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1.
N. Srinivasa Rao M. Purnima Shashidhar Bale K. Siva Kumar Syed Rahman 《Bulletin of Materials Science》2006,29(4):365-370
Pure and copper doped glasses with composition,x
Li
2
O-(40-x)Na
2
O-50B
2
O
3-10Bi
2
O
3,have been prepared over the range 0 ≤
x ≤ 40. The electron paramagnetic resonance (EPR) spectra of Cu2+ ions of these glasses have been recorded in the X-band at room temperature. Spin Hamiltonian parameters have been calculated.
The molecular bonding coefficients, α2 and β2, have been calculated by recording the optical absorption spectra in the wavelength range 200–1200 nm. It has been observed
that the site symmetry around Cu2+ ions is tetragonally distorted octahedral. The density and glass transition temperature variation with alkali content shows
non-linear behaviour. The IR studies show that the glassy system contains BO3 and BO4 units in the disordered manner. 相似文献
2.
Temperature and frequency dependence of a.c. conductivity have been studied in glassy Se100-
x
Te
x(x = 10, 20 and 30) over different range of temperatures and frequencies. An agreement between experimental and theoretical
results suggests that the a.c. conductivity behaviour of selenium-tellurium system (Se100-
xTex)can be successfully explained by correlated barrier hopping (CBH) model. The density of defect states has been determined
using this model for all the glassy alloys.
The results show that bipolaron hopping dominates over single-polaron hopping in this glassy system. This is explained in
terms of lower values of the maximum barrier height for single-polaron hopping. The values of density of charged defect states
increase with increase in Te concentration. This is in agreement with our previous results obtained from SCLC measurements. 相似文献
3.
P. T. Deshmukh D. K. Burghate V. S. Deogaonkar S. P. Yawale S. V. Pakade 《Bulletin of Materials Science》2003,26(6):639-642
The optical transmission and absorption spectra in UV- VIS were recorded in the wavelength range 350–800 nm for different
glass compositions in the system (CuO)
x
(PbO)
50−x(Bi2O3)50 (x = 2.5, 5.0, 7.5, 10.0, 12.5, 15.0, 20.0). Absorption coefficient (α), optical energy gap (Eopt), refractive index (nD), optical dielectric constant (ε′∞), measure of extent of band tailing (ΔE), constant (β) and ratio of carrier concentration to the effective mass (N/m*) have
been reported. The effects of compositions of glasses on these parameters have been discussed. It has been indicated that
a small compositional modification of the glasses lead to an important change in all the optical properties including non-linear
behaviour. The optical parameters were found to be almost the same for different glasses in the same family. 相似文献
4.
A series of calcium substituted polycrystalline ferrite ceramics with magnetoplumbite structures were synthesized using perfect
stoichiometric mixtures of oxides with chemical composition, CaAlxCoxFe12−2xO19 (x = 2−5), by standard ceramic technique. The variation in the values ofH
candM
s,which depends on the additive content and the temperature, was studied by means of a vibration magnetometer. The strong variation
observed in coercivity, saturation magnetization and Curie temperature with chemical composition give rise to the possibility
of controlling these properties and hence applying these compounds in the millimeter— microwave range. 相似文献
5.
P. P. Singh 《Bulletin of Materials Science》2003,26(1):131-135
Using density-functional-based methods, we have studied the fully-relaxed, fulltronic structure of the newly discovered superconductor,
MgB
2, and BeB2, NaB2 and AlB2. Our results, described in terms of (i) total density of states (DOS) and (ii) the partial DOS around the Fermi energy, EF, clearly show the importance of B p-electrons for superconductivity. For BeB2 and NaB2, our results indicate qualitative similarities but significant quantitative differences in their electronic structure due
to differences in the number of valence electrons and the lattice constantsa andc.
We have also studied Mg
1-xMxB2 (M = Al, Li or Zn) alloys using coherent-potential to describe disorder, Gaspari-Gyorffy approach to evaluate electron-phonon
coupling, and Allen-Dynes equation to calculate the superconducting transition temperature, Tc. We find that in Mg1-xMxB2 alloys (i) the way Tc changes depends on the location of the added/modified k-resolved states on the Fermi surface and (ii)
the variation of Tc as a function of concentration is dictated by the Bp DOS. 相似文献
6.
B. Eraiah 《Bulletin of Materials Science》2006,29(4):375-378
Glasses with the composition, (Sm2
O
3)
x
(ZnO)(40-x)(TeO
2)(60), were prepared by conventional melt quenching method. The density, molar volume, and optical energy band gap of these glasses
have been measured. The refractive index, molar refraction and polarizability of oxide ion have been calculated by using Lorentz-Lorentz
relations. Optical absorption spectra of these glasses were recorded in the range 300–700 nm at room temperature. The oxide
ion polarizabilities deduced from two different quantities, viz. refractive index and optical energy band gap, agree well
compared with other glasses. The nonlinear variation of the above optical parameters with respect to samarium dopant has been
explained. 相似文献
7.
