Low-temperaturesynthesisofnanocrystalline Ca1 xHoxMnO3 d (0pxp0.3) powders

Abstract

Nanocrystalline Ca1 xHoxMnO3 d (0<x<0.3)manganites were synthesized as phase-pure by a simple and instantaneous solution autogel combustion method,which is a low temperature initiated synthetic route to obtain fine grain size. All the samples,heated at 800 ºC for 18h,can be produced as phase-pure; the polycrystalline powders are homogeneous and possess ultrafineparticle size.The holmium-doped calcium manganites retain the orthorhombic phase of the undoped sample.The scanning electron microscope (SEM)images revealed that the combustion-derived compounds exhibit particle size that decreases with holmium contentfrom 300 to 80nm. All manganites show two active IR vibrational modes near 400 and 600cm 1. The high temperature dependence of resistivity was measured using a standard four-probe method in the range 25–600 ºC. All the samples exhibit semiconductorbehaviour and holmium induces a marked decrease in the electrical resistivity when compared with the parent CaMnO3. The results can be well attributed to the Mn4+/Mn3+ ratio and to the particle grain size.