P.K. Mahapatra

The structural, electrical and magnetoelectric properties of soft-chemically-synthesized SmFeO3 ceramics

The structural, electrical and magnetoelectric properties of SmFeO3 ceramic samples, synthesized using a soft-chemical method, were studied. A structural analysis of the material was carried out by the Rietveld refinement of room temperature x-ray diffraction data. The temperature dependence of the dielectric peaks was analyzed by fitting them with two Gaussian peaks corresponding to two phase transitions—one being electric, and the other being magnetic in nature. The depression angle of the semicircles in a Nyquist plot representing the grain and grain boundary contributions in the sample was estimated. The grain boundary effect, appearing at temperatures above 75 °C, is explained using the Maxwell–Wagner mechanism. The impedance study reveals a semi-conducting grain with an insulating grain boundary, leading to the formation of surface and internal barrier layer capacitors and resulting in a very high dielectric constant. The effect of dc conductivity on the loss tangent at low frequencies and high temperature has been analyzed. The frequency dependence of ac conductivity in the two different regions can be explained on the basis of correlated barrier hopping and quantum mechanical tunneling models. The material is found to exhibit canted antiferromagnetism and improper ferroelectric characteristics. The value of the magnetoelectric voltage-coupling coefficient (α) of a SmFeO3 ceramic is found to be 2.2 mV cm−1 Oe−1.

Structural, electrical and magnetic characteristics of improper multiferroic: GdFeO3

Studies of dielectric, impedance, conductivity, magnetic and magneto-electric (ME) properties of GdFeO3 ceramics fabricated by chemical method are reported here. The synthesized powder is phase-pure and crystallizes in the orthorhombic crystal structure. Below 50 degrees C, the impedance has only grain contribution, while at higher temperatures, it has both grain and grain boundary contributions. Based on the depression angle of the Nyquist plot, the inhomogeneity of the sample is estimated. The capacitance data reveal that at low temperatures, the sample behaves as a leaky capacitor while at higher temperatures the sample shows the effect of the diffusion of thermally excited charge carriers across a barrier. In the low-frequency domain, the dielectric characteristics were explained on the basis of the Maxwell-Wagner mechanism, while in the high-frequency range those were correlated to the grain effect. The frequency dependent characteristic of the tangent loss is explained as a combined contribution from the Debye-like relaxation and dc conductivity related mechanism at higher temperatures. The temperature dependence of the dielectric characteristic and data are found to fit with two Gaussian peaks centered at 148 degrees C and 169 degrees C. While the first peak is explained on the basis of the Maxwell-Wagner mechanism, the second has its origin in magnetic reordering and the shifting of Gd3+ ions along the c-axis. The magnetic reordering also results in a sharp decrease of conductivity between 169 degrees C and 243 degrees C. The frequency dependent ac conductivity is explained on the basis of the correlated barrier hopping model and the quantum mechanical hopping model for the different frequency domain. The existence of P-E and M-Hloops support its improper ferroelectric behavior and canted anti-ferromagnetism respectively. The ME coefficient of the sample is found to be 1.78 mV cm(-1) Oe(-1).

Structural, dielectric, impedance and modulus spectroscopy of Bi2NdTiVO9 ferroelectric ceramics

Detailed studies of electrical and resistive properties of Bi2NdTiVO9 (a member of the Aurivillius family), fabricated by a method of standard high-temperature solid-state reaction, are discussed here. The compound crystallizes in the orthorhombic crystal structure. The surface morphology studies show a uniform distribution of grains. The single semicircle of the complex impedance plot and the value of the nonlinear coefficient of the J∼E graph suggest that the polarization in the material is due to grain effect only. The semiconducting nature (i.e., negative temperature coefficient of resistance) is observed in the temperature dependence of bulk resistance and J–E characteristics of the sample. The frequency dependence of impedance and electrical modulus of the material shows the existence of non Debye-type of relaxation. The activation energy obtained from the relaxation and conduction processes is found to support the activation of oxygen vacancies in the compound. An analysis of ac conductivity, based on the Jonscher’s power law, suggests that the conduction mechanism in the material can be explained using CBH model (i.e., hopping of oxygen ions between vacancies). The nature and existence of electric field dependent polarization (P–E hysteresis loop) at room temperature show that the material has ferroelectric property.

Effect of sintering temperature on dielectric, electrical and magneto-electric properties of (Ba0.8Gd0.2)(Ti0.8Fe0.2) O3

A significant effect of sintering temperature on dielectric, electrical and magnetoelectric properties of (Ba0.8Gd0.2) (Ti0.8Fe0.2) O3 has been observed.