One-dimensional nanoferroic rods; synthesis and characterization

Accepted Manuscript One-dimensional nanoferroic rods; synthesis and characterization M.A. Ahmed, U. Seddik, N. Okasha, N.G. Imam PII:

S0022-2860(15)00465-2

DOI:

10.1016/j.molstruc.2015.05.060

Reference:

MOLSTR 21615

To appear in:

Journal of Molecular Structure

Received Date: 2 April 2015 Revised Date:

18 May 2015

Accepted Date: 19 May 2015

Please cite this article as: M.A. Ahmed, U. Seddik, N. Okasha, N.G. Imam, One-dimensional nanoferroic rods; synthesis and characterization, Journal of Molecular Structure (2015), doi: 10.1016/ j.molstruc.2015.05.060. 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.

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One-dimensional nanoferroic rods; synthesis and characterization M. A. Ahmed, U. Seddik *, N. Okasha**, and N. G. Imam*

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Material Science Lab. (1) Physics Department, Faculty of Science, Cairo University, Giza, Egypt *Physics Department, Nuclear Research Center, Atomic Energy Authority, 13759, Cairo, Egypt **Physics Department, Faculty of Girls, Ain Shams University, Cairo, Egypt

Abstract:

One-dimensional nanoferroic rods of BaTiO3 were synthesized by improved X-ray diffraction

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citrate auto-combustion technology using tetrabutyl titanate.

(XRD), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX),

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transmission electron microscopy (TEM), atomic force microscopy (AFM) and Fourier transform infrared spectroscopy (FTIR) have been used to characterize the prepared sample. The results indicated that the crystal structure of BaTiO3 is tetragonal phase with an average crystallite size of 47 nm. SEM image gives a cauliflower-like morphology of the agglomerated nanorods. The stoichiometry of the chemical composition of the BaTiO3 ceramic was confirmed by EDX. TEM

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micrograph exhibited that BaTiO3 nanoparticles have rod-like shape with an average length of 120 nm and width of 43 nm. AFM was used to investigate the surface topography and its roughness. The topography image in 3D showed that the BaTiO3 nm which in

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particles have a rod shape with an average particle size of 116

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agreement with 3D TEM result.

Keywords: Nanorods- BaTiO3, Improved citrate autocombustion technique, Butyl Titanate, XRD, SEM, TEM, FT- IR, and AFM. *

Corresponding Author: Neama Gomaa Imam (N.G. Imam) [email protected], and [email protected], Experimental Physics Department, Nuclear Research Center, Atomic Energy Authority, Cairo, Egypt; p.O: 13759 ; Tel: (+202) 01015576957; Fax: (+202) 44620812.

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ACCEPTED MANUSCRIPT Introduction: Nanomaterials have been broadly investigated for the fundamental scientific and technological interests in accessing new classes of functional materials with unique properties and applications [1, 2]. Nanoscale one-dimensional materials, such as nanowires, nanorods, and nanotubes, have unique applications in fabrication of

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nanoscale electronic and photonic devices due to their high surface-to-volume ratio and the quantum confinement effect [2, 3]. Ferroic material is that which either displays spontaneous magnetization (ferromagnetic), polarization (ferroelectric), or strain (ferroelastic) [4]. It can be used in variety of applications, such as capacitors

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and multilayer capacitors (MLCs). Barium titanate is a member of a large group of compounds normally perovskite. This material is very significant electronic materials

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and one of the most useful dielectric with low losses and ferroelectric properties. Its high purity, super fineness, and the narrow size distribution of the powder correspond to high technological applications such as MLCC [5], positive temperature coefficient (PTC) thermistors [6] and electro- optic devices.

Barium titanate gains its own ferroelectric character due to presence of the

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noncentrosymmetric unit cells [7-9]. Since nanomaterials show unusual properties compared with the traditional materials, therefore studies upon obtaining nanoparticles of BaTiO3 gradually become attractive and so more attentions have been paid upon this area [8]. Ferroelectric properties and a high dielectric constant

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make BaTiO3 useful in different arrays of applications [9] such as multilayer ceramic capacitors gate dielectrics waveguide modulators, IR detectors and holographic

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memory.