N. Srinivasa Rao Shashidhar Bale M. Purnima K. Siva Kumar Syed Rahman 《Bulletin of Materials Science》2005,28(6):589-592
The local structure around Cu2+ ion has been examined by means of electron spin resonance and optical absorption measurements in xLi2O-(40-x)Na2O-50B2O3-10As2O3 glasses. The site symmetry around Cu2+ ions is tetragonally distorted octahedral. The ground state of Cu2+ isd
x
2−y
2.The glass exhibited broad absorption band near infrared region and small absorption band around 548 nm, which was assigned
to the
2B1g →2Eg
transition. 相似文献
8.
S. S. Bellad S. C. Watawe A. M. Shaikh B. K. Chougule 《Bulletin of Materials Science》2000,23(2):83-85
Polycrystalline Li0.5-x/2CdxFe2.5-x/22O4 ferrites wherex = 0, 0.1, 0.2, 0.3, 0.4, 0.5 and 0.6 were prepared by a double sintering ceramic technique and characterized by X-ray diffraction
and scanning electron microscopy (SEM). The lattice parameter is found to increase monotonically with the cadmium content.
It is explained in terms of the sizes of component ions. The grain size of the samples increases up tox = 0.3 and then it decreases for higher values ofx. A similar trend is observed in the variation of Ms with Cd2+ content. The initial permeability (μi) is however found to increase continuously withx. The increase in μi is attributed to decrease of anisotropy constant K1 and higher grain size of the samples. 相似文献
9.
G. Srinivasa Gupta G. Vamsi Madhav A. Pandey B. Nageswara Sarma S. Lele 《Bulletin of Materials Science》2005,28(2):173-177
The powerful framework of cluster expansion- cluster variation methods (CE- CVM) expresses alloy free energy in terms of energy
(model) parameters, macroscopic variables (composition and temperature) and microscopic variables (correlation functions).
A simultaneous optimization of thermodynamic and phase equilibria data using CE- CVM is critically dependent on giving good
initial values of energy parameters, macroscopic and microscopic variables, respectively. No standard method for obtaining
the initial values of the energy parameters is available in literature. As a starting point, a method has been devised to
estimate the values of energy parameters from consolute point (miscibility gap maximum) data. Empirical relations among energy
parameters, temperature (T
c), composition (x
c) andd
2
T/dx2 at the consolute point, have been developed using CE- CVM free energy functions for bcc and fcc structures in the tetrahedron
and tetrahedronoctahedron approximations, respectively. Thus from the observed data ofT
c,x
c andd
2
T/dx2 in the above relations, good initial values of energy parameters can be obtained. Further, a necessary modification to the
classical NR method for solving simultaneous nonlinear/transcendental equations with a double root in one variable and a simple
root in the other has been presented. 相似文献
10.
Manju Malhotra Madhukar Gautam J. K. Radhakrishnan Vinod Kapoor Sudeep Verma Upendra Kumar Anand Kumar Garima Gupta Anshu Goyal S. Sitharaman 《Bulletin of Materials Science》2005,28(2):97-102
Growth of Hg1-xCdxTe epitaxial films by a new technique called asymmetric vapour phase epitaxy (ASVPE) has been carried out on CdTe and CZT
substrates. The critical problems faced in normal vapour phase epitaxy technique like poor surface morphology, composition
gradient and dislocation multiplication have been successfully solved. The epitaxial films have been electrically characterized
by using the Hall effect and capacitance-voltage (C-V) measurements. 相似文献
11.
S. N. Ekbote G. K. Padam M. Sharma N. K. Arora B. S. Khurana R. C. Goel D. K. Suri N. Mehra B. K. Das 《Bulletin of Materials Science》2001,24(6):603-609
Bulk tube conductors of Bi
1.84
Pb
0.4
Sr
2
Ca
2.2
Cu
3
O
10+x
with addition of silver varying from 0 to 25 wt% (not reported earlier) were systematically studied using X-ray diffraction
(XRD), scanning electron microscopy (SEM), electrical transport and a.c. susceptibility techniques. The tube conductors formed
by cold isostatic pressing (CIP) of the powders obtained from spray drying method have been made successfully. It was found
that Ag addition has not only affected the formation of the desired Bi-2223 phase and the microstructure of these large bulk
tube samples thereby influencing on the critical current (
I
c
),it also reduces the contact resistance to minimize the cryogen losses. These variations have been found to be Ag content dependent.
An optimized value of 10 wt% Ag has been found to produce the best quality tubes showing reproducible
I
c
value > 120 Amp at 77 K which is in general a requirement to energies of the cryogen free conventional/HTSC superconducting
magnets below 20 K. 相似文献
12.
Nano-crystal embedded PbO-P2O5 glass has been prepared and characterized by XRD and TEM measurements. The ultrasonic velocity and attenuation measured within
the temperature range 80–300 K show significant structure and interesting feature with the presence of nano-crystalline region.
The glass samples were prepared by melt-quench method and nano-crystals of different sizes were produced by heat treatment
of the glasses for different durations of heating. All the processes were carried out at or above glass transition temperature.
A theoretical model that takes account of the effects of thermally activated relaxation, anharmonicity as well as microscopic
elastic inhomogeneities arising out of fluctuations has been successfully applied to interpret the variation of ultrasonic
velocity and attenuation data. An interesting outcome of this application has been to propose a method for the determination
of the size of nano-crystals from the ultrasonic attenuation data. 相似文献
13.
