Dhiren K. Pradhan

Studies on structural, dielectric, and transport properties of Ni0.65Zn0.35Fe2O4

We report the crystal structure, dielectric, transport, and magnetic properties of Ni0.65Zn0.35Fe2O4. Rietveld refinement results of X-ray diffraction patterns confirm the phase formation of the material with cubic crystal structure ( Fd3¯m). The frequency dependent ac conductivity behavior obeys the Jonschers power law and is explained using the jump relaxation model. The observed behavior of temperature dependent bulk conductivity is attributed to the variable-range hopping of localized polarons. The correlation of polaron conduction and high permittivity behavior of NZFO is established on the basis of long range and short range conduction mechanisms. The complex impedance spectra clearly show the contribution of both grain and grain boundary effect on the electrical properties.

Photovoltaic effect in transition metal modified polycrystalline BiFeO3 thin films

We report photovoltaic (PV) effect in multiferroic Bi0.9Sm0.1Fe0.95Co0.05O3 (BSFCO) thin films. Transition metal modified polycrystalline BiFeO3 (BFO) thin films have been deposited on Pt/TiO2/SiO2/Si substrate successfully through pulsed laser deposition (PLD). PV response is observed under illumination both in sandwich and lateral electrode configurations. The open-circuit voltage (Voc) and the short-circuit current density (Jsc) of the films in sandwich electrode configuration under illumination are measured to be 0.9 V and −0.051 µA cm−2. Additionally, we report piezoresponse for BSFCO films, which confirms ferroelectric piezoelectric behaviour.

Room temperature multiferroic properties of Pb(Fe0.5Nb0.5)O3–Co0.65Zn0.35Fe2O4 composites

We report the crystal structure, magnetic, ferroelectric, dielectric, and magneto-dielectric properties of [Pb(Fe0.5Nb0.5)O3](1−x)[Co0.65Zn0.35Fe2O4]x: (x = 0.1, 0.2, 0.3, and 0.4) composites. Rietveld refinement results of X-ray diffraction patterns confirm the formation of these composites for all x values. All the composites show well-saturated ferroelectric and ferromagnetic hysteresis (multiferroic-composite behavior) at room temperature. With increase in Co0.65Zn0.35Fe2O4 (CZFO) content an increase in saturation magnetization, and decrease in saturation polarization, remanent polarization, and dielectric constant are observed. The ferroelectric phase transition temperature increases with increase in CZFO content. All of the compositions undergo second-order ferroelectric phase transitions, which can be explained by Landau-Devonshire theory. The recoverable energy density (∼0.20 to 0.04 J/cm3) and charge-curve energy density (∼0.84 to 0.11 J/cm3) decrease with increase in the CZFO content. The room-t...

Synthesis and characterization of lead-free ternary component BST–BCT–BZT ceramic capacitors

Polycrystalline sample of lead-free 1/3(Ba0.70Sr0.30TiO3) + 1/3(Ba0.70Ca0.30TiO3) + 1/3(BaZr0.20Ti0.80O3)(BST-BCT-BZT) ceramic was synthesized by solid state reaction method. Phase purity and crystal structure of as-synthesized materials was confirmed by X-ray diffraction (XRD). Temperature-dependent dielectric permittivity studies demonstrated frequency-independent behavior, indicating that the studied sample has typical diffuse phase transition behavior with partial thermal hysteresis. A ferroelectric phase transition between cubic and tetragonal phase was noticed near room temperature (~ 330 K). Bulk P–E hysteresis loop showed a saturation polarization of 20.4 μC/cm2 and a coercive field of ~ 12.78 kV/cm at a maximum electric field of ~ 115 kV/cm. High dielectric constant (e ~ 5773), low dielectric loss (tan δ ~ 0.03) were recorded at room temperature. Discharge energy density of 0.44 J/cm3 and charge energy density of 1.40 J/cm3 were calculated from nonlinear ferroelectric hysteresis loop at maximum electric field. Dielectric constant at variable temperatures and electric fields, ferroelectric to paraelectric phase transition and energy storage properties were thoroughly discussed.

Nanoscale polarisation switching and leakage currents in (Ba0.955Ca0.045)(Zr0.17Ti0.83)O3 epitaxial thin films

This paper investigates the crystal structure, ferroelectric, temperature-dependent leakage current conduction mechanism and the piezoresponse force microscopy (PFM) behaviours of (Ba0.955Ca0.045) (Zr0.17Ti0.83)O3–BZT–BCT () films at the vicinity of the morphotropic phase boundary (MPB) of the [(1 − x) BaZr0.20Ti0.80O3–xBa0.70Ca0.30TiO3] () composition. Epitaxial BZT–BCT thin films were grown on conductive La0.5Sr0.5CoO3 (LSCO) layers coated onto MgO (1 0 0) single-crystal substrates by pulsed laser deposition (PLD). High resolution x-ray diffraction (HR-XRD) reciprocal space maps (RSMs) confirmed the epitaxy with in-plane tetragonal symmetry (c < a), and Raman spectra also revealed a tetragonal perovskite crystalline lattice structure. Polarisation studies demonstrate that BZT–BCT films exhibit a high saturation polarisation of 148 µC cm−2 and a high recoverable (discharged) energy-storage density of 39.11 J cm−3 at 2.08 MV cm−1. Temperature-dependent P–E hysteresis loops resulted in a decrease in polarisation. Temperature-dependent leakage current behaviour was obtained and possible conduction mechanism is discussed. PPFM images revealed switchable ferroelectric piezoelectric contrasts after the application of a ±9 V dc voltage on the conductive tip of the piezoresponse force microscope.

