Indian Journal of

Engineering & Materials Sciences

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VOLUME 15

CODEN : IEMSEW

NUMBER 2

APRIL 2008

ISSN : 0971-4588

 

CONTENTS

 

Effect of La/Mn substitution on electrical properties of BiFeO3 multiferroics

87

        Dillip K Pradhan, R N P Choudhary, C M Tirado & R S Katiyar

 

 

Solid state synthesis and characterization of multiferroic BiFeO3 ceramics

91

        K S Nalwa, A Garg & A Upadhayaya

 

 

Synthesis and characterization of nickel titanium melt-spun ribbon for micro-actuator device application

 

95

        D Panda, M Ranot, K Das, D Bhattacharya, A Dhar, M Chakraborty & S K Ray

 

 

Design and simulation of optimum piezoelectric MEMS microactuator for smart control applications

 

99

        Soma Dutta

 

 

Synthesis and characterization of solution processed BiFeO3-PbTiO3 thin films

104

        Vijay Raj Singh, Soumya Kar & Ashish Garg

 

 

Effect of calcium variation on dielectric response of the sol-gel derived CaCu3Ti4O12 thin films

 

107

        Deepam Maurya, Parveen Kumar, Devendra P Singh & D C Agrawal

 

 

Preparation and characterization of PMN-PT nanocomposite

111

        Shrabanee Sen, S K Mishra, S Sagar & S K Das

 

 

Structural and dielectric investigations on BST-BZT composites

116

        S B Kulkarni, S S Veer, D J.Salunkhe, S R Kokare & P B Joshi

 

 

Effect of sintering aid on physical and magnetoelectric properties of La0.7Sr0.3MnO3 –BaTiO3 composites

 

121

        S S Veer, D J Salunkhe, S V Kulkarni, S B Kulkarni & P B Joshi

 

 

Low temperature ferroelectric behaviour of PVDF based composites

126

        Namrata Shukla, Archana Shukla, Awalendra K Thakur & R N P Choudhary

 

 

Temperature dependent impedance and dielectric properties of  0.7 CaTiO3-0.3 NdAlO3 ceramics

 

133

        K Sudheendran & K C James Raju

 

 

Structural, dielectric and electrical properties of Sr5GdTi3X7O30 (X = Nb and Ta) ceramics: An Impedance spectroscopic study

137

        M R Ranga Raju & R N P Choudhary

 

Impedance analysis of (Na0.5Bi0.5)(Zr0.25Ti0.75)O3 ceramic

147

        Lily, K Kumari, K Prasad& R N P Choudhary

 

 

Impedance spectroscopy of (Pb0.93Gd0.07)(Sn0.45Ti0.55)0.9825o3 ferroelectrics

152

        B P Das, R N P Choudhary & P K Mahapatra

 

 

Electrical responses of Pb2Sb3RTi5O18 (R º La, Nd, Sm, Gd, Dy) ceramics

157

        C K Suman, K Prasad & R N P Choudhary

 

 

Electrical properties of relaxor ferroelectric PMCT-PT-ZnO ceramic

163

        S Prasad, K Prasad, S N Choudhary & T P Sinha

 

 

Electrical properties of SrBi2Ta2O9 thin films deposited on Si(100) substrates by rf magnetron sputtering

 

167

        A Roy, G Jha, A Dhar, I Manna & S K Ray

 

 

Electrical properties of ferromagnetic Ag:CrO2 particles

171

        G P Singh, S Ram, A K Thakur & R N P Choudhary

 

 

Preparation and characterization of perovskite PMN [Pb(Mg1/3Nb2/3)O3]

176

        Kamal Singh & Tanveer Quazi

 

 

Dielectric relaxation and ac conductivity study in SrMg1/3Nb2/3O3

181

        Alo Dutta, Chandrahas Bharti & T P Sinha

 

 

Dielectric anomaly and magnetic order in Ba(Mn0.5Nb0.5)O3

187

        R K Mishra, R N P Choudhary, Awalendra K.Thakur & A Banerjee

 

 

Studies on dielectric behaviour of an oxygen ion conducting ceramic – CaMnO3-δ

191

        Namita Pandey, Awalendra K Thakur & R N P Choudhary

 

 

Dielectric relaxation behaviour of glycine in aqueous solution medium in the microwave frequency region

 

196

        K Ajaya Kumar, Samiran Bhaumik, T Vishwam, V Subramanian &
V R K Murthy

 

 

