B-site Fe doping effect on the structure and electronic transport properties of quasi-one-dimensional spin ladder compound Sr-14(Cu1-yFey)(24)O-41

Two groups of Sr-14 (Cu1-y Fe-y)(24)O-41 compounds with Fe3+ doping and 2/3Fe(3+) + 1/3Fe(2+) admixture doping respectively were prepared by conventional solid-state reaction. X-ray diffraction analysis shows that the samples have single phase with y <= 0.03 of Fe3+ doping and y <= 0.02 of 2/3Fe(3+) + 1/3Fe(2+) admixture doping. The lattice parameters a and b decrease gradually when the doping content increases for each group. The measurements of electronic transport properties show that the electrical resistivity decreases monotonically with the increase in y of Fe3+ doping, which indicates that free hole carriers in the ladder increase. A crossover temperature T-rho was observed in the Arrhenius plot of the resistivity versus temperature. The decrease of resistivity of the Fe3+ doped samples is interpreted in term of the dissociation of spin dimers and hole pairs located in the ladder induced by the substitution of Fe3+ for Cu2+. Two kinds of possible conduction mechanisms above and below T-rho are presented respectively. The fitting of experimental data proves that the conduction mechanism above T-rho is due to thermal activated single-holes' contribution, while below T-rho one-dimensional hopping conduction is dominant.