol as a stabilizer and annealing at temperatures of 650, 750, and 850 °C for an hour. According to the results of the performed analyses, it was found that with an increase in the annealing temperature, the average size of HoFeO3 crystallites increases from 24 to 30 nm. The magnetic characteristics of the samples were measured and it was shown that holmium orthoferrite is a paramagnet with a low coercive force. The band gap of nanocrystalline holmium ferrite is determined.
Keywords: nanoparticles, holmium orthoferrite, sol-gel technique, magnetic properties, optical properties. Received: 28 August 2020 Revised: 25 September 2020 Final revision: 20 October 2020
1. Introduction
One of the promising areas of materials science is the creation of effective magnetoelectric ferrites using various synthesis methods. Therefore, recently, orthoferrites of rare-earth metals, especially such a promising and still very poorly studied material as holmium ferrite with a perovskite structure were of interest. Nanocrystalline HoFeO3 is a multiferroic with a potentially unusual combination of electrical, magnetic, and optical properties [1-4]. AFeO3 samples are interesting due to their magnetic characteristics and application prospects. For example, they can be compatible with biological materials [5], their nanoparticles can be used as small probes [6-9], which would allow registering the cellular processes without affecting their course. In addition, particles of the nanometer size range are used to increase the density of magnetic recording of information [10-12], production of the transformer coils and other electrical devices with high efficiency [10,13,14].
Some orthoferrites are widely used in microwave devices due to their low coercive force (Hc), remnantmagnetiza-tion (Mr) and high saturation magnetization (MS), excellent mechanical and chemical stability, rectangular hysteresis loop, etc. [12,15,16].
For the synthesis of orthoferrites,the sol-gel method, which allows production of nanopowders with a narrow particle size distribution at relatively low temperatures, is especially important [15,18]. The presented method allows production of highly dispersed powders, fibers or thin films from solutions at temperatures lower than in the case of traditional solid-phase systems [19-24]. Such materials can be imparted with completely new functional characteristics, completely different from the characteristics of conventional materials by controlling the composition, size, and shape of nanocrystals [14,25].
One of the promising methods for producing orthoferrites, which allows improving the above parameters, is the solution combustion method. This method can lead to the synthesis of ferrites with small particle and grain sizes, high density and conversion rates, excellent electromagnetic parameters and a homogeneous microstructure [3,26-30].
Previously, the features of the formation of orthorhombic and hexagonal holmium orthoferrite during heat treatment (625 - 725 °C for 8 hours) of the products of glycine-nitrate combustion were studied [3]. The photocatalytic activity of orthorhombic HoFeO3 nanocrystals was studied in the process of photoinduced decomposition of methyl
orange in an aqueous solution under irradiation with visible light. Compared to this method, the sol-gel synthesis is simpler and therefore it is often more preferable. In prior research for the synthesis of holmium ferrite from a solution, absolute ethanol was used as the solvent [31]. However, for the production of a sufficiently large number of nanocrystals in large laboratories or research institutes, synthesis from an aqueous solution is more preferable for the following reasons. 1. Profitability. 2. Safety. There is no danger of ignition of vapors. 3. Possibility of changing the characteristics of absolute ethanol under the influence of the external environment.
Analysis of the literature data showed the feasibility of the synthesis of holmium ferrite by the sol-gel method. Based on these data, the goal of this study was the synthesis of HoFeO3 nanocrystals from an aqueous solution using the sol-gel method with the participation of PVA, to characterize them, to determine their magnetic characteristics and the band gap of the obtained nanocrystals, to compare the achieved results with results of other synthesis methods and properties of analogue materials.
2. Experimental
The starting materials for the synthesis of the target object were the following reagents: iron (III) nitrate nonahydrate Fe(NO3)3 • 9H2O, holmium nitrate pentahydrate Ho(NO3)3 • 5H2O, aqueous ammonia solution NH3H2O (all -"chemically pure"), PVA - polyvinyl alcohol [-CH2-CH(OH)-]n (GOST 10779-78), acting as a stabilizer-PVA, and distilled water.
Nanocrystalline holmium ferrite was synthesized from an equimolar mixture of holmium (III) and iron (III) nitrates of chemically pure grade in the presence of polyvinyl alcohol (56672 g/mol, n = 1288) in an aqueous solution according to the following procedure.
