The influence of Ca substitution on LaFeO 3 nanoparticles in terms of structural and magnetic properties

Abstract

Background:

The nanocrystalline structure of La_1-xCa_xFeO₃ was prepared by a sol–gel method involving an auto-combustion process. The incorporation of rare-earths in LaFeO₃ induces strain in magnetic properties, especially in terms of the following parameters: replacement amount, oxygen partial pressure, and calcination temperature.

Methods:

To determine the effects of the amount of Ca²⁺ ion doping agent and the calcination temperature on the microstructure, particle morphology, and magnetic properties of LaFeO₃ crystal, we performed the following respective analytical methods: X-ray powder diffraction, Fourier-transform infrared (FT-IR) spectroscopy, scanning electron microscopy, and vibrating sample magnetometer tests.

Results:

The orthorhombic structure of LaFeO₃ perovskite did not change even when it was doped with Ca²⁺ ions, and its space group continued to be Pnma (No.62). FT-IR spectra confirmed that the main band appearing at 568 cm⁻¹ is due to the antisymmetric stretching vibration of Fe–O–Fe bonds in FeO₆. The introduction of Ca inhibits the growth of grains but the morphology of particles is improved. With an increasing concentration of Ca²⁺ ions, magnetic behavior of the samples also witnessed an increasing trend in a proportionate manner. With an increase in calcination temperature, the enclosed area of the magnetic hysteresis curve of the sample reduced remarkably.

Conclusions:

The growth of nanoparticles can be restrained with an increase of Ca content that is used as doping agent. The magnetic behavior of La_1-xCa_xFeO₃ tilts towards G-type antiferromagnetism; the magnetic orientation is achieved from the super exchange interaction of Fe³⁺ ions with oxygen ions.

Keywords

Ca substitution sol–gel preparation perovskite structure magnetic properties

Introduction

Perovskite oxide is one of the new functional materials which have great potential in the future.¹ LaFeO₃ is a type of metal oxide with the perovskite structure (ABO₃). When single phase LaFeO₃ and single- or double-doped A/B chemically interact with each other during sol– gel preparation, the resultant crystal structure usually has an orthogonal perovskite structure, with the crystal’s symmetry being the space group Pnma. In this case, the lattice parameters change significantly because different elements are used as dopants during crystal preparation: these variations in lattice parameters have a direct impact on the local environment of Fe ions.^2,3 When LaFeO₃ is modified with A or B site elements that acts as substituents, the general formula of the resultant chemical compounds are La_1-xA_xFeO₃ (A = Ca, Sr, Ba, Ce or other rare earth elements), LaFe_1-xB_xO₃ (B = Mn, Co, Cr, or other transition metals elements), respectively. Because different A- or B-site elements replace LaFeO₃ material, the performance characteristics of the resultant compounds also change, especially in terms of the following parameters: replacement amount, oxygen partial pressure, and calcination temperature. Pecchi et al. conducted a study on the catalytic activity of LaFeO₃ doped with Ca.² They used the citrate method and co-precipitation method to determine the catalytic activity of the aforementioned LaFeO₃ material. Furthermore, Kong and Shen used the co-precipitation method to determine gas sensitivity of La_1-xCa_xFeO₃.³ In addition, Ahmed and El-Dek used the conventional solid phase reaction method to determine the magnetic properties of Ca-doped La_1-xCa_xFeO₃ material.⁴ When the Ca²⁺ concentration was increased steadily in the crystal, the number of Fe⁴⁺ ions increased steadily but the number of Fe³⁺ ions decreased simultaneously. Owing to these changes in the number of Fe³⁺/Fe⁴⁺ ions in the environment, the magnetic susceptibility of the Ca-doped La_1-xCa_xFeO₃ crystal increased markedly.¹ Abdel-Khalek and Mohamed synthesized La_1-xCa_xFeO₃ by the method of co-precipitation.⁵ Then they studied its structure and magnetic properties extensively. Based on the results of magnetic measurements, they inferred that the sample has weak ferromagnetic properties and spin (antiferromagnetic) ordering. When the concentration of Ca²⁺ dopants (x ≤ 0.1) is increased continuously in the crystals, there is a corresponding increase in the magnetic parameters of the crystals. The magnetic behavior of crystals may become more pronounced because Fe³⁺ ions are oxidized to Fe⁴⁺ ions, with a steady increase in Ca²⁺ dopants in the crystal environment.¹ The traditional preparation of LaFeO₃ is done by performing the solid state reaction method under a high-temperature environment (ca. 700°C) to ensure that the reaction reaches completion. The result of the reaction was different when the sintering temperature was higher.^6,7 There are also reports describing how wet chemical methods, such as co-precipitation, and other methods were used for preparing LaFeO₃; however, the sintering temperatures are too high in these methods.^8,9 In different preparation methods, raw materials and the sintering temperature play an important role in the ferroelectric, ferromagnetic, morphology, structure, and other properties of the synthesized samples.⁷ Presently, few studies have reported about how low-temperature synthesis of Ca²⁺-doped LaFeO₃ nanoparticles can be performed using the citrate sol–gel method. Moreover, the structure, morphology, and magnetic properties of Ca²⁺-doped LaFeO₃ nanoparticles have been studied to a significantly less extent in research studies. In this paper, we studied the effect of Ca²⁺ substitution La_1-xCa_xFeO₃ ferrite and investigate the influence of Ca²⁺ substitution in magnetic properties and microstructure.

