- Email: [email protected]
Investigation of structural and electrical properties of NdFeO3 perovskite nanocrystalline
Accepted Manuscript Investigation of structural and electrical properties of NdFeO3 perovskite nanocrystalline
Jada Shanker, G. Narsinga Rao, Kasarapu Venkataramana, D. Suresh Babu
PII: DOI: Reference:
S0375-9601(18)30724-2 https://doi.org/10.1016/j.physleta.2018.07.002 PLA 25203
To appear in:
Physics Letters A
Received date: Revised date: Accepted date:
11 April 2018 21 June 2018 1 July 2018
Please cite this article in press as: J. Shanker et al., Investigation of structural and electrical properties of NdFeO3 perovskite nanocrystalline, Phys. Lett. A (2018), https://doi.org/10.1016/j.physleta.2018.07.002
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 proof before it is published in its final 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.
Highlights • • • • •
Sol-gel auto-combustion process has been employed to prepare NdFeO3 perovskite nanocrystalline compound. Single phase orthorhombic symmetry with Pbnm space group. P-E loop of NdFeO3 nanocrystalline material have shown ferroelctric behaviour. Impedance data indicating the negative temperature coefficient of resistance (NTCR) nature. NdFeO3 material is a potential candidate in ferrolectric and gas sensing device applications.
Investigation of structural and electrical properties of NdFeO3 perovskite nanocrystalline Jada Shanker1,*, G. Narsinga Rao2, Kasarapu Venkataramana1, D. Suresh Babu1 1
2
Department of Physics, Osmania University, Hyderabad, Telangana, India H&S Department, Marri Laxman Reddy Institute of Technology and Management, Hyderabad, Telangana, India Corresponding author mail ID: [email protected]
*
Abstract: The permittivity, impedance and AC conductivity studies of NdFeO3 perovskite nanocrystalline material were performed in the frequency range 1KHz-1MHz, and temperature range 100K-320K. The Sol-gel auto-combustion technique employed to synthesis NdFeO3 perovskite compound. The X-ray diffraction (XRD) pattern of NdFeO3 indicating the single-phase orthorhombic structure. The Scanning electron microscopy (SEM) image shows that the grains homogeneously spread throughout the surface morphology. The average grain size found to be 50 nm. The P-E loop suggests that the NdFeO3
material is ferroelectric in nature. An impedance spectroscopy study suggests that the negative temperature coefficient of resistance (NTCR) behavior of the material. The conductivity spectrum follows the Jonscher’s law.
Keywords: Sol-gel auto-combustion; X-ray techniques; SEM; P-E loop; Impedance; Electrical properties
1. Introduction Nano-crystalline materials have often exhibited interesting properties like electric, magnetic, optical and gas sensitivity properties. In the recent years, such oxide materials have shown great properties like high-temperature superconductivity, colossal magneto-resistance and multi ferocity [1]. The Ortho-ferrites (RFeO3) have investigated for device applications such as solid-oxide fuel cells, catalytic converters, and gas sensors [1]. The perovskite materials have been prepared using various synthesis techniques, i.e. Solid-state reaction method, Coprecipitation method, Citric-gel process, Sol-gel method, etc.,. Among these methods, we have
adapted sol-gel auto-combustion method. Because this process can provide homogeneity of the sample, can control the particle size and gives nano-size particles. The sintering process is essential to the solid ceramic materials, that effect on microstructure, grain growth and densification [2]. The NdFeO3 nano-crystalline perovskite oxide has shown high catalytic and gas sensitivity property [3-4], this property play a vital role in scientific industries to detect the leakage of unwanted gasses, thereby reduce the environmental pollution and protect the nature. The most advantage of the gas sensor is stability and reliability. Hence, these types of perovskite materials can potentially use in industrial applications. The orthorhombic symmetry of the NdFeO3 perovskite exhibited interesting magnetic interactions such as Nd-Nd, Nd-Fe, and Fe-Fe. In this transition, the direction of the easy axis of magnetization changes from one crystal axis to another induced by temperature or applied field [5-7]. In the literature survey, ABO3 (A: La, Nd, Sm, and Gd; B: Fe, Co and Ni; and O: oxygen) perovskite nanomaterial have exhibited high catalytic activities and high gas sensitivity with CO and HC [3]. Hence, the authors have synthesized NdFeO3 nano-crystalline perovskite compound by the Sol-gel method. The aim of the present investigation is to understand the structural, microscopic and electrical properties of NdFeO3 perovskite nano-crystalline material. The XRD, SEM, P-E hysteresis loop, impedance and AC conductivity characteristics have correlated with each other. These properties were strongly suggesting that the material is suitable for gas sensing [3, 8, 9] and ferroelectric [10, 11] device applications. 2. Experimental Methods NdFeO3 perovskite nanoparticle has been synthesized using sol-gel auto-combustion process. In this process, the stoichiometric amounts of Nd(NO3)3.6H2O, Fe(NO3)2.9H2O and citric acid were taken in 1:3 molar ratio separately. All these stoichiometric ratios of materials have dissolved separately using double distilled water. These dissolved solutions have mixed at once in a 500 ml borosil glass. The magnetic bead placed in mixed solution and has kept on a magnetic stirrer, slowly stirred and simultaneously NH3 have added to set the PH-7 of the mixed solution. Thereafter, the temperature of mixed solution has risen slowly to 1500C. Water in the mixed solution has evaporated, resulting initial solution become reduced. The ethylene glycol
