Synthesis and CHARCTERIZATION of BATIO₃ High-K NANOMATERIAL

Synthesis and CHARCTERIZATION of BATIO₃ High-K NANOMATERIAL

Aditya N. Khare 1, Abhishek Sharma 2

1Nanotechnology, Gyan Ganga college of Technology, Jabalpur, M.P. INDIA

2 Electronics and Communication engg, Gyan Ganga College of Technology, Jabalpur

Abstrat

Synthesis of Cubic barium titanate(BaTiO3) powder by heating barium titanyloxalatehydrate (BTO) precursor in microwave heating system in air at 600c . Heating BTO in microwave 700c yielded tetragonal form of BaTiO3 Experiments repeated in silicon carbide furnace showed that BaTiO3 was formed. The product obtained was cubic.

BaTiO3 is ceramic materials with high dielectric constants. However, the high dielectric constant in BaTiO3 is due to a ferroelectric transition Barium titanate (BaTiO3), a high-tech material used for the manufacture of capacitors and sensors is the first of the ceramic type ferroelectrics to be discovered and has been most extensively studied (McQuarrie 1955). Doped BaTiO3 is a strategic material used in different electro ceramic Devices. Barium titanate, perovskite structure, is a common ferroelectric material with a high dielectric constant, widely utilized to manufacture electronic components such as multilayer capacitors (MLCs), PTC thermistors, piezoelectric transducers, and a variety of electro- optic devices. Because of the peoples demands and needs dielectric (essentially nonconducting) characteristics of ceramics materials are increasing rapidly. At the same time people are attempting to reduce the size of all communication devices as small and as light as possible. Due to this trend, high

dielectric constant materials such as barium titanate nowadays become more and more important in ceramics materials[1].The perovskite- like structure, named after the CaTiO3 perovskite mineral, is aternary compound of formula ABO3 that A and B cations differ in size. It is considered an FCC- derivative structure in which the larger A cation and oxygen together form an FCC lattice while the smaller B cation occupies the octahedral interstitial sites in the FCC array. There is only the oxygen being B cations nearest neighbor. The structure is a network of corner-linked oxygen octahedra, with the smaller cation filling the octahedral holes and the large cation filling the dodecahedral holes[3].

Structure of cubic BaTiO3. The red spheres are oxide centres , blue are Ti4+cations, and the green spheres are Ba2+.

Barium Titanate was the first developed piezoelectric ceramic and even now it is still widely used. It is also a well-known material used for capacitors. The crystallographic dimensions of the barium titanate lattice change with temperature. due to distortion of the TiO6 octahedra as the temperature is lowered from the high temperature cubic form. Because the distorted octahedra are coupled together, there is a very large spontaneous polarization, giving rise to a large dielectric constant and large temperature dependence of the dielectric constant[4].

Microwave technology uses electromagnetic waves that pass through material and cause its molecules to oscillate, generating heat. In conventional heating, the materials surface heats first and then the heat moves inward. Microwave heating generates heat within the material and heats the entire volume at about the same rate. Industrial microwave furnaces have traditionally used fixed-frequency electromagnetic waves that can cause uneven heat distribution. New technology varies the frequencies, eliminating hot and cold spots. Microwave technology can be combined with conventional heating and drying units and is easily automated.

Microwave heating system

1. Synthesis of barium titanyl oxalate (BTO)

   BTO used in the present work was synthesized from the aqueous solution of Ba(NO3)2 (BN) and K2TiO(C2O4)2 (KTO). Both the chemicals were of AnalaR grade. The method consisted of mixing of equimolar aqueous solutions of BN and KTO with constant stirring. The white BTO precipitate obtained was filtered, washed with distilled water and dried in an oven at 100°C for 12h. From chemical analysis, the product could be assigned the formula BaTiO(C2O4)2×4H2O.