Influence of temperature on the dielectric behaviour of Co2+ substituted Li-Ni-Mn ferrties

 

199

        Mamata Maisnam, Sumitra Phanjoubam, H N K Sarma, O P Thakur,
L Radhapiyari Devi & Chandra Prakash

 

 

Structural and dielectric properties of LaBi2Fe5O12

203

        K Jawahar & R N P Choudhary

 

 

Dielectric properties of In-Se-Te glassy alloys

207

        A S Maan & D R Goyal

 

 

Nonlinear wave propagation in ferroelectric/ferrite interface

211

        Michael Augustine, Roji Pius, Sunny Mathew &Vincent Mathew

 

 

Low frequency dielectric dispersion studies in ferroelectric ceramics of Pb0.77K0.26Li0.2Ti0.25Nb1.8O6

 

215

        K Sambasiva Rao, P Murali Krishna, D Madhava Prasad, T Swana Latha &
C Satyanarayana

 

 

 

 

Indian Journal of Engineering & Materials Sciences

Vol. 15, April 2008, pp. 87-90

 

Effect of La/Mn substitution on electrical properties of BiFeO3 multiferroics

Dillip K Pradhan, R N P Choudhary, C M Tirado & R S Katiyar

 

The polycrystalline fine powder (~60 nm) of Bi0.90La0.10(Fe1-xMnx)O3 (x= 0, 0.05, 0.10 and 0.20) have been synthesized by mechanical activation and mixed oxide methods. Preliminary structural analysis using X-ray diffraction exhibits formation of the single-phase compound in a hexagonal (distorted perovskites system). Detailed dielectric studies as a function of temperature show that dielectric constant of BFO (BiFeO3), and also tanδ increase significantly on increasing Mn content in BiLa(FeMn)O3 system. Impedance analysis of the system provides many interesting results.

 

 

Indian Journal of Engineering & Materials Sciences

Vol. 15, April 2008, pp. 91-94

 

Solid state synthesis and characterization of multiferroic BiFeO3 ceramics

K S Nalwa, A Garg & A Upadhayaya

 

BiFeO3 is a promising multiferroic material for future spintronic devices like sensors and actuators. The problems in the synthesis of phase‑pure BiFeO3 are well known and often lead to inferior ferroelectric properties. Work reported here was carried out to optimize the calcination temperature to obtain pure phase BiFeO3 via a solid state reaction method. The calcined samples were characterized by X-ray diffraction (XRD) for analyzing the phase purity of the samples. XRD patterns of the calcined samples suggest that the crystallization of the pure BiFeO3 phase is obtained at a heating temperature of 810°C whilst a deviation in calcination temperatures leads to the enhanced formation of impurity phases. Samples were further characterized using vibrating sample magnetometer (VSM) to study the temperature dependence of the magnetization and hysteresis behaviour of BiFeO3 at room temperature upon increasing the magnetic field strength.

 

Indian Journal of Engineering & Materials Sciences

Vol. 15, April 2008, pp. 95-98

 

Synthesis and characterization of nickel titanium melt-spun ribbon for micro-actuator device application

D Panda, M Ranot, K Das, D Bhattacharya, A Dhar, M Chakraborty & S K Ray

 

Nickel titanium shape memory alloy ribbons of different nickel ratio with refined grain size have been fabricated by rapidly quenched melt spinning technique. The nickel-titanium alloy buttons are produced by arc melting, before the ribbon fabrication. XRD has been used to study phase formation of the alloy buttons and ribbons. Microstructure, composition and surface topography of melt-spun ribbons are studied using scanning electron microscopy, energy dispersive X-ray measurements and atomic force microscopy. The phase transformation of the ribbons has been studied using resistivity measurement as a function of temperature.

 

Indian Journal of Engineering & Materials Sciences

Vol. 15, April 2008, pp. 99-103

 

 

Design and simulation of optimum piezoelectric MEMS microactuator
for smart control applications

 

Soma Dutta

 

This paper presents the design and finite element simulation of a novel piezoelectric microactuator. The optimaly designed cantilever type piezoelectric microactuator deflects at its tip by converse piezoelectric effect. It consists of a thin film PZT layer, intimately attached with a variable thickness SOI elastic layer and electrically connected with top and bottom electrodes by contact pads. The goal of this coupled piezoelectric actuator design is to multiply the force by adding a support beam, placed closer to the fixed end and by varying the width of the active layer. Structural simulation employed commercial software tool ANSYS/COVENTORWARE and the results include free tip deflection, blocked force and mechanical stresses while subjecting the actuator to a prescribed input voltage.