It is known that synthesis routes play a crucial role in preparing the target

product and determining its properties. There are different synthesis techniques for preparing BaTiO3 nanoparticles [10]. It is usually prepared via the conventional solid state reaction between titanium dioxide and barium carbonate at relatively high temperature around 1100–1300°C. On the other hand, chemical or wet routes with hydrolysis precursors are being developed to prepare BaTiO3 at relatively low temperature 650-750°C in order to produce BaTiO3 in nanoscale form. In order to obtain nanoscale ceramics at relatively low temperature, various chemical synthesis techniques have been proposed and developed over the last few decades [11-14]. 2

ACCEPTED MANUSCRIPT Usually, the techniques start from the preparation of a precursor solution, where the ions are well mixed on a molecular scale. Solid precursor compositions are then formed by co-precipitation and hydrothermal treatment [11-15]. In the present work, BaTiO3 powder is synthesized via modified citrate autoignition technique using butyl titanate. The main goal of study is to investigate the

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influence of modified preparation method on the structural and microstructure of BaTiO3 nanoparticles. This work contributes to the enhancement of the application possibilities of BaTiO3 by introducing simple and effective synthesis technique which

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produces nanorod BaTiO3. Experimental techniques:

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Preparation of nano- BaTiO3 powder:

Citrate method utilizes poly-chelates between the C=O ligands of citric acid (CA) and metal ions. Improved citrate auto-combustion technique is used to prepare fine powder of BaTiO3. Besides, this technique has proved to be a novel, extremely facile, time-saving and energy-efficient route for the synthesis process. Citrate technique or sol–gel auto-combustion route [16] is based on gelling and subsequent

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combustion of an aqueous solution containing salts of the desired metals and some organic fuel, giving a voluminous and fluffy product with large surface area. The details of this modified citrate auto-ignition process are shown schematically in Figure (1). Reagent grade of Ba(NO3)2, tetrabutyl titanate [Ti (OC4H9)]4, from (BDH)

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and citric acid (CA) were used as starting materials and chelating agent. The used molar ratio of fuel (CA) to nitrates in the initial mixture has a great effect on

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calcination condition as well as synthesized crystallites. By controlling the CA/NO3 ratio and calcination temperature, homogeneous crystalline powders were obtained with a nanoscale primary particle size. Stoichiometric amount of Ba(NO3)2 (0.1 mole) was dissolved into 500 ml deionized water in one beaker and 0.2 mole of citric acid was mixed well with 0.1 mole of tetrabutyl titanate under mechanical stirring using magnetic stirrer. The two solutions were mixed and stirred at 70 °C till evaporating all volatile components as well as water from the beaker. A very dense gel was formed and finally a black powder was observed as indicated in Figure (2a). The black powder was grinded mechanically well in agate mortar, inserted in alumina crucible and heated using Lenton Furnace VAF 1615 at 700 °C for 5h with a heating rate of

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ACCEPTED MANUSCRIPT 5°C /min; Figure (2b). A white fine powder of BaTiO3 was formed and observed after annealing. Characterization Techniques: The produced white powder was identified and characterized by XRD using X-

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ray diffractometer model Proker D8 with CuKα radiation (λ = 1.5418°A) in a wide range of Bragg’s angle (2θ) ranging from (10°-70°) at room temperature. FTIR spectrum of BaTiO3 nanopowder was carried out using thermo scientific Nicolet iS10 FT-IR Spectrometer. The morphology of the samples was observed using a low vacuum scanning electron microscope (LV-SEM, JEM-100S) equipped with an EDX

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detector. Transmission electron microscopy (TEM) was performed using a JEOL4010 electron microscope. The sample was ultrasonically dispersed in acetone and then

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collected on a carbon grid. The atomic force microscope (AFM) was performed because it is a suitable tool for characterizing nanoparticles. It offers the capability of 3D visualization and both qualitative and quantitative information on many physical properties including size, morphology, texture and roughness of surface. Statistical information, including size, surface area, and volume distributions, can be determined as well. A wide range of particle sizes can be characterized in the same scan, from 1

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nanometer to 8 micrometers. In addition, the AFM can characterize nanoparticles in multiple mediums including ambient air, controlled environments, and even liquid dispersions. The AFM images were obtained by Agilent 5500 AFM equipment using

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tapping mode.

