共查询到20条相似文献,搜索用时 15 毫秒
1.
A. Younis A. Hussain M. Asghar A. Manzoor S. Javed 《Journal of Superconductivity and Novel Magnetism》2011,24(4):1327-1332
The dielectric properties of Cu0.5Tl0.5Ba2Ca2−q
Mg
q
Cu3O10−δ
(q=0, 0.5, 1.0 1.5) superconductor samples were studied at two temperatures of 80 and 290 K by capacitance (C) and conductance (G) measurements with the test frequency (f) in the range of 10 KHz to 10 MHz. We have presented the measurements of the dielectric constants (ε′ and ε″), dielectric loss factor (tan δ) and ac-conductivity (σ
ac) as a function of frequency and temperature. A negative capacitance (NC) experience has been observed, which is most likely
due to different contact electrodes and superconductor samples’ Fermi levels. Since metals have their Fermi levels higher
than ceramics, there is a flow of the carriers from the ceramic samples towards the metal electrodes. The dielectric polarization
phenomenon is observed, which is due to dislodgment of mobile charges from their equilibrium position relative to fixed charges
of the reservoir layer. The improved inter plane coupling promoted by Mg substitution at Ca site would change the dielectric
response of Cu0.5Tl0.5Ba2Ca2−q
Mg
q
Cu3O10−δ
superconductors. To observe such effects in Mg doped Cu0.5Tl0.5Ba2Ca2−q
Mg
q
Cu3O10−δ
superconductors, di- electric measurements were carried out both at room temperature (290 K) and in the superconducting state
closer to the boiling point of liquid nitrogen (80 K). The excess conductivity arising due to superconducting state of material
has been determined, and its role in the mechanism of superconductivity is suggested. The negative dielectric constant (ε′) and dielectric loss factor (tan δ) show strong dispersion at low frequencies. The lower thermal agitation at 80 K may enhance the polarizability and hence
the dielectric constants (ε′ and ε″). 相似文献
2.
Tayyba Firdoss A. A. Khurram Nawazish A. Khan 《Journal of Superconductivity and Novel Magnetism》2010,23(3):325-328
We have studied the ac response of Sn doped Cu0.5Tl0.5Ba2Ca2Cu3−x
Sn
x
O10−δ
superconductor samples from their ac-susceptibility measurements under different magnitudes of ac magnetic fields; H
ac=0.4, 4, 16 A/m. The samples with x=0.5 and 1.0 have shown strong flux pinning and intergrain coupling. However, the sample with Sn doping of x=1.5 has shown very poor flux pinning characteristics. 相似文献
3.
Hiroyuki Sasakura Yoshiya Akagi Masashi Tanaka Shigeki Tsukui Motoaki Adachi 《Journal of Superconductivity and Novel Magnetism》2010,23(7):1381-1384
New Pb-based layered cuprates containing boron with the 1232 structure have been synthesized in the (Pb0.5B0.5)Sr2(Er3−x−y
Ce
x
Sr
y
)Cu2O
z
system. Nearly the single 1232 phase samples are obtained for the nominal composition of 1.6≤x≤1.9 and y=0.2. A sample with the composition of (Pb0.5B0.5)Sr2(Er1.2Ce1.6Sr0.2)Cu2O
z
shows resistivity-dropping phenomenon below 10 K and it shows a diamagnetic signal at about 9.0 K, though the superconducting
volume fraction is very small. From these results, the sample may well be a new Pb-based superconductor with the 1232 structure. 相似文献
4.