 

Indian Journal of Engineering & Materials Sciences

Vol. 15, April 2008, pp. 104-106

 

 

Synthesis and characterization of solution processed BiFeO3-PbTiO3

thin films

 

Vijay Raj Singh, Soumya Kar & Ashish Garg

 

In this paper, the growth and characterization of polycrystalline (BiFeO3)1‑x‑(PbTiO3)x solid solutions of composition near morphotropic phase boundary (MPB) have been reported. The films are deposited on platinized silicon (111) Pt/Ti/SiO2/Si substrate by chemical solution deposition method using spin coating technique. Morphological analysis was made by means of scanning electron microscopy. Grazing incidence X-ray diffractometry revealed the perovskite structure of the films. Although, room temperature dielectric constant (k’) suggested that the films have reasonable insulation resistance but ferroelectric measurements show the presence of  a leaky hysteresis behaviour in thin films.

 

Indian Journal of Engineering & Materials Sciences

Vol. 15, April 2008, pp. 107-110

 

Effect of calcium variation on dielectric response of the sol-gel derived CaCu3Ti4O12 thin films

 

Deepam Maurya, Parveen Kumar, Devendra P Singh & D C Agrawal

 

The giant dielectric constant exhibited by CaCu3Ti4O12 (CCTO) over a wide temperature and frequency range has generated considerable interest in this material. In this paper, we report the synthesis of sol-gel derived CCTO thin films with varying calcium content and their dielectric characterization. The room temperature XRD-patterns reveal the formation of a single perovskite phase. The dielectric constant, loss tangent and ac conductivity of these films have been investigated as a function of frequency at room temperature. The results show that with increase in the calcium content upto a certain limit the dielectric constant of these films increases.

 

Indian Journal of Engineering & Materials Sciences

Vol. 15, April 2008, pp. 111-115

 

Preparation and characterization of PMN-PT nanocomposite

Shrabanee Sen, S K Mishra, S Sagar & S K Das

 

Ferroelectric ceramic-polymer composites are considered as promising materials for applications in sensors, actuators and hydrophones. They are attractive for application as they exhibit high piezoelectric and pyroelectric response, low acoustic impedance matching with water and human skin and their properties can be tailored to various requirements. The advantage of composites over conventional ceramics is that they have better mechanical shock resistance and more durable. Lead magnesium niobate-lead titanate (PMN-PT with 35 mol% PT) ceramic powder is fabricated by citrate gel method. The calcinations temperature is optimized by thermal analysis. The formation of the ceramic powder is confirmed by XRD. The microstructural properties have been studied by, SEM and TEM. The particle size calculated from TEM was found to be between 50-55 nm and the homogeneous distribution of the powders was also observed. The composites have been prepared using solvent casting in which the powder is dispersed homogeneously in the polymer matrix. Different composites are made by varying the ceramic to polymer ratio. The structural, microstructural properties of the composite are studied.

Indian Journal of Engineering & Materials Sciences

Vol. 15, April 2008, pp. 116-120

 

Structural and dielectric investigations on BST-BZT composites

S B Kulkarni, S S Veer, D J.Salunkhe, S R Kokare & P B Joshi

 

Nanopowders of Ba0.8Sr0.2TiO3 (BST) and BaZr0.3Ti0.7O3 (BZT) are synthesized using hydroxide co-precipitation method. The nanoparticles are used to form composites z BST + (1-z) BZT for z = 0.4, 0.5 and 0.6 with 2 wt% Bi2O3 as a sintering aid. The powders of BST, BZT and composites are subjected to the investigations of XRD, complex impedance and dielectric properties. The results on variation of dielectric constant with temperature and frequency are promising and suggest usefulness of composites as a RF dielectric material, in the paraelectric region.

 

Indian Journal of Engineering & Materials Sciences

Vol. 15, April 2008, pp. 121-125

 

Effect of sintering aid on physical and magnetoelectric properties of La0.7Sr0.3MnO3 -BaTiO3 composites

 

S S Veer, D J Salunkhe, S V Kulkarni, S B Kulkarni & P B Joshi

 

The paper deals with synthesis of nanocrystalline La0.7Sr0.3Mn O3 (LSMO) and BaTiO3 (BT) powder via hydroxide co-precipitation route. The particle size of the powder is determined using Williamson Hall method and is observed to be nearly 35 nm for LSMO and 120 nm for BT. To avoid occurrence of impurity phases the composites of LSMO and BT are formed at 1273 K using Bi2O3 as a sintering aid. The paper focuses mainly on synthesis and dielectric properties of LSMO and BT composites. The effect of sintering aid on dielectric properties is also analyzed in this paper.

