Structural and Electrical Properties of CaMnO3 Prepared by Sol-Gel Method

Mechanics, Materials Science & Engineering, April 2017 – ISSN 2412-5954

Structural and Electrical Properties of CaMnO3 Prepared by Sol-Gel Method25 K. R. Nandan1, A. Ruban Kumar1, a 1 – Center for Crystal Growth, School of Advanced Sciences, VIT University, Vellore-632 014, India a – arubankumarvit@gmail.com DOI 10.2412/mmse.59.12.214 provided by Seo4U.link

Keywords: sol-gel, SEM, FT-IR, dielectric properties.

ABSTRACT. The structural and electrical properties of CaMnO3 prepared by a sol-gel technique using citric acid as a chelating agent at 8000C were studied; the phase formation was determined by powderXRD. The surface morphological studies were carried out through SEM and EDX confirmed the chemical compositions of the sample. The various modes of vibrations due to the Mn-O and O-Mn-O stretching bonds were observed by FTIR spectroscopy studies.The electrical properties of the prepared samples were analysed at different temperatures in the frequency ranges from 50Hz to 5MHz.

Introduction. The Manganese oxide based elements with the low-temperature synthesis of ABO3 perovskite type oxides has attracted due to their interesting technological applications in thermoelectric, magnetic and electrical properties have drawn more attention from the past few decades [1]. These compounds show large magnetoresistance properties due to an unusual spin – orbital and charge ordering phenomenon these can be easily altered by temperature, pressure, applied field, doping and also the way of preparation. The manganese based on CaMnO3 compound has a mixed valence system of Mn3+/Mn4+ could induce charge transfer effects and double-exchange interaction it possesses many applications such as solid fuel cells, magnetoresistance switchings, cathode materials and oxygen sensors [2].

The perovskite structure of CaMnO3 is a G-type antiferromagnetic insulator with an additional weak ferromagnetic component in ground state and it belongs to an orthorhombic structure this kind of structure is quite suitable for colossal magnetoresistance, the strong correlation between an electronic system and thermoelectric materials [3]. Recently, CaMnO3 has been one of typical perovskite oxide which shows an excellent dielectric polarisation behaviour being one kind of absorbing agent and a promising thermoelectric material with high Seebeck coefficient low electrical conductivity [4].

CaMnO3 has synthesiszed with various methods namely hydrothermal method, solid state reaction, sol-gel method and so on. To obtain a homogenous compound, uniform particle size, high crystallinity and morphology, the sol-gel method is used to reduce the agglomeration in the prepared compound.

Most of the studies of CaMnO3 have focused mainly on the magnetic and thermal properties; less attention has been paid about structural and electrical properties of the materials. Here in our report the results of structural, morphological, dielectric and impedance studies on CaMnO3. The electrical properties for the synthesised CaMnO3 as a function of frequency varying from 50 Hz to 5 MHz at different temperatures have measured.

Experimental. The perovskite CaMnO3 have synthesized the material by sol-gel method using citric acid as chelating agent. The stoichiometric ratio of Calcium nitrate (Ca (NO3)3.4H2O) and Manganese nitrate (Mn (NO3)3.4H2O), dissolved in the deionized water to form a homogenous solution and citric acid (C6H8O7) solution was added slowly drop by drop to the homogenous solution. All reagents used 25

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Mechanics, Materials Science & Engineering, April 2017 – ISSN 2412-5954

were of analytical grade and used without further purification. Then the solution was stirred continuously to ensure homogeneity continuously for 3 h at room temperature. Further the homogenous solution was heated to 800 C with stirring until the gel is formed. The obtained gel was dried overnight in a vacuum oven at 1200 C. It was then pre-sintered at 3000 C in air for 4 h to eliminate the organic constituents present. Finally the precursor was sintered at 8000c for 5 h to obtain the final product. Again the obtained CaMnO3 was ground into fine powder before subjecting it into further characterization.

The phase formation and crystal structure of the synthesized material were confirmed by X-ray diffraction with a range of 2θ from 100 to 800 with a step size of 0.02 s-1 at a scan rate of 2 min-1. The surface morphology and compositions of the samples were investigated by scanning electron microscopy equipped with an energy-dispersive X-ray spectrometer (EDX). The Fourier transform infrared spectroscopy (FT-IR) spectra were obtained by JASCO 400 Infrared spectrometer from 4000cm-1 to 400cm-1. The pellets were made from the synthesized material for electrical measurements with silver paste coating for ohmic contact. The dielectric measurements were carried out by a LCR meter in the frequency range from 50 Hz to 5 MHz for the temperature ranging from 313K to 443K. Results and discussion XRD analysis

Fig. 1. XRD pattern of synthesized CaMnO3.