The mixture of 0.05 mol/L Fe(NO3)3 and Ho(NO3)3 (30 ml) was added to 70 ml of boiling distilled water with stirring on a magnetic stirrer. After the addition of salts, magnetic stirring was continued for another 10 min at a temperature above 90 °C. Then, to 200 ml of a boiling solution containing polyvinyl alcohol, 100 ml of the resulting mixture was slowly added with stirring; the ratio of polyvinyl alcohol - sum of metal ions was 1: 3 by weight [32,33]. Over time, the resulting system became concentrated due to water evaporation and stirring was continued with a glass stirring rod until a yellow-brown powder formed.
Thermogravimetric analysis of the powders was carried out using a TGA-DSC thermal analyzer, LabsysEvo 1600 °C (dry air, high purity, 99.99 %; 10 deg/min). The phase composition of the samples was determined by X-ray phase analysis (XRD, D8-Advance diffractometer) with CuKa radiation. The obtained diffraction patterns were analyzed using the JCPDS database [34]. Parameters a, b, c and crystal cell volume V were determined from the raw file data using the X'pert High Score Plus 2.2b program.
The size of holmium ferrite crystallites according to X-ray diffraction data was determined based on the analysis of the broadening of three maximum lines using the Scherrer formula [35].
The main method for controlling the size and shape of particles was electron microscopy: high-voltage transmission (TEM; JEM-1400) and scanning microscopy (SEM, S-4800).
The elemental composition of the product was monitored by local X-ray spectral microscopy (EDX, Horiba H-7593).
For measurement of the magnetic properties (specific magnetisation and coercive force, excess magnetisation), a VSM Microsene EV11 magnetometer with a vibrating sample was used.
3. Results and discussions
A comprehensive thermal analysis of a holmium ferrite sample obtained by the sol-gel method in the presence of polyvinyl alcohol (Fig. 1a) showed that the weight loss of the sample was 60.47 wt%, which is explained by the evaporation of water and the decomposition of organometallic compounds between Ho3+, Fe3+ cations and polyvinyl alcohol, as well as the decomposition of nitrates. A similar situation was observed for lanthanum orthoferrite in the study [20]. A fast and regular weight loss was observed in the range from 50 to ~ 400 °C, and at a higher temperature the sample weight decreased more slowly (about 5.6 %). The processes of decomposition-heating of organometallic compounds under the action of atmospheric oxygen and oxygen formed during the decomposition of nitrates, with the formation of holmium (III) and iron (III) oxides, are accompanied by a number of exothermic effects at 162.21, 216.27, 339.52, 581.69 and 652.36 °C; this can be used for the production of HoFeO3 nanoparticles by the method of gel combustion as described, for example, in studies [20,32,33]. The endothermic effect at 90.82 °C was due to the evaporation of water contained in the sample due to its storage in air.
XRD results show that holmium ferrite samples (Fig. 2) after annealing at 650, 750, and 850 °C for 60 min are single-phase products, all peaks correspond to the reference diffractogram of HoFeO3 with an orthorhombic structure (map number 046-0115) [34]. With an increase in the annealing temperature from 650 to 750 °C, the intensity of
200 loo 600 soo mo t 2 3 4 5 & 7 s 9
Simple Temperature, ^ Energy, KeV
Fig. 1. TGA/DSC curves of the powders prepared by sol-gel technique using PVA (a) and Energy-Dispersive X-ray spectroscopy (EDX) of HoFeO3 nanoparticles annealed at 750 ° C for 1 h (b)
crystallization of holmium ferrite samples increases, and after annealing the samples in the range 750 - 850 °C, it did not change. According to the results of local X-ray spectral microscopy, the composition of HoFeO3 after annealing at 750 °C for 1 h consisted of only three elements - Ho, Fe, and O, i.e. impurity components were not revealed (Fig. 1b). The atomic ratio Ho:Fe = 1:1.01, which, within the within the measurement accuracy corresponds to their specified nominal composition.
