Variable-range hopping conductivity in La1-xSrxMn1-yFeyO3 (x=0.5;y=0, 0.02, 0.1)

The temperature dependences of the resistivity rho(T) of ceramicLa1-xSrxMn1-yFeyO3samples atx = 0.5, andy = 0, 0.02 and 0.10 are investigated in the temperature range of 5-300 K in magnetic fieldBup to 1 T. It was found that dependences rho(T) withx = 0.5;y = 0.02, and 0.10 obey the Shklovskii-Efros-like variable-range hopping conductivity law rho(T)=rho 0(T) exp[(T0/T)1/2].This behavior is governed by generation of a soft Coulomb gap Delta approximate to 0.3 eV in the density of localized states, as well as a rigid gap delta v approximate to 0.20 and 0.17 eV aty = 0.02 andy = 0.10, respectively. The obtained values of the rigid gap aty = 0.02 indicate the presence of charge ordering. It was shown that a decrease in the width of the rigid gap whenyis increased, is accompanied by both a growing disorder attributed to the presence of Fe and a decrease in lattice distortions caused by charge ordering aty = 0.02. It is shown that the pre-exponential factor of resistivity follows the law rho 0(T)proportional to Tm,wheremchanges from 9/2 aty = 0.02 to 5/2 aty = 0.10. This confirms that doping with Fe enhances microscopic disorder by introducing an additional fluctuating short-range potential. The calculated values of the carrier localization radius alpha approximate to 5.1 and 2.7 angstrom aty = 0.02 andy = 0.10, respectively, satisfy the condition for the formation of small polarons.