Small polaronic hole hopping mechanism and Maxwell-Wagner relaxation in NdFeO3

Abstract

In the modern micro-electronics, transition metal oxides due to their colossal values of dielectric permittivity possess huge potential for the development of capacitive energy storage devices. In the present work, the dielectric permittivity and the effects of temperature and frequency on the electrical transport properties of polycrystalline NdFeO3, prepared by solid state reaction method, are discussed. Room temperature Mossbauer spectrum confirms the phase purity, octahedral environment for Fe ion, and high spin state of Fe3+ ion. From the impedance spectroscopic measurements, three relaxation processes are observed, which are related to grains, grain boundaries (gbs), and electrode-semiconductor contact in the measured temperature and frequency ranges. Decrease in resistances and relaxation times of the grains and grain boundaries with temperature confirms the involvement of thermally activated conduction mechanisms. Same type of charge carriers (i.e., small polaron hole hopping) have been found responsible for conduction and relaxation processes through the grain and grain boundaries. The huge value of the dielectric constant (∼8 × 103) at high temperature and low frequency is correlated to the Maxwell-Wagner relaxation due to electrode-sample contact.

EFFECT OF Mn DOPING ON STRUCTURAL AND DIELECTRIC PROPERTIES OF GdFeO3.

“…Therefore, polarization increases and hence the dielectric constant also increases. The decrease of dielectric constant at higher frequency can be explained on the basis of space charge polarization model of Maxwell [21] and is also in agreement with the Koop's phenomenological theory [22]. The decrease of dielectric constant at higher frequency can be explained on the basis that the solid is assumed as composed of well conducting grains separated by poorly conducting grain boundaries.…”

Temperature dependent dielectric and magnetic properties of GdFe1−xNixO3 (0.0 ≤ x ≤ 0.3) orthoferrites

“…Pure composition possesses high dielectric constant even at room temperature, which is consistent with the dielectric reports of other orthoferrites. 18,19 This is due to the close-packing of oxygen ions having loosely bound electrons, as these electrons get distorted in an applied electric field. 19 On comparing the compositional variation of e 0 , it can be noticed that the magnitude of the dielectric constant as well as dispersion has increased in the x ¼ 0.1, 0.2, 0.3 samples as compared to the pure sample.…”

Dielectric Relaxation, Modulus Behaviour and Conduction Mechanism in NdAlO3 Ceramics

“…The exponent n has been found to behave in a variety of forms as a constant or decreasing and increasing with the temperature, but always varying within 0 < n < 1. 36 For NAO, the frequency dependence of conductivity does not follow the power law as given above but is well described by the double power law given as 43…”

“…The response of the grain boundaries, due to their higher resistance and capacitance, lies at the lower frequencies compared to the response of the grains. 36 It is observed that with the increase of temperature both grain and grain-boundary arcs shift to the higher frequency side. It is known that Z*-plots for polycrystalline dielectric materials do not always yield perfect semicircular arcs, they even become asymmetric.…”

“…37,38 In order to correlate the electrical properties of NAO with the microstructure of the material, an equivalent circuit model consisting of two parallel RQ circuits connected in series (as shown in the inset of Fig. 11a) has been employed to interpret the nature of the Z*-plots 36 Here, R and Q are the respective resistance and the CPE for the grain interiors (R g , Q g ) and the grain boundaries (R gb , Q gb ).…”