The broadening of X-ray diffraction lines was used to determine the average size of crystallites (regions of coherent scattering) by the Scherrer formula [35]; the results are presented in Table 1. Based on these calculations, we can conclude that the crystallite size does not exceed 30 nm for HoFeO3. The calculation of the unit cell parameters from the diffractometry data showed that an increase in the annealing temperature led to a slight increase in the unit cell volume (Table 1), which was also observed in studies [36,37]. As shown in the study [36], a reliable estimate of the crystallite size from the broadening of diffraction peaks is possible only in combination with additional structural data, for example, with the results of electron microscopy.
TABLE 1. Unit cell parameters and average size of HoFeO3 crystals synthesized from an aqueous solution in the presence of PVA after annealing at different temperatures for 60 min
t, °C d, nm a, A b,A c,A V, A3
650 24 5.2819 5.5801 7.6151 224.444
750 28 5.2824 5.5846 7.6085 224.451
850 30 5.2825 5.5785 7.6239 224.664
SEM, TEM images, and a histogram of the particle size distribution of HoFeO3 nanopowders synthesized by the sol-gel method from an aqueous solution in the presence of PVA after annealing at 750 °C for 60 min are shown in Fig. 3. SEM and TEM images showed that the holmium ferrite particles have different shapes: approximately round with a weakly expressed faceting and oval.The diameter of most crystallites (about 80 % of the number of particles) of the presented orthoferrite was in the range of 31 - 40 nm (TEM). In addition, some particles exhibited a shape characteristic of agglomerates, which complicated accurate determination of the size of crystallites and led to a wide distribution of nanoparticles by size.
The process of formation of agglomerates can be caused by the intergrowth of crystallites, including oriented intergrowth, in the process of nucleation and growth of nuclei, as was shown, for example, in studies [38-40] as well as the sintering of nanoparticles during annealing.
Differences in the values of the average diameter according to the Scherrer formula and according to the SEM and TEM data were due to the peculiarities of the methods: the first method allows the determination of the average crystal size in the entire sample, and electron microscopy provides information on a small sample of particles, the dispersed composition of which depends on the sample preparation procedure [42]. In addition, it is not always possible to distinguish between a crystallite and a particle consisting of intergrown crystallites from a micrograph.
Absorption spectrum of HoFeO3 nanoparticles after annealing at 750 °C for 1 h in UV light showed strong absorption in the region of ultraviolet and visible light 300 - 600 nm) (Fig. 4a). This is interesting since HoFeO3
FIG. 2. XRD patterns of HoFeO3 nanopowders annealed at 650, 750, and 850 °C for 1 h
Fig. 3. SEM (a), TEM (b) images and particle size distribution histogram of HoFeO3 powders annealed at 750 °C for 1 h
can be used as a new visible light photocatalyst. Results of determining the photocatalytic activity of the synthesized HoFeÜ3 nanocrystals are shown in Fig. 4a. The energy of direct transitions for the band gap was determined by fitting the absorption data to the direct transition, and is presented in the study [36]. As a consequence, the band gap of HoFeÜ3 nanoparticles is ~ 1.80 eV (Fig. 4b). Such a small band gap is interesting for the potential application of HoFeÜ3 in photocatalysis, sensor and electrode materials in solid oxide fuel cells.
Fig. 4. (a) Room temperature optical absorbance spectrum of the HoFeO3 sample annealed at 750 °C, (b) Plot of (Ahv)2 as a function of photon energy for HoFeO3 nanoparticles
Results of determining the field dependences of the magnetization of a holmium ferrite sample annealed at 750 ° C, measured at 300 K in a field of 5000 Oe, are presented in Fig. 5a. Nanoparticles HoFeO3, obtained by the sol-gel method from an aqueous solution in the presence of PVA, are characterised at the selected annealing temperature by low values of remnantmagnetization (Mr = 0.0044 emu/g) and coercive force (Hc = 25.14 Oe), with high value of the specific magnetization (Ms = 0.73 emu/g) and a narrow hysteresis loop (Fig. 5b) and they did not reach magnetic saturation in a field of 5000 Oe. Thus, the synthesized object is paramagnetic.
Magnetic Field, Oe Magnetic Field, Oe
Fig. 5. MH curves at ±5 kOe measured at RT of the HoFeO3 sample annealed at 750 °C for 1 h
A comparison of the magnetic characteristics of holmium ferrite nanocrystals synthesized in this study from an aqueous solution using PVA is presented in Table 2. As can be seen from the Table 2, these characteristics are not
significantly different from characteristics of the samples synthesised in absolute ethanol [31] and strongly depend on the synthesis method [1,42]. Interestingly, the synthesized nanocrystalline HoFeO3 characterized by lower values of Hc, but higher Ms compared with nanoparticles of orthoferrites of other rare earth elements such as YFeO3, NdFeO3 obtained by coprecipitation [20,43], and LaFeO3 synthesized by the ceramic method [44].