 

 

Indian Journal of Engineering & Materials Sciences

Vol. 15, April 2008, pp. 126-132

 

 

Low temperature ferroelectric behaviour of PVDF based composites

 

Namrata Shukla, Archana Shukla, Awalendra K Thakur  & R N P Choudhary

 

A polymer nanocomposite based on poly (vinylidenefluoride) (PVDF) and unmodified montmorillonite clay has been studied for structural phase transformation, ferroelectric and piezoelectric properties. The effect of clay concentration in modifying PVDF crystalline phase structure has been substantial leading to α→β phase transformation in PVDF. This aspect has been confirmed through X-ray diffraction and infrared spectroscopy data. The effect of structural change has been clearly observed in inducing dipolar characteristics in PVDF matrix supported by changes in dielectric permittivity variation as a function of temperature and frequency. A close resemblance in the permittivity and loss tangent peak position as a function of temperature has been correlated with dipolar ordering in PVDF matrix induced by clay. However, this ordering depends on clay concentration. The clay induced dipolar ordering is also supported by piezoelectric coefficient measured for various compositions of clay.

 

Indian Journal of Engineering & Materials Sciences

Vol. 15, April 2008, pp. 133-136

 

Temperature dependent impedance and dielectric properties of
0.7 CaTiO3-0.3 NdAlO3 ceramics

 

K Sudheendran & K C James Raju

 

In this paper, dielectric and impedance spectroscopic studies carried out on a 0.7CaTiO3- 0.3NdAlO3 composition have been reported. The material is synthesized by the conventional ceramic method and the dielectric measurements are carried out as a function of frequency (1 kHz-4.5 MHz) in the temperature range of 150-303 K. The impedance measurement is carried out at different temperatures to separate the grain and grain boundary contributions. The grain boundary resistance is evaluated from the measured Z-Z” plots. Both of them are found to be decreasing with the increase in temperature.

Indian Journal of Engineering & Materials Sciences

Vol. 15, April 2008, pp. 137-146

 

Structural, dielectric and electrical properties of Sr5GdTi3X7O30 (X = Nb and Ta) ceramics: An impedance spectroscopic study

 

M R Ranga Raju & R N P Choudhary

 

Polycrystalline samples of Sr5GdTi3Nb7O30 and Sr5GdTi3Ta7O30 ceramics were prepared by a high-temperature solid-state reaction technique. The formation of single-phase compounds in the orthorhombic system has been confirmed by room temperature X-ray diffraction studies. Scanning electron micrographs of the sintered samples were recorded at room temperature to study the surface morphology and the grain distribution over the surface. It has been found that the grain size decreases on substitution of Ta5+ in the Nb5+ site. Detailed studies of the dielectric constant (ε) and loss tangent (tanδ) with frequency at different temperatures suggest that both the compounds have a dielectric anomaly of diffuse nature. It was interesting to observe that the transition temperature (Tc) shifts to the low temperature side after Ta5+ is substituted at the Nb site of Sr5GdTi3Nb7O30. Detailed analysis of the impedance data suggests that the conduction processes is due to both bulk as well as grain boundary contributions. The scaling behaviour of the loss spectra of the material suggests that the distribution of relaxation time is temperature dependent and polydispersive in nature. The frequency dependent electrical properties of the compounds were also studied.

 

 

Indian Journal of Engineering & Materials Sciences

Vol. 15, April 2008, pp. 147-151

 

Impedance analysis of (Na0.5Bi0.5)(Zr0.25Ti0.75)O3 ceramic

Lily, K Kumari, K Prasad & R N P Choudhary

(Na0.5Bi0.5)(Zr0.25Ti0.75)O3, having perovskite-type orthorhombic structure, is prepared using via high-temperature solid-state reaction technique. The electrical behaviour has been assessed by electric modulus, pseudo Cole-Cole, and ac conductivity analyses. Electric modulus and pseudo Cole-Cole analyses indicated the dielectric relaxation to be of non-Debye type. The electrical conductivity studies showed the negative temperature coefficient of resistance character of (Na0.5Bi0.5)(Zr0.25Ti0.75)O3. The ac conductivity is found to obey the universal power law and correlated barrier hopping model is found to successfully explain the electrical conduction in the system.