Material and methods

Sample synthesis

In this experiment, the citrate sol–gel method of synthesis was used to prepare La_1-xCa_xFeO₃ (x = 0–0.5) perovskite nanoparticles.¹ The resultant nanoparticles were prepared using different proportions of Ca²⁺ as dopants in the aforementioned nanoparticles. In addition, the effect of varying calcination temperature of the reaction was quantified by determining the structure, morphology, and magnetic properties of as-synthesized samples in the reaction mixture. The starting composition of the principal sample was as follows: La(NO₃)₃·6H₂O, Fe(NO₃)₃·9H₂O, Ca(NO₃)₂·4H₂O, and citric acid. During the synthesis process, citric acid was dissolved in deionized water. To obtain a solution, it was necessary to completely dissolve citric acid in water. Then, a variety of nitrates were dissolved completely in citric acid (solution A) to yield solution B. Thereafter, ammonia was slowly added to solution B to adjust its pH to 7. At this stage, the ammoniacal solution B was transformed into a sol. Then, the resultant sol was placed in a water bath pot and subjected to stirring continuously; the temperature of the water bath was maintained at 60°C. After being kept for about 3 h in the water bath, the sol transforms into a wet gel. At this stage, the stirring of the gel was stopped. The resultant wet gel was aged for about 12 h. Then, it was placed in a blast oven and dried at 130°C for 6 h to yield a xerogel; the accelerant ethanol was added to the dry gel obtained from the spread, and a yellow fluffy powder was obtained subsequently. After polishing the powder, we transferred it into a crucible. Then, the powder was calcined in a muffle furnace, after being calcined at 500°C, 700°C, 800°C for 2 h.

Sample characterization

The integrated technique of thermogravimetric analysis and differential scanning calorimetry (TGA-DSC; SDT Q600, TA Instruments, USA) was performed to analyze the dry gel through thermal decomposition process. In this experiment, X-ray diffraction (XRD; D/max-2500v/pc, Rigaku, Japan) was used to further characterize the structure of the material: the main parameters of the XRD process were as follows: pressure pipe, 40 kV; pipe flow, 20 mA; Cu-K_α target radiation; scanning speed 10°/ min; scanning range 10°–80°(2θ). Furthermore, Fourier-transform infrared (FT-IR) spectrometer analysis (Spectrum Two; Perkin Elmer, USA) was performed to observe functional groups and chemical bonds of the samples, with a spectral resolution of 1 cm⁻¹. Then, IR spectroscopic analysis of the samples was performed in the wavelength range 400–4000 cm⁻¹. Scanning electron microscopy(SEM) analysis (NoVa^TM Nano 430; FEI, USA) was performed to observe the microstructural properties of LaFeO₃ nanomaterial, including particle size, geometrical shape, uniformity, and reunion phenomenon. Vibrating sample magnetometer (VSM) analysis (VSM-100; CCYPCD, China) was performed to observe the magnetic properties. We tested hysteresis loop of samples at room temperature under the following conditions: the maximum magnetic field H = 0.8 T and the highest sensitivity was 5 × 10⁻⁵ emu. With this process, we determined the magnetic parameters of samples, including the saturation magnetization (M_s), remnant magnetization (M_r), and coercive force (H_c) values.