was added to the 1/3 of the initial mixed solution to form the homogeneous gel. After a few minutes, stopped the stirring and magnetic bead removed from the dried gel. Further, slowly heating has risen until the dried gel gets combusted itself, such process so-called sol-gel autocombustion process. The obtained powder was pelletized using uniaxial pressure and then sintered at 9000C for 4 hours for densification. Finally, these pellets were used for XRD, microstructure, density, dielectric and P-E measurements. Phase and crystal symmetry of NdFeO3 nano-crystalline material have identified using Bruker D8 Advance X-ray diffractometer; it has monochromatic CuKߙ radiation with 0.154 nm wavelength. Microscopic measurements have performed using ZISS EVO-18 microscopy. The density of sintered pellet has estimated using the Archimedes method and Xylene used as solvent. P-E measurements have done using P-E tracer at IUC Indore. Impedance measurements have performed by Dielectric Analyzer at National University, Taipei, Taiwan. The silver electrode coated samples have used for both P-E and impedance measurements. 3. Results and Discussion 3.1. Material characterization X-ray diffraction pattern of the sintered pellet of NdFeO3 perovskite compound have shown in Figure 1a). The XRD pattern have refined by Rietveld refinement Fullproof suite program. The XRD pattern suggests single-phase orthorhombic symmetry with Pbnm space group. The average crystallite size has determined by the Debye Scherer principle and found to be 42 nm. The inset Figure 1a) shows the surface morphology of NdFeO3 sintered pellet. The grains in the compound homogeneously spread throughout the surface. However, the agglomerated grains loosely bounded. Hence, this material has high porosity, and the high porosity materials can useful in gas sensing applications [3, 8, 9]. The percentile density of NdFeO3 has estimated and found to be around 63%. 3.2. Hysteresis (P-E) loop analysis Figure 1b) shows the room temperature hysteresis (P-E) loop of NdFeO3 perovskite compound at different applied fields (200 V to 2000 V). The value of the remanence polarization and coercive field increased with an increase in the external electric field. The maximum polarization (Pmax) is 0.088 ߤ ܥΤܿ݉ଶ , and the remanence polarization (Pr) is 0.014 ߤ ܥΤܿ݉ଶ at the
applied field 2 kV. No saturation loop found up to 2 kV. The P-E loop suggests that the NdFeO3 material is of ferroelectric in nature [10, 11]. The P-E loop has displayed spontaneous and remanence polarizations, and which depends on the various aspects such as shape, dimension, temperature and electrical properties of the materials [12]. 3.3. Impedance analysis Figure 2a) shows the frequency dependence of the imaginary part impedanceሺܼ ᇱᇱ ) of NdFeO3 Perovskite compound at different temperatures. It shows a monotonous decrease in ZƎ with the increase in frequency and temperature. In the low-frequency region (<104) ZƎ is more significant and the gradual decreasing with the rising in temperature and frequency, indicating the negative temperature of the coefficient of resistance (NTCR) nature of the material. The imaginary impedance plot merged at the high frequencies, it is due to the existence of space charges and it controls the electrical relaxation process in the high-frequency region [13]. Inset of Fig. 2a shows the temperature dependent relaxation time & DC conductivity. The relaxation time is decreased with the rise in temperature and it shows the spared of relaxation in the range ͳǤͷ ିͲͳ כସ to ͵Ǥʹ ିͲͳ כସ sec this behavior of the material indicates temperature dependent electrical relaxation. The DC conductivity increased with the rising in temperature. Both of these plots follow the Arrhenius law. Activation energies of DC conductivity and relaxation time have estimated from inset Fig 2a, found to be ~0.13 eV. Figure 2b) represents the Cole-Cole plots of the NdFeO3 Perovskite compound. With increasing the temperature the slope of the line decreases, i.e. they bend towards Z’ axis and finally they form semicircles and the intercept of the point on the x-axis shifts towards the origin, suggesting that the resistance of the material become decreased with an increase in temperature indicating the semiconducting property of material [14]. The formation of single semicircle at all temperatures, suggesting that the electrical properties of the material emerge mainly due to the contribution of grain in the NdFeO3 Perovskite ceramic material [15]. The electrical relaxation process in the materials can explain using RC Circuit based on the bricklayer model. The RC model circuit has drawn and represented in inset Fig. 2b).