M. A. A. Moussa N. M. Al-Hosiny 《Journal of Superconductivity and Novel Magnetism》2011,24(4):1309-1314
The chemical solution nitrate route was used to prepare Y0.5[Yb1−x
Nd
x
]0.5Ba2Cu3O
z
superconducting phase with x=0.1, 0.2 and 0.3. Different calcination temperatures from 870 to 900 °C were used. Both XRD and DSC techniques were utilized
in monitoring the Y0.5[Yb1−x
Nd
x
]0.5Ba2Cu3O
z
superconducting phase and the non-superconducting impurity phases such as BaCuO5, CuO and RE2BaCuO5. These two techniques were used to study the effect of impurity phases on the decomposition temperature of Y0.5[Yb1−x
Nd
x
]0.5Ba2Cu3O
z
superconducting phase. The value of x, the Nd amount, and the calcination temperature both influenced the type and number of impurity phases, which resulted in
changing the eutectic and peritectic reaction temperatures. 相似文献
5.
Nawazish A. Khan Rehana Begum Mazhar Mehmood 《Journal of Superconductivity and Novel Magnetism》2010,23(3):351-359
A reproducible synthesis and characterization of Zn-doped Cu0.5Tl0.5Ba2Ca2Cu3−y
Zn
y
O12−δ
(y=0, 0.5, 1.0, 1.5) superconductors at a relatively lower synthesis temperature of 840°C are studied by using X-ray diffraction,
resistivity, ac-susceptibility and FTIR absorption measurements. The X-ray diffraction (XRD) studies of these samples have
shown a tetragonal structure in which the c-axis length has been found to decrease with increased Zn doping. The critical temperature and magnitude of diamagnetism have
not been significantly affected with the doping of Zn at this synthesis temperature. The magnitude of diamagnetism in the
as-prepared undoped samples is decreased, whereas it remains stable (unchanged) in oxygen post-annealed samples. The apical
oxygen phonon’s modes of type Tl–OA–M(2) and Cu(1)–OA–M(2) {where M=Cu/Zn} and the planar oxygen phonon modes of type M(2)–OP–M(2) are also softened with the increase of Zn doping. We interpreted the softening of these oxygen related phonon modes
linked with the decreased c-axis length, reduced John–Teller distortions and increased mass of Zn (65.38 amu) as compared to that of Cu (63.54 amu) (Kaplan
et al., Phys. Rev. B 65, 214509, 2002). 相似文献
6.
H. Khelifi A. Aydi N. Abdelmoula A. Simon A. Maalej H. Khemakhem M. Maglione 《Journal of Materials Science》2012,47(4):1943-1949
Lead-free (1 − x)NaNbO3/xBa(Ti0.5Sn0.5)O3 (x = 0.1, 0.125, 0.15, 0.175, 0.2, and 0.3) ceramics were elaborated by the conventional ceramic technique. Sintering has been
made at 1523 K for 2 h. The crystal structure was investigated by X-ray diffraction with CuKα radiation at room temperature.
As a function of composition, these compounds crystallize with tetragonal or cubic symmetry. Dielectric measurements show
that the materials have a classical ferroelectric behavior for compositions in the range 0.10 ≤ x ≤ 0.15 and relaxor one for compositions in the range 0.15 < x ≤ 0.30. Temperatures T
C or T
m decrease as x content increases. The ferroelectric behavior has been confirmed by hysteresis characterization. For x = 0.1, a piezoelectric coefficient d
31 of 42.146 pC N−1 was obtained at room temperature. The evolution of the Raman spectra was studied as a function of temperature for x = 0.1. 相似文献
7.
M. Mumtaz Nawazish A. Khan Faheem Ashraf 《Journal of Superconductivity and Novel Magnetism》2011,24(6):1985-1989
The relatively higher electronegative elements (M = Pd, Nb, Bi, Hg) have been partially doped at Tl sites in Cu0.5Tl0.5−x
M
x
Ba2O4−δ
(x=0,0.25) charge reservoir layer of Cu0.5Tl0.5−x
M
x
Ba2Ca2Cu3O10−δ
superconductor. These elements may retain more oxygen in the charge reservoir layer due to their higher electronegativity
as compared to Tl, and the higher population of oxygen in the charge reservoir layer can optimize the charge carriers’ density
in the conducting CuO2 planes. The optimum density of mobile charge carriers in the conducting CuO2 increases Fermi wave-vector K
F and Fermi velocity v
F of the carriers, which results in the improvement of superconducting properties of the material. 相似文献
8.