Results and discussion

TGA results

Figure 1 shows that the weight loss of the samples starts from 30°C in the TGA curve. In the differential thermal analysis (DTA) curve, weak endothermic peaks appeared at 47.5°C because of evaporation of water from the wet gel. Furthermore, endothermic peaks appeared at 131.5°C and 169.5°C owing to the expulsion of water that was present hitherto inside the dry gel. For example, adsorption water, water of crystallization, and water vapor generated during the reaction are some types of water molecules entrapped within the dry gel. A sharp exothermic peak appears at 226°C; this peak may correspond to that at about 219°C on the TGA curve, where it primarily represents extensive weight loss caused by the decomposition of organic matter and the combustion of residual organic substances generating CO₂ and N₂ gases. After attaining a temperature of 226°C, the sample does not undergo any significant weight loss. As a result, weak exothermic peaks appear at about 325°C and 420°C in the DTA curve. The temperature 420°C is crystallization temperature of LaFeO₃.^10–12

Figure 1.

TGA and DTA curves of La_0.9Ca_0.1FeO₃ xerogel.

XRD analysis

Figures 2 and 3 display the XRD patterns of La_1-xCa_xFeO₃ (x = 0–0.5). In the presence of the contrast standard JCPDS 37-1493, the orthorhombic structure of LaFeO₃ showed a perovskite structure, and its space group was Pnma.^2,13,14 With an increase in the proportion of Ca substitution in the crystal lattice, the diffraction peaks shifted to 2θ values in a remarkably increasing direction. The shift in diffraction peaks occurred because the ionic radius (0.134 nm) of the Ca²⁺ ion was smaller than the ionic radius (0.136 nm) of the La³⁺ ion. The Ca doping consequently decreased the cell volume of La_1-xCa_xFeO₃, although to slight extent.^15–17 In addition, La³⁺ ion was replaced partially by the lower state Ca²⁺ ion so as to maintain charge neutrality of the entire compound. Subsequently, the perovskite structure either produced an Fe⁴⁺ ion, which is a B-site element having higher valence state, or an oxygen hole.^4,18–20 Because the Fe⁴⁺ ion radius (0.0585 nm) is less than the Fe³⁺ ion radius (0.0645 nm), the cell became still smaller in size. When x = 0.2, the diffraction peaks (141) and (311) appear as a merged peak (141). This phenomenon indicates that the structure of the sample will be distorted when the level of Ca dopants reaches a certain concentration in the reaction mixture. At x = 0.5, the diffraction peak decreased. This indicates that there may be an impurity phase of CaCO₃ in the temperature range 25–35°C.

Figure 2.

XRD diffraction pattern of La_1-xCa_xFeO₃ (x = 0–0.5) without calcination.

Figure 3.

XRD diffraction pattern of La_1-xCa_xFeO₃(x = 0–0.5) through 2 h of calcination at 500°C.

Figure 4 shows the XRD pattern of La_0.6Ca_0.4FeO₃ samples obtained after subjecting them to calcination at different temperatures. It can be seen that all the samples have a single-phase structure, and the shape of the diffraction peak is sharp and well-defined. This indicates that even if calcination temperature is increased steadily, the crystallinity of the crystal continues to be intact. In addition, an impurity phase of CaCO₃ appears in both non-calcined samples and samples calcined at 500°C for 2 h. The appearance of the impurity phase despite calcination indicates that the sample was probably not fully calcined at that temperature.

Figure 4.

XRD diffraction pattern of La_0.6Ca_0.4FeO₃ samples without calcination and with calcination at 500°C or 700°C after 2 h.

Figure 5 illustrates the trends in the average grain size corresponding with the variation in the amount of Ca dopants. The variation in the average grain size was calculated using Jader 5.0 software. Scherrer’s formula was used to do the estimation as follows:

D = \frac{K \cdot γ}{β \cdot \cos θ}

where D is the average grain size, β is full width at half maximum (FWHM), and γ is the wavelength of copper target (0.15405 nm). The Bragg’s diffraction angle is denoted by θ. Based on Figure 5, we infer the following observation: The average grain size of the sample reduces with an increase in the amount of Ca²⁺ dopants. This indicates that that Ca²⁺ ion replaces La³⁺ ion in the crystal lattice and inhibits the growth of particles.

