Influence of Grain Formation on Electrical Properties of La<sub>0.67</sub>Sr<sub>0.33</sub>MnO<sub>3</sub>

Abstract

In this work, polycrystalline perovskite manganites of La0.67Sr0.33MnO3 (LSMO) sample was prepared by two wet chemical methods: co-precipitation (CP) and sol-gel (SG) methods. Both samples were sintered at high temperature (1300 °C) for longer duration (24 hours) to investigate the effect of grains formation on its electrical properties. XRD results show that both samples were forming single LSMO phase with hexagonal structure (R-3c). SG sample shows smaller grain size (~220nm) however the CP sample (~4.45μm) was about 20-fold larger. Slower grain growth takes place in SG sample due to the triple junction effect where grain growth in nanocrystal is limited. Terrace patterns are noticed on the surface of CP sample which is suspected as the occurrence full crystallization or recrystallisation. TP of SG sample was shifted to lower temperature (298 K) due to the significant magnetically disordered layer across the grain boundaries which had weakened double exchange effect. SG sample displays higher extrinsic MR (-10.8%, 1 kG) and intrinsic MR (-25.1%, 10 kG) at 80 K due to the Core-Shell effect in the nanograin. However, grain boundaries (shell) effect is weakening in full crystallite CP sample. Hence, only intrinsic MR can be observed which is-15.6% at 10 kG applied field. Consequently, extrinsic MR is dominant in sol-gel sample however intrinsic MR is dominant in co-precipitation sample. Therefore, the grain size and microstructure formation affect the Tp, resistivity and magnetoresistive effect.