Dielectric relaxations and alternating current conductivity in manganese substituted cobalt ferrite

Abstract

Manganese (Mn) substituted cobalt ferrites (CoFe 2-x Mn x O 4 , referred to CFMO) have been synthesized by the solid state reaction method and their dielectric properties and ac conductivity have been evaluated as a function of applied frequency and temperature. X-ray diffraction measurements indicate that CFMO crystallize in the inverse cubic spinel phase with a lattice constant $8.38 Å . Frequency dependent dielectric measurements at room temperature obey the modified Debye model with relaxation time of 10 À4 s and spreading factor of 0.35(60.05). The frequency (20 Hz-1 MHz) and temperature (T ¼ 300-900 K) dependent dielectric constant analyses indicate that CFMO exhibit two dielectric relaxations at lower frequencies (1-10 kHz), while completely single dielectric relaxation for higher frequencies (100 kHz-1 MHz). The dielectric constant of CFMO is T-independent up to $400 K, at which point increasing trend prevails. The dielectric constant increase with T > 400 K is explained through impedance spectroscopy assuming a two-layer model, where low-resistive grains separated from each other by high-resistive grain boundaries. Following this model, the two electrical responses in impedance formalism are attributed to the grain and grain-boundary effects, respectively, which also satisfactorily accounts for the two dielectric relaxations. The capacitance of the bulk of the grain determined from impedance analyses is $10 pF, which remains constant with T, while the grain-boundary capacitance increases up to $3.5 nF with increasing T. The tan d (loss tangent)-T also reveals the typical behavior of relaxation losses in CFMO. V C 2014 AIP Publishing LLC.

Modification of structural and dielectric properties of polycrystalline Gd-doped BFO–PZO

“…Similar behavior was observed by Kolekar et al where doping of Mn in ferrite material gives rise to a temperature-dependent increment in the dielectric constant. 49 In the present case, the slower increase of dielectric constant at lower temperature can be explained by considering the mobility of the charge carriers. In fact, as the mobility of the charge carriers at lower temperature is low (due to lack of enough thermal energy), their rate of hopping is less.…”

Analysis of the alternating current conductivity and magnetic behaviors for the polycrystalline Y-type Ba0.5Sr1.5Co2(Fe1-xAlx)12O22 hexaferrites

“…At low frequencies, the conductivity is found to be nearly frequency independent, which is considered as a dc plateau. 12,26,27 This is a typical behavior of ionic materials for the frequency region of constant conductivity (r dc ) extends to higher frequencies with increasing temperature. 27 The transition from the frequencyindependent to the frequency-dependent region signals the onset of conductivity relaxation phenomena.…”

Dependence of Lattice Distortion and Dielectric Response of Zinc Aluminate on Milling Frequency

“…The specimen is more resistive at room temperature. It is observed that arc of semicircle decreases as temperature increases which indicates the bulk resistance decrease at high temperature [29]. It gives the clue that resistance of grains is the main barrier for movement of ions.…”

“…This observation is consistent with dielectric results. However, in present study, spectrum contains a single semicircle which represents the contribution of grain interior (bulk) [29]. An equivalent circuit consisting of resistance of grains (R g ), resistance of grain boundary (R gb ), capacitance of grains (C g ) and capacitance of grain boundary (C gb ) were suggested and values of R g , R gb , C g and C gb , were determined as listed in Table II.…”