3.4. Dielectric properties study Frequency dependent dielectric constant (ߝԢ) of NdFeO3 at the different temperatures (100k to 320k) have been shown in Figure 3a). It is observed that the dielectric constant (ߝԢ) decreases with increasing frequency at a given temperature. The dielectric constant (ߝԢ) increases with increasing temperature, and which grow into more significant at low frequency. The decrease in İ' with increasing frequency may be due to space charges, which leads to the high dielectric constant and momentous frequency diffusion in the low-frequency region. The dielectric constant (ߝԢ) increased with an increase in temperature, suggests that the thermally stimulated dielectric relaxation in the material [16]. 3.5. Conductivity study Figure 3b) shows the frequency dependence AC conductivity ሺߪ ሻ of the NdFeO3 perovskite compound. To understand the conduction mechanism, the AC conductivity of the sample have evaluated by using the formula given in [17-18]. ߪ =2ߨ݂ߝ ߝ ᇱ ߜ݊ܽݐ Where ݂ is the applied frequency (Hz), ߜ݊ܽݐis a dielectric loss, ߝ is a dielectric constant in free space (8.854 *1012 F/m), ߝ ᇱ is a dielectric constant of the sample. The frequency dependence of AC conductivity plots displaying two different regions. The low-frequency region plot relates to DC conductivityሺߪௗ ሻ, and is almost independent of frequency (<104 Hz) & temperature. The high-frequency region of the plot indicates AC conductivity ሺߪ ሻ and is increasing rapidly with both frequency and temperature. It may be due to hopping between B (Fe3+) site ions. In the high-frequency region, the conductive grains grow into more active, therefore the hopping of charge carriers are rising and which lead to rising in conductivity. The frequency dependence of ߪ of NdFeO3 samples follows the Jonscher's power law [19-22]. The values of the frequency exponent (n) have calculated using Jonscher's power law relation. Exponent (n) has gradually increased from 0.4 to 0.93 with the rise in temperature. Conclusions The NdFeO3 perovskite nanoparticle compound has prepared by Sol-gel auto-combustion method. The phase formation of the NdFeO3 perovskite sample has confirmed by XRD and has
found to be single-phase orthorhombic structure. P-E loop suggesting that the NdFeO3 material is ferroelectric in nature. The Activation energies of DC conductivityሺߪௗ ሻ, relaxation time (߬) has been evaluated, and are following the Arrhenius law. A negative temperature coefficient of resistance (NTCR) seen in the material. In the high-frequency region, AC conductivity increases more rapidly with increasing frequency may be due to hopping between Fe3+ (B- site) ions. Frequency-dependent conductivity follows the Jonscher’s law. However, NdFeO3 is a good candidate for gas sensing and ferroelectric applications. Acknowledgments One of the authors, Jada Shanker would like to thank SRF-UGC-RGNF Delhi for the providing the financial assistance to carry out this work. In addition, authors are thankful to Dr. V. R. Reddy, IUC Indore for providing the P-E tracer measurements. Figure Captions Figure 1: a) XRD-Rietveld refinement (Inset Fig.1a: SEM image), b) hysteresis (P-E) loop of NdFeO3 respectively. Figure 2: a) Frequency dependence imaginary impedance (ࢆᇱᇱ ) (Inset Fig.2a Relaxation time and DC Conductivity function of temperature), b) Complex impedance (Cole-Cole) plot of NdFeO3 respectively. Figure 3: a) Frequency dependence dielectric constant (ࢿᇱ ), b) Frequency dependence of AC Conductivity of NdFeO3 respectively References [1].
Sujoy Saha, Saehan Chanda, Alo Dutta, T. P. Sinha, “Dielectric relaxation and phonon modes of NdCrO3 nanostructure,” J. Sol-Gel Sic. Techno., (2014) 69:553-563.
[2].
Leow Chun Yan, Jumian Hassan, Mansor Hashim, Wong Swee Yin, Tan Foo Khoon and Wong Yick Jeng, “Effect of Sintering Temperatures on the Microstructure and Dielectric Properties of SrTiO3,” World Applied Sciences Journal, 14 (7): 1091-1094, 2011.
[3].
Truong Giang Ho, Thai Duy Ha, Quang Ngan Pham, Hong Thai Giang, Thi Anh Thu Do and Ngoc Toan Nguyen, “Nanosized perovskite oxide NdFeO3 as material for a carbon-monoxide catalytic gas sensor”, Adv. Nat. Sci.: Nanosci. Nanotechnol., 2 (2011) 015012.
[4].
You Wang, Xuecheng Yan, Jun Chen, Jinxia Deng, Ranbo Yu and Xianran Xing “Shape controllable synthesis of NdFeO3 micro single crystals by a hydrothermal route” Cryst Eng Comm, 2014, 16, 858–862.
[5].
R. Przenioslo, I. Sosnowska, P. Fischer, “Magnetic moment ordering of Nd3+ ions in NdFeO3,” Journal of Magnetism and magnetic materials, 140-144 (1995) 2153-2154.
[6].
G H Hu, I Umehara, X Shuang, S Yuanband S X Cao, “Pressure Effect in Multiferroic Phase Transition of Perovskite Ferrite Crystals NdFeO3 and ErFeO3,” Journal of Physics: Conference Series, 400 (2012) 032023.