Results and Discussion:

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XRD Analysis:

Powder X-ray diffraction technique is frequently employed to determine the

crystal structure and average crystallite diameter of the as- prepared samples [17]. Figure (3) shows XRD pattern for the obtained white powder to examine its crystallization. The obtained chart indicated that, BaTiO3 is formed in single phase with tetragonal crystal structure as compared with ICDD card (067519). Moreover, the results of XRD revealed the nanocrystalline nature of BaTiO3 with the average crystallite size ~ 47 nm. The combination of (002) and (200) peaks was sufficiently broad to suggest the nanometric tetragonal structure. These results agree with those

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ACCEPTED MANUSCRIPT obtained for BaTiO3 [15]. The observation of the peaks (001) and (100) confirms the tetragonal structure of BaTiO3 and the lattice parameters are a =0.39949 nm, c= 0.401308 nm and V=0.064045 nm3. Figure (4) reveals the calculated crystallite size distribution at different diffraction angle (2θ). The crystallite size (t) was calculated from X- ray broadening the FWHF and λ is the wavelength of the radiation. FT-IR Analysis:

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of the main peak (110) using Debye- Scherer's equation [18]; t = 0.89 λ / β cosθ; β is

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Generally, FTIR spectroscopy is a useful tool to detect the functional group of organic molecules [19,20]. Herein in this work, FTIR technique is used to investigate

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the chemical bonding or the chemical composition of BaTiO3 nanoparticles. The FTIR spectrum (Figure (5)) and the appeared absorption bands around 1600 and 3600 cm-1 of BaTiO3 coincide with that published in the literatures [21]. The band around 3600 cm-1 is due to O−H stretching vibrations of hydroxyls present in this system because O−H bonds form chelation organic complex in the solution. The band at 1600 cm-1 is due to the symmetric and asymmetric stretching vibrations of the carboxylate

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functional group (-COO-). One of the fingerprint stretches for BaTiO3 was also observed at ~ 420 cm−1 which is mainly due to the formation of metal oxides (M−O: Ba−O, Ti−O).

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SEM-EDX Analysis:

Figure (6) shows the SEM images of synthesized barium titanate sample. It

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confirms the porous nature with some agglomerations indicating the cauliflower-like morphology. This morphology is similar to that obtained by other authors [22]. Point analysis of the chemical composition in the micro-area for BaTiO3 was studied by energy dispersive-X-ray analysis (EDX). Stoichiometric ratios of the main metallic components of BaTiO3 were recalculated in mass %: Ba – 58.88 %, O – 20.6 % and Ti – 20.53 %. Results of the EDX depicted in Figure (7), reveal the following chemical composition: Ba – 52.17 %, O – 25.92 %, Ti – 21.87 % which is nearly similar to the nominal composition.

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ACCEPTED MANUSCRIPT TEM Analysis: Figure (8) presents the TEM images of the prepared BaTiO3 sample. It is evident that, the image exhibits rod-like morphology for BaTiO3 with length of 120 nm and width of 43 nm. TEM images prove that the modified citrate auto-combustion method was successful and easy method for obtaining nanorods bundle filaments in

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this perovskite. AFM Analysis

AFM offers the capability of 3D rather than 2D visualization and both qualitative and quantitative information on many physical properties including size,

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morphology, surface texture and roughness as in Figure (9a). Statistical information, including size, surface area, and volume distributions, can be determined for BaTiO3

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[23-25]. It is clear from the photograph that, the surface, in general, is very smooth. The grains are densely and regularly packed without cracks or voids. Besides, the particles have almost rod shape with average particle size 116 nm . It is important to note that the average particle size estimated by AFM images is larger than the size calculated by the Debye–Scherrer formula [18], pointing out a possible polycrystalline nature of BaTiO3 grains. The surface roughness determined from

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Figure (9b) has the value of 653 nm. Figures (9c, d) depict the AFM image for one island, with mean volume of 139 nm3, mean height of 6.68 µm and mean height to surface ratio equals to 0.162 V/ µm2 indicated that the crystal structure of BaTiO3 is

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tetragonal phase. Figure (10) illustrates the statistical information, including size, surface area, and volume distributions of the investigated sample. Figures (9, 10 and 11) provide the analysis of AFM and give qualitative information about the surface

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topography and grains shape of BaTiO3 which has grains of rod (bean)-like shape with average particle size 59.1 nm. Figures (12 and 13) provide quantitative or statistical information about roughness, spatial parameters and grains size. From a deep look to these images, we can say that, the surface, in general, is relatively smooth due to almost small values of roughness parameters such as average roughness Ra=29.3 nm, maximum profile peak height (Rp=84.3 nm), maximum profile valley depth (Rv=89.1.5 nm ), and total roughness (Rt =Rp+Rv = 173 nm) as shown in Figure (13).

