Sushrisangita Sahoo

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 and electrical characteristics of barium modified bismuth-sodium titanate (Bi 0.49 Na 0.49 Ba 0.02 )TiO 3

The lead-free polycrystalline ceramic, barium titanate modified bismuth–sodium titanate 0.98 (Bi0.5Na0.5TiO3) + 0.02 BaTiO3 (BNT–BT-2) was synthesized by using a mixed oxide route at high temperature. The structural (crystal structure, microstructure, molecular structure), and electrical (dielectric constant and loss, impedance, conductivity) characteristics of the parent compound (Bi0.5Na0.5TiO3) have greatly been influenced by the addition of even a small amount of barium titanate in it. Preliminary structural study of BNT–BT-2 using X-ray diffraction data clearly shows the formation of a single-phase perovskite structure with the coexistence of hexagonal (major phase) and tetragonal (minor) phases. The existence of diffuse phase transtition and the relaxor behaviour in the material is confirmed by analysis of temperature-frequency dependence of dielectric parameters. The composition (0.98BNT − 0.02BT) of the material shows non-Ohmic conduction in its J–E characteristics. In this lead-free ceramic, permittivity anomalies are matched to modulus anomalies. The highlighted features are determined by structural phase transitions of the ferroelectric-like.