Rabichandra Pandey

Phase diagram of Sm and Mn co-doped bismuth ferrite based on crystal structure and magnetic properties

Sm and Mn co-substituted BiFeO3 (BFO) ceramic has been synthesized by the tartaric acid modified sol-gel method to understand the effect of structural modification on the magnetic properties. The secondary phases (i.e., Bi2Fe4O9, Bi25FeO39 etc.) present in the parent compound BiFeO3 have been significantly reduced with increase in the substitution percentage of Sm and Mn at Bi and Fe sites of BFO respectively. The Rietveld refinement of the X-ray diffraction (XRD) patterns reveals a structural transition from rhombohedral (R3c, space group) to orthorhombic (Pbnm, space group) crystal symmetry with the concentration of Sm and Mn in the sample. The chemical state and elemental ratio of the samples have been studied by analyzing the X-ray photoelectron spectroscopy (XPS) data. Crystallite size obtained from the transmission electron microscopy analysis is in well comparable with the XRD analysis. Fourier transform infrared spectroscopy (FTIR) analysis supports the XRD results. A change in the phonon frequency and line widths in Raman spectra confirms the lattice distortion in the co-substituted samples which are in agreement with the XRD analysis. Ferromagnetic signature has been observed in Sm and Mn co-substitution. The magnetic hysteresis loop at room temperature has been analyzed by considering both ferromagnetic and antiferromagnetic contribution. The saturation magnetization for ferromagnetic phase increases up to 10% substitution of Sm and Mn in BFO and, decrease with the further increase of percentage of substituents. A correlation between crystal structure and magnetic behavior has been observed for Sm and Mn co-substituted sample.Graphical abstractPhase diagram of crystal symmetries percentage, saturation magnetization (MS), remnant magnetization (Mr) and coercivity (HC) of Bi1-xSmxFe1-xMnxO3 for x = 0.000, 0.025, 0.050, 0.075, 0.100 and 0.150 ceramics.

Existence of multi crystallographic phase in BNT-BTO solid solution near morphotropic phase boundary (MPB)

Lead free Bismuth sodium titanate (BNT) base solid solutions are focusing intensively due to their potential applications as an alternative for Pb-base compounds. In this work, Solid solutions of BNT and barium titanate [(1-x) BNT + x BTO with x=0.00, 0.06, 1.00] have been prepared via conventional solid state route by using the planetary ball mill method. Crystallinity of the samples characterized by XRD and various structural parameters are calculated by employing Rietveld refinement technique. The distinct peak (002/200) splitting around 460 to 470 confirmed the presence of both rhombohedral and tetragonal phase in the solid solution. Dielectric constant of the solid solution near the morphotropic phase boundary (x= 0.06) is significantly enhanced as compared to BNT and BTO. The electrical conductivity of the solid solution was found to reduce w.r.t to BNT. The above results indicate the possible application of BNT-BTO solid solution near MPB in the field of energy storage.

Crystal structure and magnetic properties of Cr doped barium hexaferrite

The Cr3+ substituted BaFe12O19 has been synthesized by modified sol-gel method to tailor the magnetic anisotropy and coercivity for technological applications. Some basic studies have revealed that this substitution leads to unusual interactions among the magnetic sublattices of the M-type hexaferrite. In order to investigate these interactions, BaFe12-xCrxO19 (x = 0.0, 0.5, 1.0, 2.0, and 4.0) M-type hexaferrites were characterized by employing XRD (X-ray Diffractometer). It is confirmed that, all the samples are in nanocrystalline and single phase, no impurity has been detected within the XRD limit. The magnetic hysteresis (m-H) loops revealed the ferromagnetic nature of nanoparticles (NPs). The coercive field were increasing with the increasing Cr3+ content, but after the percolation limit it decreases. The magnetocrystalline anisotropy is increasing with the Cr3+ concentration in samples and high values of magnetocrystalline anisotropy revealed that all samples are hard magnetic materials. Magnetic hysteresis loops were analyzed using the Law of Approach to Saturation method.The Cr3+ substituted BaFe12O19 has been synthesized by modified sol-gel method to tailor the magnetic anisotropy and coercivity for technological applications. Some basic studies have revealed that this substitution leads to unusual interactions among the magnetic sublattices of the M-type hexaferrite. In order to investigate these interactions, BaFe12-xCrxO19 (x = 0.0, 0.5, 1.0, 2.0, and 4.0) M-type hexaferrites were characterized by employing XRD (X-ray Diffractometer). It is confirmed that, all the samples are in nanocrystalline and single phase, no impurity has been detected within the XRD limit. The magnetic hysteresis (m-H) loops revealed the ferromagnetic nature of nanoparticles (NPs). The coercive field were increasing with the increasing Cr3+ content, but after the percolation limit it decreases. The magnetocrystalline anisotropy is increasing with the Cr3+ concentration in samples and high values of magnetocrystalline anisotropy revealed that all samples are hard magnetic materials. Magnetic hys...

