Processing, dielectric and impedance spectroscopy of lead free BaTiO3-BiFeO3-CaSnO3
Introduction
In the days of modernization, smart materials, including ferro-electro-magnetics, ferroics, piezoelectrics, optical fibers and shape-memory alloys are tailored by external stimuli. The main reason of being smart may be due to its application for specific uses exhibiting certain nature more than its usual properties. Multiferroic materials are a special class of smart materials which contains two or more ferroic domains (ferroelectric, ferromagnetic, ferroelastic, etc.) in a single-phase system. Such type of materials has a great potential for fabrication of devices (i.e., sensors, storage devices, spintronic device, etc.) and diversely in industries, like automotive, defense, aerospace and robotics [[1], [2], [3]]. In an extended meaning, this class of materials is capable of switching the electrical field with the virtue of magnetic field as well as the spontaneous magnetization, switched by means of an applied electric field [4]. One of the promising multiferroic materials at room temperature is bismuth ferrite, BiFeO3 (BFO). It has a ferroelectric transition temperature of 830 °C and anti-ferromagnetic transition temperature of 370 °C [5]. It is observed that BFO has difficulty in getting proper ferroelectric hysteresis loop due to large leakage current and low resistivity. At room temperature, due to semi-conducting nature of BFO, the experimental data also show low values of dielectric constant, high loss and low spontaneous polarization [6]. In order to resolve these inherent problems of BFO, the fabrication of solid solutions/composites, suitable doping/substitution at the cation sites and the development of new techniques to get single phase of BFO has extensively been attempted [[7], [8], [9]]. It has also been found that the preparation of pure BFO has a significant presence of the secondary phase/impurity (Bi40Fe2O63 or Bi36Fe2O57) leading to a controversial composition. For increasing the structural stability of BFO, the fabrication of BFO-ABO3 (A = mono to -divalence ions, B = tri to hexavalence ions) system has been found very important for scientific as well technological importance. Some of past investigation shows that the BFO-PbTiO3 [10] composite has enhanced electrical polarization and reduced leakage current, BFO-DyFeO3 [11] composite reveals enhanced dielectric properties, whereas BFO-BaTiO3 [12] revels both ferroic order and low loss (less than 3%). Yang et al. fabricated BFO-BTO-YIG composites and reported the basic crystal structure, proper (less leaky) P-E loop and enhanced electrical and magnetic properties [13]. Out of many perovskites, some members of alkaline-earth stannate family have been used to fabricate its composites with bismuth ferrite for the enhancement of dielectrsic properties, manufacturing of thermally stable capacitors and photo-catalysis. In both the states (i.e., doped or pure), such type of materials is considered as a base material for gas detection sensors which involves various gas like H2, Cl2, NO2, CO, HC [14]. Despite such potential applications, some alkaline earth stannate composites have not been examined extensively except a few. Mandal et al. [15] reported the processing and electrical properties of CaSnO3 porous sample. But, the correlation of such prepared material was not established with BFO-BTO solid solutions. The porous sample prepared by them cannot be a better capacitor material, because the electric charge carriers will sink in the pore leading to a reduced grain to grain connectivity. The availability of pores within the sample will lead to the interaction with humidity. In this context, firstly, we have added a small amount (7 wt %) of CaSnO3 in the BTO (major)-BFO(minor) system which leads to high reactivity and a reduction in the reaction temperature.
Taking the environmental concerns, the elimination of lead compounds from device engineering leads to focus on the synthesis, and characterization (phase evolution, microstructure, molecular and electrical properties (conductivity, impedance, modulus, and dielectric) of an electronic composite of three perovskites in a 80/13/07 ratio (i.e., 0.8(BaTiO3)-0.13(BiFeO3)-0.07(CaSnO3) = BTO-BFO-CSO-7).
Section snippets
Experimental
The fabrication of BTO-BFO-CSO-7 was carried out by a standard mixed-oxide route using starting materials; BaCO3 (M/S Loba Chemie Co Ltd, 99% pure), Fe2O3 (M/S Loba Chemie Co Ltd, 98% pure), Bi2O3 (M/S Central Drug House Pvt Ltd, 99% pure), TiO2 (M/S Loba Chemie Co Ltd, 98% pure), SnO2 (M/S Loba Chemie Co Ltd, 99.9% pure), CaCO3 (M/S Sigma-Aldrich, 99.99% pure). These raw powders of oxides and carbonates were carefully weighed in required stoichiometry. The starting materials were mixed in a
Crystal data and morphology
To check the phase purity, the crystal structure determination, and lattice parameters X-ray diffraction analysis was undertaken. Fig. 1 exhibits the X-ray diffraction (XRD) pattern of BTO-BFO-CSO-7 which analysis confirms the coexistence of BTO-BFO and CSO phases in the fabricated composite. It shows a number of sharp peaks which are totally different from that of raw materials. Analysis of XRD pattern confirms the presence of desirable phases (i.e. both BTO-BFO and CSO) in the composites with
Conclusion
In the present study, the structural, capacitive (dielectric constant, tangent loss) and resistive (impedance, modulus and conductivity) properties of BTO-BFO-CSO-7 were intensively studied. The compound was synthesized by a cheap cost (high-temperature solid-state reaction) route. The room temperature XRD reveals the presence of all BTO, BFO, CSO phases along with some impurity peaks in the prepared composite. Substitution of CSO in BTO-BFO has improved the microstructure, with high density,
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