An International Research Journal

AJP

ISSN : 0971 - 3093

Vol  21,  No. 2 , April-June, 2012

Asian Journal of Physics                                                                                                        Vol. 21, No 2 (2012) 135-144


Dielectric and ferroelectric properties of SrBi2Nb2O9 and SrBi1.8Gd0.2Nb2O9 ceramics

 

K Sambasiva Rao, J N Kiran, A Swathi, D Gangadharudu and  Rajan Singh1

  Department of Physics, Andhra University,Visakhapatnam - 530003, India

                                                                                  1IIT Bombay, Powai, Mumbai-400 076, India  

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Strontium Bismuth Niobate, SrBi2Nb2O9 (SBN) is a technologically important ferroelectric material and excellent candidate for the application in data storage in digital memory systems, in addition to many other important applications such as piezoelectric, pyroelectric and electro-optics in sensors, actuators and micromechanical systems (MEMS). As this material is fatigue free, lead-free and possess good ferroelectric properties, un-substituted SBN and Gadolinium (Gd) substituted SBN, SrBi1.8Gd0.2Nb2O9  are chosen for present study. These ceramic compositions have been prepared using the conventional solid state reaction method. The sintering conditions are established to achieve maximum density in the materials. The effect of Gd on structure, dielectric and polarization has been studied. The powder X-Ray diffraction analysis reveals single phase of bismuth layered structure ferroelectric (BLSF) with orthorhombic structure with lattice parameters, a = 5.522 A0, b= 5.511 A0 and c = 25.114 A0 in SBN. Substitution of Gd in SBN not only decreased cell parameters but also cell volume. Variation of ε1 with temperature at different frequencies has been studied in SBN and Gd- SBN ceramic samples. A well defined phase transition (Tc) from ferroelectric to paraelectric phase at 4300C in SBN has been observed. The value of Tc has been found to 3900C in Gd-SBN. Further, the room temperature dielectric constant is also found to decrease in SBGN from SBN composition. No shift in Tc has been noticed from dielectric constant versus temperature studies at different frequencies in both SBN and SBGN reveal the materials are of traditional ferroelectrics. In the paraelectric region the curie-Weiss law is fitted and curie constants are estimated. P-E loops are recorded and estimated the values of spontaneous polarization (PS), remanent polarization (Pr) and coercive field (EC).

Total Ref : 62

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Asian Journal of Physics                                                                                                        Vol. 21, No 2 (2012) 145-152

 

Optimization of Efficiency in a 1D Grating Structure at 1310nm Wavelength for Application in Optical Interconnect

 

G Palai1, *S K Tripathy2, N Muduli3, S K Patnaik2

1Gandhi Institute for Technological Advancement, Bhubaneswar

2National Institute of Science and Technology, Berharmpur

3Gandhi Engineering College, Bhubaneswar

2National Institute of Science and Technology, Berharmpur

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This paper optimizes the diffraction efficiency of 1D silicon-a silicon grating structure at wavelength 1310 nm. Optimization is made with respect to absorption and transmission losses using plane wave expansion (PWE) method. The simulation results showed the efficiency of 1D grating structure is more than 99% for 1 µm-1 µm, 1 µm-4 µm, 4 µm-1 µm and 10 µm-1 µm thickness of silicon-a silicon layer at 1310 nm. 

Keywords: 1 D grating, PWE, Reflectance, SOI

Total Ref : 12

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Asian Journal of Physics                                                                                                        Vol. 21, No 2 (2012) 153-158


Fluctuations induced conductivity in YBYBa2Cu3O7-d  + x CoFe2O4 composites


M Sahooa, B Bhola, D Beheraa,*

aDepartment of physics, National institute of technology, Rourkela-769008, India


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Fluctuations on the electrical conductivity of polycrystalline YBa2Cu3O7-d  + x CoFe2O4(x = 0.0, 0.1, 0.2, and 0.3 wt.%) superconductors were investigated from the resistivity vs. temperature(R-T) data. Attempts have been made to identify the optimum inclusion of ferromagnetic CoFe2O4 particles in YBa2Cu3O7-d δ (YBCO) superconductor. With the increase of CoFe2Oaddition, it is found that the superconducting transition temperatures (Tc) determined from standard four-probe method and magnetization vs. temperature (M-T) studies, were decreased and dropped sharply with higher wt.% addition of CoFe2O4. M-T graphs shows that the composites satisfy Meissner effect. Excess conductivity fluctuation analysis using Aslamazov-Larkin (AL) model fitting reveals transition of two dominant regions (2D and 3D) above Tc. The decrease in 2D-3D crossover temperature (TLD) (Lawerence-Doniach temperature) in the mean field region has been observed as a consequent dominance of 3D region with increase in wt.% of CoFe2O4 in the composite.