Phase transition and magneto-electric coupling of BiFeO3–YMnO3 multiferroic nanoceramics

We report the crystal structure, dielectric, magnetic, and magneto-electric properties of (1−x) BiFeO3-xYMnO3 (0.00 ≤ x ≤ 0.2) multiferroic nanoceramics prepared by auto-combustion technique. YMnO3 substitution is found to induce a structural phase transition from R3c to R3c+Pbnm after x ≈ 0.1 using Rietveld refinement technique. Field emission scanning electron micrographs show decrease in grain size with increase in YMnO3 content. The dielectric permittivity and loss tangent are found to be increased with composition x. The anomalies noticed from the temperature dependent dielectric analysis reveal the signature of magneto-electric coupling in the system. A decrease in magnetic ordering temperature as a function of composition is found from dielectric study. At room temperature, the dielectric permittivity of all the YMnO3 modified samples decrease with increasing magnetic field. The maximum value of magneto-electric coupling coefficient (e(H)-e(0))/e(0) is found to be ∼ −5.5% at H = 2 T for x = 0.2. Th...

Phase transition and enhanced magneto-dielectric response in BiFeO3-DyMnO3 multiferroics

We report systematic studies on crystal structure and magneto-dielectric properties of (1 − x) BiFeO3-x DyMnO3 (0.0 ≤ x ≤ 0.2) nanoceramics synthesized by auto-combustion method. Rietveld refinement of X-ray diffraction data indicates a structural transition from R3c to R3c + Pn21a at x = 0.1. Field emission scanning electron micrographs display a decrease in grain size with increase in x. The presence of dielectric anomalies around antiferromagnetic transition temperature implies the magnetoelectric coupling. Dielectric measurements showed decrease in magnetic ordering temperature with increasing x in agreement with differential scanning calorimetry results. A significant increase in magnetization has been found with increasing DyMnO3 substitution. Magneto-impedance spectroscopy reveals a significant change (∼18%) in dielectric permittivity at H = 2 T for x = 0.2.

Structure, Ferroelectric, Dielectric and Energy Storage Studies of Ba0.70Ca0.30TiO3, Ba(Zr0.20Ti0.80)O3 Ceramic Capacitors

Ba0.70Ca0.30TiO3-(BCT),Ba(Zr0.2Ti0.8)O3-(BZT) ceramics were fabricated by conventional mixed oxide route to develop inorganic dielectric materials suitable for use as an insulator with high dielectric constant and low energy loss for capacitor applications. The structural phase transition, ferroelectric, dielectric and energy storage properties of BCT, BZT ceramic capacitors were investigated. Room temperature X-ray diffraction (XRD) patterns revealed prominent peaks corresponding to tetragonal perovskite crystal structure for both BCT, BZT solid solutions. Slim ferroelectric hysteresis (P-E) loops were observed for BCT, BZT solid solutions. Temperature dependent dielectric property measurements of BCT, BZT solid solutions have shown a high dielectric constant and low dielectric loss. Room temperature (300K) breakdown field strength and energy densities were obtained from the integral area of P-E loops. For the BCT ceramics, the largest recoverable energy (unreleased energy) density is 1.41 J/cm3 with dielectric breakdown strength as high as 150 kV/cm. For the BZT ceramics, the largest recoverable energy (unreleased energy) density is 0.71 J/cm3 with dielectric breakdown strength as high as 150 kV/cm. Bulk BCT, BZT ceramics have shown interesting energy densities; these might be the strong candidate materials for capacitor applications.

Effect of thickness on dielectric, ferroelectric, and optical properties of Ni substituted Pb(Zr0.2Ti0.8)O3 thin films

We report thickness dependent dielectric, ferroelectric, and optical properties of Ni substituted Pb(Zr0.2Ti0.8)O3 thin films. The Pb(Zr0.2Ti0.8)0.70Ni0.30O3−δ (PZTNi30) thin films for various thicknesses, ranging from 5 nm to 400 nm, were fabricated by pulsed laser deposition technique. Giant dielectric dispersion, low dielectric loss, large dielectric constant ∼1000–1500 from 100 Hz to 100 kHz, and diffused dielectric anomaly near 570–630 K were observed in PZTNi30 thin films. These films show well saturated ferroelectric hysteresis, with large remanent polarization. It also illustrated excellent optical transparency which decreased from 82 to 72% with increasing film thickness from 5 nm to 400 nm for the probe wavelengths ranging from 200 to 1100 nm. A decrease in direct bandgap (Eg) values from 4 eV to 3.4 eV and indirect-Eg values from 3.5 eV to 2.9 eV were observed for PZTNi30 thin films with increase in film thickness from 5 nm to 400 nm, respectively. The direct and indirect bandgaps were discusse...

Investigations on electrical and magnetic properties of multiferroic [(1−x)Pb(Fe0.5Nb0.5)O3−xNi0.65Zn0.35Fe2O4] composites

Here, we report the magnetic, ferroelectric, dielectric properties, and Raman spectroscopic studies of multiferroic [(1−x)Pb(Fe0.5Nb0.5)O3−xNi0.65Zn0.35Fe2O4] composites at room temperature. The phase formation of composites was confirmed independently from the X-ray diffraction and Raman studies. The room temperature magnetic studies reveal ferromagnetic like behavior of these composites in contrast to the paramagnetic nature of Pb(Fe0.5Nb0.5)O3. Furthermore, with increasing x, the saturation magnetization, remnant magnetization, and coercive fields are found to increase. The electrical characterizations of these composites reveal a decrease in remnant polarization and dielectric constant with increasing x. More importantly, the x = 0.2 composite is found to be a very good multiferroic material at room temperature among the composites and could be a potential candidate for future potential applications.