R. G. Mendiratta

Dielectric properties of Mn-substituted Ni–Zn ferrites

The dielectric properties of MnxNi0.5−xZn0.5Fe2O4 ferrites with x varying from 0.05 to 0.4 synthesized by the citrate precursor method have been investigated as a function of frequency, temperature, composition, and sintering temperature. An increase in the dielectric constant is observed with the increase in Mn concentration except for x=0.3. Dispersion in the dielectric constant with frequency in the range of 100 Hz–1 MHz is observed. Resonance peaks were observed in tan δ∈ versus frequency curves for all samples. A shift in the resonance frequency towards higher frequency is observed with increase in temperature. The peak height also increases with increase in temperature. Possible mechanisms contributing to these processes have been discussed. From the temperature variation of the dielectric relaxation, activation energies for various samples have been calculated and compared with those obtained from dc resistivity.

Magnetic properties of Mn-substituted Ni–Zn ferrites

MnxNi0.5−xZn0.5Fe2O4 ferrites with x=0.05, 0.1, 0.2, 0.3, and 0.4, have been synthesized by the citrate precursor method and investigated for their magnetic properties. The initial relative permeability is observed to increase with increase in manganese concentration up to x=0.2 followed by a decrease, the maximum value being 632. An initial increase followed by a subsequent decrease of saturation magnetization with increase in x is observed. Curie temperature is observed to decrease continuously from 488 to 418 °C when x increases from 0.05 to 0.4. Frequency variation of complex initial permeability indicates that resonance peak due to domain wall oscillations is at a frequency above 13 MHz. Saturation magnetization is observed to increase by about 22% when the sintering temperature is increased from 1200 to 1400 °C. Initial permeability and B–H loops are observed to increase and constrict, respectively, with increase in sintering temperature.

Structural, dielectric and pyroelectric studies of Pb1−XCaXTiO3 thin films

Abstract Thin films of Pb 1− x Ca x TiO 3 [ x =0.20, 0.24 and 0.28] have been prepared on ITO coated Corning glass substrates by sol gel technique. The perovskite phase of PCT films is formed at 650 °C with a polycrystalline tetragonal structure. The tetragonal factor ( c / a ) decreases with increasing Ca concentration. Dielectric, pyroelectric and ferroelectric studies have been carried out on these films. The effects of introduction of Ca ion in PbTiO 3 have also been discussed.

Synthesis and Characterization of Sol–Gel-Derived (Pb1-xLax)Ti1-x/4O3 Thin Films

Ferroelectric lead lanthanum titanate (Pb1-xLaxTi1-x/4O3) (PLTx) thin films (x=0.04, 0.08 and 0.12) have been prepared by sol–gel spin-coating process on ITO- coated 7059 Corning glass substrates. Investigations have been made on the crystal structure, surface morphology, dielectric and ferroelectric properties of the thin films. Characterization of these films by X-ray diffraction shows that the films annealed at 650°C exhibit tetragonal structure with perovskite phase. Replacement of lanthanum in lead titanate results in reduction of the tetragonal ratio (c/a), thereby resulting in better mechanical stability. Microstructural analyses of the films are carried out by obtaining atomic force microscope (AFM) images. AFM images are characterized by slight surface roughness with a uniform crack-free, densely packed structure. Dielectric, pyroelectric and ferroelectric studies carried out on these films have been reported. The dielectric constant increases with La concentration. The Curie temperature is found to decrease with the addition of lanthanum. The pyroelectric coefficient increases from 17 nC/cm2K to 31 nC/cm2K as La content increases from 4 to 12%. The pyroelectric figures of merit of the films have been calculated from these studies. These studies indicate that 8% lanthanum is the material best suited for infrared detectors owing to its high pyroelectric coefficient (~29 nC/cm2K), high voltage responsivity (~420 Vcm2/J), high detectivity (~1.04×10-5 Pa-1/2) and low variation of pyrocoefficient with temperature.

Dc resistivity of Mn-Ni-Zn ferrites

DC resistivity of MnxNi0.5-xZn0.5Fe2O4 with compositions x=0.05 to 0.4 prepared by the citrate precursor method has been investigated. It has been observed that resistivity decreases with increase in Mn concentration. The observed temperature variation curves show two linear regions. Activation energy corresponding to both regions has been calculated. Possible conduction mechanisms contributing to the processes have been discussed. Variation of resistivity with sintering temperature establishes a correlation between microstructure and conductivity.