Babar Shabbir Anayat Ullah Najmul Hassan M. Irfan Nawazish A. Khan 《Journal of Superconductivity and Novel Magnetism》2011,24(5):1521-1526
Fluctuation Induced Conductivity (FIC) of Co-doped Cu0.5Tl0.5Ba2Ca2Cu3−y
Co
y
O10−δ
(y=0, 0.05, 0.1, 0.5) Superconductors have been studied as to find the possible cause of T
c suppression in these compounds. We used Aslamazov–Larkin (AL) and Lawrence–Donaich (LD) equations to analyze the FIC of our
samples. In this regard, it is observed that the data seems to fit well with 3D (three-dimensional) AL equations. In addition,
crossover temperature from 2D to 3D has been found. The width of the temperature window for 3D conductivity is continuously
decreasing with enhanced Co concentration. The shrinking of 3D temperature region with increased Co doping can be correlated
with the suppression of superconductivity. It is observed that the coherence length and th interplanar coupling strength have
also been decreased with increased Co doping, consistent with the magnetic pair-breaking effect. 相似文献
9.
I. A. Verbenko O. N. Razumovskaya L. A. Shilkina L. A. Reznichenko K. P. Andryushin 《Inorganic Materials》2009,45(6):702-708
The influence of past history on the possibility of obtaining high-density ferroelectric ceramics of solid solutions [(Na0.5K0.5)1 − x
Li
x
](Nb1 − y − z
Ta
y
Sb
z
)O at x = 0–0.14, y = 0, 0.1, 0.2, and z = 0–0.1 is identified. The dynamics of behavior of materials under a field in the process of polarization is evaluated. The
relative dielectric permeability of samples in a wide range of temperatures (20–700°C) and frequencies (25 Hz-1 MHz) of a
variable electric field is studied. On the basis of study of dielectric, piezoelectric, and elastic properties of solid solutions,
prospective objects for further technological elaboration and modification of chemical composition with the goal of improving
the electrophysical parameters are selected.
Original Russian Text ? I.A. Verbenko, O.N. Razumovskaya, L.A. Shilkina, L.A. Reznichenko, K.P. Andryushin, 2009, published
in Neorganicheskie Materialy, 2009, Vol. 45, No. 6, pp. 762–768. 相似文献
10.
M. Y. Lin Y. F. Wang D. C. Ling H. S. Sheu H.-C. I. Kao 《Journal of Superconductivity and Novel Magnetism》2010,23(5):721-724
A series of single phase (La1−x
Sr1+x
) (Mn0.5Co0.5)O4 (0≤x≤0.40) materials with a tetragonal K2NiF4 structure was prepared by a solid state reaction method at 1400 or 1450 °C with a short period of heating time. Powder X-ray
diffraction (XRD) and the Rietveld refinement method were employed for the structural analysis. Unit cell a- and c-axes decrease with increasing amount of Sr substitution. A discrepancy between the zero-field-cooled and the field-cooled
magnetization is observed in all samples investigated below a characteristic temperature, T
*, which likely arises from the canted nature of spins or the random freezing of spins. It appears that T
* decreases with increasing amount of Sr substitution, which is possibly due to the enhancement of chemical pressure induced
by Sr and a corresponding increases of the valence of Mn and/or Co. 相似文献
11.
Kandasami Asokan Jae Young Park Sunwoo Choi Changhwan Chang Sang Sub Kim 《Nano Research》2010,3(4):256-263
We experimentally investigate the stabilization of the anatase phase of Ti1−x
Sn
x
O2 (x < 0.5) nanofibers when synthesized by an electrospinning method. The as-spun nanofibers became nano-grained, polycrystalline
nanofibers after calcination and the diameters of the nanofibers depend on Sn content. Stabilization of the anatase phase
in Ti-rich compositions and incorporation of Sn ions were confirmed by X-ray diffraction, Raman, X-ray absorption near-edge
structure, and photoluminescence (PL) spectroscopies. Results from the PL study also demonstrated the tunable nature of the
optical properties, with the emission maximum shifting towards higher wavelength with increasing Sn concentration.
