Enhancement in thermoelectric properties of n-type (La0.7Sr0.3MnO3)0.5.(NiO)0.5: composite and nano-structure effect

In the enhancement of thermoelectric properties of material for energy harvesting applications, the role of nano-composite made of two different materials plays a very crucial role. When materials with different crystal and electronic structure are synthesized in nano-crystalline phase to form a composite, they provide large power factor via energy filtering effect, whereas the lattice mismatching and grain boundaries of two phase scatter the phonons having wide range of frequencies, and effectively maintain the low thermal conductivity. In the present work, we have reported the structural and thermoelectric properties of (La0.7Sr0.3MnO3)(0.5)(NiO)(0.5) composite synthesized by sol-gel method. Rietveld refinement of the XRD pattern confirms the presence of both phases. Thermoelectric properties are measured in 300-600 K temperature range. The magnitude of Seebeck coefficients, electrical resistivity, and thermal conductivity found to be monotonically increase with temperature upto the similar to 450 K, which decrease gradually with further increase in temperature. Such variation in transport properties are resulted from the combine effect from the composite materials formed with semiconducting/metallic, and insulating electronic structure mixed in a 50:50 weight ratio. The calculated 'figure-of-merit' (ZT) shows an increasing trend with temperature. The value of ZT(max) is found to be similar to 0.05 at 600 K, which is nearly three times larger than that of La0.7Sr0.3MnO3 (ZT = 0.013) reported earlier. Our strategy of making nano-composite two materials with different electronic structures enhanced the ZT by similar to 285%. The improvement in thermoelectric properties of n-type oxide materials can be useful to consider this material for applications in mid-temperature range.