[7].
M. Khorasani Motlagh, M. Noroozifar, M. Yousefi, Sh. Jahani, “Chemical Synthesis and Characterization of Perovskite NdFeO3 Nanocrystals via a Co-Precipitation Method,” Int. J. Nanosci. Nanotechnol, Vol. 9, No. 1, March 2013.
[8].
Jada Shanker, M.Buchi Suresh, D. Suresh Babu, “Synthesis, Characterization and Electrical Properties of NdXO3 (X=Cr, Fe) Nanoparticles,” Materials Today: Proceedings, 3 (2016) 2091-2100.
[9].
Maike Siemons, Annika Leifert, and Ulrich Simon, “Preparation and Gas Sensing Characteristics of Nanoparticulate p-Type Semiconducting LnFeO3 and LnCrO3 Materials,” Adv. Funct. Mater., 2007, 17, 2189–2197.
[10].
N. Aparnadevi, K. Saravana Kumar, M. Manikandan, D. Paul Joseph, and C. Venkateswaran, “Room temperature dual ferroic behavior of ball mill synthesized NdFeO3 orthoferrite,” J. Appl. Phys., 120, 034101 (2016).
[11]
Swagatika Dasha,n, R.N.P. Choudharya, Ashok Kumar, “Impedance spectroscopy and conduction mechanism of multiferroic (Bi0.6K0.4)(Fe0.6Nb0.4)O3,” Journal of Physics and Chemistry of Solids, 75 (2014) 1376–1382
[12]
B. Jaya Prakash, B. H. Rudramadevi & S. Buddhudu, “Analysis of Ferroelectric, Dielectric and Magnetic Properties of GdFeO3 Nanoparticles,” Ferroelectrics Letters Section, 41:110–122, 2014.
[13].
Balgovind
Tiwari,
R.N.P.
Choudhary,
“Frequency–temperature
response
of
Pb(Zr0.65íxCexTi0.35)O3 ferroelectric ceramics: Impedance spectroscopic studies,” Journal of Alloys and Compounds, 493 (2010)1-10. [14].
B. B. Mohanty, P. S. Shoo, R.N.P. Choudhary, “Electrical properties of rare earth based tungsten bronze vanadates,” Journal of rare earths, Vol. 30, No. 11, Nov. 2012, P. 1134.
[15].
Rajiv Ranjan, Nawnit Kumar, Banarji Behead, R. N. P. Choudhary, “Investigations of impedance and electric modulus properties of Pb1-xSmx(Zr0.45Ti0.55)1-x/4O3 ceramics,” Adv. Mat. Let., 2014, 5(3), 38-142.
[16].
Subrat K. Barik, R.N.P. Choudhary, A.K. Singh, “AC impedance spectroscopy and conductivity studies of Ba0.8Sr0.2Ti0.3 ceramics,” Adv. Mat. Let., 2011, 2(6), 419-424.
[17].
Khalid Sultan, M. Ikram, K. Asokan, “Structural, optical and dielectric study of Mn doped PrFeO3 ceramics,” Vacuum, 99 (2014) 251-258.
[18].
Jada Shanker, B. Vittal Prasad, M. Buchi Suresh, R. Vijaya kumar, D. Suresh Babu, “Electrical properties of NdCr1-xFexO3 perovskite ceramic nanoparticles-An impedance spectroscopy studies,” Material Research Bulletin, 94 (2017) 385-398.
[19].
Sarmistha Basu, K. Ramesh Babe, R.N.P. Choudhary, “Studies on the piezoelectric and magnetostrictive phase distribution in lead zirconate titanate–cobalt iron oxide composites, Materials Chemistry and Physics, 132 (2012) 570–580.
[20].
A. K. Jonscher, “The 'universal' dielectric response,” Nature, Vol. 267, 673-679, 23 Jun 1977.
[21].
M. J. Miah, M.N.I. Khan, A.K.M. Akther Hossain, “Weak ferromagnetism and magnetoelectric effect in multiferroic xBa0.95Sr0.05TiO3-(1-x)BiFe0.9Gd0.1O3 relaxors,” Journal of Magnetism and Magnetic Materials, 401 (2016) 600–611.
[22].
Jada Shanker, K. Venkataramana, B. Vittal Prasad, R. Vijaya Kumar, D. Suresh Babu, “Influence of Fe substitution on structural and electrical properties of Gd orthochromite ceramics,” Journal of Alloys and Compounds, Vol. 732, 25 January 2018, Pages 314-327.
Figure 1 a) XRD-Rietveld refinement (Inset Fig.1a: SEM image), b) hysteresis (P-E) loop of NdFeO3 respectively.
Figure 2 a) Frequency dependent imaginary impedance (ࢆᇱᇱ ) (Inset Fig.2a: Relaxation time and DC Conductivity function of temperature), b) Complex impedance (Cole-Cole) plot of NdFeO3 respectively.