Total Ref : 18

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Asian Journal of Physics                                                                                                        Vol. 21, No 2 (2012) 159-164


Dynamic study of phonon excitation spectrum in some heavy fermion systems

 

J Sahoo1*, N Shadangi2 and P Nayak3

1Regional office of vocational Education, Sambalpur

2Padmashree Krutartha Acharya College of Engineering, Bargarh

3School of Physics, Jyoti Vihar, Sambalpur

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The phonon excitation spectrum of some Heavy Fermion (HF) systems in the presence of electron-phonon interaction is studied in the dynamic limit (ω¹i H*0). The renormalized excitation phonon frequencies (ώ=ω/ω0) are evaluated through Periodic Anderson Model (PAM) in presence of electron –Phonon interaction using Zubarev type double time temperature dependent Green function .The calculated renormalized phonon energy is analyzed through the plots of (ώ=ω/ω0) against temperature for different system parameters like effective coupling strength ‘g’, the position of f-level‘d’ and the onsite coulomb interaction ‘U’. The observed behaviour is analyzed and found to agree with the general features of HF systems found in experiments

Total Ref : 18    

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Asian Journal of Physics                                                                                                        Vol. 21, No 2 (2012) 165-170


Dielectric anomaly in Na2Pb2Dy2W2Ti4Nb4O30 ceramic

 

L Biswal1,3, Piyush R Das2,*, and Banarji Behera3

1Department of Physics, SOT, KIIT University, Bhubaneswar - 751 024, Odisha, India

2Department of Physics, ITER, S. O. A. University, Odisha, Bhubaneswar - 751 030, India

3School of Physics, Sambalpur University, Jyoti Vihar, Burla-768 019, Odisha, India

 

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A new polycrystalline ceramic Na2Pb2Dy2W2Ti4Nb4O30 was prepared by high temperature solid state reaction technique. Preliminary X-ray diffraction (XRD) study showed the formation of single-phase compound in an orthorhombic structure. Surface morphology of the compound was studied by scanning electron microscopy (SEM). The frequency and temperature dependence of dielectric properties (er and tand) of the compound was investigated in the frequency range of 102 to 106 Hz and temperature range 300K to 800 K. The ceramic compound showed non-relaxor type diffused dielectric anomaly at 577K. Ferroelectric property of the compound was confirmed with polarization (hysteresis) study. Using modified Curie-Weiss law around transition temperature, the order and type of transition has been suggested.

Keywords: Ceramics; Sintering; Dielectric Properties; Hysteresis

Total Ref : 24

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Asian Journal of Physics                                                                                                        Vol. 21, No 2 (2012) 171-174


Analysis of grains grown on pond-ash treated soils

 

K C Patraa,b, N R Mahapatrac,d, P  Nayaka, and Tapash R. Rautrayd,e*

aDepartment. of Physics, Sambalpur University, Jyoti Vihar, Sambalpur - 768 019, Odisha, India

bInstitute of Physics, Sachivalaya Marg, Bhubaneswar - 751005, Odisha, India

cDepartment of Physics, Silicon Institute of Technology, Patia, Bhubaneswar, Odisha, India

dCentre of Excellence in Theoretical and Math Sciences, SOA University, Bhubaneswar - 751030, Odisha, India

eCentre for Functional Biomaterials and Tissue Engineering, Saheed Nagar, Bhubaneswar - 751007, Odisha, India


____________________________________________________________________________________________________________________________________ Elements namely Mn, Fe, Cu, Zn, Mo and Pb were determined in the current study by using Energy dispersive X-ray fluorescence (EDXRF) technique. The increase in yield of the rice grains using pond ash was 16% and 22% produced at Malud and Dhenkanal (in Orissa, India) respectively as compared to their control values. The concentration of trace elements in rice grains was well below the critical levels in the plants for human consumption.

Total Ref : 17

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Asian Journal of Physics                                                                                                        Vol. 21, No 2 (2012) 175-178


Competence of 4H-SiC IMPATT diode for terahertz application

J Pradhan1, S K  Swain1, G N Dash1 and S R Pattanaik2

1School of Physics, Sambalpur University, Jyoti Vihar, Sambalpur-768 019, Odisha, India

2Apex Institute of Technology and Management, Bhubaneswar -752 101, Odisha, India 

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The competence of 4H-SiC material for being used as a base material for possible terahertz application was examined following our computer simulation method. The computed power density value of 8.3 × 1011 W/m2 with a DC-to-RF conversion efficiency of 11% at the operating frequency of 1.0 THz are note worthy. A significant negative conductance value of 9.7×108 Sm–2 and a noise measure of 56dB are also computed at the frequency of 1.0 THz using a small signal model for sub-mm-wave or terahertz applications. The results speak about the potential of SiC material for terahertz application.