TABLE 2. Magnetic characteristics of HoFeO3 nanoparticles in this study and from the literature as a comparison
Objects Coercive force (Hc), Oe Remnant magnetization (Mr ), emu/g Saturation magnetization (Ms), emu/g
HoFeO3 in this study 25.14 4.410-3 0.73
HoFeO3 [31] 8.19 ^ 22.70 1.310-3 ^ 4.310-3 0.71 ^ 0.79
HoFeO3 [1] 2959 40.8 10-1 2.55
HoFeO3 [42] 461.13 6.0510-2 —
YFeO3 [20] 53.36 0.1910-3 0.39
NdFeO3 [43] 136.76 68.010-2 0.80
LaFeO3 [44] 1217.6 5.43 10-4 6.4910-3
4. Conclusion
Based on the analysis of the data obtained, it can be concluded that the proposed synthesis procedure leads to the formation of a single-phase nanocrystalline orthoferrite HoFeO3 with an average crystallite size of about 30 nm. Changing the solvent from absolute ethanol to water with the addition of PVA did not adversely affect the properties of the final product, but it is preferable due to the higher cost effectiveness, safety, and stability of the solvent properties. Synthesized HoFeO3 nanopowders were characterized by a low band gap, demonstrating the properties of a paramagnetic material, therefore, it is potentially possible to use them not only in photocatalysis, but also as magnetic materials.
Conflict of interests
The authors maintain that they have no conflict of interest with respect to this communication. Acknowledgements
Nguyen Anh Tien is grateful for the financial support of Ho Chi Minh City University of Education, Ho Chi Minh City, Vietnam, through Grant No. CS.2020.19.21.
References
[1] Habib Z., Majid K., et al. Influence of Ni subsmitution at B-site for Fe3+ ions on morphological, optical, and magnetic properties of HoFeO3 ceramics. Applied Physics A. Materials Science & Processing, 2016, 122 (5), P. 550-557.
[2] Shao M., Cao Sh., et al. Single crystal growth, magnetic properties and Schottky anomaly of HoFeO3 orthoferrite. Journal of Crystal Growth, 2011, 318 (1), P. 947-950.
[3] Kondrashkova I.S., Martinson K.D., Zakharova N.V., Popkov V.I. Synthesis of nanocrystalline HoFeO3photocatalyst via heat treatment of products of glycine-nitrate combustion. Russian Journal of General Chemistry, 2018, 88 (12), P. 2465-2471.
[4] Martinson K.D., Kondrashkova I.S., et al. Magnetically recoverable catalyst based on porous nanocrystalline HoFeO3 for processes of n-hexane conversion. Advanced Powder Technology, 2020, 31 (1), P. 402-408.
[5] Mushtaq M.W., Imran M., et al. Synthesis, structural and biological studies of cobalt ferrite nanoparticles. Bulgarian Chemical Communications, 2016, 48 (3), P. 565-570.
[6] Nikiforov V.N., Filinova E.Yu. Biomedical applications of the magnetic nanoparticles. In book: Magnetic Nanoparticles, Wiley-VCH Verlag GmbH & CO. KGaA, Weinheim, 2009, 10, P. 393-455.
[7] Gu H., Xu K., Xu C., Xu B. Biofunctional magnetic nanoparticles for protein separation and pathogen detection. Chemical Communications, 2006, 37 (9), P. 941-949.
[8] Albadi Y. Popkov V.I. Dual-modal contrast agent for magnetic resonance imaging based on gadolinium orthoferrite nanoparticles: synthesis, structure and application prospects. Medicine: theory and practice, 2019, 4 (S), P. 35-36.
[9] Albadi Y., Martinson K.D., et al. Synthesis of GdFeO3 nanoparticles via low-temperature reverse co-precipitation: the effect of strong agglomeration on the magnetic behavior. Nanosystems: Physics, Chemistry, Mathematics, 2020, 11 (2), P. 252-259.
