Structural, Dielectric and electrical properties of Antimony doped Strontium Bismuth Niobate ceramic Rajveer Singha,b,c*, Vandna Luthrab and R. P. Tandona aDepartment of Physics & Astrophysics, University of Delhi, Delhi-110007, India bDepartment of Physics, ARSD College, University of Delhi Dhaula Kuan, New Delhi-110021,Delhi, India. cDepartment of Physics, Gargi College, University of Delhi, Delhi-110049, India
Abstract: Polycrystalline Sr0.8SbxBi(2.2-x)Nb2O9 (SSBN) was prepared using solid state reaction route. SSBN was characterized by X-ray diffraction (XRD) and scanning electron microscopy and Raman spectroscopy for structural analysis. The XRD reveals that SSBN has single phase orthorhombic structure. The dielectric and impedance spectroscopy studies on SSBN were investigated in the frequency range 20 Hz – 1 MHz and in the temperature range room temperature (RT) to 500 oC. The dielectric study reveals that SSBN have relaxor behavior at lower temperature
Motivation Ferroelectric materials have been widely studied and applied to the application of nonvolatile random access memory (NVRAM), particularly over the last decade. PZT has been of the leading materials, which exhibits a high value of remnant polarization; it also can be fabricated at relatively low crystallization temperature. Fatigue (defined as loss of polarization with repeated switching of the field) and imprint are the principle factors limiting commercialization of PZT based NVRAMs. Presently, PZT thin films do not show fatigue resistance above 106 switching cycles on metal electrodes such as Pt. Bi- layered compounds, showed fatigue resistant up to 1012 switching cycles. Bi-layered compounds were first discovered by B. Aurivillius. These Aurivillius compounds have the general chemical formula of (An-1BnO3n+1)-2 (Bi2O2)+2 where ‘A’ is a divalent and ‘B’ is a pentavalent atom respectively .Recently ferroelectric thin films of SrBi2Ta2O9(SBT) and SrBi2Nb2O9 (SBN), has been considered as a prime candidate materials for non-volatile random access memory (NVRAM) devices. The fatigue free, low leakage current density ,and fast switching characteristics of these materials are extremely are useful for the reliable device operation. The crystal structure of SBN consists of Bi2O2 layers and perovskite – type units with double octahedral layers.
EXPERIMENTAL DETAILS Sr0.9Sb0.1Bi2Nb2O9 (SSBN) ceramics doped was prepared via solid state reaction method using oxide precurrsors. Wet ball milled powders were calcined at 1173K for 5 hour in furnace. Green pellets were prepared using polyvinyl alcohol (PVA) as binder and sintered at 1100 0C for 3 hour in furnace. Sintered pellets were lapped to thickness to ~1mm using silicon carbide abrasive powder. Microstructure and elemental analysis of fractured surfaces was recorded using Scanning Electron Microscope (SEM) (Zeiss, MA15) having EDAX attachment. Silver paste was used on both faces of the pellets for making electrical contacts. Impedance Figure 1. Experimental setup of ZnOwas nanostructure by measurement vapor phase transport. analyzer (Wayne Kerr 6500B) used for thegrowth dielectric as a function of frequency and temperature.
RESULTS AND DISCUSSION
Fig. 1 XRD pattern of SSBN
Fig. 2 SEM micrograph
Fig. 3 Variation of (a) Dielectric constant and (b) Dielectric tangent loss with temperature
Fig. 5 Variation of (a) critical exponent n(T) and (b) pre-factor A(T) with temperature
Fig. 6 ln(1/ε - 1/ ε max) as a function of ln(T-T0)
XRD analysis indicates that single phase layered with orthorhombic structure was formed without any secondary phase. The Dielectric study revels that the transition temperature increased from 400 oC for Pure SBN to 470 oC for SSBN and the dielectric loss was found to decreased. In fig. 4 the dielectric constant was found to follow the power Joncher’s law ε* = ε΄ - iε΄΄ = ε∞ + σ/iε0ω + (A(T)/ε0)(iω n(T)-1) Where, ε∞ is the high frequency value of the dielectric constant, n (T) is the temperature dependent and A (T) determines the strength of the polarizability. The real and imaginary part of dielectric constant can be written as ε΄ = ε∞ + (A (T)/ε0) Sin (n (T) π/2) (ω n (T)-1) ε΄΄ = σ/ε0ω + (A (T)/ε0) Cos (n (T) π/2) (ω n (T)-1) The n(T) was found to decrease with temperature and shows a minima corresponding to transition temperature and A(T) was found to increase with temperature and show a maxima at transition temperature shown in fig. 5 In fig. 6 a linear relationship was observed above the transition temperature at 500 kHz. The degree of diffuseness γ = 1.53 which shows a normal relaxor ferroelectric behavior.
Fig. 7 the inverse dielectric constant 1/ε as a function of Temperature
SEM micrograph for Sb doped SBN shows the uniform grain distribution. The grain size was found in the range 1μm to 3 μm. The permittivity of a normal ferroelectric is known to follow the Curie- Weiss law which is described by the relation: 1/ ε = (T – Tc)/C (T>Tc) The degree of deviation from the Curie- Weiss behavior could be given by ΔTm = TCW - Tm Where TCW is the temperature from which ε start to deviate from the Curie- Weiss law and Tm is the temperature of maximum ε. The dielectric behavior of a relaxor ferroelectric could be described by a modified Curie-Weiss law 1/ ε - 1/ εm = (T – Tc)γ/C Where C is the Curie-like constant and γ is the degree of diffuseness and the value lie between 1 and 2. The value γ = 1 is for the case of normal ferroelectric and the quadratic dependence is valid for ideal relaxor ferroelectric. In fig. 7 the dielectric constant (ε) was fitted at 50 kHz to the CurieWeiss law. The parameters C = 4.55×104 K, T0 = 710 K and ΔTm = 6 K were obtained. The curies constant was found to decrease with increase in frequency.
Conclusion
. In the present study, Sr0.9Sb0.1Bi2Nb2O9 (SSBN) was synthesized by solid state reaction method. Dielectric studied revel that Curie- Weiss law is satisfied with Curie constant value of 4.55×104 K. and the transition temperature was also found to increased.
Acknowledgement
Fig. 4 Variation of Dielectric constant with frequency and theoretical fitting (a) below the transition temperature and (b) above the transition temperature
The authors are grateful to Department of Physics and Astrophysics, university of Delhi, Delhi, for providing the research facilities. One of us, Rajveer Singh, would like to thank Principal ,Atmaram Sanatan Dharma College, University of Delhi, Dhaula kuan New Delhi, Delhi for providing the study leave. Email: rajveersingh@arsd.du.ac.in References 1. C.A.P. de Araujo, J.D.Cuchlaro, et al., Nature 374 (1995) 627. 2. Huiling Du, Ying li, Solid state ionics 148 (2008) 357-360. 3. K.S.Rao, D.M. Prasad et al., J. Mater Sci. (2007) 42: 7363 -7374.