2. Preparation of barium Titanate (BaTiO3)

The BTO precursor was heated in the range 300 750°C microwave heating system fabricated indigenously. The power to the unit could be maintained to a constant set value to fix the desired temperature needed for the experiments, employing the proportional type (PID) temperature controller coupled to a solid state relay (SSR). A shielded chromelalumel thermocouple was used as a sensor for controlling the input power to the microwave oven at the set temperature. The thermocouple shield had to be grounded to obtain steady temperature values at the set point. The temperature of the sample could be maintained constant to ± 1°C and measured by a separate calibrated chromelalumel thermocouple. The products obtained after heat treatment of reactants at different temperatures were analysed by X-ray diffraction, SEM, EDX, FTIR, Dielectric constant.

XRD Analysis

The Ba1-xBi2x/3TiO3 ceramics were prepared by solid state reaction route. The synthesized powders were characterized by X-ray diffraction using a PANALYTIC diffractometer. XRD pattern were obtained using Cu K radiation and the Fig.1(a) show the XRD pattern of the Bi doped BaTiO3 range from 20-80o in 2 scale at the rate of 0.04o/second. According to JCPDS no.05-0626, all the peaks in the patterns are matching and its showing purely tetragonal single phase crystal related to tetragonal BaTiO3.

Fig. 1a Fig. 1b

Fig. 1c Fig. 1d

Fig. 1e

From Fig.1(b), it is well known that the tetragonal phase was identified by an analysis of the peaks [002] and [200] at the 2 from 44.5-46o. The splitting of [002] and [200] peaks indicates the tetragonal phases. While increasing the concentration of Bi in BaTiO3, the intensity of is peak [002] at 44.9 is minimizing. This minimization indicates the conversion of tetragonal phase to cubic phase after the certain limit of doping concentration. Fig.1(c) and (d) shows the lattice parameter as well as the unit cell volume results of Ba1-xBi2x/3TiO3 ceramics.

Table 3, shows the parameters about the peak position, FWHM, a, b, c parameters, volume, c/a, crystallite size, lattice strain, Dhkl and dhkl for all x values at the major peaks of the XRD patterns at 31.4o. In Fig.1(e) variation of crystalline size as a result of Bi substitution is clearly seen. Crystalline size decreases with increasing concentration of the Bi in BaTiO3 and these effects is clearly seen in the peak broadening of Fig.12.

Peak position, FWHM, a, b, c, volume, c/a, crystalline, lattice strain, dhkl and Dhkl parameters for all composition of x.

SEM

Fig.2 shows the surface structures of all sintered pellets at 1300oC for 4 hours. The microstructure of the sintered specimens of the BaTiO3 with x=0 to 0.1, Bi were shown the grain increment when the doping concentration is increasing and these result also exactly related to the crystalline size of the calcined powders from the XRD pattern. Due to surface volume ratio of the calcined powder reduces the melting temperature and increasing the grain size at the time of sintering. But in the undoped (x=0) BaTiO3 having high grain and well sintered.

Figure 2 SEM picture of Ba1-xBi2x/3TiO3 pellets for all composition of x

Fig.3 shows the EDX spectra of Ba1-xBi2x/3TiO3 ceramic, in EDX spectra it is clearly seen that the prepare Ba1- xBi2x/3TiO3 ceramic compound is only composition of Ba, Bi, Ti, ad O. It gives the weight percentage and atomic percentage of the compound. Little amount of Bismuth is modifying the whole part of the crystal symmetry. Table.4 Weight % and Atomic % of all elements present in the Ba1-xBi2x/3TiO3 pellets.

Figure 3 EDX spectrum of Ba1-xBi2x/ 3TiO3 pellets

Weight % and Atomic % of all elements present in the Ba1-xBi2x/ 3TiO3

In Fig.4 shows the Relative permittivity of sintered pellets of Ba1-xBi2x/3TiO3 for x= 0, 0.025 and 0.05. The sintered samples were coated with silver paste on both sides and heated at 500oC for 30 minutes for perfect conductivity of the electrodes. The permittivity at 1 kHz as a function of temperature for Ba1-xBi2x/3TiO3 ceramics under different concentration of x= 0, 0.025 & 0.05.

