Low-pressure air plasma induced modification of structural and electrical properties of Gd_1−x Sr_xMnO₃ manganites

The structural and electrical properties of Gd_1−xSr _x MnO₃ manganites pellets with different doping concentrations x (= 0.2,0.3,0.4,0.5) are modified using an easy low-pressure plasma irradiation method. Powder x-ray diffraction studies of the samples revealed that lattice parameters a and c increase with doping as well as plasma exposure except for x = 0.5 for which a decreases. On the contrary, lattice parameter b decreases with doping as well as plasma exposure and is more pronounced. The crystallite size increases with increasing doping concentration both with or without plasma exposure. Plasma exposure tends to decrease the Mn–O–Mn bond angle as well as the Mn–O bond length. The temperature-dependent electrical resistivity of samples reveals that the pristine Gd_1−xSr _x MnO₃ exhibits insulating behavior for all the doping concentrations. However, the resistivity is enhanced at low temperature for all samples after plasma exposure. The variation of electrical resistivity after plasma exposure may be attributed to the disorder near the grain boundaries and cell volume. The resistivity behavior is unaffected by plasma exposure for all samples. The small polaron hoping model explains the conduction mechanism at high temperature while the conduction at low temperature is attributed to variable range polarons.