Lead free Bi0.5Na0.5TiO3 (BNT) and polyvinylidene fluoride (PVDF) based nanocomposite for energy storage applications

Novel ceramic-polymer nanocomposites have great potential for electrical energy storage applications due to its high energy storage density. In the present work, BNT and PVDF based flexible polymer nanocomposites (BNT-PVDF) with different volume fraction (ϕ = 0, 5, 10, 15) were fabricated by solution casting method. Enhancement in beta phase of PVDF polymer matrix with the volume fraction (ϕ = 5, 10, 15) of BNT has been confirmed by X-ray diffraction (XRD) technique as well as Fourier transform infrared (FTIR) spectroscopy analysis. The enhancement of β phase increases as compared to (α) phases with volume fraction (ϕ) of nanofiller (BNT) in the matrix (PVDF) due to internal stress at the interface as well as structural modification of PVDF matrix. BNT-PVDF nanocomposites (with ϕ=10) showed a high dielectric constant (er ≈ 78) relative to pure PVDF (er ≈ 10) at 100 Hz. In addition to this, it exhibits relaxor type ferroelectric behavior with energy storage efficiency up to 77% for the volume fraction (ϕ) of 10.Novel ceramic-polymer nanocomposites have great potential for electrical energy storage applications due to its high energy storage density. In the present work, BNT and PVDF based flexible polymer nanocomposites (BNT-PVDF) with different volume fraction (ϕ = 0, 5, 10, 15) were fabricated by solution casting method. Enhancement in beta phase of PVDF polymer matrix with the volume fraction (ϕ = 5, 10, 15) of BNT has been confirmed by X-ray diffraction (XRD) technique as well as Fourier transform infrared (FTIR) spectroscopy analysis. The enhancement of β phase increases as compared to (α) phases with volume fraction (ϕ) of nanofiller (BNT) in the matrix (PVDF) due to internal stress at the interface as well as structural modification of PVDF matrix. BNT-PVDF nanocomposites (with ϕ=10) showed a high dielectric constant (er ≈ 78) relative to pure PVDF (er ≈ 10) at 100 Hz. In addition to this, it exhibits relaxor type ferroelectric behavior with energy storage efficiency up to 77% for the volume fraction (ϕ) ...

Lattice strain induced multiferroicity in PZT-CFO particulate composite

Lead Zirconate Titanate [Pb(Zr0.52Ti0.48)O3/PZT] and Cobalt Ferrite [CoFe2O4/CFO] based multiferroic composites [(1-x)PZT-(x)CFO] with (x = 0.10–0.40) have been prepared to study its magnetoelectric (ME) and multiferroic properties. X-ray diffraction method along with the Rietveld refinement technique reveals that the crystal symmetries corresponding to PZT and CFO exist independently in the composites. The effect of interfacial strain on lattice distortion in PZT has been observed. It is well correlated with the magnetoelectric coupling of the composites. Dispersion behavior of dielectric constant with frequency can be explained by the modified Debye model. Different relaxation phenomena have been observed in PZT-CFO particulate composites. The ferroelectric properties of composites decrease with the increase in percentage of CFO in the composite. Both saturation (Ms) and remanent (Mr) magnetization increase with the increase in CFO content in the composite. The maximum ME coupling was found to be 1.339 ...