 

Indian Journal of Engineering & Materials Sciences

Vol. 15, April 2008, pp. 152-156

 

 

Impedance spectroscopy analysis of (Pb0.93Gd0.07)(Sn0.45Ti0.55)0.9825O3 ferroelectrics

B P Das, R N P Choudhary  & P K Mahapatra

 

The sample of (Pb0.93Gd0.07)(Sn0.45Ti0.55)0.9825O3 is prepared by a standard mixed oxide method. The prepared powder has been analyzed by XRD, and it is found to have tetragonal structure. The impedance spectrum analysis of (Pb0.93Gd0.07)(Sn0.45Ti0.55)0.9825O3 compound exhibits the appearance of single semicircular arc whose radii decreases gradually with increase in temperature. The bulk resistance at 425, 450, 475 and 500oC are found to be 325, 200, 130, 70 kΩ respectively. Nyquist plots (Z// versus Z/) show the dominance of grain contribution, which allows the determination of relaxation frequency. The activation energy, calculated from the slope of lnτ versus 103/T plot, is found to be the nearly same as calculated from ac conductivity.  The room temperature ac conductivity at 10 kHz lies in the range of 10-5-10-6 (ohm-1m-1).

 

Indian Journal of Engineering & Materials Sciences

Vol. 15, April 2008, pp. 157-162

 

 

Electrical responses of Pb2Sb3RTi5O18 (R º La, Nd, Sm, Gd, Dy) ceramics

C K Suman, K Prasad & R N P Choudhary

 

Single-phase orthorhombic tungsten bronze ceramics of Pb2Sb3RTi5O18 (R º La, Nd, Sm, Gd, Dy) are prepared via high temperature solid-state reaction method. The values of cell parameters phase transition temperature and activation energy are found to depend on rare earth ion content. These materials have low dielectric constant, low loss and high resistivity. The samples showed dielectric relaxation which are found to be of non Debye type. The nature of variation of resistivity with temperature and Nyquist plots suggested the NTCR character. The ac conductivity is found to obey the universal power law and supports the correlated barrier hopping of the carriers as conduction mechanism.

 

 

Indian Journal of Engineering & Materials Sciences

Vol. 15, April 2008, pp. 163-166

 

 

Electrical properties of relaxor ferroelectric PMCT-PT-ZnO ceramic

 

S Prasad, K Prasad, S N Choudhary & T P Sinha

 

Polycrystalline samples of 0.85Pb[(Mg2/3Cd1/3)1/3Ta2/3]O3-0.15PbTiO3 with 7.5% of ZnO having a tetragonal perovskite type structure have been prepared using high temperature solid-state reaction method. Dielectric studies indicate relaxor behaviour with diffuse phase transition. High value of εm > 3000 is realized with Tm (phase transition temperature) at 43°C at 1 kHz. Fitting of dielectric data using Vogel-Fulcher relationship indicates that the system is analogous to magnetic relaxation in spin-glass system with polarization fluctuations above a static freezing temperature. Cole-Cole analyses showed the non-Debye type relaxation in the system. The electrical conduction in the system may be due to the short-range translational hopping of charge carriers.

 

 

Indian Journal of Engineering & Materials Sciences

Vol. 15, April 2008, pp. 167-170

 

 

Electrical properties of SrBi2Ta2O9 thin films deposited on Si(100) substrates by rf magnetron sputtering

A Roy, G Jha, A Dhar, I Manna & S K Ray

 

Recently, metal-ferroelectric-semiconductor (MFS) structures have attracted much attention because of its potentials as nonvolatile memory device with nondestructive readout operation. In the present study ferroelectric SrBi2Ta2O9 (SBT) thin films are grown on p-type (100) Si substrates by rf magnetron sputtering method at different deposition conditions. The crystallinity of the films is studied using grazing incidence X-ray diffraction (GIXRD) pattern. The spectra show the films are polycrystalline with dominant orientation along (115) plane. The capacitance-voltage (C-V) characteristics of Al/SBT/Si capacitors were measured at 100 kHz. The (C-V) characteristic of Al/SBT/Si capacitor post-annealed at 700-800°C shows a hysteresis nature with a clockwise rotation and the memory window of the hysteresis loop is 0.88 V when the gate voltage is ± 5 V. The interface trap density (Dit) calculated by using Hills method at room temperature and a value in the order of [1011-1012 eV-1cm-2 was found at mid gap region depending on the crystallization temperature. The surface morphology was investigated by atomic force microscope (AFM). The study showed the potential of SBT for application in metal-ferroelectric-silicon nonvolatile memory devices.

