Ashwini Kumar

Room temperature structure vibrational and dielectric properties of Ho modified YMnO3

The structural, vibrational, and dielectric properties of bulk Ho-doped Y1−xHoxMnO3 (x = 0, 0.03, 0.05) solids prepared by standard solid-state reaction route were investigated. X-ray diffraction (XRD) patterns confirmed the hexagonal P63cm structure of Y1−xHoxMnO3 (x = 0.0, 0.03, 0.05) ceramics. Rietveld refinements of XRD data revealed that the doping ions led to unit cell contraction in three directions due to nearly equal ionic radii of Ho3+ ion (0.901 A) substituted at the Y-site ion. The grain size of Ho-doped solids varied from 5 to 10 μm. For pristine h-YMnO3, the experimentally observed Raman scattering lines at around 151, 305, 460, and 682 cm−1 are of A1 symmetry, those at 410 cm−1 are of E1 symmetry, and the lines at 139 and 219 cm−1 are of E2 symmetry. Another interesting observation is the existence of an A1 line at 682 cm−1 and an E1 line at about 410 cm−1 which are much stronger than the remaining lines of A1 and E1 symmetries, respectively. The high value of dielectric constant and dielectric loss tangent at low frequency is explained by space charge polarization and the saturation in the high-frequency region is due to the electric dipoles not being in pace with the frequency of the applied electric field.

Structural Transition and Enhanced Ferromagnetic Properties of La, Nd, Gd, and Dy-Doped BiFeO3 Ceramics

The structural, electrical, and magnetic properties of rare-earth-doped Bi0.8 RE0.2FeO3 ceramics (rare-earth (RE) = La, Nd, Gd, and Dy) synthesized by solid-state reaction are reported and discussed. The x-ray diffraction (XRD) patterns of Bi0.8La0.2FeO3 and Bi0.8Nd0.2FeO3 were indexed to rhombohedral (R3c) and triclinic (P1) structures, respectively. Rietveld refinement of the XRD pattern of Bi0.8Dy0.2FeO3 confirmed its biphasic nature (Pnma + R3c space groups) whereas for Bi0.8Gd0.2FeO3 the orthorhombic phase with Pna21 symmetry made a major contribution, with minor contributions from the orthorhombic (Pnma) and rhombohedral (R3c) phases. Raman spectroscopy revealed changes in BiFeO3 mode positions, in addition to structural changes, on RE ion substitution. The effect of RE ion substitution on dielectric constant and loss tangent were studied at room temperature in a wide range of frequency, 50 Hz–1 MHz. Room temperature magnetization–magnetic field (M–H) measurements indicated that magnetization increased with increasing structural distortion and with partial destruction of the spin cycloid as a result of doping of BiFeO3 ceramics with rare earth ions. These compounds, with improved remnant magnetization and coercive field, are suitable for use in spin-based electronic devices.

Structural, dielectric and ferroelectric properties of La and Ni codoped BiFeO3

The codoped Bi1-xLaxFe1-yNiyO3 (x = 0.0, 0.1; y = 0.0, 0.05) samples are processed by solid-state reaction route in order to study structural, dielectric and ferroelectric properties. X-ray diffraction patterns of La/Ni doped samples have been performed using the rhombohedral (R3c) symmetry. Raman scattering measurement infers nine Raman active phonon modes. The substitution of Ni ion at Fe-site in BiFeO3 essentially changes the modes position i.e. all the modes are observed to shift at lower wave number. Frequency variation of the dielectric constant (e′) and dielectric loss (tanδ) has been investigated. It decreases with increasing frequency of the applied alternating field and become constant at high frequencies signifies substantial role of interfacial polarization. The remnant polarization and coercive field for BLFO, BFNO, BLFNO are 0.08, 0.03, 0.64 μC/cm2 and 0.24, 0.22, 0.25u2005kV/cm, respectively. La/Ni ion doping in BFO has successfully enhanced the polarization.

Rare earth (La) and metal ion (Pb) substitution induced structural and multiferroic properties of bismuth ferrite

In this study, bulk samples of multiferroic with compositional formula, BiFeO3 and Bi0.825A0.175FeO3 (A = La, Pb), were synthesized by solid state reaction route. X-ray diffraction (XRD) along with the Rietveld refinement revealed the distorted rhombohedral (R3c) structure for pristine BiFeO3 and Bi0.825La0.175FeO3 and tetragonal (P4/mmm) for Bi0.825Pb0.175FeO3 ceramic. To support the structural results, bond length between atoms for both of the compounds was calculated. A change in Raman mode position in BiFeO3 (BFO) has been observed with La and Pb substitution from Raman scattering measurements and also recommended a structural change with rare earth and metal ion substitution at Bi site. From the frequency dependent dielectric constant and dielectric loss plots, a decrease in dielectric values with increase in frequency was observed for both of the samples. For microelectronic devices, porous ceramics with lower value of dielectric constant are most useful. Thus, further studies are also needed to carefully tune the magnetoelectric properties and structural distortion after La/Pb substitution in BFO.

Structural study of Ti-doped CoFe2O4 mixed spinel ferrite

We present the results on atomic and lattice structure of the polycrystalline spinel ferrites system Co1-x TixFe2O4 (x = 0.0, 0.25, 0.50) synthesized by following the conventional solid-state reaction route. The observed X-ray diffraction (XRD) data confirms that all the prepared samples are indexed in cubic crystal structure (space group Fd3m). Diffraction pattern showed TiO2 phase due to presence of Ti+4 ions. Four Raman active phonon modes are observed for CoFe2O4 sample existing around 295, 462, 585, 689, cm−1 as Eg, T2g(2), T2g(3), and A1g, respectively. With 25 % Ti ion doping, the peak T2g(3) disappears, while to that T2g(1) emerges. This is an indication of presence of TiO2 phase in Co0.75Ti0.25Fe2O4 and Co0.5Ti0.5Fe2O4 ceramics.

Effect of Zn doping on structural and dielectric properties of tetragonal Ni1-xZnxFe2O4 (0.0 ≤ x ≤ 0.5)

A series of Ni-Zn ferrite with compositional formula Ni1-xZnxFe2O4 (0.0 ≤ x ≤ 0.5) were prepared by solid-state reaction route. The influence of the Zn content on the structural and dielectric properties of NiFe2O4 was investigated using X-ray powder diffraction (XRD), Raman spectroscopy and dielectric measurements. XRD analysis reveals that the samples are polycrystalline single-phase cubic spinel in structure excluding the presence of any secondary phase corresponding to any structure. Slight variation in the lattice parameter of Zn doped NiFe2O4 has been observed due to difference in ionic radii of cations. Raman analysis reveals the doublet like nature of A1g mode for all synthesized samples. Small shift in Raman modes and increment in the line width has been observed with the doping ions. Furthermore, room temperature dielectric properties of all the prepared samples have been reported. It is observed that for each sample the dielectric constant decreases with an increase of frequency and becomes con...