A new polymer electrolyte (PEG)
x
NH4ClO4(x = 5, 10, 15, 20) has been prepared that shows protonic conduction. The room temperature conductivities are of the order of
10−7S/cm, and increase with decrease in salt concentration. NMR line width studies indicate fairly low glass transition temperatures
of the polymer salt complexes.
Paper presented at the poster session of MRSI AGM VI. Kharagpur, 1995 相似文献
14.
Suchitra Rajput Sujeet Chaudhary Subhash C. Kashyap Pankaj Srivastava 《Bulletin of Materials Science》2006,29(3):207-211
Superconducting bulk MgB2 samples have been synthesized by employing sintering technique without using any additional process steps, generally undertaken
in view of the substantial loss of magnesium, during heat treatment. Starting with Mg rich powders having different atomic
ratios of Mg : B, as against the nominally required Mg : B = 1:2 ratio, we have obtained superconducting MgB2 samples of different characteristics. The effect of excess Mg in the starting mixture and processing temperature on the phase-formation,
transition temperature (T
C) and critical current density (J
C) have been investigated by electrical transport and a.c. susceptibility measurements. The X-ray diffraction and X-ray photoelectron
spectroscopic analyses of MgB2 bulk samples have been carried out to understand the role of excess Mg and the effect of processing temperature. It is established
that MgB2 samples with high critical current density can be synthesized from a Mg rich powder having Mg : B in 2:2 ratio, at temperatures
around 790°C. Critical current density has been found to vary systematically with processing temperature. 相似文献
15.
The reentrant magnetic phase transition in Pr
0.5Sr0.41Ca0.09MnO3 perovskite is explained using the Ising spin model on the square lattice with mixed ferromagnetic and antiferromagnetic exchange
interactions. It is shown using numerical calculations that this effect is strongly affected by the external magnetic field
and lattice disorder. 相似文献
16.
S. R. Murthy 《Bulletin of Materials Science》2001,24(6):611-616
Polycrystalline NiZn ferrites with different grain sizes (1.2 (Am to 10.2 (Am) were prepared by the usual ceramic method.
The magnetic properties were measured at room temperature. The ultrasonic velocity and attenuation were measured on Ni-Zn
ferrite by using the pulse transmission method at 1 MHz, in the temperature range 300–600 K. The velocity was found to be
slightly sample dependent at room temperature and decreased with increasing temperature, except near the Curie temperature,
T
c
,where a small anomaly was observed. The longitudinal attenuation (α
1
)at room temperature was found to be more sample dependent. The temperature variation of ultrasonic longitudinal attenuation
exhibited a broad maximum around 400 K and a sharp maximum just below Curie temperature (
T
c
).The above observations were carried out in the demagnetized state. The application of a 380 mT magnetic field allowed us to
reach the saturated state of the sample at all the measuring temperatures. The anomaly observed in the thermal variation of
velocities (longitudinal and transverse) and attenuation has been qualitatively explained with the help of the temperature
variation of the magneto-crystalline anisotropy constant. 相似文献
17.
18.
Pellets of ceramic Na1−xKxNbO3 (x = 0, 0.2 and 0.5), were prepared by conventional solid-state reaction method. Prepared samples were characterized using
XRD and SEM. The frequency and temperature variation of dielectric constant, loss tangent and dielectric conductivity of prepared
samples were measured in the frequency range from 10 KHz-1 MHz, and in the temperature range from 50–250°C for x = 0.2 and
0.5, and between 50 and 480°C for x = 0 compositions. It was observed that the dielectric constant and loss tangent decrease,
and conductivity increases with increasing frequency. Near the transition temperature the material shows anomalous behaviour
for the observed properties, and the peaks of dielectric constant and loss tangent were observed shifting towards lower temperature
with increasing frequency. 相似文献
19.
The metallic glass samples of Fe
67Co18B14Si1 (2605CO), prepared by the melt spinning technique were procured from the Allied Corporation. The kinetics of crystallization
of this multicomponent glassy alloy is studied using differential scanning calorimetry (DSC). The crystallization data have
been examined in terms of modified Kissinger and Matusita equations for the nonisothermal crystallization. The results show
enhanced bulk nucleation in general. At high heating rates added to it is surface induced abnormal grain growth resulting
in fractal dimensionality.
5th IUMRS ICA98, October 1998, Bangalore. 相似文献
20.
The interface of Fe
3
Al/Q235 dissimilar materials joint, which was made by vacuum diffusion welding, combines excellently. There are Fe
3
Al, FeAl phases and α-Fe (Al) solid solution at the interface of Fe
3
Al/Q235. Aluminum content decreases from 28% to 1.5% and corresponding phase changes from Fe
3
Al with DO
3
type body centred cubic
bcc
structure to α-Fe (Al) solid solution with B2 type
bcc
structure. All phases are present in sub-grain structure level and there is no obvious brittle phases or micro-defects such
as pores and cracks at the interface of Fe
3
Al/Q235 diffusion joint. 相似文献