Structural, Morphological and Dielectric Studies of (0.5) LA0.8SR0.2MNO3 + (0.5) BA0.5K0.5TIO3 Composite

Abstract

IntroductionExtensive research has been carried out on ABO 3 -type manganites of the general formula R 1−x A x MnO 3 (R = La, Nd, Pr, Y, etc. and A = Ca, Sr, Ba, Pb, etc.). Because of their extraordinary magnetic and electronic properties as well as their edge for the promising technological applications, these materials gained considerable attention [1,2]. These compounds exhibit a high degree of chemical flexibility which together with a complex interplay between structures, electronic and magnetic properties leads to a very rich phase diagram involving various metallic, insulating and magnetic phases [3]. These properties are sensitive to the doping concentration x, which determine the Mn 3+ /Mn 4+ ratio to maintain charge neutrality, the average cationic radii and the ionic size mismatch between the various A-site ions.La 0.8 Sr 0.2 MnO 3 (LSMO) belong to hole doped manganite and it is a potential candidate for technological applications because of its higher ferromagnetic transition temperature (T C ) around 370 K and a large magnetic moment at room temperature and high magnetoresistance (MR) value. The LSMO with the typical composition La 0.8 Sr 0.2 MnO 3 is broadly established as the cathode material for high temperature solid oxide fuel cells (SOFCs) [4]. The particle size and microstructure of electrode are significant for the electrode performance [5,6]. Parent compound LaMnO 3 , the antiferromagnetic insulator when doped with the divalent ions (A 2+ ), it is driven into a ferromagnetic metallic state as a result of conversion of Mn 3+ to Mn 4+ through double exchange (DE) mechanism [7]. Mason and Matthias suggested that Ti 4+ ions are the influencing factor for ferroelectric nature of BaTiO 3 [8]. Barium titanate (BaTiO 3 ) is a ferroelectric oxide that undergoes a transition from a ferroelectric tetragonal phase to a paraelectric cubic phase upon heating above 130 °C. In cubic perovskite BaTiO 3 , titanium atoms are octahedrally coordinated by six oxygen atoms. Ferroelectricity in tetragonal BaTiO 3 arises due to an average relative displacement along the c-axis of titanium from its centrosymmetric position in the unit cell and consequently the creation of a permanent electric dipole. The elongation of the unit cell along the c-axis and consequently the deviation of the c/a ratio from unity are used as an indication of the presence of the ferroelectric phase [9,10]. BaTiO 3 is particularly challenging since it exhibits three solid-solid phase transitions. BaTiO 3 is the most important perovskite (ABO 3 ) oxide with excellent dielectric and ferroelectric properties. For improvement in the performance and miniaturization of electronic devices using BaTiO 3 based materials, it is important to ensure the high dielectric constant, low dielectric loss, high remnant polarization and high dielectric strength and hence is the subject of modification. A-site substitution often comes from alkaline-earth (Sr 2+ or Mg 2+ ), alkali metals (Na + , K + ) and rare-earth ions (La 3+ etc.) whose cation size effects ...