Govind K. Bichile

X-ray and infrared studies of chromium substituted magnesium ferrite

Abstract The ferrites of the composition MgCr x Fe 2− x O 4 with x =0.0, 0.1, 0.3, 0.5, 0.7, 0.9 and 1.0 were prepared by using the usual double sintering technique and characterized by X-ray diffraction and Infrared studies in the range of 200 to 800 cm −1 . The lattice parameters are calculated and are found to decrease with Cr substitution. The X-ray density decreases as Cr content increases. The distance between magnetic ions in both octahedral and tetrahedral sites decreases with increase in Cr. The cation distribution in this spinel system is determined from X-ray intensity calculations. The far infrared spectra obtained at room temperature in the range 200 to 800 cm −1 showed two absorption bands. The high frequency band ( ν 1 ) and low frequency band ( ν 2 ) are assigned to the tetrahedral and octahedral complexes, respectively. The force constants have been obtained from the infrared absorption data and their dependence with the internuclear distance has been discussed.

X-ray diffraction and dielectric study of Co1−xCdxFe2−xCrxO4 ferrite system

Abstract The samples of the Cd–Cr co-substituted cobalt ferrite (Co 1− x Cd x Fe 2− x Cr x O 4 ) with x =0.0, 0.1, 0.2, 0.3, 0.4 and 0.5 were prepared by the usual double sintering ceramic technique and were characterized by means of X-ray diffraction (XRD) and dielectric measurements. X-ray analysis shows that the samples are cubic spinels (single phase). The lattice parameter a is determined from XRD data with an accuracy of ±0.002 A for x =0.0 to 0.5 and their variation with Cd and Cr addition is studied. The lattice parameter a increases with the compositional parameter x . the dielectric constant ( e ″), dielectric loss (tan δ ) and dielectric loss tangent (tan δ ) of Co 1− x Cd x Fe 2− x Cr x O 4 were measured at room temperature as a function of frequency. The measurements were carried out with the help of HP 4192 LF impedance analyzer in the range 100 Hz–1 MHz. It is observed that e ′, e ″ decrease with increasing frequency. The dielectric loss ( e ″) decreases with increasing frequency at a faster rate that the dielectric constant ( e ′). The parameter (tan δ ) decreases with increasing frequency.

Magnetic and electrical properties of aluminium and chromium co-substituted yttrium iron garnets

Abstract Polycrystalline yttrium aluminium-chromium iron garnets (Y 3 Al x Cr x Fe 5 − 2 x O 12 ) with varying Al-Cr substitution (0 ≤ x ≤ 1.0) have been prepared in the pellet form, and studied by X-ray diffraction, magnetization, a.c. susceptibility and electrical resistivity measurements. The lattice constants are determined and the applicability of Vegards law has been tested. The saturation magnetization (4π M s ) decreases linearly with increasing x from x = 0.1 to 1.0 indicating reduction in ferrimagnetic behaviour. Variation of saturation magnetic moment per formula unit at 300 K with x can be explained satisfactorily assuming the collinear spin ordering model. The Curie temperature ( T C ) decreases with increasing x which is consistent with the observed decrease in 4π M s with x . The activation energy ( E ) initially increases up to x = 0.6 and thereafter it levels off for further increase in x > 0.6.

Structural, magnetization and susceptibility studies on cobalt–ferri-aluminates synthesized by wet-chemical method

Abstract Spinel ferrites having the general formula CoAl x Fe 2− x O 4 ( x =0.0–1.0) were prepared using the wet-chemical method. The samples were sintered at 200°C, 500°C and 800°C temperature and were studied by means of X-ray diffraction, magnetization and low-field AC susceptibility measurements. The observed features for the wet samples, such as the intense peak in χ AC – T curve, the co-existence of paramagnetic doublet and magnetic sextets in Mossbauer spectra and lower saturation magnetization values confirm fine particle ferrite behaviour. The variation of saturation magnetization with Al 3+ substitution is explained on the basis of the Neels collinear spin model. The cation distribution is estimated from the X-ray intensity calculations and magnetization measurements.

Structural properties and magnetic interactions in Al3+ and Cr3+ co-substituted CoFe2O4 ferrite

A series of CoAlxCrxFe2−2xO4 systems (x = 0.1 to 0.5 in steps of x = 0.1) spinel ferrites have been synthesized successfully using wet chemical co-precipitation technique. The samples were characterized by X-ray diffraction (XRD), infrared spectroscopy (IR) and magnetization measurements. The powder XRD patterns confirm the single phase spinel structure for the materials synthesized. X -ray diffraction measurements were performed to yield the lattice constant as function of the amount x corresponding to Al-Cr substitution. Lattice parameters, X-ray density, bulk density and particle size decrease whereas porosity increases with the increase in Al-Cr content, ‘x’. Infrared studies show two absorption bands at about 400 cm−1 and 600 cm−1 for octahedral and tetrahedral sites, respectively. Saturation magnetization decreases with the increase in Al-Cr content x. AC magnetic susceptibility measurements were carried out as a function of temperature to measure the Curie temperature, which was found to decrease with Al-Cr content x. The decrease of Curie temperature has been explained by A-B interaction.