相似文献
12.
A series of oxidized La2–x
Sr
x
CuO4+y
compounds has been prepared by treating the starting materials with a solution of Br2 in NaOH at room temperature. The structural modifications due to the oxidation of the materials have been studied by X-ray diffraction. Some of the observed changes are: (i) a large increase in the long parameter of the unit cell for samples with Sr content
and (ii) a slight decrease in a along the whole range ofx. Interesting features have been observed regarding the critical temperatures of these materials: transition temperatures are higher for those containing lower Sr amounts (some of them were even nonsuperconducting before the oxidation treatment) in contrast to materials with x0.15, whoseT
c's do not change very much. The influence of both oxygen and strontium contents on the structural modifications and the superconducting properties of the oxidized materials will be discussed. 相似文献
13.
Superconducting properties of cadmium doped Cu0.5Tl0.5Ba2Ca2Cu3−y
Cd
y
O10−δ
(y=0,0.5,1.0,1.5,2.0) samples have been studied using X-ray diffraction, resistivity, ac-susceptibility and FTIR absorption
measurements. In X-ray diffraction studies these samples have shown to have tetragonal structure. The zero resistivity critical
temperature and magnitude of diamagnetism are suppressed with the increased incorporation of Cd in the final compound. A change
in the shape of FTIR absorption spectra, after doping, has shown the incorporation of Cd in the unit cell. A systematic hardening
of the apical oxygen modes and softening of the CuO2 planar modes of vibration with increased Cd doping have shown that it is incorporated in the unit cell of Cu0.5Tl0.5Ba2Ca2Cu3−y
Cd
y
O10−δ
(y=0,0.5,1.0,1.5,2.0) superconductors. The FTIR absorption measurements of these samples have shown that hardening of the apical
oxygen modes of types Cu(1)–O(2)–Tl and Cu(1)–O(2)–Cu(2)/Cd
y
(y=0,0.5,1.0,1.5,2.0) increases with the increase of Cd doping in the samples. A softening of the CuO2 planar oxygen mode Cu(2)–O–Cu(2) is also observed with the increased Cd doping in the final compound. It is most likely that
hardening of the apical oxygen modes and the softening of the planar modes of vibration are associated damped harmonic oscillations
produced by heavier Cd atoms in the CuO2 planes, which suppress the phonon population from a desired level, reducing the magnitude of superconductivity in the final
compound. 相似文献
14.
15.
M. Mumtaz Nawazish A. Khan S. M. Hasnain Adnan Younis 《Journal of Superconductivity and Novel Magnetism》2011,24(6):1939-1945
The main role played by mobile carriers and fluctuation induced conductivity (FIC) in (Cu0.5Tl0.5−x
K
x
)Ba2Ca3Cu1Zn3O12−δ
(x=0, 0.25) superconductor samples are analyzed in the light of the Aslamazov–Larken (AL) theory. The enhancement of three-dimensional
(3D) conductivity and grain size is achieved with K-doping at Tl sites in the (Cu0.5Tl0.5−x
K
x
)Ba2O4−δ
charge reservoir layer, which are further improved by post-annealing the samples in oxygen. The improvement of these factors
causes the increase in cross-over temperature (T
o), zero resistivity critical temperature {T
c(R=0)} and T
c(onset) of diamagnetism to their higher values. We have also evaluated the exponents (λ
2D and λ
3D), zero temperature coherence lengths ξ
c(0), and interlayer coupling (J) for these samples and tried to correlate them to the superconductivity order parameters. 相似文献
16.