Figure 5.

The average grain size of La_1-xCa_xFeO₃ (x = 0–0.5) sample calcined at 500°C for 2 h.

Infrared analysis

Figure 6 shows the FT-IR spectra of a La_1-xCa_xFeO₃ sample that was calcined at 500°C for 2 h. Using an FT-IR spectrometer with pure KBr as the background, the main band appeared at about 568 cm⁻¹; this band represents the antisymmetric stretching vibration in the Fe–O–Fe bond of FeO₆, a regular octahedron. The main band represents the vibrational stretching of Fe–O–Fe bond in the absorption spectra of samples. According to Abdel-Khalek and Mohamed and Li et al.,^5,21 the aforementioned main band appeared at around 574 cm⁻¹ and 400 cm⁻¹, respectively, in samples of La_1-xCa_xFeO₃. Furthermore, Thirumalairajan et al. found that a small vibration peak appears at about 1058 cm⁻¹;²² this peak was found to be the main vibration band of the CO₃²⁻ functional group. The appearance of this peak in the absorption spectra indicates that the samples might have been exposed to air, and that La carbonate might be present on the surface of LaFeO₃.

Figure 6.

Infrared spectrum of La_0.9Ca_0.1FeO₃ calcined at 500°C for 2 h.

However, the XRD spectra did not detect this chemical species in the sample. Furthermore, a small vibration speak appears at about 1382 cm⁻¹, which indicates the asymmetric stretching vibration of the metal. The appearance of this band at 1382 cm⁻¹ wavelength is in good agreement with the spectra presented in other studies.²³ At around 1627 cm⁻¹, a vibrational band appears in the spectrum; this band is attributed to the asymmetric stretching vibration of carboxyl group. In addition, Thirumalairajan et al. reported the appearance of a vibrational band at about 1627 cm⁻¹.²⁴ A very small absorption band appeared at around 2929 cm⁻¹, which was then attributed to CO₂ species in our sample compound. Moreover, Thirumalairajan et al. reported the appearance of a vibrational band at about 2924 cm⁻¹.²² At about 3428 cm⁻¹, a broad peak appears due to the symmetric and asymmetric stretching vibration of water molecules absorbed from air; these latent water molecules are present in our sample compound. Furthermore, this broad band extends between 3300 cm⁻¹ and 3600 cm⁻¹, manifesting the correlation between the vibrational levels of various kinds of latent water molecules in the sample.^21,25,26

Structures and grain sizes

Figure 7 shows that the dispersion and morphology have not changed much despite the sample being doped with Ca²⁺ ions. With an increase in the concentration of Ca substitution, the particle size becomes smaller because the Ca²⁺ ion replaces the node position of La³⁺ ion. Consequently, the stacking-fault energy increases in the material, thereby increasing the nucleation node and inhibiting the growth of particles. In summary, the doping impact of Ca²⁺ is change on the performance of the sample.¹⁵

Figure 7.

SEM images of La_1-xCa_xFeO₃ (x = 0, 0.2, 0.4) calcined at 700°C.

The statistical data was obtained using particle size distribution analysis software (Mac-View ver.4.0; Mountech Co. Ltd, Tokyo, Japan). From Figure 8, which displays the particle size histogram of La_1-xCa_xFeO₃ (x = 0, 0.2, 0.4), we conclude that the particle size of undoped samples was mainly in the range 28–68.8 nm. However, when the content of Ca dopant was 0.2, the particle size was in the range 25–56.2 nm. Furthermore, when the calcium dopant’s content was 0.4, the particle size was in the range 20–53 nm. These results indicate that the particle size decreases with an increase in the amount of Ca²⁺ dopants. The trend of the average grain size is in good agreement with previous studies, as confirmed by statistical data obtained with Jader 5.0 software and distribution analysis software.^27,28

Figure 8.

Particle size histogram of La_1-xCa_xFeO₃ (x = 0, 0.2, 0.4) calcined at 700°C.

