ABSTRACT

La_0.4Pr_0.25Ca_0.35-xAg_xMnO₃ samples were elaborated using sol–gel method. X-ray diffraction study indicates that the investigated compounds exhibit an orthorhombic structure with Pbnm space-group symmetry. Introducing Ag in the investigated system leads to changes in the unit cell parameters and cell volume. The electrical properties have been investigated using the impedance spectroscopy technique. Dc-electrical resistivity study shows a metal-semiconductor transition at T_MS= 220 K, which is Ag independent. Also, it is found that the resistivity decreases with increasing silver content. Then, the activation energy of the hopping mechanism is reduced with increasing Ag concentration. For different silver concentration, the conduction is dominated by thermally activated small polaron hopping (SPH) process at the high temperature and by variable range hopping (VRH) process at lower temperatures.

摘要

La _0.4 Pr _0.25 Ca _{0.35- x} Ag _x MnO ₃样品采用溶胶-凝胶法制备。X 射线衍射研究表明，所研究的化合物表现出具有 Pbnm 空间群对称性的正交结构。在所研究的系统中引入 Ag 会导致晶胞参数和单元体积发生变化。已经使用阻抗谱技术研究了电特性。直流电阻率研究显示T _MS处的金属-半导体转变= 220 K，与 Ag 无关。此外，还发现电阻率随着银含量的增加而降低。然后，跳跃机制的活化能随着银浓度的增加而降低。对于不同的银浓度，传导在高温下由热激活小极化子跳跃（SPH）过程和在较低温度下由可变范围跳跃（VRH）过程支配。