IJARBAS, Vol. 1(1) Dec. 2014
ISSN 2394-4072
Sol-gel Auto Combustion Synthesis of Barium Zirconate (BaZrO3) Nanocrystalline Ceramics Pankaj P. Khirade1, Shankar D. Birajdar1, S.P.Jadhav2, K.M.Jadhav1 1
Department of Physics, Dr. Babasaheb Ambedkar Marathwada University, Aurangabad, India. 2 Department of Chemistry, Adarsha College, Omerga, Osmanabad, India. Corresponding Author:
[email protected];
[email protected]
Abstract: A sol-gel auto combustion method was employed to synthesize perovskite structured barium zirconate (BaZrO3) nanocrystalline ceramics. Precursors in the form of nitrates were used; citric acid was used as a fuel in the reaction. The metal nitrate to fuel ratio was taken as 1:1. The asprepared sample was calcinated at 850 ˚C to form single phase perovskite structure, which is significantly lower that solid state reaction method. The structural analysis was carried out by using X-ray diffraction (XRD) technique. The average crystal size determined by using Debye Scherrer’s formula was of the order of 38 nm. The lattice constant (a) and other structural parameter were obtained using XRD data and it is found that the structural data is in reported range.
Keywords: sol-gel auto combustion, barium zirconate, nanocrystalline, ceramics,
INTRODUCTION Perovskites having the general chemical formula ABO3 (A being the cation of larger size e.g. Ca, Ba, Sr etc and B = Ti, Zr, Mn etc) are materials of interest for a wide range of applications [1, 2]. Ceramic materials with perovskite type structure are value added materials used for several applications such as capacitors, non-volatile memories, actuators and sensors, piezoelectric, ultrasonics and underwater devices, high temperature heating applications, frequency filters for wireless communications etc [3-5]. Barium zirconate (BaZrO3) are of great industrial and technological interest due to their attractive characteristics like high melting point (2920 ˚C), poor thermal conductivity, excellent mechanical and structural integrity under extreme thermal conditions, high protonic conductivity etc [6-8]. Also the high dielectric constant and low loss characteristics in BaZrO3 ceramics make it as a promising material for various microwave applications [9]. As far as the synthesis processing is concerned, the traditional solid state reaction method was usually used to prepare BaZrO3 perovskite ceramics which requires relatively high sintering temperature (1400-1500 ˚C). Despite its simplicity this method is difficult to form homogenous distribution of compositions, sometimes leading to the appearance of impurity phases. By comparison, wet chemical methods such as sol-gel auto combustion method can effectively avoid these disadvantages owing to the control
of accurate stoichiometry and the mixing of various precursors on a molecular level [10]. Morever, powders obtained from wet chemical methods are significantly smaller particle size i.e. in nanoscale, leading to the improved and distinct properties [11]. The other advantages are, it is one of the simple and rapid method of preparation, control of particle size and composition is possible, possibilities to modify the particle surface and maintain overall homogeneity. According to literature survey, BaZrO3 ceramics has been synthesized by several other methods like ceramic [12], hydrothermal [13], coprecipitation [14] etc methods. But BaZrO3 nanoparticles by sol-gel auto combustion method was not been yet reported much. In this study, a sol-gel auto combustion method was explored to prepare barium zirconate (BaZrO3) nanoparticles.
EXPERIMENTAL For the synthesis of barium zirconate (BaZrO3), raw materials in the form of nitrates such as Ba(NO3)2 (≥99.0%) and ZrO(NO3 )2(≥99.9%) were used. Citric acid (C6H8O7) was used as a fuel. All chemicals used were AR grade and purchased from DODAL Chemicals Aurangabad. The metal nitrate to fuel ratio was taken as 1:1. The detailed procedure is given in Fig.1. The aqueous solutions of respective nitrates were prepared by dissolving in distilled water. After mixing they initially gives clear solution.