Magnetic property of particles

As shown in Figure 9, the hysteresis loop of La_1-xCa_xFeO₃ (x = 0–0.5) samples is not the same as that representing a sample subjected to calcination. In this case, a La_1-xCa_xFeO₃ sample exhibits a tilting toward G-type antiferromagnetism. The magnetic hysteresis (M–H) of La_1-xCa_xFeO₃ compound originated from Fe³⁺ ion tilting toward antiparallel spin; this kind of change in magnetic orientation is achieved by super exchange interaction of Fe³⁺ ions with oxygen ions.¹ The shape of the hysteresis loop exhibits a weak ferromagnetic behavior, which does not reach the state of saturation. In these conditions, magnetization increases with an increase in the amount of Ca dopants, and the doped crystals exhibit important features of spin antiferromagnetic ordering. In summary, the magnetization level increases in crystals due to a gradual increase in the strength of ferromagnetic interactions and a subsequent decrease in antiferromagnetic interactions in the sample.^4,16–18

Figure 9.

Hysteresis loop of the La_1-xCa_xFeO₃ (x = 0–0.5) samples without calcination.

Figure 10 illustrates the hysteresis loop of La_1-xCa_xFeO₃ (x = 0–0.5) sample compounds subjected to calcination for 2 h at a temperature of 500°C. Because Ca²⁺ ions replace La³⁺ ions in the sample compound, there will be two possible scenarios: when the Ca²⁺ doping amount (x) reaches a certain value, La_1-xCa_xFeO₃ would form two or more phases; with an increase in the value of (x), Fe³⁺ to Fe⁴⁺ transition would progress certainly leading to two phases.⁴ According to the Figure 10, magnetization had has an increasing trend with an increase in Ca²⁺ concentration (x) as doping agent. Thus, magnetic mutation occurs when x = 0.3. The phenomenon is attributed to the generated Fe₃O₄ impurities,¹⁶ and it leads to an enhancement in the magnetic behavior of the sample.

Figure 10.

Hysteresis loop of La_1-xCa_xFeO₃ (x = 0–0.5) calcined at 500°C.

Figure 11 shows the hysteresis loop of La_0.8Ca_0.2FeO₃ samples subjected to calcination at different temperatures. Figure 11 clearly suggests that the enclosed area of the M–H curve of the sample area is reduced with an increase in calcination temperature. When the temperature is increased from room temperature to 500°C, the round solid symbol representing the area of the curve moves down but there is no obvious change in hysteresis loop At this stage, the magnetic area of the curve does not exhibit a significant change with changes in temperature; however, saturation magnetization (M_s) of the sample does change with changes in temperature. When the temperature is increased from 500°C to 800°C, the enclosed area of the M–H curve of the sample exhibits mutation, because the spin ferromagnetic ordering weakens gradually and the sample now tilts towards antiferromagnetic ordering. This change in magnetic ordering of the sample has been attributed to the steady increase in sintering temperature. With an increase in the sintering temperature from 500 to 800°C, the iron oxide content decreases in the sample compound. As a result, the magnetic properties of the sample also change dramatically.¹⁹ In addition, the M–H curve appears horizontal and it seems to have moved from its previous inclination toward vertical direction. This change in direction has been attributed to the ferromagnetic and antiferromagnetic coupling in the sample.

Figure 11.

Hysteresis loop of La_0.8Ca_0.2FeO₃ without calcinations and calcined conditions of 500°C or 800°C for 2 h.

Figure 12 illustrates the variation trend of magnetic parameters with different values of Ca²⁺ doping content (x). The residual magnetization (M_r) and saturation magnetization (M_s) show a tendency to increase with an increase in x values. The coercive force (H_c) exhibits an exactly opposite change trend: with an increase in the x value, there is attenuation in the value of H_c in the sample. Figure 12 also reflects the influence of calcination temperature on the magnetic parameters of the sample; the calcination temperature (T) has the same effect on variation trends of M_r, H_c, and M_s: the values of the aforementioned magnetic parameters decrease as T increases. The coercive force (H_c) of the sample is related to magnetic anisotropy,^13,27,29 indicating that the introduction of Ca²⁺ and high-temperature calcination probably weakens the magnetic anisotropy of the sample, and evidence for this is indicated in experiments using energy-dispersive X-ray spectroscopy or X-ray photoelectron spectroscopy.^24,30,31 As a result, there is a decrease in coercive force (H_c).^32,33

Figure 12.