Effect of manganese impurity on the conductivity, dielectric behavior and magnetic properties of Ni0.3MnxZn0.7-xFe2O4

Ni0.3MnxZn0.7-xFe2O4 samples, with x=0.1, 0.2, 0.3, 0.4, 0.5, have been prepared by the citrate precursor method and their dc resistivity, complex initial permeability, permittivity and saturation magnetization are studied. Initial increase followed by a decrease is observed in dc resistivity and saturation magnetization (maximum 57 emu/gm) with increase in x. Initial relative permeability is observed to decrease from 550 to 100 with increase in manganese content. A shift in dielectric relaxation peak towards higher frequencies is observed with increase in x. A slight variation of resistivity is observed with increasing applied field.

Structural, Dielectric and Ferroelectric Properties of La Doped PbTiO3 Sol Gel Derived Thin Films

Ferroelectric lead lanthanum titanate (Pb1−x La x Ti1−x/4O3) thin films (x = 0.04 & 0.08) have been fabricated by sol-gel spin coating process on ITO coated 7059 glass substrates. Characterization of these films has been done by x-ray diffraction and atomic force microscope images. Tetragonality decrease with addition of La content. While dielectric constant and pyrocoefficient increase, Curie temperature decreases with La content. Also, there is decrease in remanent polarization and coercive field with addition of La content.

Structural, dielectric and pyroelectric properties of lanthanum/calcium modified lead titanate thin films

Ferroelectric lead lanthanum titanate (Pb1−x La x Ti1−x/4O3) (PLT) thin films (x = 0.04, 0.08 & 0.12) have been prepared by sol-gel process on ITO coated 7059 Corning glass substrates. Investigations have been made on the structure, surface morphology, dielectric and ferroelectric properties of the thin films. XRD patterns show that the films annealed at 650°C exhibit tetragonal structure with perovskite phase. AFM images are characterized by slight surface roughness with a uniform densely packed structure. Also Fourier Transform Infrared Spectra (FTIR) of PLT thin films at 650°C on Si substrates sintered at 650°C were taken to get more information about the film formation. Dielectric, pyroelectric and ferroelectric studies carried out have been discussed. The figures of merit have been calculated. Similar investigations on calcium modified PbTiO3 films (PCT) (Pb1−x Ca x TiO3) (x = 0.20, 0.24 & 0.28) have also been reported. Our results show that PCT with x = 0.24 is best suited material for pyroelectric detector.

Structural Distortions and Behavioural Changes in Phase Transition of Aurivillius Type Sr1-xPbxBi2Nb2O9 Ferroelectric

In this paper effects of lead doping on the lattice response and phase transitions of bismuth-layered structure Sr1−xPbx Bi2Nb2O9 (x = 0.0 to 0.5 in steps of 0.1) ferroelectric ceramic are reported. It is observed that structure attains more tetragonality with doping of lead up to 40%. Increased orthorhombic distortion is also observed. Curie temperatures of all samples were measured and the phase transition is explained in terms of lattice response of these ceramics. Sample with x = 0.5 shows decreased tetragonal strain and Curie temperature. Also, relationship of polarization with lattice response is discussed.

Effect of calcium doping on lattice parameters resulting in structural distortions of SrBi2Nb2O9 ferroelectric ceramics

Studies on the effect of 10 - 50 atomic % Ca doping on structural distortions are reported in the present work. Bismuth layered structured ferroelectrics oxides of the composition Sr1-xCaxBi2Nb2O9; with x = 0.0 - 0.5 were synthesized by the solid-state reaction method. X-ray diffraction analysis revealed the formation of perovskite ferroelectric ceramic sample and a few additional peaks were observed as concentration of calcium varied from 10 to 50%, gradual shift in peaks with doping is discussed with respect to observed anomalous change in lattice parameters. Also, transformation of structure from pseudo-orthorhombic to pseudo-tetragonal phase is observed at room temperature as concentration of calcium is increased. This suggests that structural distortions are pronounced in such a manner so as to stabilize the structure of unit cell, which may lead to high value of Curie temperature and remanent polarization useful in non-volatile random access memory (NvRAM) devices.