Thermopower and electrical resistivity of La1−xSrxMnO3 (x=0.2, 0.3): Effect of nanostructure on small polaron transport

•High quality La1−xSrxMnO3 ceramic samples are prepared using mechanical alloying.•Samples with nano-micrometric grain sizes are obtained by sintering at T⩽1200°C.•Thermopower and electrical resistivity were measured vs. temperature for x=0.2, 0.3.•Nanostructure induces changes in polaron activation energies.•Our results are consistent with enhanced carrier localization in nano-La1−xSrxMnO3. In this work we report on thermopower S(T) and electrical resistivity ρ(T) measurements performed on La1−xSrxMnO3 (x=0.2, 0.3) ceramic samples, obtained by cold compaction and sintering of mechanically alloyed nanocrystalline powders. The samples studied in this work display grain sizes between d∼70nm and O(2μm). The effects induced by the nanostructure on the thermoelectric and electrical properties in the paramagnetic state have been studied and discussed in terms of current theories about small polaron electrical transport in manganites. The observed changes in the conductivity and thermopower activation energies can be interpreted as a consequence of enhanced carrier localization and higher polaron formation energy WH for nanocrystalline La1−xSrxMnO3.