1-Physics - IJPR - Ferro - CK Dixit

International Journal of Physics and Research (IJPR) ISSN 2250-0030 Vol.2, Issue 2, Sep 2012 1-6 © TJPRC Pvt. Ltd.,

FERRO-ELECTRIC BEHAVIOR OF POTASSIUM RUBIDIUM TRI TITANATES CHANDRA KUMAR DIXIT & A.K SRIVASTAVA 1 2

Feroze Gandhi Institute of Engineering andTechnology Raebareli U.P India

Physical Research Laboratory Kamla Nehru Institute of Physical and Social Sciences Sultanpur India

ABSTRACT Ferroelectric sample of polycrystalline KRB)Ti3O8 has been prepared using high temperature solid state reaction. Room temperature X-ray diffracto grams confirm the phase evolution. Rubidium ions occupy the Potassium lattice sites giving rise to electric dipoles which increases electric permittivity. Dielectric data reveal that occupancy of Rubidium ions on Potassium ions leads to decrease in dielectric loss and an increase in the electric permittivity as well. The sample shows ferroelectric phase transition and hysteresis also.

KEYWORDS: Dielectric Properties, Alkali tri-titanates, ferroelectrics.

INTRODUCTION Layered compound exhibit highly anisotropic structural and elastic properties. They are characterized by rather layers, loosely stacked together perpendiculars to each other and can intercalated with other chemical species [1]. Tritanets nanotubes made by single alkali treatment [2]. The crystal structure of more than ten sodium titanates were established while the Na2Ti3O7 phase among the first to be synthesized and structurally studied [3]. Electrical studies in some alkali tritanates have been reported by Shripal et. al.

[4] The sodium titantes Na4TiO4 α, β and γ- Na2TiO, Na8Ti5O14 , Na2Ti3O7 and Na2Ti6O13 all of which can be synthesized in the temperature range 8000C to 12000C have been characterized by X-ray diffraction and Raman Spectroscopy[5]. The phase composition of NaXMXTi8-XO16 (M=Al, Ga, In) materials was studied by X-ray diffraction. A total of about 130 phases including a dozen of sodium titanates [7-15] are known.

Recently, the crystal structure of Na2Ti3O7 has been refined by O.V Yakubovich and V.V Kirev [16]. Shripal et. al. have been reported the dielectric spectroscopic and a. c conductivity studies of pure and manganese doped Na2Ti3O7 [17,18] .Since orbital overlap is crucial for electrical conduction it is important to take in consideration the joining nature of the octahedral. In case of layered pervoskite structure, corner sharing of octahedral is spread over two directions [19, 20]. The zigzag layer tritanates are composed of Ti06 distorted octahedral. The position of titanium ion deviates from the centre of gravity of surrounding oxygen ions and so gives rise to a dipole moment. The zigzag layer of has been shown to exhibit three dipole moments [21].The zigzag layer of Na2Ti3O7 has been shown tp exhibit three dipoles moments, 5.0, 5.8 and 6.2D

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Chandra Kumar Dixit & A.K Srivastava

[21].EPR and electrical studies in layered Na1.9Li0.1Ti3O7 and its Copper and manganese doped derivatives have been reported. No attempt has been made through dielectric –spectroscopic studies of pure Potassium Rubidium Tri-Titanates. In this paper we have carried out the dielectric spectroscopic studies of KRbTi3O8.

EXPERIMENTAL The ceramic sample has been synthesized using sintering process. The method of preparation of palletized ceramic samples is similar to that reported earlier in the literature .XRD patterns for all the compositions were collected by Iso-Debeflex 2002. Richsie-frierst and Co diffracto meter using CuKα radiation generated at 30 kV and 20 mA. The formation of this Tri Titanates is confirmed by the XRDpatterns obtained at room temperature.

The flat faces of the sintered pellets were painted with an air dried high purity silver paste and then mounted in the sample holder evacuated up to 10-3 mbar for the electrical measurements. The loss tangent and parallel capacitance of the palletized samples were directly measured as a function of temperature and frequency by HP 4194A impedance analyzer.

RESULTS AND DISCUSSIONS

Fig.1 Loss tangent versus Temperature

Fig.1 shows the dependence of loss tangent on temperature in the temperature range 373-773K at some fixed frequencies for PRT. From these plots it can be seen that the value of dielectric constant (tanδ) remains invariant with rise in temperature up to 523K for PRT. The rate of increase of tanδ with temperature in the high frequency range decreases with increasing frequency. The increase of dielectric loss may be due to the space charge polarization [21] which can be explained by using Shockley-Read mechanism [22]. The

Ferro-Electric Behavior of Potassium Rubidium Tri Titanates.

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general increase of tanδ with temperature can be explained by assuming that the number of ions that takes part in relaxation polarization continuously grows with rise in temperature [25].

Fig. 2 Loss tangent versus frequency Fig 2. Shows the dependence of loss tangent (tanδ) on frequency in temperature range 373—773K for PRT. The curves show that at lower temperature tanδ decrease gradually when frequency increases but at higher temperature, tanδ decrease exponentially with the rise in frequency. This may be due to dipole mechanism of losses [23] along with the losses due to motion of bound ions i.e. due to electrical conduction [24].

Fig. 3 Dielectric constant versus Temperature Fig. 3 shows the variation of dielectric constant (ε’) with respect to temperature at some fixed frequencies. It can be seen that dielectric constant (ε’) increases rapidly for PRT with temperature up to 573K than a broad peak appears at 598K and finally increases with the rise in temperature. These results can be explained by assuming that micro structural phase change exists between these temperatures. The existence

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Chandra Kumar Dixit & A.K Srivastava

of broad peak may be due to the possible ferroelectric phase transition. The remaining variation of all the curves can be easily explained proposing that the dipoles are not aligned in the low temperatures region so when the temperature rises the orientation of dipoles is facilitated and this increase dielectric constant. As the temperature grows the chaotic thermal oscillation of molecules are intensified and degree of orderliness of their orientation is diminished. This causes the curves of dependence of dielectric constant to pass through the maximum and then drop.

Fig. 4 Dielectric constant versus Temperature

Fig.4 shows the variation of dielectric constant (ε’) versus frequency curves for PRT and its manganese doped derivatives at various temperatures. The curves have the same nature for PRT. The value of dielectric constant (ε) is lower at higher frequency. All these curves have the same nature as for polar dielectric. It is reported [24, 25] that when the frequency of alternating voltage increases the value of dielectric constant of polar dielectric remains invariable but beginning with a certain frequency when polarization fails to settle itself during one half period, dielectric constant (ε’) begins to drop approaching at very high frequencies to the value of non polar dielectric. Dielectric dispersion is seen for these compounds.

CONCLUSIONS Dielectric –Spectroscopic investigations show the presence of dipole mechanism of losses along with the losses due to the motion of loosely bound ions and space charge-polarization at higher temperature.

The possible ferroelectric phase transition at 598K for Potassium Rubidium Tri-Titanates indicates that the ferroelectric behaviors have been identified. Layered Potassium Rubidium Tri-Titanates ceramic can be put in the class of mixed ionic –electronic materials.

Ferro-Electric Behavior of Potassium Rubidium Tri Titanates.

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ACKNOWLEDGEMENTS This work is partially supported by Department of Science and Technology, New Delhi and also Indian Institute of Technology Kanpur India

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