Figure 3 a) Frequency dependence of the dielectric constant (ࢿᇱ ), b) Frequency dependence of AC Conductivity of NdFeO3 respectively
Jada Shanker, G. Narsinga Rao, Kasarapu Venkataramana, D. Suresh Babu
PII: DOI: Reference:
S0375-9601(18)30724-2 https://doi.org/10.1016/j.physleta.2018.07.002 PLA 25203
To appear in:
Physics Letters A
Received date: Revised date: Accepted date:
11 April 2018 21 June 2018 1 July 2018
Please cite this article in press as: J. Shanker et al., Investigation of structural and electrical properties of NdFeO3 perovskite nanocrystalline, Phys. Lett. A (2018), https://doi.org/10.1016/j.physleta.2018.07.002
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 proof before it is published in its final 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.
Highlights • • • • •
Sol-gel auto-combustion process has been employed to prepare NdFeO3 perovskite nanocrystalline compound. Single phase orthorhombic symmetry with Pbnm space group. P-E loop of NdFeO3 nanocrystalline material have shown ferroelctric behaviour. Impedance data indicating the negative temperature coefficient of resistance (NTCR) nature. NdFeO3 material is a potential candidate in ferrolectric and gas sensing device applications.
Investigation of structural and electrical properties of NdFeO3 perovskite nanocrystalline Jada Shanker1,*, G. Narsinga Rao2, Kasarapu Venkataramana1, D. Suresh Babu1 1
2
Department of Physics, Osmania University, Hyderabad, Telangana, India H&S Department, Marri Laxman Reddy Institute of Technology and Management, Hyderabad, Telangana, India Corresponding author mail ID: [email protected]
*
Abstract: The permittivity, impedance and AC conductivity studies of NdFeO3 perovskite nanocrystalline material were performed in the frequency range 1KHz-1MHz, and temperature range 100K-320K. The Sol-gel auto-combustion technique employed to synthesis NdFeO3 perovskite compound. The X-ray diffraction (XRD) pattern of NdFeO3 indicating the single-phase orthorhombic structure. The Scanning electron microscopy (SEM) image shows that the grains homogeneously spread throughout the surface morphology. The average grain size found to be 50 nm. The P-E loop suggests that the NdFeO3
material is ferroelectric in nature. An impedance spectroscopy study suggests that the negative temperature coefficient of resistance (NTCR) behavior of the material. The conductivity spectrum follows the Jonscher’s law.
Keywords: Sol-gel auto-combustion; X-ray techniques; SEM; P-E loop; Impedance; Electrical properties
1. Introduction Nano-crystalline materials have often exhibited interesting properties like electric, magnetic, optical and gas sensitivity properties. In the recent years, such oxide materials have shown great properties like high-temperature superconductivity, colossal magneto-resistance and multi ferocity [1]. The Ortho-ferrites (RFeO3) have investigated for device applications such as solid-oxide fuel cells, catalytic converters, and gas sensors [1]. The perovskite materials have been prepared using various synthesis techniques, i.e. Solid-state reaction method, Coprecipitation method, Citric-gel process, Sol-gel method, etc.,. Among these methods, we have
adapted sol-gel auto-combustion method. Because this process can provide homogeneity of the sample, can control the particle size and gives nano-size particles. The sintering process is essential to the solid ceramic materials, that effect on microstructure, grain growth and densification [2]. The NdFeO3 nano-crystalline perovskite oxide has shown high catalytic and gas sensitivity property [3-4], this property play a vital role in scientific industries to detect the leakage of unwanted gasses, thereby reduce the environmental pollution and protect the nature. The most advantage of the gas sensor is stability and reliability. Hence, these types of perovskite materials can potentially use in industrial applications. The orthorhombic symmetry of the NdFeO3 perovskite exhibited interesting magnetic interactions such as Nd-Nd, Nd-Fe, and Fe-Fe. In this transition, the direction of the easy axis of magnetization changes from one crystal axis to another induced by temperature or applied field [5-7]. In the literature survey, ABO3 (A: La, Nd, Sm, and Gd; B: Fe, Co and Ni; and O: oxygen) perovskite nanomaterial have exhibited high catalytic activities and high gas sensitivity with CO and HC [3]. Hence, the authors have synthesized NdFeO3 nano-crystalline perovskite compound by the Sol-gel method. The aim of the present investigation is to understand the structural, microscopic and electrical properties of NdFeO3 perovskite nano-crystalline material. The XRD, SEM, P-E hysteresis loop, impedance and AC conductivity characteristics have correlated with each other. These properties were strongly suggesting that the material is suitable for gas sensing [3, 8, 9] and ferroelectric [10, 11] device applications. 2. Experimental Methods NdFeO3 perovskite nanoparticle has been synthesized using sol-gel auto-combustion process. In this process, the stoichiometric amounts of Nd(NO3)3.6H2O, Fe(NO3)2.9H2O and citric acid were taken in 1:3 molar ratio separately. All these stoichiometric ratios of materials have dissolved separately using double distilled water. These dissolved solutions have mixed at once in a 500 ml borosil glass. The magnetic bead placed in mixed solution and has kept on a magnetic stirrer, slowly stirred and simultaneously NH3 have added to set the PH-7 of the mixed solution. Thereafter, the temperature of mixed solution has risen slowly to 1500C. Water in the mixed solution has evaporated, resulting initial solution become reduced. The ethylene glycol