IJARBAS, Vol. 1(1) Dec. 2014 These samples were heated at 80 ˚C for 15 min. The pH of the solution was maintained at 7 by adding ammonia solution with constant stirring. It gives white precipitate as shown in Fig.2(a). The temperature of the mixed solution is again increased to 100 0C, which results in the gel formation. After 4 h, the self ignitions starts and dried gel burnt in a self propagating combustion process to obtain fine particles of barium zirconate (shown in Fig.2(b)). The obtained powder was dried, crushed and sintered at 850 0 C for 4 h in high temperature heating furnace to obtain the required sample.
ISSN 2394-4072 The X-ray diffraction (XRD) technique was employed to confirm the phase purity and nanocrystalline nature of the prepared barium zirconate nanoparticles (Rigaku, ModelMiniflux-II). The X-ray diffraction pattern was recorded in the 2θ range of 200 - 700 at room temperature using Cu-Kα radiation (having wavelength 1.5405 Ǻ).
RESULTS AND DISCUSSION The X-ray diffraction pattern shows (Fig.3) the presence of desired phase of pure perovskite structure; no extra peak of impurity phase was observed in the XRD pattern, confirming the single phase nature of the sample.
Fig.3. X-ray diffraction pattern of BaZrO3 nanoparticles. Fig.1. Flowchart of sol-gel auto combustion synthesis of BaZrO3 nanoparticles.
Fig.2. (a) white precipitate (b) after combustion the formed product.
The reflections (001), (100), (101), (111), (002), (200), (102), (210), (201), (112), (211) (022) and (220) belonging to single phase cubic perovskite structure are present in the XRD pattern. The reflection (101) is found to be more intense and is used to determine the crystallite size. All the peaks are sharp and are good agreement with the XRD pattern of pure barium zirconate reported in the literature (JCPDS NO. 06-0399). The crystallite size was determined from the value of full width at half maximum (FWHM) of the most intense reflection (101), using the Debye Scherrer’s formula [15]: 0 .9 (1) t cos where, t is the average diameter in nm, β is the FWHM, λ is the wavelength of X-ray radiation and is the Bragg’s diffraction angle. The calculated value of average crystallite size was given in Table 1 and is in nanometer scale confirming the nanocrystalline nature of the prepared samples. The lattice constant of the present barium zirconate nanoparticles was computed using the
IJARBAS, Vol. 1(1) Dec. 2014
ISSN 2394-4072
inter-spacing values and the respective (hkl) parameters from the classical formula [16]:
a
[ h 2 k 2 l 2 ]1 / 2 2 sin
(2)
The value of lattice constant was also given in Table 1. The lattice constant of the present barium zirconate nanoparticles is found to be in the reported range. The unit cell volume (V) was calculated by using the following equation and is represented in table 1: (3) V = a3 where, V is the unit cell volume and a is the lattice constant. The value of lattice constant and molecular weight were used to determine the X-ray density of the prepared sample by using the following relation [16]: ZM (4) d x V NA where, dx is X-ray density, Z is the number of molecules per unit M is molecular mass of the sample, V is the unit cell volume, NA is the Avogadro’s number. The perovskite structure of the prepared sample is confirmed by calculating tolerance factor (t’) by using Goldschmidt relation [17]:
t'
( rA rO ) 2 (rB rO )
(5)
where, rA and rB are the ionic radii of the A and B cations and rO is ionic radius of oxygen anion (in A° unit). Tolerance factor (t’) was found to be 1.004 confirming the perovskite structure. Table 1: Lattice constant (a), Unit cell volume, X-ray density (dx), Average crystallite size (t), and tolerance factor (t’) for barium zirconate nanoparticles. Sample
a (A0 )
V (A0)3
dx (gm/cm3)
t (nm)
t’
BaZrO3
4.1556
71.763
6.374
38
1.004
CONCLUSION Perovskite structured barium zirconate (BaZrO3) nanocrystalline ceramics have been successfully synthesized by sol-gel auto combustion method. The structural analysis was done by X-ray diffraction technique. All the peaks observed in
XRD pattern belong to single phase cubic perovskite structure. The average particle size obtained was about 38 nm. All the parameters obtained from XRD, lattice constant (a), X-ray density (dx) and unit cell volume (V) were in the reported range.
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