 

Indian Journal of Engineering & Materials Sciences

Vol. 15, April 2008, pp. 171-175

 

 

Electrical properties of ferromagnetic Ag:CrO2 particles

 

G P Singh, S Ram, A K Thakur  & R N P Choudhary

 

A stable silver modified CrO2, i.e., Ag:CrO2 of nanocomposite particles was synthesized with a novel chemical method involving Cr6+, Ag+ and NO3- species in an aqueous solution. A single phase Ag:CrO2 of submicron size particles (~33 nm average crystallite size) of a Pnnm orthorhombic structure (lattice parameters a = 0.4405 nm, b = 0.4452 nm and c = 0.2885 nm) is obtained after annealing at 573 K in air. Microstructure reveals single domain Ag:CrO2 particles of prismatic shapes (aspect ratio L/b ~ 1-2) of average b ~30 nm width and 40 to 50 nm length (L). The temperature dependence electrical resistance R (T) shows a phase transition from a metallic to a semiconductor like at a specific temperature TC , which is found to be 405 K at a frequency f = 1 kHz. At 10 kHz, the dielectric constant εr has as large a value as 49, with power loss 0.42. As a function of increasing the f-value, both εr and power loss have been shown to decrease monotonically to the values 28 and 0.06 respectively. The εr gets saturated at f ³ 400 kHz.

 

 

Indian Journal of Engineering & Materials Sciences

Vol. 15, April 2008, pp. 176-180

 

 

Preparation and characterization of perovskite PMN [Pb(Mg1/3Nb2/3)O3]

 

Kamal Singh & Tanveer Quazi

 

Lead magnesium niobate (PMN) of different compositions are prepared by combustion method using Pb(NO3)2, Mg(NO3)2, Nb2O5, and urea. Obtained material is sintered at 870°C/3 h and the density of sintered pellet measured by using Archimedes principle. The formation of phase has been confirmed by X-ray powder diffraction (XRD) pattern at room temperature and phase change by high temperatures XRD analysis. The dielectric constant (εr) and dissipation factor (tanδ) are measured at frequencies 100 Hz, 1 kHz and 10 kHz in temperature range of 25–200°C using 4192A LF impedance analyzer. The composition (110% excess urea) has shown higher dielectric constant (approx.7000 at room temperature).

 

 

Indian Journal of Engineering & Materials Sciences

Vol. 15, April 2008, pp. 181-186

 

 

Dielectric relaxation and ac conductivity study in SrMg1/3Nb2/3O3

 

Alo Dutta, Chandrahas Bharti & T P Sinha

 

The frequency-dependent dielectric dispersion of strontium-magnesium-niobate, SrMg1/3Nb2/3O3 ceramic synthesized by the solid state reaction technique is investigated in the temperature range from room temperature to 613 K. The X-ray diffraction of the sample at room temperature shows monoclinic phase. An analysis of the real and imaginary parts of impedance is performed, assuming a distribution of relaxation times as confirmed by Cole-Cole plot as well as the scaling behaviour of the imaginary part of impedance spectra. The frequency dependent electrical data were analyzed in the framework of the conductivity and modulus formalisms. The activation energy of the non-Debye process evaluated from the modulus formalism resembles with energy activation evaluated for the current conductivity process, indicating the similar nature of relaxation and conductivity.

 

 

Indian Journal of Engineering & Materials Sciences

Vol. 15, April 2008, pp. 187-190

 

 

Dielectric anomaly and magnetic order in Ba(Mn0.5Nb0.5)O3

R K Mishra, R N P Choudhary, Awalendra K Thakur & A Banerjee

 

The polycrystalline barium manganese niobiate Ba(Mn0.5Nb0.5)O3 has been prepared by a solid state reaction technique. The formation of single phase compound is confirmed by an X-ray diffraction analysis. The surface morphology examined through scanning electron microscope (SEM) confirmed polycrystalline texture of the material. Detailed studies of dielectric properties are carried out at different temperatures (23-350°C) and in a wide frequency range of 102-106 Hz . A dielectric anomaly with transition temperature at 283°C is observed. The real and imaginary part of permittivity (ε' and ε") were found to be strongly frequency and temperature dependent. The variation of ac conductivity with inverse of absolute temperature is found to obey Arrhenius law. The activation energy in lower temperature range was found to be 0.19 eV and its value in higher temperature range was 0.87 eV. Magnetization as a function of temperature from 2 K to 300 K is measured in different fields in both zero-field cooled (ZFC) and field-cooled (FC) mode. An antiferromagnetic transition is observed at 7 K. Non-linear M-H and a finite opening in the hysteresis loop at 2 K substantiate the presence of ferromagnetic component in the antiferromagnetic matrix.