was added to the 1/3 of the initial mixed solution to form the homogeneous gel. After a few minutes, stopped the stirring and magnetic bead removed from the dried gel. Further, slowly heating has risen until the dried gel gets combusted itself, such process so-called sol-gel autocombustion process. The obtained powder was pelletized using uniaxial pressure and then sintered at 9000C for 4 hours for densification. Finally, these pellets were used for XRD, microstructure, density, dielectric and P-E measurements. Phase and crystal symmetry of NdFeO3 nano-crystalline material have identified using Bruker D8 Advance X-ray diffractometer; it has monochromatic CuKߙ radiation with 0.154 nm wavelength. Microscopic measurements have performed using ZISS EVO-18 microscopy. The density of sintered pellet has estimated using the Archimedes method and Xylene used as solvent. P-E measurements have done using P-E tracer at IUC Indore. Impedance measurements have performed by Dielectric Analyzer at National University, Taipei, Taiwan. The silver electrode coated samples have used for both P-E and impedance measurements. 3. Results and Discussion 3.1. Material characterization X-ray diffraction pattern of the sintered pellet of NdFeO3 perovskite compound have shown in Figure 1a). The XRD pattern have refined by Rietveld refinement Fullproof suite program. The XRD pattern suggests single-phase orthorhombic symmetry with Pbnm space group. The average crystallite size has determined by the Debye Scherer principle and found to be 42 nm. The inset Figure 1a) shows the surface morphology of NdFeO3 sintered pellet. The grains in the compound homogeneously spread throughout the surface. However, the agglomerated grains loosely bounded. Hence, this material has high porosity, and the high porosity materials can useful in gas sensing applications [3, 8, 9]. The percentile density of NdFeO3 has estimated and found to be around 63%. 3.2. Hysteresis (P-E) loop analysis Figure 1b) shows the room temperature hysteresis (P-E) loop of NdFeO3 perovskite compound at different applied fields (200 V to 2000 V). The value of the remanence polarization and coercive field increased with an increase in the external electric field. The maximum polarization (Pmax) is 0.088 ߤ ܥΤܿ݉ଶ , and the remanence polarization (Pr) is 0.014 ߤ ܥΤܿ݉ଶ at the
applied field 2 kV. No saturation loop found up to 2 kV. The P-E loop suggests that the NdFeO3 material is of ferroelectric in nature [10, 11]. The P-E loop has displayed spontaneous and remanence polarizations, and which depends on the various aspects such as shape, dimension, temperature and electrical properties of the materials [12]. 3.3. Impedance analysis Figure 2a) shows the frequency dependence of the imaginary part impedanceሺܼ ᇱᇱ ) of NdFeO3 Perovskite compound at different temperatures. It shows a monotonous decrease in ZƎ with the increase in frequency and temperature. In the low-frequency region (<104) ZƎ is more significant and the gradual decreasing with the rising in temperature and frequency, indicating the negative temperature of the coefficient of resistance (NTCR) nature of the material. The imaginary impedance plot merged at the high frequencies, it is due to the existence of space charges and it controls the electrical relaxation process in the high-frequency region [13]. Inset of Fig. 2a shows the temperature dependent relaxation time & DC conductivity. The relaxation time is decreased with the rise in temperature and it shows the spared of relaxation in the range ͳǤͷ ିͲͳ כସ to ͵Ǥʹ ିͲͳ כସ sec this behavior of the material indicates temperature dependent electrical relaxation. The DC conductivity increased with the rising in temperature. Both of these plots follow the Arrhenius law. Activation energies of DC conductivity and relaxation time have estimated from inset Fig 2a, found to be ~0.13 eV. Figure 2b) represents the Cole-Cole plots of the NdFeO3 Perovskite compound. With increasing the temperature the slope of the line decreases, i.e. they bend towards Z’ axis and finally they form semicircles and the intercept of the point on the x-axis shifts towards the origin, suggesting that the resistance of the material become decreased with an increase in temperature indicating the semiconducting property of material [14]. The formation of single semicircle at all temperatures, suggesting that the electrical properties of the material emerge mainly due to the contribution of grain in the NdFeO3 Perovskite ceramic material [15]. The electrical relaxation process in the materials can explain using RC Circuit based on the bricklayer model. The RC model circuit has drawn and represented in inset Fig. 2b).
