Electrical and dielectric properties of the Ca2MnO4−δ system

The materials Ca 2 MnO 4 − δ ( δ = 0.0 – 0.5 ) were prepared in two steps: the preparation of the parent compound Ca2MnO4 by the sol–gel method followed by the creation of oxygen vacancies δ . The morphology has been studied by scanning electron microscopy (SEM) technique and has revealed that the free surface morphology becomes more densified when increasing the oxygen vacancies δ . The electrical properties have been studied using dc conductivity and ac impedance spectroscopy techniques. From the dc conductivity measurements it was found that, at high temperatures, the conduction mechanism is controlled by small polarons. The activation energy increases with δ , indicating an increase in the height of the potential barriers. The dielectric properties were studied using the modulus formalism, showing a non-Debye relaxation process, which is thermally activated presenting activation energy independent of δ .