 

 

Indian Journal of Engineering & Materials Sciences

Vol. 15, April 2008, pp. 191-195

 

 

Studies on dielectric behaviour of an oxygen ion conducting
ceramic – CaMnO3-δ

 

Namita Pandey, Awalendra K Thakur & R N P Choudhary

 

An oxygen deficient ceramic oxide having perovskite structure has been prepared by the conventional solid state reaction method. X–ray diffraction studies have confirmed the sample formation in single phase polycrystalline form. The scanning electron micrographs have confirmed polycrystalline texture of the material alongwith indications of porous microstructure. The temperature dependence of the dielectric properties (permittivity/loss tangent) in the sub-ambient and ambient temperature region suggests the possibility of a strong dipolar ordering. The appearance of maxima in both the permittivity and loss factor pattern at a very close temperature range (emax~1879 at 29oC, tan dmax~9.7 at 35oC at a common frequency of 10 kHz) supports the presence of dipolar interaction in CaMnO3-d. It has been attributed to a strong interaction of the oxide ion-oxygen vacancy pair in the crystal lattice of an oxygen deficient perovskite (CaMnO3-d) that in turn reduces the net mobility of oxygen ion at lower temperatures and imparts it a higher dielectric permittivity as well as high loss factor close to room temperature. A decrease in the permittivity and monotonous increase in loss factor with rise in temperature above the ambient value suggest a thermally activated weakening of the dipolar ordering in the system. In view of a very high value of loss factor at and above room temperature, it would be premature to conclude the existence of ferroelectric ordering in the material system just by the presence of a peak in both the permittivity and loss factor pattern.

 

 

Indian Journal of Engineering & Materials Sciences

Vol. 15, April 2008, pp. 196-198

 

 

Dielectric relaxation behaviour of glycine in aqueous solution medium in the microwave frequency region

K Ajaya Kumar, Samiran Bhaumik, T Vishwam, V Subramanian & V R K Murthy

 

 

 

          A study on the dielectric properties of glycine in aqueous solution medium in the microwave frequency region (130 MHz-20 GHz) is carried out using the open-ended coaxial probe technique. Dielectric parameters such as dielectric constant, dielectric loss of various weight percentage levels of glycine in double distilled aqueous medium such as water are determined. It is observed that the real part of dielectric permittivity decreases and imaginary part of the dielectric permittivity increases with increase in the weight percentage level of glycine in water. From these parameters we calculated the relaxation time and its behaviour is analysed. Dipole moment value is calculated from the optimized geometrical structure of the glycine molecule from the AM1, PM3, and MNDO ab initio quantum mechanical calculations using the Argus Lab chemical modeling Software 2004.

 

Indian Journal of Engineering & Materials Sciences

Vol. 15, April 2008, pp. 199-202

 

 

Influence of temperature on the dielectric behaviour of Co2+ substituted
Li-Ni-Mn ferrites

 

Mamata Maisnam, Sumitra Phanjoubam, H N K Sarma, O P Thakur, L Radhapiyari Devi & Chandra Prakash

 

Li-Ni-Mn ferrites substituted with Co2+ having compositional formula Li0.45-x/2Ni0.1Mn0.1CoxFe2.35-x/2O4 with x ranging from 0 to 0.1 in steps of 0.02 were prepared by the conventional ceramic technique. The temperature dependence of the dielectric constant and loss tangent have been investigated. The dielectric constant increased with the increase of temperature, the increase being more pronounced at lower frequencies indicating the dominant role played by the interfacial polarisation. Dielectric constant studied as a function of temperature showed peaks, which gets shifted to higher temperature as the frequency increased. The dielectric loss tangent was observed to increase with temperature. The results obtained are explained on the basis of Debye’s equation.