3.4. Dielectric properties study Frequency dependent dielectric constant (ߝԢ) of NdFeO3 at the different temperatures (100k to 320k) have been shown in Figure 3a). It is observed that the dielectric constant (ߝԢ) decreases with increasing frequency at a given temperature. The dielectric constant (ߝԢ) increases with increasing temperature, and which grow into more significant at low frequency. The decrease in İ' with increasing frequency may be due to space charges, which leads to the high dielectric constant and momentous frequency diffusion in the low-frequency region. The dielectric constant (ߝԢ) increased with an increase in temperature, suggests that the thermally stimulated dielectric relaxation in the material [16]. 3.5. Conductivity study Figure 3b) shows the frequency dependence AC conductivity ሺߪ ሻ of the NdFeO3 perovskite compound. To understand the conduction mechanism, the AC conductivity of the sample have evaluated by using the formula given in [17-18]. ߪ =2ߨ݂ߝ ߝ ᇱ ߜ݊ܽݐ Where ݂ is the applied frequency (Hz), ߜ݊ܽݐis a dielectric loss, ߝ is a dielectric constant in free space (8.854 *1012 F/m), ߝ ᇱ is a dielectric constant of the sample. The frequency dependence of AC conductivity plots displaying two different regions. The low-frequency region plot relates to DC conductivityሺߪௗ ሻ, and is almost independent of frequency (<104 Hz) & temperature. The high-frequency region of the plot indicates AC conductivity ሺߪ ሻ and is increasing rapidly with both frequency and temperature. It may be due to hopping between B (Fe3+) site ions. In the high-frequency region, the conductive grains grow into more active, therefore the hopping of charge carriers are rising and which lead to rising in conductivity. The frequency dependence of ߪ of NdFeO3 samples follows the Jonscher's power law [19-22]. The values of the frequency exponent (n) have calculated using Jonscher's power law relation. Exponent (n) has gradually increased from 0.4 to 0.93 with the rise in temperature. Conclusions The NdFeO3 perovskite nanoparticle compound has prepared by Sol-gel auto-combustion method. The phase formation of the NdFeO3 perovskite sample has confirmed by XRD and has
found to be single-phase orthorhombic structure. P-E loop suggesting that the NdFeO3 material is ferroelectric in nature. The Activation energies of DC conductivityሺߪௗ ሻ, relaxation time (߬) has been evaluated, and are following the Arrhenius law. A negative temperature coefficient of resistance (NTCR) seen in the material. In the high-frequency region, AC conductivity increases more rapidly with increasing frequency may be due to hopping between Fe3+ (B- site) ions. Frequency-dependent conductivity follows the Jonscher’s law. However, NdFeO3 is a good candidate for gas sensing and ferroelectric applications. Acknowledgments One of the authors, Jada Shanker would like to thank SRF-UGC-RGNF Delhi for the providing the financial assistance to carry out this work. In addition, authors are thankful to Dr. V. R. Reddy, IUC Indore for providing the P-E tracer measurements. Figure Captions Figure 1: a) XRD-Rietveld refinement (Inset Fig.1a: SEM image), b) hysteresis (P-E) loop of NdFeO3 respectively. Figure 2: a) Frequency dependence imaginary impedance (ࢆᇱᇱ ) (Inset Fig.2a Relaxation time and DC Conductivity function of temperature), b) Complex impedance (Cole-Cole) plot of NdFeO3 respectively. Figure 3: a) Frequency dependence dielectric constant (ࢿᇱ ), b) Frequency dependence of AC Conductivity of NdFeO3 respectively References [1].
Sujoy Saha, Saehan Chanda, Alo Dutta, T. P. Sinha, “Dielectric relaxation and phonon modes of NdCrO3 nanostructure,” J. Sol-Gel Sic. Techno., (2014) 69:553-563.
[2].
Leow Chun Yan, Jumian Hassan, Mansor Hashim, Wong Swee Yin, Tan Foo Khoon and Wong Yick Jeng, “Effect of Sintering Temperatures on the Microstructure and Dielectric Properties of SrTiO3,” World Applied Sciences Journal, 14 (7): 1091-1094, 2011.
[3].
Truong Giang Ho, Thai Duy Ha, Quang Ngan Pham, Hong Thai Giang, Thi Anh Thu Do and Ngoc Toan Nguyen, “Nanosized perovskite oxide NdFeO3 as material for a carbon-monoxide catalytic gas sensor”, Adv. Nat. Sci.: Nanosci. Nanotechnol., 2 (2011) 015012.
[4].
You Wang, Xuecheng Yan, Jun Chen, Jinxia Deng, Ranbo Yu and Xianran Xing “Shape controllable synthesis of NdFeO3 micro single crystals by a hydrothermal route” Cryst Eng Comm, 2014, 16, 858–862.
[5].
R. Przenioslo, I. Sosnowska, P. Fischer, “Magnetic moment ordering of Nd3+ ions in NdFeO3,” Journal of Magnetism and magnetic materials, 140-144 (1995) 2153-2154.
[6].
G H Hu, I Umehara, X Shuang, S Yuanband S X Cao, “Pressure Effect in Multiferroic Phase Transition of Perovskite Ferrite Crystals NdFeO3 and ErFeO3,” Journal of Physics: Conference Series, 400 (2012) 032023.
[7].