[10] Zhou Zh., Guo L., et al. Hydrothermal synthesis and magnetic properties of multiferroic rare-earth orthoferrites, Journal of Alloys and Compounds, 2014, 583, P. 21-31.
[11] Park T., Papaefthymiou G.C., et al. Size-dependent magnetic properties of single-crystalline multiferroic BiFeO3 nanoparticles. Nano Letters, 2007, 7 (3), P. 766-772.
[12] LomanovaN.A., Tomkovich M.V., et al. Magnetic properties of Bii_xCaxFeO3_^ nanocrystals. Physics of the Solid State, 2019, 61, P. 25352541.
[13] Martinson K.D., Ivanov V.A., et al. Facile combustion synthesis of TbFeO3 nanocrystals with hexagonal and orthorhombic structure. Nanosys-tems: Physics, Chemistry, Mathematics, 2019,10 (6), P. 694-700.
[14] Kovalenko A.N., Tugova E.A. Thermodynamics and kinetics of non-autonomous phases formation in nanostructured materials with variable functional properties. Nanosystems: Physics, Chemistry, Mathematics, 2018, 9 (5), P. 641-662.
[15] Popkov V.I., Almjasheva O.V., et al. Magnetic properties of YFeO3 nanocrystals obtained by different soft-chemical methods. Journal of Materials Science: Materials in Electronics, 2017, 28 (10), P. 7163-7170.
[16] Lomanova N.A., Tomkovich M.V., et al. Thermal and magnetic behavior of BiFeO3 nanoparticles prepared by glycine-nitrate combustion. Journal of Nanoparticle Research, 2018, 20 (2).
[17] Dmitriev A.V., Vladimirova E.V., et al. Synthesis of hollow spheres of BiFeO3 from nitrate solutions with tartaric acid: Morphology and magnetic properties. Journal of Alloys and Compounds, 2019, 77 (10), P. 586-592.
[18] TominaE.V., Kurkin N.A., Mal'tsev S.A. Microwave synthesis of yttrium orthoferrite doped with nickel. Condensed Matter and Interphases, 2019, 21 (2), P. 306-312.
[19] Almjasheva O.V., Krasilin A.A., Gusarov V.V. Formation mechanism of core-shell nanocrystals obtained via dehydration of coprecipitated hydroxides at hydrothermal conditions. Nanosystems: Physics, Chemistry, Mathematics, 2018,9 (4), P. 568-572.
[20] Nguyen T.A., Almjasheva O.V., et al. Synthesis and magnetic properties of YFeO3 nanocrystals. Inorganic Materials, 2009, 45 (11), P. 13041308.
[21] Popkov V.I., Almyasheva O.V., Schmidt M.P., Gusarov V.V. Formation mechanism of nanocrystalline yttrium orthoferrite under heat treatment of the coprecipitated hydroxides. Russian Journal of General Chemistry, 2015, 85 (6), P. 1370-1375.
[22] Nguyen T.A., Mittova I.Ya., et al. Sol-gel preparation and magnetic properties of nanocrystalline lanthanum ferrite. Russian Journal of General Chemistry, 2014, 84 (7), P. 1261-1264.
[23] Proskurina O.V., Abiev R.S., et al. Formation of nanocrystalline BiFeO3 during heat treatment of hydroxides co-precipitated in an impinging-jets microreactor. Chemical Engineering and Processing — Process Intensification, 2019, 143, 107598.
[24] Proskurina O.V., Nogovitsin I.V., et al. Formation of BiFeO3 Nanoparticles Using Impinging Jets Microreactor. Russian Journal of General Chemistry, 2018, 88 (10), P. 2139-2143.
[25] Gusarov V.V., Almjasheva O.V. Nanomaterials: properties and promising applications. Scientific world publishing house, Moscow, 2014, P. 378-403.
[26] Martinson K.D., Kondrashkova I.S., Popkov V.I. Synthesis of EuFeO3 nanocrystals by glycine-nitrate combustion method. Russian Journal of Applied Chemistry, 2017, 90 (8), P. 1214-1218.
[27] Bachina A., Ivanov V.A., Popkov V.I. Peculiarities of LaFeO3 nanocrystals formation via glycine-nitrate. Nanosystems: Physics, Chemistry, Mathematics, 2017, 8 (5), P. 647-653.