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ACCEPTED MANUSCRIPT Conclusion: We have successfully synthesized ferroelectric nanocrystalline BaTiO3 with crystallite size around 47 nm with rod shape by modified citrate auto-ignition method in which introduced simple and more effective synthesis technique. Accordingly we have concluded that:

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1- Tetra-n-butyl titanate was succeeded to derive the titania at relatively low temperature and with safe manner.

2- Nanocrystalline tetragonal BaTiO3 with the average crystallite size less than

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~50 nm was formed by the well-crystallized fine particles obtained by heating at 700 0 C for 5 hs.

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3- SEM image gave a cauliflower-like morphology of the agglomerated nanorods. 4- The EDX result exhibited that Ba, Ti and O ions were formed in stoichiometric ratios.

5- TEM micrographs exhibited that nano-BaTiO3 particles have rod-like shape

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with average length 120 nm and width of 43 nm.

6- AFM introduces a more resolution and 3D visualization of the sample surface

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confirming the nanorods shape of BaTiO3 with narrow distribution. Finally this synthesis method has a great effect on the desired characteristics of BaTiO3 (in comparison with different researches about BaTiO3). We succeeded to

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prepare nanorods of technological important material (BaTiO3) by using modified new method and introduce it in different technological applications such as in memory devices. References:

[1] A. Sobhani-Nasab, S. Mostafa Hosseinpour-Mashkani, M. Salavati-Niasari, S.

Bagheri, J. Clust. Sci. (2014) doi: 10.1007/s10876-014-0814-1. [2] S. Mandizadeh, F. Soofivand, M. Salavati-Niasari, S. Bagheri, J. Ind. Eng. Chem. (2014), http://dx.doi.org/10.1016/j.jiec.2014.10.044.

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ACCEPTED MANUSCRIPT [3] M. A. Ahmed, U. Seddik, and N. G. Imam, World J. Cond. Matt. Phys. 2(2012)2

[4] C. Pithan, D. Hennings, R. Waster, Int. J. Appl. Ceram. Technol., 2 (2005)1. [5] K. Park, Mater. Sci. Eng. B, 107 (2004) 19.

[7] Baorang Li, Xiaohui Wang, Longtu Li,Materials, (2002) 292.

Chemistry and Physics 78

[8] L. Zhang, Literature review, 04019/CISM/llz (2004).

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[6] M. M. Vijatović, J. D. Bobić, B. D. Stojanović; Sci. of Sintering, 40 (2008) 155.

[9] S W Ding, Y Y Zhang, C Y Feng and H J Zhang, J. of Physics: Conference Series 188 (2009) 012059.

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[10] M. A. Ahmed and S. I. El-Dek, Mat. Lett., 60(2006)1437. doi:10.1016/j.matlet.2005.11.076

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[11] M. A. Ahmed, N. Okasha and R. M. Kershi, J. Magn. and Magnet. Mat., 321(2009)3967. doi:10.1016/j.jmmm.2009.07.002 [12] C. Otero Areán, M. Peñarroya Mentruit, E. Escalona Platero, F.X. Llablrés i Xamena and J.B. Parra, Mater. Lett., 39 (1999) 22. [13] K. Okuyama and I.W. Lenggoro, Chem. Eng. Sci., 58 (2003) 47.

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[14] X. Yu, X. He, S. Yang, X. Yang and X. Xu, Mater. Lett., 58 (2003) 48. [15] W. Li, J. L and J. Guo, J. Eur. Ceram. Soc., 23 (2003) 95. [16] F. Ansari, A. Sobhani and M. Salavati-Niasari, RSC Adv., 2014, 4, 63946.

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[17] S. Zinatloo-Ajabshir, M. Salavati-Niasari, New J. Chem., 2015, doi: 10.1039/C4NJ02106A.

