Microwave Dielectric Resonator Based on Ba[(Bi0.2 D3+0.3)Nb0.5]O3(D3+=Y,Pr,Sm,Gd,Dy,Er)

Dielectric resonator ceramics with composition formula Ba[(D3+0.3 Bi0.2)Nb0.5]O3,where D3+=Y,Pr,Sm,Gd,Dy and Er,were prepared by the conventional ceramic preparation route

Preparation, Characterization, and Microwave Properties of RETiNbO6 (RE = Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Y, and Yb) Dielectric Ceramics

Microwave ceramic dielectric resonators (DRs) based on RETiNbO6 (RE = Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Y, and Yb) have been prepared using the conventional solid -state ceramic route. The DR samples are characterized using XRD and SEM methods. The microwave dielectric properties are measured using resonant methods and a net work analyzer . The ceramics based on Ce, Pr, Nd, and Sin have dielectric constants in the range 32-54 and positive coefficient of thermal variation of resonant frequency (r,). The ceramics based on Gd, Tb, Dy, Y. and Yb have dielectric constants in the range 19-22 and negative Tf

Microwave Dielectric Properties of RETiTaO6 (RE = La, Ce,Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Y, Er, Yb, Al, and In) Ceramics

Microwave dielectric ceramics based on RETiTaO6 (RE = La, Cc, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Y, Er, Yb, Al, and In) were prepared using a conventional solid-state ceramic route. The structure and microstructure of the samples were analyzed using x-ray diffraction and scanning electron microscopy techniques. The sintered samples were characterized in the microwave frequency region. The ceramics based on Ce, Pr, Nd, Sm, Eu, Gd, Tb, and Dy, which crystallize in orthorhombic aeschynite structure, had a relatively high dielectric constant and positive T f while those based on Ho, Er, and Yb, with orthorhombic euxenite structure, had a low dielectric constant and negative Tf. The RETiTaO6 ceramics had a high-quality factor. The dielectric constant and unit cell volume of the ceramics increased with an increase in ionic radius of the rare-earth ions, but density decreased with it. The value of Tf increased with an increase in RE ionic radii, and a change in the sign of Tf occurred when the ionic radius was between 0.90 and 0.92 A. The results indicated that the boundary of the aeschynite to euxenite morphotropic phase change lay between DyTiTaO6 and HoTiTaO6. Low-loss ceramics like ErTiTaO6 (Er = 20.6, Qxf = 85,500), EuTiTaO6 (Er = 41.3, Qxf = 59,500), and YTiTaO6 (Er = 22.1, Q„xf = 51,400) are potential candidates for dielectric resonator applications

Preparation, Characterization and Microwave Dielectric Properties of Ba (B1/2Nb1/2)03 [B' = La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Y, Yb and In] Ceramics

Microwave dielectric resonators (DRs) based on Ba(B1,2Nbi/2)03 [B' = La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Y, Yb, and In] complex perovskites have been prepared by conventional solid state ceramic route. The dielectric properties (relative permittivity, Er; quality factor, Q; and resonant frequency, rr) of the ceramics have been measured in the frequency range 4-6 GHz using resonance methods. The resonators have relatively high dielectric constant in the range 36-45, high quality factor and small temperature variation of resonant frequency. The dielectric properties are found to depend on the tolerance factor (t), ionic radius (r), and lattice parameter (ap)

Colossal thermoelectric power in Gd-Sr manganites

Manganites belonging to the series Gd1−xSrxMnO3 (x=0.3, 0.4 and 0.5) were prepared by wet solid-state reaction and their thermoelectric power was evaluated. Thermoelectric power measurements revealed a peak value at ∼40 K. All the samples exhibited a colossal thermopower at ∼40K and in that Gd0.5Sr0.5MnO3 exhibited a maximum value of ∼35mV/K, which is the largest reported for these class of materials at this temperature. Temperaturedependent magnetisation measurements showed that the samples exhibit a phase transition from paramagnetic to spin-glass–like state at these temperatures. Plausible mechanisms responsible for the observed colossal thermoelectric power in Gd-Sr manganites are discussed

Multiferroic Behavior of Gd Based Manganite

Here we report the multiferroic nature of charge ordered manganite Gd0.5Sr0.5MnO3 for the first time. The temperature variation of dielectric constant shows broad relaxor type ferroelectric transition at around 210K and magnetization measurements shows weak ferromagnetism at 50K. The dielectric peak is very close to charge ordering temperature which is an evidence of the link between electronic state and increase of dielectric response. Butterfly variation of capacitance with voltage confirms ferroelectric nature of the sample at room temperature

On conduction mechanism in paramagnetic phase of Gd based manganites

Materials belonging to the family of manganites are technologically important since they exhibit colossal magneto resistance. A proper understanding of the transport properties is very vital in tailoring the properties. A heavy rare earth doped manganite like Gd0·7Sr0·3MnO3 is purported to be exhibiting unusual properties because of smaller ionic radius of Gd. Gd0·7Sr0·3MnO3 is prepared by a wet solid state reaction method. The conduction mechanism in such a compound has been elucidated by subjecting the material to low temperature d.c. conductivity measurement. It has been found that the low band width material follows a variable range hopping (VRH) model followed by a small polaron hopping (SPH) model. The results are presented here

