Abstract
The influence of the potassium substitution for Pb ions in the mixed valence perovskites La
0.67
Pb
0.33−
x
K
x
MnO
3
(0 ≤
x
≤ 0.15) was investigated by X-ray diffraction, magnetic and electric transport measurements. All the compositions were synthesized using the sol–gel technique. X-ray diffraction and structure refinement showed that they crystallize in the rhombohedral structure with R
3
¯
c space group. Upon K doping on Pb sites, the lattice parameters, unit cell volume, and the Mn–O–Mn bond angle were reduced. All the samples exhibited a ferromagnetic–paramagnetic transition and metallic–semiconductor one with increasing temperature. The analysis of the electrical resistivity data concluded that the metallic (ferromagnetic) part of the resistivity (below
T
M-Sc
) can be explained by the following equation
ρ
(
T
) =
ρ
0
+
ρ
2
T
2
+
ρ
4.5
T
4.5
, signifying the importance of the domain boundary/grain, combination of electron-magnon, electron-electron and electron-phonon scattering processes. At higher-temperature (
T
>
T
M-Sc
) paramagnetic semiconducting regime, the adiabatic small polarons hopping mechanism (ASPH) was found to fit well.