James T. Joseph Shyla Joseph Annamma John J. K. Thomas V. S. Prasad Sam Solomon 《Journal of Materials Science: Materials in Electronics》2011,22(3):228-232
Microwave dielectric ceramics of the type (Sm0.5Y0.5)Ti(Nb1−x
Ta
x
)O6 were prepared for x = 0, 0.2, 0.4, 0.6, 0.8 and 1 through the conventional solid state ceramic route. The ball-milled compositions were calcined
at 1,250 °C. The cylindrical pellets were sintered at temperatures between 1,385 and 1,450 °C. The densities were determined
by Archimedes method. The structure was analyzed using X-ray diffraction method. The microwave dielectric properties of the
polished pellets were measured using cavity resonator method. The morphological studies were done using Scanning Electron
Microscopy and Transmission Electron Microscopy. The Raman spectra were recorded and analyzed to confirm the structural change.
The photoluminescence spectra were also taken and the emission lines were identified. A correlation study was done among the
measured properties and parameters. Most of the samples have high dielectric constant, high quality factor and low temperature
coefficient of resonant frequency and hence suitable for microwave applications. 相似文献
17.
The electrical conductivity, band gap, dielectric permittivity, and molar polarizability of Zn2(Ti
a
Sn
b
)1 − x
Zr
x
O4 solid solutions have been determined. All of the synthesized samples are dielectrics with semiconducting behavior of conductivity.
The phase diagram of the Zn2TiO4-Zn2SnO4-Zn2ZrO4 system is presented. 相似文献
18.
The heat capacity (C
p
0) of the tellurite glasses
$\begin{gathered}
(TeO_2 )_{0.70} (ZnO)_{0.15} (Na_2 O)_{0.10} (Bi_2 O_3 )_{0.05} (I), \hfill \\
(TeO_2 )_{0.75} (ZnO)_{0.10} (Na_2 O)_{0.10} (Bi_2 O_3 )_{0.05} (II),and \hfill \\
(TeO_2 )_{0.75} (ZnO)_{0.15} (Na_2 O)_{0.05} (Bi_2 O_3 )_{0.05} (III) \hfill \\
\end{gathered}
$\begin{gathered}
(TeO_2 )_{0.70} (ZnO)_{0.15} (Na_2 O)_{0.10} (Bi_2 O_3 )_{0.05} (I), \hfill \\
(TeO_2 )_{0.75} (ZnO)_{0.10} (Na_2 O)_{0.10} (Bi_2 O_3 )_{0.05} (II),and \hfill \\
(TeO_2 )_{0.75} (ZnO)_{0.15} (Na_2 O)_{0.05} (Bi_2 O_3 )_{0.05} (III) \hfill \\
\end{gathered}
相似文献
19.
The solubility of Nd at the Ba sites and the superconductivity of YBa2–x
Nd
x
Cu3O
y
were investigated by X-ray powder diffraction and measurements of the electrical resistance and ac susceptibility. The single Re123 phase was obtained for x0.30. The onset transition temperature
is insensitive to the Nd content x in the region of x0.40. All are higher than 95 K. The zero resistance transition temperatures
, however, exhibits two-step variation with the increase of x. For x0.25,
are all above 92 K. The highest
of 94 K was obtained for x=0.25. For x0.3
drops sharply to about 84 K. Finally
falls to 30 K and
is below 10 K for x=0.5. The two-step variation of T
c might be an indication of the existence of two trap levels for holes. 相似文献
20.
New NASICON type materials of composition, Li3−2x
Al2−x
Sb
x
(PO4)3 (x = 0·6 to 1·4), have been prepared and characterized by powder XRD and IR. D.C. conductivities were measured in the temperature
range 300–573 K by a two-probe method. Impedance studies were carried out in the frequency region 102−106 Hz as a function of temperature (300–573 K). An Arrhenius behaviour is observed for all compositions by d.c. conductivity
and the Cole-Cole plots obtained from impedance data do not show any spikes on the lower frequency side indicating negligible
electrode effects. A maximum conductivity of 4·5 × 10−6 S cm−1 at 573 K was obtained for x = 0·8 of the Li3−2x
Al2−x
Sb
x
(PO4)3 system. 相似文献
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