Synthesis, Structural, and Electrical Properties of Pure PbTiO3 Ferroelectric Ceramics

Single-phase polycrystalline samples of lead titanate with perovskite structure have been synthesized using solid-state reaction technique. The processing parameters have been optimized to obtain phase pure, dense, crack-free, and homogeneous samples. The sintering behavior of PT-powders has been investigated using X-ray diffraction patterns. The X-ray powder diffraction data have been analyzed to confirm the phase formation and phase purity, to obtain unit cell parameters and unit cell volume. The porosity of the samples has been obtained through X-ray density and bulk density. The average particle sizes of the phase pure samples were obtained from the X-ray peak width using Scherrer’s formula. The influence of sintering temperature and time on the microstructure of samples has also been studied by carrying out SEM investigations. The notable feature of this microstructure study shows that the samples sintered at 900°C for 12 hours possess a fairly uniform grain distribution. The electrical behavior (complex impedance Z*, complex permittivity e*, etc.) of the samples sintered at 900°C for 12 hours has been studied by complex impedance spectroscopy. The temperature variation of real permittivity gives evidence of the ferroelectric phase transition as well as of the relaxation behavior.

Study of Phase Transitions and Response of Dielectric Behavior of Pb1–1.5xLaxTiO3 Ceramics

Polycrystalline samples of ferroelectric perovskite type lanthanum doped lead titanate, Pb1–1.5xLaxTiO3 (PLT) with x ranging from 0.00 ≤ x ≤ 0.3 ceramic system have been synthesized through the modified solid-state reaction technique. One of the objectives of this work was to optimize carefully the process variables which influence the structural and microstructural properties of the samples prepared. X-ray diffraction studies have been used to follow the evolution of the structural phases that occur with the increase of lanthanum content. The sharp peaks observed in XRD patterns and the absence of any impurity peaks confirmed the formation of single phase compounds. The analysis of the X-ray diffraction patterns for the samples with 0.00 ≤ x ≤ 0.2 confirmed the tetragonal phase formation. For x = 0.3 the observed X-ray diffraction peaks confirmed the presence of cubic phase as also evident from the absence of splitting of (101 110) and (002 200) peaks. The average linear particle sizes for all the compositions estimated using Scherrers formula lie in the range 230–570 nm. The grain sizes of the lead lanthanum titanate ceramic powders increases with the increase of lanthanum content. The grain morphology and size were directly imaged using scanning electron microscopy (SEM) and the average grain size was determined by using a mean linear intercept method. Detailed studies of dielectric constant (ϵ) and tangent loss (tan δ) as a function of frequency (5 Hz–13 MHz) at room temperature (RT) and temperature (RT-900 K) suggest that compounds undergo ferroelectric-paraelectric phase transition of diffuse type. The value of diffusivity γ is extracted from the ln (1/ϵ−1/ϵmax) vs. ln (T−Tmax)γ plots and the values of γ vary between 1.18 to 1.75, which confirm that diffuse phase transition occurs in the lead lanthanum titanate (PLT) system. The results of differential scanning calorimetry (DSC) study also support the phase transition temperature observed in the dielectric measurements.

Identification of morphotropic phase boundary (MPB) region in (Pb1-x Lax) (Zr0.65 Ti0.35)1-0.25XO3 (PLZT) ceramics

Polycrystalline samples of lanthanum doped lead zirconate titanate (PLZT) with formula (Pb1−x Lax) (Zr0.65 Ti0.35)1−0.25XO3, (x = 0.02, 0.04, 0.06. 0.08 and 0.1) have been prepared by a high temperature solid state reaction technique. The optimum sintering temperature was found to be 950°C for 12 h. The structural phase, density and microstructure of all the samples prepared have been investigated using X-ray diffraction and scanning electron microscopic (SEM) studies. The X-ray diffraction analysis suggest the formation of single phase compounds with rhombohedral phase for x = 0.02, 0.04 and 0.06 with the space group (R3m). For x = 0.08 and 0. 1 the samples showed cubic phase (Pm3m). The notable feature of these microstructural studies showed that the samples sintered at 950°C for 12 h. possess a fairly uniform grain distribution without the presence of any cracks. The phase evolutions on rhombohedral - Cubic have been analyzed by using deconvolution of peaks.

Sol–gel synthesis and characterization of lead titanate films

Abstract Lead titanate thin films have been deposited by spin coating on stainless steel substrate using the precursor sol, which was synthesized from acetylacetone chelating with titanium isopropoxide and ethylene glycol as a solvent, in the sol–gel process. The influence of film thickness, pyrolysis temperature, and heating rate on (the formation of thin films) microstructure and morphology of thin films have been systematically investigated. The phase purity, particle size, and morphology are studied using X-ray diffraction and scanning electron microscopy (SEM) measurements. It is observed that the preferred oriented thin films could be obtained by pyrolysis of wet films at 150°C and annealed at 600°C at a slow heating rate of 4°C/min. It is also confirmed from X-ray patterns that the tetragonal perovskite structure of the titanate exists without any impurity peaks in the films formed. The TGA/DSC curves of the PT precursor show weight loss of ~7% and two exotherms at 492 and 522°C. They are attributed to the crystallization of tetragonal PbTiO3. SEM shows that the PbTiO3 thin films annealed at 600°C for 1 h crystallized well. The FTIR analysis showed the characteristic absorption bands of Pb–O groups at 663 cm−1 and Ti–oxo groups at 600 cm−1.