ELECTRICAL CONDUCTION IN SUBSTITUTED Li-FERRITES PREPARED BY MICROWAVE PROCESSING

2005 ◽  
Vol 19 (21) ◽  
pp. 1051-1055 ◽  
Author(s):  
MAMATA MAISNAM ◽  
SUMITRA PHANJOUBAM ◽  
H. N. K. SARMA ◽  
CHANDRA PRAKASH ◽  
L. RADHAPIYARI DEVI ◽  
...  
Keyword(s):  
Activation Energy ◽  
Lattice Constant ◽  
Electrical Conduction ◽  
Spinel Structure ◽  
Single Phase ◽  
Microwave Sintering ◽  
Microwave Processing ◽  
Conventional Sintering

Samples with representative formula Li 0.45 Ni 0.1 Mn 0.1 Fe 2.35 O 4 have been sintered by conventional sintering technique and microwave sintering technique. Both the samples showed single-phase with spinel structure. The lattice constant for the microwave sintered (MS) sample showed a lower value than the conventionally sintered (CS) sample. The density of the MS sample has been found to be higher than the CS sample. And MS sample showed a higher value of resistivity and activation energy compared to the CS sample. The possible mechanisms are discussed.

DIELECTRIC PROPERTIES OF Ni2+ AND Mn3+ SUBSTITUTED Li-FERRITE PREPARED BY MICROWAVE SINTERING TECHNIQUE

2007 ◽  
Vol 21 (08) ◽  
pp. 497-503 ◽  
Author(s):  
MAMATA MAISNAM ◽  
SUMITRA PHANJOUBAM ◽  
H. N. K. SARMA ◽  
L. RADHAPIYARI DEVI ◽  
O. P. THAKUR ◽  
...  
Keyword(s):  
Dielectric Properties ◽  
Electrical Properties ◽  
Comparative Study ◽  
Lattice Constant ◽  
Spinel Structure ◽  
Single Phase ◽  
Microwave Sintering ◽  
Dielectric Behavior ◽  
Phase Spinel ◽  
Xrd Studies

Li 0.45 Ni 0.1 Mn 0.1 Fe 2.35 O 4 ferrite samples were prepared by microwave-sintering (MS) and conventional (CS) techniques. XRD studies have confirmed the single-phase spinel structure of the sample. The lattice constant was found to be 8.334 Å which is lower than that of the conventionally sintered (CS) sample. Upon microwave sintering, improved physical and electrical properties (like density, resistivity etc.) were obtained. A comparative study has been made on the dielectric behavior of samples processed by both techniques. The possible mechanisms are discussed.

The diffusion of Fe2+ ions in spinels with relevance to the process of maghemitization

1980 ◽  
Vol 43 (331) ◽  
pp. 889-899 ◽  
Author(s):  
W. Freer ◽  
R. O'Reilly
Keyword(s):  
Activation Energy ◽  
Spinel Structure ◽  
Single Phase ◽  
Sea Water ◽  
Magnetic Minerals ◽  
Magnetic Studies ◽  
Water Leaching ◽  
Lower Activation ◽  
Diffusion Activation ◽  
Lower Activation Energy

SummaryThe maghemitization process, by which magnetic minerals with spinel structure become progressively oxidized but remain single phase spinels, seems to be an important feature of submarine weathering. Whether the process takes place by the minerals acquiring oxygen from the sea-water or by the sea-water leaching out iron, the controlling process is the diffusion of Fe2+ in the spinel structure. Magnetic studies have suggested that during maghemitization the availability for oxidation of Fe2+ in the tetrahedral (A) sites of the spinel structure is much less than that in octahedral (B) sites. In this study the Fe2+-containing spinels FeAl2O4, FeCr2O4, FeGa2O4, and Fe2GeO4, in which Fe2+ is predominantly in either A or B sites were prepared, and the diffusion of Fe2+ was studied by (1) interdiffusion experiments with the Mg2+ counterparts and (2) oxidation experiments in air. Fe2GeO4 (Fe2+ in B sites) was found to be associated with a higher interdiffusion coefficient and lower activation energy than FeAl2O4 (75% Fe2+ in A sites). Oxidation/diffusion activation energies of 0.27 and 0.71 eV were assigned to Fe2+ in B and A sites respectively. The experiments thus provide support for the maghemitization model in which Fe2+ in B sites is preferentially oxidized.