Keywords: Terahertz, IMPATT, 4H-SiC

Total Ref : 20

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Asian Journal of Physics                                                                                                        Vol. 21, No 2 (2012) 179-186


Synthesis and characterization of Na2Pb2Y2W2Ti4Ta4O30 ferroelectric ceramic

 

S Behera1, Piyush R Das2*, P Nayak3 and R N P Choudhary2

2Department of Physics, Hi-tech College Engineering, Bhubaneswar- 751 025, India

2Department of Physics, Institute of Technical Education & Research, Siksha OAnusandhan
University, Bhubaneswar-751015, Odisha, India
 

3School of Physics, Sambalpur University, Jyoti Vihar, Burla – 768019 

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In the present work, sample of composition Na2Pb2Y2W2Ti4Ta4O30 (NYT) was prepared by a high-temperature solid-state reaction technique. X-ray diffraction (XRD) analysis reveals the formation of single-phase compound with an orthorhombic structure at room temperature. Surface morphology of the compound was studied by scanning electron microscope (SEM). Temperature dependence of dielectric constant indicates the presence of two dielectric anomalies at 408K and 586K, which may be attributed to the ferroelastic-ferroelectric and ferroelectric-paraelectric transitions respectively as suggested by hysteresis loop at room temperature. Complex impedance spectroscopy analysis has been carried out as a function of frequency at different temperatures to establish the correlation between microstructure and electrical properties of the material. The frequency dependence of ac conductivity obeys the Jonscher's universal power law. The values and nature of temperature variation of dc conductivity exhibit the NTCR behavior of the material like a semiconductor.

Keywords: Electronic material; Ferroelectricity; XRD; Electrical conductivity.

Total Ref : 34 

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Asian Journal of Physics                                                                                                        Vol. 21, No 2 (2012) 187-192


Study of interface sheet charge density of AlGaAs/InGaAs/GaAs-based pseudomorphic HEMT

 

T R Lenka, Sudhakar Das, Rasmita Ku Nayak, G N Dash and A K Panda

National Institute of Science and Technology, Palur Hills, Berhampur-761 008, Odisha, India

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In this paper a new AlGaAs/InGaAs/GaAs based pseudomorphic heterostructure device is proposed and various subbands are calculated by solving 1D Schrodinger and Poisson's equation self-consistently in the heterostructure by applying suitable boundary conditions. The interface sheet charge density (ns) for each subband is calculated from the various eigenvalues by numerical approach. The conduction band profile followed by the formation of 2DEG and electric field as a function of distance (Ao) are also discussed. The 2DEG density and electric field at the heterointerface are measured to be 1.092 ´ 1012 cm–2 and 2 ´ 105 V/cm respectively. The dependency of interface charge density on doping density of barrier layer and thickness of spacer is also discussed.

Index Terms: 2DEG, HEMT, Heterostructure, MBE, Pseudomorphic, Subband

Total Ref : 9

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Asian Journal of Physics                                                                                                        Vol. 21, No 2 (2012) 193-200


Impedance-Spectroscopy Analysis of (Bi0.5Na0.5)TiO3 –SrTiO3 Lead-Free  Ceramic Systems


B Parija1,2 & S Panigrahi1*

1Department of Physics, NIT, Rourkela-769008, India

2Department of Physics, P C E, Rourkela-76002, India

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The polycrystalline (1-x)(Bi0.5Na0.5)TiO3 –xSrTiO(x = 0.01, 0.05 & 0.09) (abbreviated as BNT-ST) ceramics have been synthesized by conventional solid state sintering technique. X-ray diffraction analysis indicated that a solid solution is formed when SrTiO3 diffuses into the (Bi0.5Na0.5)TiO3 lattice and revealing that the system is stable perovskite type structure. The microstructure indicated that the grain size reduces and the shape changes from rectangular to quasispherical with increasing in SrTiO3 content. Complex Impedance Spectroscopy analysis suggested the presence of temperature-dependent relaxation process in the materials. The ac conductivity was found to obey the universal power law. The activation energies have been calculated from the dc conductivity(increases with increasing of ST content) which suggests that the conductions are ionic in nature.  

Keywords: Impedance Spectroscopy; Electrical Modulus; Relaxations; Conductivity

Total Ref : 28 

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