The diagram depicting the variation trend of magnetic parameters with different values of Ca²⁺ doping content (x) and calcination temperatures.

Conclusion

In this study, we developed an innovative citrate sol–gel method that was easy to implement with precision control.²⁹ With this novel method, we carried out the synthesis of La_1-xCa_xFeO₃ nanoparticles at a low temperature. Furthermore, the structure, morphology, and magnetic properties of the as-synthesized nanoparticles were also studied in this experiment. The XRD spectra illustrated that La_1-xCa_xFeO₃ nanoparticles have an orthorhombic perovskite structure. With an increase in the proportion of Ca substituents as dopants in the sample, the diffraction peaks of La_1-xCa_xFeO₃ crystals moved remarkably in an increasing direction, leading to a sharp change in Bragg’s angle of diffraction (2θ). SEM showed that the growth of nanoparticles can be restrained with an increase of Ca content that is used as doping agent. This is because the particle size decreases with an increase in the content of Ca²⁺ ions as dopants. Furthermore, La_1-xCa_xFeO₃ exhibits weak ferromagnetism. With an increasing concentration of Ca²⁺ ions, the magnetic behavior of the samples also witnessed an increasing trend in a proportionate manner. With an increase in calcination temperature, the enclosed area of the M–H curve of the sample reduced remarkably.

Footnotes

Declaration of conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This work was supported by the National Natural Science Foundation of China (grant numbers 11364004 and 11164002) and by Guangxi Key Laboratory of Nuclear Physics and Nuclear Technology.

References

Mandal

Rakshit

Ray

SK.

Nanostructures of Sr²⁺ doped BiFeO₃ multifunctional ceramics with tunable photoluminescence and magnetic properties. J Phys Condens Matter 2013; 25: 055303.

Pecchi

Reyes

Zamora

et al . Effect of the preparation method on the catalytic activity of La_1-xCa_xFeO₃ perovskite-type oxides. Catal Today 2008; 133–135: 420–427.

Kong

L-B

Shen

Y-S.

Gas-sensing property and mechanism of Ca_xLa_1-xFeO₃ ceramics. Sens Actuators B 1996; 30: 217–221.

Ahmed

El-Dek

SI.

Extraordinary role of Ca²⁺ ions on the magnetization of LaFeO₃ orthoferrite. Mater Sci Eng B 2006;128: 30–33.

Abdel-Khalek

Mohamed

HM.

Synthesis, structural and magnetic properties of La_1-xCa_xFeO₃ prepared by the co-precipitation method. Hyperfine Interact 2013; 222: S57-S67.

Jadhav

Gaikwad

Samuel

et al . A low temperature route to prepare LaFeO₃ and LaCoO₃. Mater Lett 2007; 61: 2030–2032.

Sivakumar

Gedanken

Zhong

et al . Sonochemical synthesis of nanocrystalline LaFeO₃. J Mater Chem 2004; 14: 764–769.

Zhou

Yue

et al . A simple way to prepare nanosized LaFeO₃ powders at room temperature. Ceram Int 2003; 29: 347–349.

Zhou

Yue

et al . Auto-combustion synthesis of nanocrystalline LaFeO₃. Mater Chem Phys 2002; 78: 25–29.

10.

F-T

Liu

R-H

et al . Preparation of Ca-doped LaFeO₃ nanopowders in a reverse microemulsion and their visible light photocatalytic activity. Mater Lett 2010; 64: 223–225.

11.

Wang

Zhu

Zhang

et al . Preparation and characterization of perovskite LaFeO₃ nanocrystals. Mater Lett 2006; 60: 1767–1770.

12.

Shabbir

Qureshi

Saeed

Nano-crystalline LaFeO₃ powders synthesized by the citrate-gel method. Mater Lett 2004; 60: 3706–3709.

13.

Janbutrach

Hunpratub

Swatsitang

Ferromagnetism and optical properties of La_1-xAl_xFeO₃ nanopowders. Nanoscale Res Lett 2014; 9: 1–7.

14.

Gaikwad

Acharya

SA.