ELECTRICAL PROPERTIES OF Cd2+ SUBSTITUTED Li–Zn FERRITES

2010 ◽  
Vol 24 (20) ◽  
pp. 2195-2200 ◽  
Author(s):  
MAMATA MAISNAM ◽  
SUMITRA PHANJOUBAM ◽  
CHANDRA PRAKASH
Keyword(s):  
Dielectric Constant ◽  
Electrical Properties ◽  
Curie Temperature ◽  
Lattice Constant ◽  
Spinel Structure ◽  
Single Phase ◽  
Dc Resistivity ◽  
Constant Density ◽  
Zn Ferrite

Cd 2+ substituted Li – Zn ferrite with compositional formula Li 0.4-x/2 Zn 0.2 Cd x Fe 2.4-x/2 O 4 with x = 0.02, 0.03 and 0.04 were prepared by the conventional double sintering ceramic technique. XRD technique confirmed the formation of single phase with spinel structure. The substitution causes an increase in the lattice constant, density and DC resistivity, while the Curie temperature and dielectric constant decreases with Cd 2+ substitution. The mechanisms involved are discussed.

Microwave Processing and Sintering of PZT and PLZT Ceramics

1988 ◽  
Vol 124 ◽  
Author(s):  
W. B. Harrison ◽  
M. R. B. Hanson ◽  
B. G. Koepke
Keyword(s):  
Lead Titanate ◽  
Microwave Sintering ◽  
Ferroelectric Properties ◽  
Lead Zirconate ◽  
Microwave Processing ◽  
High Density ◽  
Pzt Ceramics ◽  
Conventional Sintering ◽  
Processing Techniques ◽  
Fast Firing

ABSTRACTMicrowave processing techniques were established for all of the thermal treatment steps necessary to prepare high density PZT and PLZT. The microstructure and ferroelectric properties of the microwave processed materials were compared to conventionally sintered and fast fired PZT. Unique high density, small grain size, PZT and PLZT were obtained by microwave sintering either conventionally or fully microwave processed powders. It was estimated that microwave sintering would use only five percent of the energy used by conventional sintering.The suitability of microwave processing for the production of two modifications (Sr and La) of lead zirconate - lead titanate (PZT) ceramics was investigated in this program. A commercial microwave oven was used to evaluate drying, calcining, binder burnoff, and sintering. These materials were then compared to those produced by fast-firing and conventional sintering methods.

Apparent Activation Energy in High Frequency Microwave Sintering of Alumina Ceramic

2015 ◽  
Vol 1123 ◽  
pp. 391-396 ◽  
Author(s):  
I. Nyoman Sudiana ◽  
Seitaro Mitsudo ◽  
Shunsuke Inagaki ◽  
La Ode Ngkoimani ◽  
Usman Rianse ◽  
...  
Keyword(s):  
Activation Energy ◽  
Apparent Activation Energy ◽  
High Frequency ◽  
Driving Force ◽  
Microwave Sintering ◽  
High Frequencies ◽  
Conventional Sintering ◽  
Series Of Experiments ◽  
High Frequency Microwave ◽  
Sintering Method

The observed enhancements in the high frequency microwave processing alumina compared to those in conventional method at the same sintering temperatures have been studied. Some possible mechanisms responsible for the enhancements were investigated and are discussed in this paper. The enhancements could be associated with the increase either in driving force or in apparent activation energy of diffusion. An experiment to estimate the driving force of sintering is not easy to perform because the force depends not only on the density and grain size but also on the electric field in the materials. Therefore, a series of experiments to estimate the apparent activation energy were performed in high frequencies microwave and in conventional sintering method, as well. It was observed that the apparent activation energy in conventional sintering was much lower than that of microwave sintering. These activation energy values suggested that diffusion rate in microwaves sintering was faster, which led to the higher densification.