Synthesis,Characterization and Properties of [REI_xREX]TiNb06 Dielectric Ceramics

Dielectric ceramics based on solid solution phases of [RE1_x= REr]TiNb06, where REI_s = Nd, Pr, Sm and RE' = Dy, Gd and Y, were prepared by the conventional solid-state ceramic route for values of x. The ceramic samples are characterized by X-ray diffraction and microwave methods. Ceramics based on RE (Pr, Nd and Sm) belonging to aeschynite group shows positive value of Tf and those based on RE (Gd, Dy and Y) belonging to euxenite group show negative value of r f. The solid solution phases between the aeschynite and the euxenite group shows intermediate dielectric constant and r f values. The results indicate the possibility of tailoring the dielectric properties by varying the composition of the solid solution phases. The range of solid solubility of euxenite in aeschenite and aeschenite in euxenite are different for different rare earth ions

Investigations on the Multiferroic and Thermoelectric properties of Low and Intermediate band width Manganites

This thesis lays importance in the investigation on the multiferroic and thermooelectric properties of selected representatives of low bandwidth and intermediate band width manganites. The first candidate, Strontium doped Gd manganite, is prepared by wet solid state reaction method and the second candidate, Na doped La manganite, by citrate gel method. In addition to the above mentioned properties, magneto resistance and dielectric properties are investigated. Using dielectric spectroscopic the dispersion parameters are correlated to the relaxation mechanisms and an attempt is made to obtain the grain and grain boundary contribution to the impedance of the sample through impedance spectroscopy studies.

Photoluminescence studies on rare earth titanates prepared by self-propagating high temperature synthesis method

The laser-induced luminescence studies of the rare earth titanates (R2Ti2O7) (R = La, Nd and Gd) using 355 nm radiation from an Nd:YAG laser are presented. These samples with submicron or nanometer size are prepared by the self-propagating high temperature synthesis (SHS) method and there is no known fluorescence shown by these rare earths in the visible region. Hence, the luminescence transitions shown by the La2Ti2O7 near 610 nm and Gd2Ti2O7 near 767 nm are quite interesting. Though La3+ ions with no 4f electrons have no electronic energy levels that can induce excitation and luminescence processes in the visible region, the presence of the Ti3+ ions leads to luminescence in this region.

Measurements of Electromagnetic Shielding Effect Using Htsc Materials

A simple experimental set-up is described to measure the electromagnetic shielding property of high Tc superconducting samples. Measurements were performed using HTSC materials in the form of laser ablated thin films, powders and sintered pellets. Samples used were Gd-123 in pure and doped form as well as a few Bi-based superconducting ceramics. For comparison, similar measurements were carried out on metals like aluminium, copper and μ metal. Very effective shielding was observed for HTSC materials compared to the conventional materials mentioned above. However it also depended on the sample types and poor shielding was observed for powdered HTSC material in comparison to thin films prepared by laser ablation.

A new inexpensive method for the preparation of acicular precursors for magnetic recording media

Magnetic materials meant for audio/video recording applications necessitate that polycrystalline materials be in acicular shape. So preparation of acicular precursors for magnetic storage materials assumes significance. The employment of aqueous solutions do not produce needle shape crystallites. Glycerol is one of the complexing media used for the precipitation of ferrous oxalate dihydrate. An inexpensive method using starch for preparation of acicular particles is described. The influence of an additive namely Gd on acicularity is also investigated

Influence of dopants on the properties of maghemite

Preparatiun or aci cular maghemi te containing dopan ls li ke Mg. i and Gd and their characleris,llion us ing different analytica l techniques have been reported. These in vestigat ions reveal that the addition of dopants li ke Mg. Ni and Gd modifies the magnetic properties without cfrecting any structural changes. The opt ical bandgaps of these doped compositions have ,li S() hecn determ ined. Evidence is ,li so av,li lab le from spectroscopic investi gations suggest ing thalmaghcllli te prepared vi,l the ()xa l,ltc precursor route does nm exhi bit a hydrogen fe rrite structure

Behaviour of REEs in a tropical estuary and adjacent continental shelf of southwest coast of India: Evidence from anomalies

The distribution and accumulation of the rare earth elements (REE) in the sediments of the Cochin Estuary and adjacent continental shelf were investigated. The rare earth elements like La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and the heavy metals like Mg, V, Cr, Mn, Fe, Cu, Zn, U, Th were analysed by using standard analytical methods. The Post-Archean Australian Shale composition was used to normalise the rare earth elements. It was found that the sediments were more enriched with the lighter rare earth elements than the heavier ones. The positive correlation between the concentrations of REE, Fe and Mn could explain the precipitation of oxyhydroxides in the study area. The factor analysis and correlation analysis suggest common sources of origin for the REEs. From the Ce-anomalies calculated, it was found that an oxic environment predominates in all stations except the station No. 2. The Eu-anomaly gave an idea that the origin of REEs may be from the feldspar. The parameters like total organic carbon, U/Th ratio, authigenic U, Cu/Zn, V/Cr ratios revealed the oxic environment and thus the depositional behaviour of REEs in the region