K. N. Singh

Bio: K. N. Singh is an academic researcher from Guru Ghasidas University. The author has contributed to research in topics: Dielectric & Relaxation (physics). The author has an hindex of 3, co-authored 9 publications receiving 40 citations.

Dielectric relaxation and ac conductivity study of Ba(Sr1/3Nb2/3)O3

Abstract: Single phase perovskite Ba(Sr 1/3 Nb 2/3 )O 3 ceramics was prepared using the columbite precursor method. X-ray diffraction (XRD) technique is used to verify the single phase formation. It stabilizes in hexagonal phase with lattice constants a =12.1243 A and c =15.3747 A. Impedance analysis shows distributed relaxation time. Single semicircular arc observed in complex impedance plot confirms that only semiconducting grains are contributing to the polarization. The scaling behavior of both Z ″ and M ″ infers that the dynamical processes are temperature independent. Comparison of the impedance and electrical modulus data shows that the bulk response has contributions from both localized, i.e. defect relaxation, and non-localized conduction, i.e. ionic or electronic conductivity. The ac conductivity of the ceramics at higher temperatures indicates NTCR (negative temperature coefficient of resistance) behavior like semiconductors. The ac conduction activation energies are estimated from Arrhenius plots and conduction is largely due to hopping process.

Relaxor behavior and dielectric relaxation in Pb(Ba1/3Nb2/3)O3: A phase pure new relaxor material

Abstract: Pb(Ba1/3Nb2/3)O3 was prepared by two steps solid state reaction route. Material stabilized in orthorhombic perovskite phase with lattice constants a=4.0849(3) A, b=11.8469(4) A, and c=10.6818(9) A. The scanning electron micrograph exhibits heterogeneous grain distribution with average grain size of 1–3 μm. Temperature dependent dielectric constant exhibits a broad peak at 316 K (em=2250) that shows frequency dependent shifts toward higher temperature—typical relaxor behavior. Modified Curie–Weiss law is used to fit the dielectric data that exhibits almost complete diffuse phase transition characteristics. The dielectric relaxation obeys the Vogel–Fulcher relationship with the freezing temperature 286 K. In addition to relaxation observed due to transformation of the material into ergodic relaxor phase below Burn temperature, significant dielectric dispersion is observed in low frequency regime in both components of dielectric response and a small dielectric relaxation peak is observed in the temperature r...

Synthesis, characterization and dielectric relaxation of phase pure columbite MgNb2O6: Optimization of calcination and sintering

Abstract: A tungsten bronze ceramic oxide, MgNb2O6, has been prepared by standard solid state reaction route by optimizing the calcination and sintering temperatures as well as heating/cooling rates during calcination/sintering, respectively. Material calcined at 1100 °C and sintered at 1125 °C gives pure columbite phase in orthorhombic structure with lattice parameters a=5.692A, b=14.231 A and c=5.023 A as revealed from X-ray diffraction study. FESEM micrographs reveal nano-size grain formation with average grain size ≈80 nm. The dielectric permittivity and the loss tangent of the sample have been measured in the frequency range 1 kHz–1 MHz and temperature range 30–400 °C. The frequency dependent peak observed at ≈350 °C in dielectric response is associated with the onset of dielectric relaxation mechanism associated with the coupling of off-center Mg2+ and Nb5+ dipoles with thermally activated conduction electrons. Dielectric dispersion in the material is fitted with Jonscher's relation and values of coefficients a(T) and exponent n(T) were determined from experimental data. Electrical properties of the material were studied using impedance spectroscopy technique. Detailed analysis of impedance spectrum suggested that the electrical properties are strongly temperature dependent. The relaxation is polydispersive and conduction is mainly through grains. The frequency dependent ac conductivity at different temperatures indicated that the conduction is thermally activated process. AC conduction activation energies are estimated from Arrhenius plots and conduction mechanism are discussed.

Effect of Process Parameter Optimization in Reducing Sintering Temperature in the Synthesis and Characterization of Ba(Zn1/3Nb2/3)O3

Abstract: Controlling the cooling rate during calcination and sintering, phase pure perovskite Ba(Zn1/3Nb2/3)O3 has been prepared by simple solid state reaction route with density >93% at relatively low sintering of 1175°C making it compatible for microwave dielectric applications. The samples are characterized by X-ray diffraction analysis and scanning electron microscopy. The X-ray diffraction shows pure perovskite phase with cubic structure. The lattice constants were obtained a = 4.1032 A. Detailed studies of e′ and e′′ show that the compound exhibits dielectric anomaly at 430°C. Material shows distributed relaxation at higher temperature. Impedance analysis revealed that the impedance is mainly due to the grains. AC conduction activation energies are estimated from Arrhenius plots, and conduction mechanism is discussed.

Energy-storage properties and high-temperature dielectric relaxation behaviors of relaxor ferroelectric Pb(Mg1/3Nb2/3)O3–PbTiO3 ceramics

Abstract: (1 − x)Pb(Mg1/3Nb2/3)O3−xPbTiO3 (x = 0, 5, and 10 mol%) ceramics were prepared using a conventional mixed oxide solid state reaction method. The low-temperature relaxor behavior of (1 − x)Pb(Mg1/3Nb2/3)O3–xPbTiO3 ceramics were examined in the temperature range from 120 to 523 K. A broad dielectric maximum that shifted to higher temperatures with increasing frequency, signified the relaxor-type behavior of these ceramics. The value of the relaxation parameter γ = 1.61–1.94 estimated from the linear fit of the modified Curie–Weiss law indicated the relaxor nature. High-temperature dielectric relaxation phenomena were found in the temperature region 600–850 K. Energy-storage properties were also analyzed, and the energy-storage density calculated from hysteresis loops reached about 0.47 J cm−3 at room temperature.

Dielectric and Raman spectroscopic studies of Na0.5Bi0.5TiO3-BaSnO3 ferroelectric system

Abstract: A series of lead-free perovskite solid solutions of (1 − x) Na0.5Bi0.5TiO3(NBT)—x BaSnO3(BSN), for 0.0 ≤ x ≤ 0.15 have been synthesized using a high-temperature solid-state reaction route. The phase transition behaviors are studied using dielectric and Raman spectroscopic techniques. The ferroelectric to relaxor phase transition temperature (TFR) and the temperature corresponding to maximum dielectric permittivity (Tm) are estimated from the temperature-dependent dielectric data. Dielectric studies show diffuse phase transition around ~335°C in pure NBT and this transition temperature decreases with increase in x. The disappearance of x-dependence of A1 mode frequency at ~134 cm−1 for x ≥ 0.1 is consistent with rhombohedral-orthorhombic transition. In situ temperature dependence Raman spectroscopic studies show disappearance and discontinuous changes in the phonon mode frequencies across rhombohedral (x < 0.1)/orthorhombic (x ≥ 0.1) to tetragonal transition.