Structural, dielectric and transport properties of Na x Fe 1/2 Mn 1/2 O 2 ( x = 1 and 2/3).

Na x Fe 1/2 Mn 1/2 O 2 ( x = 1 and 2/3) layered oxides were prepared by an improved solid-state synthesis method. The XRD analysis confirmed the high purity of these samples. The Rietveld refinement of the crystalline structure illustrated that the prepared materials crystallize in a hexagonal system in the R3̄m space group with the P3 structure for x = 1 and in a rhombohedral system with the P 6 3 / mmc space group and P2 structure type for x = 2/3. The vibrational study undertaken using IR and Raman spectroscopy techniques yielded the existence of an MO 6 group. Their dielectric properties were determined in frequency range 0.1-10 7 Hz for a temperature range 333-453 K. The permittivity results indicated the presence of two types of polarization, namely dipolar polarization and space charge polarization. The frequency dependence of the conductivity was interpreted in terms of Jonscher's law. The DC conductivity followed the Arrhenius laws either at low or at high temperatures. The temperature dependence of the power law exponent which corresponds to the grain ( s 2 ) suggested that the conduction of the P3-NaFe 1/2 Mn 1/2 O 2 compound is ascribed to the CBH model, while P2-Na 2/3 Fe 1/2 Mn 1/2 O 2 can be attributed to the OLPT model.