Role of lattice distortion on diffuse phase transition temperatures in Bi0.5Na0.5TiO3-BaTiO3 [BNBTO] solid solutions

Effect of lattice distortion on diffuse phase transition in BNBTO solid solutions near Morphotropic phase boundary (MPB) has been investigated. Solid solutions of (Bi0.5Na0.5)1−xBaxTiO3 (with mole % of x= 0.04, 0.05, 0.06, 0.07 and 0.08) were prepared by the planetary ball mill method in ethanol medium. Rietveld refinement technique with rhombohedral (R3c) and tetragonal (P4bm) crystal symmetry has been employed for structural as well as phase analysis of the solid solutions. Both rhombohedral and tetragonal lattice distortion (c/a) tends toward the pseudo-cubic crystal symmetry with the increase of mole fraction of Ba2+ near MPB (x= 6 mole %). Also, the average crystallite size and grain size decrease with increase of mole fraction of Ba2+ in BNT ceramic are due to larger ionic radius of Ba2+ and grain boundary pinning process in the solid solutions respectively. Additionally, depolarization temperature (Td) and maximum temperature (Tm) reduces due to the lattice distortion of both the phases in BNBTO solid solutions, which is explained extensively. Significant increase of dielectric constant has been observed near MPB composition (x=6%) in BNBTO solid solutions.Effect of lattice distortion on diffuse phase transition in BNBTO solid solutions near Morphotropic phase boundary (MPB) has been investigated. Solid solutions of (Bi0.5Na0.5)1−xBaxTiO3 (with mole % of x= 0.04, 0.05, 0.06, 0.07 and 0.08) were prepared by the planetary ball mill method in ethanol medium. Rietveld refinement technique with rhombohedral (R3c) and tetragonal (P4bm) crystal symmetry has been employed for structural as well as phase analysis of the solid solutions. Both rhombohedral and tetragonal lattice distortion (c/a) tends toward the pseudo-cubic crystal symmetry with the increase of mole fraction of Ba2+ near MPB (x= 6 mole %). Also, the average crystallite size and grain size decrease with increase of mole fraction of Ba2+ in BNT ceramic are due to larger ionic radius of Ba2+ and grain boundary pinning process in the solid solutions respectively. Additionally, depolarization temperature (Td) and maximum temperature (Tm) reduces due to the lattice distortion of both the phases in BNBTO so...

Study of ferroelectric properties on PVDF-PZT nanocomposite

ABSTRACT PVDF with 0, 2, 4, 6, 8, 10 mole% of PZT has been prepared by the solvent casting method. Prominent β phase has been observed from the XRD, FT-IR and Raman studies. The polarization of these samples starts at high field of 100 kv/cm and it increases with the increase in applied electric field. The 4 mole% PZT doped PVDF shows maximum polarization and high coercive field. The coercive field also increases with the increase in applied electric field. Hence, 4 mole% PZT doped PVDF composites can be used in high electric fields applications.

Role of grain and grain boundary on the electrical and thermal conductivity of Bi0.9Y0.1Fe0.9Mn0.1O3 ceramics

Role of grain and grain boundary on electrical and thermal conductivity of Bi0.9Y0.1Fe0.9Mn0.1O3 ceramic was investigated systematically. Tartaric acid modified sol gel method was used to synthesize the compound. X-ray diffraction technique was used to confirm the formation of single phase orthorhombic (Pbnm) structure. Electrical properties of the sample were measured with a wide frequency range from 100Hz to 10MHz at different temperature from 40°C to 250°C. AC impedance studies indicate the presence of grain and grain boundary effect. The negative temperature coefficient of resistance (NTCR) behaviour of the compound has been confirmed by the cole-cole plot. DC electrical and thermal conductivities of the compound were explained on the basis of grain and grain boundaries.