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[18] A. Sweyllama, K. Alfaramawi, S. Abboudy, N. G. Imam and H. A. Motaweh, Thin Solid Films, 519(2010)681. doi:10.1016/j.tsf.2010.08.112. [19] F. Ansari, F. Soofivand, M. Salavati-Niasari, Mat. Characterizatio 103 (2015) 1117, http://dx.doi.org/10.1016/j.matchar.2015.03.010. [20] F. Beshkar, S. Zinatloo-Ajabshir, M. Salavati-Niasari, J Mater Sci: Mater Electron, 2015, doi: 10.1007/s10854-015-3024-1. [21] K. Al faramawi, A. Sweyllam, S. Abboudy, N.G. Imam and H. A. Motaweh , Inter. J. Modern Phys.B, 24(2010) 4717. doi:10.1142/S0217979210056165 [22] M. A. Ahmed, N. Okasha and N. G. Imam, The African Review of Phys., North America Vol 7, No. 2 (2012)7. http://www.aphysrev.org/index.php/aphysrev/article/view/516/222 8

ACCEPTED MANUSCRIPT [23] M. A. Ahmed, N. Okasha, and N. G. Imam, J. Magnetism and Magnetic Mater. (MAGMA), 324 (2012) 4136–4142. [24] M. A. Ahmed, N. Okasha, and N. G. Imam, Prime J. Engin. and Tech. Res. (PJETR), 1, 1 (2012) 19-25.

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[25] J. Scalf, P. West," Part I: Introduction to Nanoparticle Characterization with AFM", Pacific Nanotechnology, Inc. 3350 Scott Blvd., Suite 29, Santa Clara, CA 95054

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ACCEPTED MANUSCRIPT Preparation of BaTiO3 by modified citrate method using Butyle Titanate

500 ml. deionized water

0.1 M Butyl Titanate Ti(OC4H9)4(99.9 %)

Mixed solution with stirring at 70°C for 1 h

0.1M Ba(NO3)2(>99.9 %)

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0.2 M Citric Acid solution (pH 6)

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Mixed solution with stirring

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Mixed solution with stirring at 70°C adjust pH at 7-9

Combustion on hot plate at 120°C

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Formation of a fluffy black mass

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Grinding the powder to be fine and homogeneous.

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XRD

EDX

Sintering at 700oC for 5 hours with heating rate of 5°C/min

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SEM TEM

FT-IR

Figure (1): Flow chart of the citrate autoignition procedure of synthesis BaTiO3 nanoparticles.

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Figure (2a): BaTiO3 prepared as black powder by citrate method before loading to the furnace.

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Figure (2b): The formation of BaTiO3 after annealing, the color changed from dark to white.

a

b

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2500

20

30

40

50 o 2θ ( )

60

(301)

70

(311)

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0

(221)

(202)

(102)

(100)

(001)

500

(111)

1000

(211)

1500

(002) (200)

CPS (a.u)

2000

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Figure (3): XRD pattern of nanopowder BaTiO3

80 60 40 20 0

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3

4

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1

2Theta

Cry size

5

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7

8

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22.1 31.5 38.8 45.2 50.9 56.1 65.8 70.4 74.8 39 58.3 75.6 33.5 50.2 48.3 42

46 27.3

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Figure (4): Crystallite size distribution at different diffraction angles (2θ θ).

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0.3

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Absorbance %

0.4

0.1 4000

3600

3200

2800

2400

2000 -1

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W ave num ber (cm )

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800

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Figure (5): FTIR spectrum of BaTiO3 nanoparticles.

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2 µm

700 X

2000 X

(c)

1 µm

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4000 X

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(d)

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5 µm

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(b)

250 nm 11000 X 5

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Figure (6): SEM micrograph of BaTiO3 with different magnification.

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Counts

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Figure (7): EDX analysis of BaTiO3 perovskite sample

Table 1: EDX of BaTiO3 sample

Percentage%

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element

52.17

Ti

25.92

O

21.87

Total %

99.96

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Ba

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Figure (8): TEM micrograph of BaTiO3 nanopowder.

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(c)

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Figure (9): AFM topography image (6×6 µm2 area and 1.32 µm in height); (a): AFM topography image in 3D, (b): The surface roughness, (c, d): AFM image for one island showing the surface roughness.

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Figure (10): Histogram of the number of grains per µm2 .

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Figure (11): AFM images for BT for a surface area = 6×6 µm2 showing the surface topography and grain shape and size.

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Figure (12): AFM images for BT nanopowder for a surface area = 6.4×6.4µm2 showing the surface roughness in 3D and grain size.

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Figure (13): AFM analysis for BT nanopowder showing the roughness profile and parameters.

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Highlights: 1- One-dimensional nanoferroic rods of BaTiO3 were prepared. 2- SEM image gives a cauliflower- like morphology of the agglomerated nanorods. 3- The EDX result exhibited Ba, Ti, O in the stoichiometric amount.

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4- 3D AFM images confirm the nanorods shape of BaTiO3 with narrow size

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distribution.