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Oxygen deficiency induced suppression of JT-distortion and stabilization of chargeordering in La0.2Sr0.8MnO3-d
Aga Shahee,R. J. Choudhary,R. Rawat,N. P. Lalla
Physics , 2014, DOI: 10.1002/pssb.201350217
Abstract: Structural phase transition studies employing low-temperature transmission electron microscopy, and low-temperature x-ray diffraction have been carried out on nearly stoichiometric ({\delta}=0.01) and off-stoichiometric ({\delta}=0.12) versions of La0.2Sr0.8MnO3-{\delta} manganite. The nearly stoichiometric La0.2Sr0.8MnO3-{\delta} under goes a cubic to Jahn-Teller distorted C-type antiferromagnetic tetragonal phase-transition at 260K. For off-stoichiometric La0.2Sr0.8MnO3-{\delta} the Jahn-Teller distorted tetragonal phase transition gets totally suppressed and the basic perovskite lattice remains cubic but shows a charge ordered phase. Stabilization of charge ordered phase in the absence of cooperative Jahn-Teller distortion has been attributed to coulomb-repulsion and Hunds coupling energy. The off-stoichiometric sample shows characteristically different physical properties. This has been realized through transport, magnetic and calorimetric measurements. A smooth crossover from variable range hopping transport to power-law dependence of resistivity ({\rho}) on temperature (T) i.e. {\rho}=C.T-{\alpha} has been realized. This has been attributed to multistep inelastic tunneling through channels involving localized states around oxygen vacancy sites.
Synthesis, Characterization and Copolymerization of N-(phenylamino)maleimide with MMA
B. L. Hiran,S. N. Paliwal,Jyoti Choudhary,P. R. Choudhary
Journal of Chemistry , 2007, DOI: 10.1155/2007/234768
Abstract:
Complex Impedance Spectroscopic Properties of Ceramics
Praveen Khatri,Banarji Behera,V. Srinivas,R. N. P. Choudhary
Advances in Materials Science and Engineering , 2008, DOI: 10.1155/2008/746256
Abstract: The polycrystalline sample of Ba3V2O8 was prepared by a high-temperature solid-state reaction technique. The effect of temperature on impedance parameters was studied using an impedance analyzer in a wide frequency range (102-106 Hz). The real and imaginary parts of complex impedance trace semicircles in the complex plane. The temperature-dependent plots reveal the presence of both bulk and grain boundary effects above 125°C. The bulk resistance of the material decreases with rise in temperature. This exhibits a typical negative temperature coefficient of resistance (NTCR) behavior of the material. The modulus analysis suggests a possible hopping mechanism for electrical transport processes of the material. The nature of variation of dc conductivity suggests the Arrhenius type of electrical conductivity.
Effect of Sm Substitution on Structural, Dielectric, and Transport Properties of PZT Ceramics
Rajiv Ranjan,Rajiv Kumar,R. N. P. Choudhary
Physics Research International , 2009, DOI: 10.1155/2009/382578
Abstract: The polycrystalline samples of Pb1?Sm(Zr0.45Ti0.55)1?/4O3 (PSZT) (where   =  0.00,  0.03,  0.06, and 0.09) were prepared by a high-temperature solid-state reaction technique. Preliminary X-ray structural analysis of the materials at room temperature has confirmed their formation in single-phase with tetragonal crystal structure. The temperature dependence of dielectric response of the samples at selected frequencies has exhibited their phase transition well above the room temperature. The variation of ac conductivity with temperature and the value of activation energy reveal that their conduction process is of mixed type (i.e., singly ionized in ferroelectric region and doubly ionized in paraelectric phase).