Novel perovskite-spinel composite approach to enhance the magnetization of LaFeO₃. RSC Adv 2015; 5: 14366–14373.

15.

Andoulsi

Horchani-Naifer

Férid

Structural and electrical properties of calcium substituted lanthanum ferrite powders. Powder Technol 2012; 230: 183–187.

16.

Benali

Bejar

Dhahri

et al . Magnetic, Raman and Mössbauer properties of double-doping LaFeO₃ perovskite oxides. Mater Chem Phys 2015; 149–150: 467–472.

17.

Kou

Qin

et al . Microstructure and magnetic properties of La_1-xSr_xFeO₃ nanoparticles. Phys Status Solidi A 2002; 191: 255–259.

18.

Liang

Y-Q

N-L

Cheng

Z-H.

Charge-disproportionation-induced magnetic glassy behavior in La_0.5Ca_0.5FeO₃. Phys Rev B 2005; 72: 134416.

19.

Vázquez-Vázquez

Kögerler

López-Quintela

et al . Preparation of LaFeO₃ particles by sol–gel technology. J Mater Res 1998; 13: 451–456.

20.

Cyza

Cieniek

Kopia

Perovskite La_1-xSr_xFeO₃ thin films deposited by laser ablation process. Arch Metall Mater 2016; 61: 1063–1067.

21.

Jing

et al . Photoinduced charge property of nanosized perovskite-type LaFeO₃ and its relationships with photocatalytic activity under visible irradiation. Mater Res Bull 2007; 42: 203–212.

22.

Thirumalairajan

Girija

Ganesh

et al . Novel synthesis of LaFeO₃ nanostructure dendrites a systematic investigation of growth mechanism, properties, and biosensing for highly selective determination of neurotransmitter compounds. Cryst Growth Des 2013; 13: 291–302.

23.

Abazari

Sanati

Perovskite LaFeO₃ nanoparticles synthesized by the reverse microemulsion nanoreactors in the presence of aerosol-OT: morphology, crystal structure, and their optical properties. Superlattices Microstruct 2013; 64: 148–157.

24.

Thirumalairajan

Girija

Ganesh

et al . Controlled synthesis of perovskite LaFeO₃ microsphere composed of nanoparticles via self-assembly process and their associated photocatalytic activity. Chem Eng J 2012; 209: 420–428.

25.

Lebid

Omari

Synthesis and electrochemical properties of LaFeO₃ oxides prepared via sol–gel method. Arabian J Sci Eng 2014; 39: 147–152.

26.

Bhat

Husain

Khan

et al . Effect of Zn doping on structural, magnetic and dielectric properties of LaFeO₃ synthesized through sol–gel auto-combustion process. Mater Res Bull 2013; 48: 4506–4512.

27.

Yang

Lin

et al . Mössbauer spectroscopy, structural and magnetic studies of Zn²⁺ substituted magnesium ferrite nanomaterials prepared by sol–gel method. J Nanomater 2015: 854840.

28.

Jagadeesha Angadi

Anupama

Choudhary

et al . Mechanism of gamma-irradiation induced phase transformations in nanocrystalline Mn_0.5Zn_0.5Fe₂O₄ ceramics. J Solid State Chem 2017; 246: 119–124.

29.

Swatsitang

Karaphun

Phokha

et al . Investigation of structural, morphological, optical, and magnetic properties of Sm-doped LaFeO₃, nanopowders prepared by sol–gel method. J Sol Gel Sci Technol 2017; 81: 483–492.

30.

Liu

et al . XPS study of adsorbed oxygen of nanocrystalline LaFeO₃, materials. J Alloys Compd 1992; 186: 315–319.

31.

Longo

Topuria

Rice

et al . Simultaneous high-speed dual EELS and EDS acquisition at atomic level across the LaFeO₃/SrTiO₃ interface. Microsc Microanal 2014; 20(S3): 128–129.

32.

Kumar

Bhatnagar

AK.

Spontaneous exchange bias effect in superparamagnetic LaFeO₃, nanoparticles. J Sol Gel Sci Technol 2017; 84: 192–197.

33.

Jain

Srivastava

Structural investigation and zero-field-cooled exchange bias in nanocrystalline LaFeO₃. J Supercond Novel Magn 2016; 29: 2089–2097.