M. Khorasani Motlagh, M. Noroozifar, M. Yousefi, Sh. Jahani, “Chemical Synthesis and Characterization of Perovskite NdFeO3 Nanocrystals via a Co-Precipitation Method,” Int. J. Nanosci. Nanotechnol, Vol. 9, No. 1, March 2013.
[8].
Jada Shanker, M.Buchi Suresh, D. Suresh Babu, “Synthesis, Characterization and Electrical Properties of NdXO3 (X=Cr, Fe) Nanoparticles,” Materials Today: Proceedings, 3 (2016) 2091-2100.
[9].
Maike Siemons, Annika Leifert, and Ulrich Simon, “Preparation and Gas Sensing Characteristics of Nanoparticulate p-Type Semiconducting LnFeO3 and LnCrO3 Materials,” Adv. Funct. Mater., 2007, 17, 2189–2197.
[10].
N. Aparnadevi, K. Saravana Kumar, M. Manikandan, D. Paul Joseph, and C. Venkateswaran, “Room temperature dual ferroic behavior of ball mill synthesized NdFeO3 orthoferrite,” J. Appl. Phys., 120, 034101 (2016).
[11]
Swagatika Dasha,n, R.N.P. Choudharya, Ashok Kumar, “Impedance spectroscopy and conduction mechanism of multiferroic (Bi0.6K0.4)(Fe0.6Nb0.4)O3,” Journal of Physics and Chemistry of Solids, 75 (2014) 1376–1382
[12]
B. Jaya Prakash, B. H. Rudramadevi & S. Buddhudu, “Analysis of Ferroelectric, Dielectric and Magnetic Properties of GdFeO3 Nanoparticles,” Ferroelectrics Letters Section, 41:110–122, 2014.
[13].
Balgovind
Tiwari,
R.N.P.
Choudhary,
“Frequency–temperature
response
of
Pb(Zr0.65íxCexTi0.35)O3 ferroelectric ceramics: Impedance spectroscopic studies,” Journal of Alloys and Compounds, 493 (2010)1-10. [14].
B. B. Mohanty, P. S. Shoo, R.N.P. Choudhary, “Electrical properties of rare earth based tungsten bronze vanadates,” Journal of rare earths, Vol. 30, No. 11, Nov. 2012, P. 1134.
[15].
Rajiv Ranjan, Nawnit Kumar, Banarji Behead, R. N. P. Choudhary, “Investigations of impedance and electric modulus properties of Pb1-xSmx(Zr0.45Ti0.55)1-x/4O3 ceramics,” Adv. Mat. Let., 2014, 5(3), 38-142.
[16].
Subrat K. Barik, R.N.P. Choudhary, A.K. Singh, “AC impedance spectroscopy and conductivity studies of Ba0.8Sr0.2Ti0.3 ceramics,” Adv. Mat. Let., 2011, 2(6), 419-424.
[17].
Khalid Sultan, M. Ikram, K. Asokan, “Structural, optical and dielectric study of Mn doped PrFeO3 ceramics,” Vacuum, 99 (2014) 251-258.
[18].
Jada Shanker, B. Vittal Prasad, M. Buchi Suresh, R. Vijaya kumar, D. Suresh Babu, “Electrical properties of NdCr1-xFexO3 perovskite ceramic nanoparticles-An impedance spectroscopy studies,” Material Research Bulletin, 94 (2017) 385-398.
[19].
Sarmistha Basu, K. Ramesh Babe, R.N.P. Choudhary, “Studies on the piezoelectric and magnetostrictive phase distribution in lead zirconate titanate–cobalt iron oxide composites, Materials Chemistry and Physics, 132 (2012) 570–580.
[20].
A. K. Jonscher, “The 'universal' dielectric response,” Nature, Vol. 267, 673-679, 23 Jun 1977.
[21].
M. J. Miah, M.N.I. Khan, A.K.M. Akther Hossain, “Weak ferromagnetism and magnetoelectric effect in multiferroic xBa0.95Sr0.05TiO3-(1-x)BiFe0.9Gd0.1O3 relaxors,” Journal of Magnetism and Magnetic Materials, 401 (2016) 600–611.
[22].
Jada Shanker, K. Venkataramana, B. Vittal Prasad, R. Vijaya Kumar, D. Suresh Babu, “Influence of Fe substitution on structural and electrical properties of Gd orthochromite ceramics,” Journal of Alloys and Compounds, Vol. 732, 25 January 2018, Pages 314-327.
Figure 1 a) XRD-Rietveld refinement (Inset Fig.1a: SEM image), b) hysteresis (P-E) loop of NdFeO3 respectively.
Figure 2 a) Frequency dependent imaginary impedance (ࢆᇱᇱ ) (Inset Fig.2a: Relaxation time and DC Conductivity function of temperature), b) Complex impedance (Cole-Cole) plot of NdFeO3 respectively.
Figure 3 a) Frequency dependence of the dielectric constant (ࢿᇱ ), b) Frequency dependence of AC Conductivity of NdFeO3 respectively