Structural, Electrical and Magnetic Properties in the System Na0.5CoO3

The present study reports the structural, magnetic and electrical properties of the Na 0.5 CoO 3 system produced by the conventional solid state reaction method. The X-ray diffraction analysis allows to infer that the compound crystallizes in a monoclinic system with spatial group C 2 / m and network parameters: a = 5.55 (8) Å, b = 4.87 (3) Å y c = 2.85 (8) Å. It is found that the mean grain size of the stoichiometric of system amounts approximately to 76 nm. Below 40 K, an antiferromagnetic behavior with T N ≈ 40 K was observed, while in the region between 80 and 190 K the system obeys the law of Curie–Weiss, and the effective magnetic moment was determined experimentally of 5.62 μ B , indicating a high spin configuration for the Co 2 + ion ( S = 3/2) in the fundamental state 4 T 1 g . The system shows cluster spin glass properties with low temperatures, the temperature of magnetic moment freezing from ∼ 40 K . The behavior of the resistivity under absence of magnetic field and the presence of an insulating state between two different metallic states was observed. The metal–insulator transition occurred at two temperatures, the first around 170 K, and the second around 40 K, the latter in accordance with the magnetic transition temperature.