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1.
The dielectric properties of the ceramics of (1 − x)BiFeO3 − x(KBi)1/2TiO3 (0.40 < x < 0.85) solid solutions with an orthorhombic structure have been studied using impedance spectroscopy in the frequency range
25–106 Hz at different temperatures. It has been shown that these solid solutions undergo a diffuse ferroelectric phase transition.
The Curie temperature is found to be in the range 620–640 K. The activation energies of dielectric polarization relaxation
(δE
M
) and dc charge carriers (ΔE
dc) are determined. It has been established that, in the vicinity of 460 K, ΔE
dc increases jumpwise as the temperature increases. 相似文献
2.
Both the gas atmosphere (Ar, 15% H2S−H2, H2) and the temperature of treatment strongly affect the distribution of iron atoms among different phases (FeS2-pyrite, Fe1−x
S-pyrrhotite, FeS-troilite, mixed Fe−Mo−S structure) in Fe- and FeMo sulfide catalysts. In FeMo sulfide catalysts FeS2 (pyrite) and the Fe−Mo−S structure are stabilized by MoS2. 相似文献
3.
K. I. Gnanasekar M. Sharon R. Pinto A. S. Tamhane S. C. Purandare S. P. Pai L. C. Gupta R. Vijayaraghavan 《Zeitschrift für Physik B Condensed Matter》1995,99(1):173-177
Structural and superconducting properties of the system Lu1−x
Ca
x
Ba2 Cu3O7−δ, both in bulk as well as thin film form, have been investigated. Presence of large Ca-ions at the Lu-sites is responsible
for phase stability (in 1–2–3 phase) in bulk. In argon annealed tetragonal samples (δ:1) superconductivity is reinstated as
in these samples, presence of Ca-ions lead to the generation of holes in the Cu−O planes. In oxygen annealed bulk samples
and thin films, there is a large depression ofT
c due to divalent Ca-ions present in concentrationx<0.2. Our data indicate that this depression ofT
c is likely due to overdoping effect. 相似文献
4.
V. I. Lavrent’ev 《Physics of the Solid State》1998,40(3):354-357
The temperature variations in the modulus of elasticity (Young’s modulus) E and internal friction Q
−1 of the amorphous metal alloys Ti50Cu50−x
Nix (5⩽x⩽20) are studied at temperatures of 300–800 K. There is an anomalous increase in E(T) at temperatures above T
x (which varies from 440 to 525 K, depending on the composition). When the amount of nickel in the alloy is high (x>12 at. %), a small peak shows up in Q
−1(T). These effects are related to structural transitions in near-ordering regions (clusters). A model for structural relaxation
of near ordering in amorphous alloys is proposed on the basis of these experiments.
Fiz. Tverd. Tela (St. Petersburg) 40, 389–392 (March 1998) 相似文献
5.
Polycrystalline MgxAl2xLi0.5(1−x)Fe2.5(1−x) O4 (x = 0.0, 0.2, 0.5, 0.6 and 0.7) ferrites were prepared by standard ceramic method, and characterized by X-ray diffraction and
infrared absorption spectroscopy. The spectra show two significant absorption bands in the wave number range of 400–1000 cm−1 arising from interatomic vibrations in the tetrahedral and octahedral coordination compounds. The decrease in intensity and
increase in broadness of bands with concentration (x) are explained on the basis of cation distribution. The force constants and bulk modulus are found to decrease with Mg-Al
content (x) which suggested weakening of interatomic bonding. An alternate method for the determination of bulk modulus, longitudinal
and transverse velocities is suggested. The magnetic and electrical properties of these compounds are explained in the light
of structural and optical properties. 相似文献
6.
