Investigations on Dielectric phase transition behavior of Pb(Fe 0.5-x Sc x )Nb 0.5 O 3 Multiferroic Ceramics
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Investigations on Dielectric phase transition behavior of Pb(Fe0.5-xScx)Nb0.5O3 Multiferroic Ceramics Bandi Mallesham 1, Ranjith Ramadurai 1
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1) Department of Materials Science and Metallurgical Engineering, Indian Institute of Technology Hyderabad, Kandi, Sangareddy-502285, Telangana, India ABSTRACT Phase pure Pb[(Fe0.5-xScx)Nb0.5]O3 [x = 0 to 0.5] multiferroic relaxors have been synthesized to study the effect of Sc on dielectric phase tansition. Rietveld refinement of x-ray diffraction patterns confirm that the structure transforms from monoclinic (Cm) to rhomobohedral (R3m) at x = 0.3. Absence of low frequency dielectric response in compositions with low Sc content attributed to interfacial polarizabilty arising due to differences in conductivities of grain and grain boundary. Moreover, value of diffusivity parameter (γ) of high of Sc content compositions is near to 2, confirms relaxor charactertistic of these compositions. However, an essential feature of relaxors i.e., frequency dependent dielectric permittivity as a function of temperature is observed only in x = 0.5 composition [Pb(Sc0.5Nb0.5)O3 (PSN)]. In addition, ferroelectric phase transition temperature (Tmax) increases initially at lower Sc content (upto x ≤ 0.25), and further drops beyond x ≥ 0.3. Such behavior of Tmax in these compositions is due to the onset of B'-B" local cation ordering at x = 0.3. High temperature Raman spectra of Pb(Sc0.5Nb0.5)O3 (x = 0.5) confirm the stability of cation ordering in compositions with high Sc content well above the phase transition temperature. INTRODUCTION Single phase multiferroic relaxors Pb(Fe0.5Nb0.5)O3 (PFN), Pb(Fe0.5Ta0.5)O3, Pb(Fe0.67W0.33)O3 [General formula: A(B'B")O3] have gained great interest to understand the fundamental science behind, the structural and physical properties. Among these lead iron niobate [Pb(Fe0.5Nb0.5)O3] is an interesting compound exhibiting a weak magnetoelectric coupling at room temperature [1]. PFN exhibits ferroelectric to paraelectric transition around 380 K, with a G - type canted antiferromagnetic ordering below 143 K [2, 3]. However, there exists an anomaly associated to structural and dielectric properties of PFN. Room temperature crystal structure of PFN remains ambiguous with plausible rhombohedral (space group: R3m) and monoclinic (space group: Cm) symmetry at room temperature [4, 5, 6]. In addition, though PFN belongs to family of ralxor ferroelectrics it does not exhibit frequency dependent dielectric permittivity as a function of temperature [7, 8, 9]. Hence, the present study focuses on the effect of Sc substitution on dielectric phase transition behavior of Pb[(Fe0.5-xScx)Nb0.5]O3 [x = 0 to 0.5)] ceramics. EXPERIMENTAL WORK Phase pure compounds of Pb(Fe0.5-xScx)Nb0.5O3 [PSFN] (x = 0, 0.1, 0.15, 0.2, 0.25, 0.3, 0.4, 0.5) ceramic powders have been synthesized using wolframite precursor method. Wolframite precursor method is commonly used to synthesize these complex oxides to reduce *
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