Studies on transport properties of manganite based nano–micro particles–matrix composites

Abstract

In this communication, low resistive bulk La0.7Ca0.3MnO3 (LCMO) was prepared by solid state reaction (SSR) route whereas high resistive nanoparticles of LaMnO3 (LMO) was prepared by cost effective sol–gel technique. Composites of LMO and LCMO were prepared by mixing them in different weight ratios, i.e. LMO = 10%, 20% and 30% in LCMO manganite matrix. In the present study, LMO have been used as nanoparticle fillers in the LCMO matrix lattice to study the transport properties of the composites. X–ray diffraction (XRD) measurement reveals the single phasic nature of the composites without any detectable impurity within the measurement range studied. XRD pattern of higher LMO content based composite possesses slightly different structural phases of LMO and LCMO. Resistivity measurement reveals that all the composites exhibit metal to insulator electronic phase transition at respective TP, wherein values of resistivity and TP get modified due to the cooling or heating cycles performed, measurement current used and LMO nanoparticle filler content in the composites. These variations have been discussed in the context of scattering centres created due to the presence of LMO fillers and complex phase separation scenario of the composites. A clear phase separation in higher filler content based composite has been displayed in its resistivity behaviour. To understand the charge transport mechanisms responsible for metallic and insulating (or semiconducting) regions in resistivity behaviours of the composites, most suitable zener double exchange polynomial law and Mott type variable range hopping mechanism were fitted theoretically to the obtained experimental results. Fittings show that spin fluctuations in the composites are highly dependent on the cycles performed, current applied and LMO nanoparticle filler content in the composites. Applied negative and positive current and voltage dependent resistance of the composites reveal the negative electroresistance. Both, resistance of the composites as well as electroresistance are highly affected by the cycles performed, current applied and LMO nanoparticle filler content in the composites understudy. Temperature dependent electroresistance was studied for better insight into an active role of phase separation near electronic phase transition temperatures for all manganite based composites.