Structural and Electron-Hopping Studies of Pr- and Nd-Substituted La2/3Ba1/3MnO3 Manganites

摘要

The significance of substituting concentrations of Pr and Nd at La-sites, in Lao6vBao33Mn03 perovskite compounds, for the structural and electrical properties have been studied. Polycrystalline samples (Lai..x Prx)0 67Bao 33MnO3 and (Lai.x Ndx)o.67Bao33MnC>3 with x = 0.00, 0.167, 0.333, 0.5, 0,667, 0.833 and 1.0 were synthesized via conventional solid-state reaction in the bulk, All of the samples were calcined at 900°C for 12 hours, pelletized and sintered at 1300°C for 24 hours and investigated In this paper the structural patterns and microstructural properties of bulk samples have been investigated via x-ray diffractometry (XRD) and scanning electron microscopy (SEM). XRD patterns show that these systems are single-phase, with oithorhombic distorted perovskite structures. The electrical property, Tp, was determined by using standard four-point probe resistivity measurements in the temperature range of 20 K to 300 K. The result shows that Pr and Nd dopants shift the value of Tp to a lower temperature. When the temperature is above Tp, T> Tv, the variation of the electrical resistance was found to follow the an Arhenius-type law, p = p0 exp (-EH/KBT). It was used to calculate the activation energy of every sample. The resistivity curves show semiconducting behavior of all samples above their T_p.