Enhancement of Optical, Electrical, Magnetic, and Thermopower Properties of LaMnO₃ by Potassium‐Doping

Abstract

Optical, magnetoresistance, and thermoelectric properties of La1−xKxMnO3 (x = 0.05, 0.15, and 0.25) compounds have been investigated. The crystallography demonstrates that the samples x = 0.05 and 0.15 are a single‐phase rhombohedral () structure, while x = 0.25 is near to a single rhombohedral phase with a minor amount of Mn3O4 (with a ratio of ≈2%). The optical properties manifest that the reflectivity decreases slightly with increasing x‐doping, where the sample of x = 0.05 has the lowest reflection value, making it a promising material for photovoltaic applications. Electrical resistivity measurements show that the samples have a metal–semiconductor transition, and the transition temperature Tms decreases with the K content. The thermoelectric data show a remarkable coincidence behavior of the ρ–T relationship, which has a peak at a transition temperature (TS). Magnetic susceptibility data show that the samples undergo ferro‐paramagnetic transition at a certain temperature (Curie temperature).

Bandgap Energy of Ion‐Doped LaMnO3 Nanoparticles

“…The magnetization M decreases (see Figure 2, curves 3 and 4) whereas the bandgap energy in LMO NPs increases (see Figure 3, curves 3 and 4). Mohamed et al [ 10 ] reported also an increase of in K‐doped bulk LMO, as well as Tran et al [ 5 ] in Sr‐doped LMO NPs.…”

“…Doping LMO with various ions allows the adjustment of the bandgap energy in both bulk and NP forms. [ 6–11 ] is reduced by doping with ions like Ga, Gd, Fe, Co, Ba, and Ag, [ 6–9 ] while it increases with K or Ce substitution. [ 10,11 ] Such a contrary behavior in LMO could be caused by varying strains induced by the different ionic radii between the dopant and host ions.…”

“…[ 6–11 ] is reduced by doping with ions like Ga, Gd, Fe, Co, Ba, and Ag, [ 6–9 ] while it increases with K or Ce substitution. [ 10,11 ] Such a contrary behavior in LMO could be caused by varying strains induced by the different ionic radii between the dopant and host ions. Additionally, the interaction between La and the doping ions (DIs) might play a role in altering electronic properties and consequently, the bandgaps.…”