[28] Popkov V.I., Almjasheva O.V., et al. Crystallization behaviour and morphological features of YFeO3 nanocrystallites obtained by glycine-nitrate combustion. Nanosystems: Physics, Chemistry, Mathematics, 2015, 6 (6), P. 866-874.
[29] Popkov V.I., Almjasheva O.V., et al. Effect of spatial constraints on the phase evolution of YFeO3-based nanopowders under heat treatment of glycine-nitrate combustion products. Ceramics International, 2018, 44 (17), P. 20906-20912.
[30] Lomanova N.A., Tomkovich M.V., Sokolov V.V., Gusarov V.V. Special Features of Formation of Nanocrystalline BiFeO3 via the Glycine-Nitrate Combustion Method. Russian Journal of General Chemistry, 2016, 86 (10), P. 2256-2262.
[31] Nguyen T.A., Nguyen T.Tr.L., et al. Optical and magnetic properties of HoFeO3 nanocrystals prepared by a simple co-precipitation method using ethanol. Journal of Alloys and Compounds, 2020, 834, P. 155098-155103.
[32] Jiang L., Liu W., et al. Low-temperature combustion synthesis of nanocrystalline powders via a sol-gel method using glycin. Ceramics International, 2012, 38 (5), P. 3667-3672.
[33] Luu M.D., Dao N.N., et al. Sol-gel synthesis of LaFeO3 nanomaterials with perovskite structure. Vietnam Journal of Chemistry, 2014, 52 (1), P. 130-134.
[34] JCPDS PCPDFWIN: A Windows Retrieval/Display Program for Accessing the ICDD PDF-2 File, ICDD, 1997.
[35] Patterson A.L. The Scherer formula for X-ray particle size determination. Physics Review, 1939, 56 (10), P. 978-982.
[36] Nguyen T.A., Chau H.D., et al. Structural and magnetic properties of YFe1-xCoxO3 (0.1 < x < 0.5) perovskite nanomaterials synthesized by co-precipitation method. Nanosystems: Physics, Chemistry, Mathematics, 2018, 9 (3), P. 424-429.
[37] Nguyen T.A., Nguyen V.Y., et al. Synthesis and magnetic properties of PrFeO3 nanopowders by the co-precipitation method using ethanol. Nanosystems: Physics, Chemistry, Mathematics, 2020, 11 (4), P. 468-473.
[38] Ivanov V.K., Fedorov P.P., Baranchikov A.Y., Osiko V.V. Oriented aggregation of particles: 100 years of investigations of non-classical crystal growth. Chemical Reviews, 2014, 83 (12), P. 1204-1222.
[39] Popkov V.I., Tugova E.A., Bachina A.K., Almyasheva O.V. The formation of nanocrystalline orthoferrites of rare-earth elements XFeO3 (X = Y, La, Gd) via heat treatment of coprecipitated hydroxides. Journal of General Chemistry, 2017, 87 (11), P. 2516-2524.
[40] Almjasheva O.V., Gusarov V.V. Metastable Clusters and Aggregative Nucleation Mechanism. Nanosystems: Physics, Chemistry, Mathematics, 2014, 5 (3), P. 405-416.
[41] Almjasheva O.V., Fedorov B.A., Smirnov A.V., Gusarov V.V. Size, morphology and structure of the particles of zirconia nanopowder obtained under hydrothermal conditions. Nanosystems: Physics, Chemistry, Mathematics, 2010, 1 (1), P. 26-37.
[42] Bhat M., Kaur B., et al. Swift heavy ion irradiation effects on structural and magnetic characteristics of RFeO3 (R = Er, Ho and Y) crystals. Nuclear Instruments and Methods in Physics Research B, 2006, 243, P. 134-142.
[43] Nguyen T.A., Pham V., et al. Simple synthesis of NdFeO3 nanoparticles by the so-precipitation method based on a study of thermal behaviors of Fe (III) and Nd (III) hydroxides. Crystals, 2020, 10 (3), P. 219-227.
[44] Sasikala C., Durairaj N., et al. Transition metal titanium (Ti) doped LaFeO3 nanoparticles for enhanced optical structure and magnetic properties. Journal of Alloys and Compounds, 2017, 712, P. 870-877.
