Synthesis and Characterization of BNT based Magnetoelectric Composites

Abstract

The magnetoelectric (ME) composites has gained great deal of attention over to single phase multiferroics due to its strain mediated coupling between piezoelectric and magnetostrictive phases. Such composites with high coupling have paved the way for practical device application in meRAMs, sensors, and low frequency energy harvesters etc. The resultant ME coupling depends upon the type of magnetic and piezoelectric phase, their relative fraction, and type of geometry. Amongst lead-free piezoelectric materials, BNT-based ternary solid-solution, i.e., 72.5Bi0.5Na0.5TiO3-22.5Bi0.5K0.5TiO3-5BiMg0.5Ti0.5O3 (BNKMT) is prominent due to its excellent piezoelectric coefficient. On the other hand, NiFe2O4 or Ni1-xZnxFe2O4 (x = 0 - 0.5) exhibit high piezomagnetism. Therefore, in this work, the main focus is to study the influence of relative weight fraction and geometry on the magnetoelectric coupling of their composites. The work is organized into seven chapter, where the content of each chapter is shown below. Chapter 1 (Introduction): This chapter provides a concise introduction about magnetoelectric (ME) properties in multiferroic materials. Further, an overview of ME coupling in single-phase multiferroics and composites is given. Some basic definitions and terminology used in the thesis are given along with their important role in ME properties are discussed. The factors that influence the ME coupling in composites are discussed in detail. At last, applications of ME composites in several areas are highlighted. Chapter 2 (Literature review): This chapter is mainly focused on the factors that have influence on the ME coupling of composites. Initially, the impact of substitution and doping on the BNT-based solid solutions is reviewed followed by the effect of substitution on magnetostrictive phase. The ME coupling in particulate and laminates has been discussed. The effect of phase fraction and applied f of H on ME coupling among particulates and laminates is also presented. Based on these studies, the literature gap