 

 

Indian Journal of Engineering & Materials Sciences

Vol. 15, April 2008, pp. 203-206

 

 

Structural and dielectric properties of LaBi2Fe5O12

 

K Jawahar & R N P Choudhary

 

The polycrystalline sample of LaBi2Fe5O12 (LBIG) distorted perovskite compound is prepared using a high-temperature solid-state reaction technique. Room temperature preliminary X-ray diffraction (XRD) studies of the compound show the tetragonal splitting. It confirms the formation of single-phase compound with »2% of pyrochlore phase. The elemental content of the compound has been verified by energy dispersive spectroscopy (EDS) microanalysis. Microstructural analysis by scanning electron microscopy (SEM) shows that the grains are homogeneously as well as uniformly distributed throughout the surface of the sample. Dielectric studies as a function of temperature (30-360°C) at four different frequencies (1, 10, 100, 1000 kHz) yielded a dielectric anomaly at 325°C. It is interesting to note that the loss tangent (tand) seems to be reduced at higher frequencies after reaching the instrumental saturation. Also, dielectric measurement as a function of frequency (100 Hz-1 MHz) at room temperature reveals the presence of different types of polarization mechanisms involved in the material. Again the frequency dependent loss tangent (tand) shows the sinusoidal variation, which is unusual for this kind of measurement. This variation has been confirmed by repeating the measurement at various temperatures.

 

Indian Journal of Engineering & Materials Sciences

Vol. 15, April 2008, pp. 207-210

 

 

Dielectric properties of In-Se-Te glassy alloys

A S Maan & D R Goyal

 

In this paper, the dielectric properties of In40SexTe60-x glassy alloys (x = 10, 20 & 30) have been reported. These measurements are carried out as a function of temperature and frequency in the range 120-350 K and 0.1-10 kHz respectively. The frequency and temperature dependence of dielectric constant ε΄ and dielectric loss ε΄΄ is almost similar in nature in all the alloys and the experimental results indicate that dielectric dispersion sets in at temperature exceeding 150 K and is more prominent at lower frequencies. ε΄ and ε΄΄ values as a function of temperature and frequency are maximum for x = 20 alloy, though similar behaviour is observed in all the samples. The experimental results seem to be explained in terms of the theory of dielectric dispersion based on two electrons hopping over a potential barrier. The frequency dependence of dielectric loss in present set of glasses at a fixed temperature is in good agreement with theory of dielectric dispersion.

 

 

Indian Journal of Engineering & Materials Sciences

Vol. 15, April 2008, pp. 211-214

 

 

Nonlinear wave propagation in ferroelectric/ferrite interface

Michael Augustine, Roji Pius, Sunny Mathew &Vincent Mathew

 

The propagation of electromagnetic wave through the interface of magnetized ferrite and nonlinear ferroelectric half-spaces has been theoretically studied. A dispersion relation for the wave propagation corresponding to the TE mode has been derived and numerically solved. It is observed that the propagation is non-reciprocal. The dependence of power on frequency has also been evaluated.

 

Indian Journal of Engineering & Materials Sciences

Vol. 15, April 2008, pp. 215-223

 

 

Low frequency dielectric dispersion studies in ferroelectric ceramics of
Pb0.77K0.26Li0.2Ti0.25Nb1.8O6

 

K Sambasiva Rao, P Murali Krishna, D Madhava Prasad, T Swana Latha & C Satyanarayana

 

Temperature and frequency dependence of dielectric constant and conductivity properties of Pb0.77K0.26Li0.2Ti0.25Nb1.8O6 (PKLTNO) ceramics are modeled through universal dielectric response (UDR). Partial substitution of Ti4+ in Nb5+ increased the B- sites ordering, supported by charge compensation and creation of oxygen vacancies that obeys Kroger-Vink notation. The release of electrons by this reaction are captured by the Nb5+ and Ti4+ to generate Nb3+ and or Ti3+. Thus the possibility of the hopping of electrons among Nb5+ and Nb3+ and Ti4+ and Ti3+ entering in the crystal structure participate in the conductivity. The dielectric characterization is performed from room temperature to 590°C, in the frequency range of 45 Hz-5 MHz. The measured dielectric constant has been found to fit to Jonscher’s dielectric dispersion relations: ε¢ = ε + sin(n(T)л/2) (a(T)/ε0) (ωn(T)-1) and ε" = σ/iε0ω + cos(n(T)л/2) (a(T)/ε0) (ωn(T)-1). Cole-Cole plots are found inclined at an angle (1-n(T))X л/2 which obeys the universal material behaviour ε + A(T) (ωn(T)-1). The exponent n(T) and coefficient A(T) = [a(T)S/L] has been observed to be minimum and maximum respectively at TC~425°C. The conductivity studies reveal the conduction in the material arisising due to hopping of bound charges.