Synthesis, Electrochemical, Spectroscopic, Antimicrobial, and Superoxide Dismutase Activity of Nickel (II) Complexes with Bidentate Schiff Bases
R. N. Patel,S. P. Rawat,Mukesh Choudhary
International Journal of Inorganic Chemistry , 2013, DOI: 10.1155/2013/617837
Abstract: Five new nickel (II) complexes, namely, [Ni(L1)2](ClO4)2(1); [Ni(L2)2](ClO4)2(2); [Ni(L3)2](ClO4)2(3); [Ni(L4)2](ClO4)2(4); [Ni(L5)2](ClO4)2(5), where L1 = benzoylhydrazide; L2 = N-[(1)-1-(2-methylphenyl)ethylidene]benzohydrazide; L3=N-[(1)-1-(4-methylphenyl)ethylidene]benzohydrazide; L4=N-[(1)-1-(2-methoxyphenyl)ethylidene]benzohydrazide; L5 = N-[(1)-1-(4-methoxy-phenyl)ethylidene]benzohydrazide, have been synthesized and characterized by various physicochemical and spectroscopic techniques. The synthesized complexes are stable powders, insoluble in common organic solvents such as ethanol, benzene, carbon tetrachloride, chloroform, and diethyl ether, and are nonelectrolytes. The magnetic and spectroscopic data indicate a distorted square planar geometry for all complexes. The superoxide dismutase activity of these complexes has been measured and discussed. Antibacterial and antifungal properties of these complexes were also tested. 1. Introduction The synthesis of low molecular weight nickel (II) complexes mimicking superoxide dismutase (SOD) activity has been challenging for bioinorganic chemists and recently some complexes with high catalytic activity have been reported [1–3]. Nickel-containing superoxide dismutase (Ni-SOD) has been isolated from several Streptomyces species [4]. The enzymatic activity of Ni-SOD [5] is as high as that of Cu-Zn SOD at about 109?M?1S?1 per metal center. Oberley and Buettner [6] have reported that cancer cells had less superoxide dismutase (SOD) activity than normal cells. Superoxide ion is toxic to cells; a defense mechanism must have been initiated by nature. All organisms, which use dioxygen and many that have to survive an oxygenated environment, contain at least one SOD. The superoxide radical ( ) is an inevitable byproduct of aerobic metabolism which if not eliminated may cause significant cellular damage and has been implicated in numerous medical disorders [7]. To avoid such harmful consequences, all oxygen metabolizing organisms possess metalloenzymes known as superoxide dismutases (SODs). These SODs disproportionate the toxic radical to molecular oxygen and hydrogen peroxide [8, 9]. All SODs employ the two-step Ping-Pong mechanism shown in where M is a redox active metal center capable of both oxidizing and reducing superoxide. Metal complexes of bidentate Schiff bases have been extensively studied [10, 11], because such ligands can bind with one, two, or more metal centers involving various coordination modes and allow synthesis of homo- and heteronuclear metal complexes with interesting stereochemistry [12,
Evidence of ferromagnetic short-range correlations in cubic La1-xSrxMnO3-δ (x=0.80, 0.85) above antiferromagnetic ordering
Aga Shahee,Kiran Singh,R. J. Choudhary,N. P. Lalla
Physics , 2015, DOI: 10.1002/pssb.201451552
Abstract: We report the existence of ferromagnetic correlations (FMC) in paramagnetic (PM) matrix of cubic La1-xSrxMnO3-{\delta} (x = 0.80, 0.85) well above its coupled structural, magnetic and electronic phase transitions. The dc-magnetization vs temperature [M(T)] behaviour under different magnetic fields (from 100 Oe to 70 kOe) shows the presence of short range magnetic correlations up to (TFMC ~) 365 K, far above the antiferromagnetic ordering temperatures (TN =) 260 K and 238 K for x=0.80 and 0.85, respectively. More importantly the observed short-range FMC survive even up to 70 kOe, which indicates their robust nature. The temperature region between TN to TFMC is dominated by the presence of correlated ferromagnetic (FM) entities within the PM matrix and stabilized due to A-site chemical disorder. Our results further illustrate that for the studied compositions, the oxygen off-stoichiometry does not have any significant effect on the nature and strength of these FM entities; however, FM interactions increase in the oxygen deficient samples. These compositions are the unique examples, where the presence of FMC is observed in an undistorted basic cubic perovskite lattice well above TN and therefore are novel to understand the physics behind the colossal magneto-resistance effect.