The XRD pattern for the synthesized material CaMnO3 is shown in Fig.1. The patterns of the synthesized material confirmed the single phase formation and crystal structure orthorhombic with space group Pnma. It is observed that all the diffraction peaks apparently were indexed with hkl values by conformed with standard JCPDS 89-0666. The unit cell parameters are a=5.3010 Å, b= 7.5137 Å and c=5.3130 Å calculated using Powder X software [5].

SEM-EDX analysis. The surface morphology of the CaMnO3 sintered at 8000C is shown in the Fig. 2. From the image, it is evident that the particles have uniformly distributed with uniform size. The morphology of the sample revealed that grains have a well defined spherical structure [4]. From the elemental X-ray diffraction analysis spectra shows the presence of chemical composition and confirm no other impurities present in the prepared material.

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Fig. 2. SEM image and EDX spectra, inset shows percentage of chemical composition of CaMnO3.

FTIR Spectroscopy. Fig. 3 shows the FTIR spectra of the as-prepared CaMnO3 samples prepared in sol-gel method. The bending mode and stretching mode at around 410 and 590 cm-1 is corresponds to the changes in the Mn-O or Mn-O-Mn bonds [6]. This also confirms the formation of single phased compound of synthesized material at 8000C without any impurity in the FT-IR spectrum and also from the previous analysis by XRD spectrum.

Fig. 3. FT-IR Spectra of synthesized CaMnO3.

Dielectric studies. The dielectric constant has been analysed at the frequency ranging from 50 Hz to 5 MHz at the different temperatures ranging from 300 to783 K. From Fig. 4 shows dielectric constant decreases gradually with increase in the frequency in low-frequency region whereas it is almost independent of the frequency in the high-frequency region. The prepared material exhibits high dielectric constant in low frequency which is due to the presence of space charge polarisation present in the prepared material [7-8].

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Mechanics, Materials Science & Engineering, April 2017 – ISSN 2412-5954

Fig. 4. Variation of Dielectric constant with frequency for different temperatures.

Summary. Nanocrystalline CaMnO3 material was synthesized by the sol-gel method using citric acid as chelating agents were prepared at 8000C. The single phase formation was confirmed by the XRD analysis. The morphology was analyzed by SEM and chemical composition by EDX. The various modes of vibrations due to the Mn-O and O-Mn-O stretching bonds were observed by FTIR spectroscopy studies. The dielectric constant in these materials confirmed the presence of space charge polarization.

Acknowledgment. The authors would like to thank Dr. S. Kalainathan for providing dielectric facilities and also thank VIT University for their constant encouragement and support.

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[2] Loshkareva, N. N., & Mostovshchikova, E. V. (2012). Electron-doped manganites based on CaMnO3. The Physics of Metals and Metallography, 113 (1), 19-38. DOI: 10.1134/S0031918X12010073.

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[6] Soleymani, M, Moheb, A, & Joudaki, E. (2009). High surface area nano-sized La0. 6Ca0. 4MnO3 perovskite powder prepared by low temperature pyrolysis of a modified citrate gel. Open Chemistry, 7 (4), 809-817. DOI: 10.2478/s11532-009-0083-2.

[7] Lobo, L. S., & Kumar, A. R. Investigation of structural and electrical properties of ZnMn2O4 synthesized by sol–gel method. Journal of Materials Science: Materials in Electronics, 1-9. DOI 10.1007/s10854-016-4714-z MMSE Journal. Open Access www.mmse.xyz 108

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[8] Murugesan, G., Nithya, R., Kalainathan, S., & Hussain, S. (2015). High temperature dielectric relaxation anomalies in Ca0.9Nd0.1Ti0.9Al0.1O3−δ single crystals. RSC Advances, 5 (96), 7841478421. DOI 10.1039/C5RA15876A.

Cite the paper K. R. Nandan, A. Ruban Kumar (2017). Structural and Electrical Properties of CaMnO3 Prepared by Sol-Gel Method. Mechanics, Materials Science & Engineering, Vol 9. doi:10.2412/mmse.59.12.214

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