Mechanisms for nonthermal effects on ionic mobility during microwave processing of crystalline solids

1992 ◽  
Vol 7 (2) ◽  
pp. 495-501 ◽  
Author(s):  
John H. Booske ◽  
Reid F. Cooper ◽  
Ian Dobson
Keyword(s):  
Activation Energy ◽  
Brillouin Scattering ◽  
Microwave Sintering ◽  
Microwave Frequency ◽  
Radiation Energy ◽  
Ionic Mobility ◽  
Microwave Processing ◽  
Tracer Diffusion ◽  
Crystalline Solids ◽  
Resonant Coupling

Models for nonthermal effects on ionic motion during microwave heating of crystalline solids are considered to explain the anomolous reductions of activation energy for diffusion and the overall faster kinetics noted in microwave sintering experiments and other microwave processing studies. We propose that radiation energy couples into low (microwave) frequency elastic lattice oscillations, generating a nonthermal phonon distribution that enhances ion mobility and thus diffusion rates. Viewed in this manner, it is argued that the effect of the microwaves would not be to reduce the activation energy, but rather to make the use of a Boltzmann thermal model inappropriate for the inference of activation energy from sintering-rate or tracer-diffusion data. A highly simplified linear oscillator lattice model is used to qualitatively explore coupling from microwave photons to lattice oscillations. The linear mechanism possibilities include resonant coupling to weak-bond surface and point defect modes, and nonresonant coupling to zero-frequency displacement modes. Nonlinear mechanisms such as inverse Brillouin scattering are suggested for resonant coupling of electromagnetic and elastic traveling waves in crystalline solids. The models suggest that nonthermal effects should be more pronounced in polycrystalline (rather than single crystal) forms, and at elevated bulk temperatures.

scholarly journals Rapid Microwave Synthesis and Structural Phase Diagram of LnxY1−xMnO3

2014 ◽  
Vol 69 (7) ◽  
pp. 761-766 ◽  
Author(s):  
Fred P. Marlton ◽  
Darren J. Goossens ◽  
Reyner White ◽  
Wayne D. Hutchison
Keyword(s):  
Phase Diagram ◽  
Microwave Synthesis ◽  
Single Phase ◽  
Microwave Sintering ◽  
Structural Phase ◽  
Conventional Sintering ◽  
The Stability ◽  
Related Compounds ◽  
Sintering Method

YMnO3 is one of the primary examples of a multiferroic ceramic. We present a novel solid-state microwave sintering method for making high-purity ceramic samples of YMnO3 and related compounds in a few hours. This leads to determination of the structural phase diagram for the formation of single-phase, hexagonal samples when doping lanthanides into YMnO3. It is found that the solidstate microwave synthesis allows manufacture of high-quality samples in hours rather than days. The resulting phase diagram accords well with results from the literature, and from calculations based on the Goldschmidt tolerance factor for the stability of perovskite structures, suggesting that the transformation from hexagonal to perovskite with doping is driven essentially by ion sizes. Some results concerning the microwave synthesis of BaLnInO4 compounds, where Ln is a lanthanide, are noted. Microwave sintering of BaNdInO4 yields single-phase samples where conventional sintering does not.