Fig. 4a Fig. 4b

Fig. 4c

(Relative permittivity Vs Temperature of sintered pellets of Ba1-xBi2x/ 3TiO3 for x= 0, 0.025 and 0.05)

In the relative permittivity versus temperature plots of x=0, 0.025 and 0.05 samples displayed sharp peaks at a transition temperature of around 140oC. The Ba1-xBi2x/3TiO3 ceramics exhibited a decrease in the transition temperature with increased concentration of Bi2O3. The results showed an increase in permittivity up to a maximum for the composition of x = 0 is 4455 at transition temperature 128oC, for the composition x = 0.025 is 1635 at transition temperature 149oC and for composition x = 0.05 the maximum relative permittivity is 2674 at transition temperature 133oC.

FTIR analysis

Figure 5 (a-b) shows the FTIR spectra of the Barium Titanate powder and the powder modified with 0.1 wt% of silane. The broad band at 568 to 577 cm-1 are due to TiO stretching modes of BaTiO3 while peaks at 1430 and 1625 cm-1 are related to the CO2 absorption20. Moreover, peaks at 853 are the characteristic peak of CC stretching modes. Figure 3 a shows an additional peak at 1364 cm-1 corresponding to organic groups of silane21-22.

IR spectra of 0.1 % silane modified Barium Titanate

IR spectra Barium Titanate

The results obtained in this investigation show that Ba-TiO3 in the cubic form could be synthesized from BTO at temperature as low as 500°C. Thermal decomposition of BTO presumably yields hypostoichiometric TiO2 by virtue of the presence of evolved CO in the reaction, which in the presence of the microwave field combines with BaO to yield the cubic phase. The cubic BaTiO3 transformed completely to the tetragonal form on heating it in the microwave field above 700°C. In the recent studies (Potdar et al 1998; Khollam et al 2002), it was reported that BTO on heating in the resistance heated furnace above 700°C in air produced cubic form of BT. The production of tetragonal form of BaTiO3 at low temperatures following the present procedure could provide considerable edge over other existing processes and make it economically much more viable for commercial exploitation.

1. Y S MALGHE, A V GURJAR and S R DHARWADKAR*Synthesis of BaTiO3 powder from barium titanyl oxalate (BTO) precursor employing microwave heating technique

   Bull. Mater. Sci., Vol. 27, No. 3, June 2004, pp. 217220. © Indian Academy of Sciences.Department of Chemistry, The Institute of Science, Mumbai Condensed Matter Physics and Materials Science Division, Tata Institute of Fundamental Research, Mumbai.

2. HyeongSeok Lee1, 2, Sang Man Koo1 and Jung Whan Yoo2 Characteristics of BaTiO3 Particles Synthesized by Precipitation from Low-Temperature Aqueous SolutionsJournal of Materials Science and Engineering A 2 (1) (2012) 7-15. Department of Chemical Engineering, Hanyang University, Haengdang-dong, Seongdong-Gu, Seoul 133-791, Korea.

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3. Borkar S A and Dharwadkar S R 2004 Ceram. Int. 30 509 Clabaugh W S, Swigbard E M and Gilchrist R 1956 J. Res. Nat.

4. PusitPookmanee ,ChanitpaKhantha , SukonPhanichphant Department of chemistry, Faculty of Science, Maejo University, Chiang Mai, Thailand

5. Guang J. Choi,Sang K. Lee,Kyoung J. Woo,Kee K. KooandYoung S. Cho Characteristics of BaTiO3 Particles Prepared by SprayCoprecipitation MethodUsing Titanium Acylate-Based Precursors Chem. Mater., 1998, 10 (12), pp 41044113

   DOI: 10.1021/cm980520h Publication Date (Web): December 1, 1998 American Chemical Society, Division of Chemical Engineering, Korea Institute of Science & Technology, Cheongryang, Seoul , South Korea, and Department of Chemical Engineering, Sogang University

6. R. Maier and J. L. Cohn Department of Physics, University of Miami, Coral Gables, Florida Ferroelectric and ferrimagnetic iron-doped thin-film BaTiO3: Influence of iron on physical properties R. Maier and J. L. Cohn Department of Physics, University of Miami, Coral Gables, Florida 33124 (Received 14 December 2001; accepted 3 August 2002)