Dielectric and electrical properties of Na2Pb2La2W2Ti4Ta4O30 electroceramics
P. R. Das,S. Behera,R. Padhee,P. Nayak,R. N. P. Choudhary
Journal of Advanced Ceramics , 2012, DOI: 10.1007/s40145-012-0024-y
Abstract: The polycrystalline sample of complex tungsten-bronze type compound (Na2Pb2La2W2Ti4Ta4O30) was prepared by a high-temperature solid-state reaction technique. Room temperature preliminary structural study using X-ray diffraction (XRD) data exhibits the formation of a single-phase new compound. The SEM micrograph of the compound exhibits non uniform rectangular grains distributed throughout the sample surface. Detailed studies of dielectric parameters ( r, tan δ) as a function of temperature and frequency, and P-E hysteresis (spontaneous polarization) confirmed the existence of ferroelectricity in the material. Complex impedance spectroscopy analysis, carried out as a function of frequency at different temperatures, established a correlation between the microstructure and electrical properties of the material. The electrical relaxation process occurring in the material is temperature dependent. The activation energy found from the Arrhenius plot that the conduction process in the material is of mixed type. The nature of frequency dependence of ac conductivity suggests that the material obeys Jonscher’s universal power law.
Complex impedance properties of LiSr2Nb5O15 ceramic
N. K. Mohanty,S. K. Satpathy,Banarji Behera,P. Nayak,R. N. P. Choudhary
Journal of Advanced Ceramics , 2012, DOI: 10.1007/s40145-012-0025-x
Abstract: The polycrystalline sample of LiSr2Nb5O15 (LSN) was prepared by a high-temperature solid state reaction technique. The impedance parameters were studied using an impedance analyzer in a wide range of frequencies (102–106 Hz) at different temperatures (28–500 °C). Nyquist plot reveals the presence of bulk effect only. The bulk resistance of the compound decreases with rise in temperature which shows the negative temperature coefficient of resistance (NTCR) like a semiconductor. The ac conductivity spectrum was found to obey Jonscher’s universal power law. DC conductivity (bulk) with temperature demonstrates that the compound exhibits Arrhenius type of electrical conductivity and the activation energy found to be 0.97 eV.
Impedance Spectroscopy of Zr Modified Ba5SmZr3V7O30 Ceramic  [PDF]
B. K. Giri, B. B. Mohanty, P. S. Sahoo, R. N. P. Choudhary
Open Access Library Journal (OALib Journal) , 2018, DOI: 10.4236/oalib.1104639
Abstract:
Ba5SmZr3V7O30 is a new tungsten bronze structured ceramic compound prepared by substituting Zr at Ti site in Ba5GdTi3V7O30 following high-temperature solid-state reaction route. The X-ray diffraction analysis of the compound confirms the formation of single-phase orthorhombic structures at room temperature. Surface morphology of the compound was studied by scanning electron microscopy. Using a Hioki LCR meter, the effects of temperature (32℃ - 500℃) and frequency (102 - 106 Hz) on structural and electrical properties were studied. Detailed analysis of impedance parameters furnishes a better conception of the electrical properties and type of relaxation processes in the material. The plateau region of the Z~ frequency plot also indicates the presence of relaxation process in the material. The bulk resistance is observed to be decreased with rise in temperature showing a typical negative temperature coefficient of resistance (NTCR) behavior.
Ferroelectric Properties of (R = Dy, Pr) Ceramics
Piyush R. Das,Banarji Behera,R. N. P. Choudhary,B. K. Samantray
Advances in Materials Science and Engineering , 2007, DOI: 10.1155/2007/91796
Abstract: The polycrystalline samples of Na2Pb2R2W2Ti4V4O30 (R = Dy, Pr) were prepared by low-temperature, (i.e., at 650∘C) solid-state reaction technique. The preparation conditions have been optimized using thermogravimetry analysis (TGA) technique. X-ray diffraction (XRD) studies of the compounds showed the formation of a single-phase orthorhombic crystal structure at room temperature. Studies of dielectric properties (ɛr and tan δ) of the compounds at frequencies 10, 100, and 1000 kHz in a wide temperature range (room temperature–500∘C) exhibit ferroelectric phase transitions at 132∘C for NPDWTV and at 122∘C for NPPWTV of diffuse type. Ferroelectric properties of the materials are confirmed by polarization study.
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