Microwave Sintering of Zirconia Toughened Mullite (ZTM)

1994 ◽  
Vol 347 ◽  
Author(s):  
J. Cai ◽  
C. Y. Song ◽  
B. S. Li ◽  
X. X. Huang ◽  
J. K. Guo ◽  
...  
Keyword(s):  
Grain Size ◽  
Grain Growth ◽  
Microwave Sintering ◽  
Single Mode ◽  
Microwave Processing ◽  
Toughening Mechanism ◽  
Conventional Sintering

ABSTRACTMicrowave sintering of zirconia toughened mullite (ZTM) has been performed in a single mode applicator. In comparison with conventional sintering, microwave processing of ZTM leads to a higher density and finer grain size. Microstructure of microwave sintered ZTM was characterized by TEM and HRTEM techniques. The pinning of intergranular ZrO2 dispersoids retarded the grain growth of mullite matrix. The observation of a considerable number of trans-granular microcracks indicates that microcracking toughening is the main toughening mechanism for ZTM.

STRUCTURAL, ELECTRICAL AND MAGNETIC CHARACTERIZATION OF Ni–Cu–Zn SPINEL FERRITES

2011 ◽  
Vol 25 (03) ◽  
pp. 211-222 ◽  
Author(s):  
M. PENCHAL REDDY ◽  
M. VENKATA RAMANA ◽  
N. RAMA MANOHAR REDDY ◽  
K. V. SIVA KUMAR ◽  
R. RAMA KRISHNA REDDY ◽  
...  
Keyword(s):  
Single Phase ◽  
Sintering Temperature ◽  
Microwave Sintering ◽  
Initial Permeability ◽  
Electromagnetic Devices ◽  
Zn Ferrite ◽  
Conventional Sintering ◽  
Tan Δ ◽  
Sintering Method

Ni – Cu – Zn ferrite materials have been extensively used in multilayer chip inductors because of their remarkable properties at higher frequencies. In the present work, single phase Ni 0.35 Cu 0.05 Zn 0.60 Fe 1.98 O 4-δ ferrite, has been prepared by microwave sintered (MS) method. In comparison with the conventional sintering method (CS), the sintering temperature and time for this MS method were significantly reduced to 30 min and 950°C from 5 h and 1250°C for the CS process. The frequency dependence of the dielectric properties such as dielectric constant (ε'), dielectric loss ( tan δ) were studied. The temperature dependence of magnetic initial permeability (μi) was studied. The saturation magnetization was also studied as a function of magnetic field. These microwave sintered ferrites results were compared with the properties of ferrites prepared by conventional sintering method in normal heating. Microwave sintering improves structural as well as electromagnetic parameters measured and thus makes the ferrite more suitable in microwave applications and electromagnetic devices.

Dielectric Properties of Vanadium Substituted Lithium Zinc Titanium Ferrites

2003 ◽  
Vol 17 (21) ◽  
pp. 3881-3887 ◽  
Author(s):  
Mamata Maisnam ◽  
Sumitra Phanjoubam ◽  
H. N. K. Sarma ◽  
O. P. Thakur ◽  
L. Radhapiyari Devi ◽  
...  
Keyword(s):  
Dielectric Constant ◽  
Dielectric Properties ◽  
Curie Temperature ◽  
Saturation Magnetization ◽  
Spinel Structure ◽  
Single Phase ◽  
Xrd Analysis ◽  
Dielectric Behaviour ◽  
Conventional Sintering ◽  
Vanadium Substitution

This paper reports the influence of vanadium substitution on the properties of Li – Zn – Ti ferrite. Samples with compositional formula Li 0.5+t Zn 0.2 Ti 0.2 V t Fe 2.1-2t O 4 (t ranging from 0 to 0.25 in steps of 0.05) were prepared by the conventional sintering technique. XRD analysis confirmed all the samples to be single phase with spinel structure. The lattice constant a density, Curie temperature and Saturation magnetization were measured. The dielectric behaviour was studied as a function of frequency and temperature. The dielectric behaviour showed dispersion with the frequency in the range 100 Hz to 1 MHz. The dielectric constant increases with the increase of temperature for all the samples. The possible mechanisms involved are discussed.

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