The amorphous fine particles of Fe100−x
B
x
(20.7≤x≤36.5) and (Fe70Co30)100−x
B
x
(26.9≤x≤40.2) were prepared by borohydride reduction. The amorphous state of the samples was identified with both X-ray and electron
diffraction measurements. With increasing boron content, the average hyperfine magnetic fields decrease. Comparing the hyperfine
parameters of the glassy powder with those of the ribbons having the same compositions, the average hyperfine fields and the
isomer shifts are different. The differences may be due to the amorphous polymorphism which is produced by the different preparation
methods.
Project is partly supported by the National Natural Science Foundation of China. 相似文献
7.
M. Lambacher T. Helm M. Kartsovnik A. Erb 《The European physical journal. Special topics》2010,188(1):61-72
High quality electron-doped HTSC single crystals of Pr2−xCexCuO4+δ and Nd2−xCexCuO4+δ have been successfully grown by the container-free traveling solvent floating zone technique. The optimally doped Pr2−xCexCuO4+δ and Nd2−xCexCuO4+δ crystals have transition temperatures T
c of 25 K and 23.5 K, respectively, with a transition width of less than 1 K. We found a strong dependence of the optimal growth
parameters on the Ce content x. We discuss the optimization of the post-growth annealing treatment of the samples, the doping extension of the superconducting
dome for both compounds as well as the role of excess oxygen. The absolute oxygen content of the as-grown crystals is determined
from thermogravimetric experiments and is found to be ≥ 4.0. This oxygen surplus is nearly completely removed by a post-growth
annealing treatment. The reduction process is reversible as demonstrated by magnetization measurements. In as-grown samples
the excess oxygen resides on the apical site O(3). This apical oxygen has nearly no doping effect, but rather influences the
evolution of superconductivity by inducing additional disorder in the CuO2 layers. The very high crystal quality of Nd2−xCexCuO4+δ is particularly manifest in magnetic quantum oscillations observed on several samples at different doping levels. They provide
a unique opportunity of studying the Fermi surface and its dependence on the carrier concentration in the bulk of the crystals. 相似文献
8.
A series of amorphous ribbons Fe85−x
Co
x
B15 was subjected to the isothermal crystallization annealing. The alloys forx=12, 15, 17, 19, 21, 23, and 25 at.% Co were measured at room temperature by standard transmission technique during interrupted
annealing. The samples with 12 and 21 at.% Co were used for direct scanning at constant velocity of the outermost metallic
peak. In both cases gradually increasing content of the metallic Fe−Co phase was observed in at least two stages. Several
scanning temperatures applied with the 12 and 21 at.% Co samples made it possible to draw the Arrhenius plots and to estimate
the activation enthalpies of the processes. By analysing the Avrami exponents and activation enthalpies, the first process
is attributed to a comparatively fast primary Fe−Co crystallization followed by the transformations of the amorphous rest. 相似文献
9.
A. Maignan Ch. Simon V. Caignaert B. Raveau 《Zeitschrift für Physik B Condensed Matter》1995,99(1):305-310
The exploration of the magnetic and transport properties of four series of manganese perovskites, Pr0.7Ca0.34−xAxMnO3−δ (A=Sr, Ba), Pr0.7−xLaxCa0.3 MnO3−δ and Pr0.66Ca0.34−x
SrxMnO3−δ has allowed four phases with colossal magnetoresistive (CMR) properties to be isolated: Pr0.7Ca0.25Sr0.025MnO3−δ and Pr0.66Ca0.26Sr0.08MnO3−δ that exhibit a variation of resistance of 2.5. 107% and 109% at μ0 H=5 T for T=88 K and 50 K respectively, Pr0.58La0.12Ca0.3 MnO3−δ that exhibits a variation of 6.106% for μ0 H=5 T at T=80 K and Pr0.7Ba0.025Ca0.275MnO3−δ for which a resistance variation of 5.109%, at T=50 K, for μ0 H=5 T is evidenced. for each compound of this series except the barium phase, one observes that the temperature Tmax, which corresponds to the resistance maximum on the R(T) curves in zero magnetic field, increases dramatically as the mean
size of the interpolated cations increases, and that the CMR effect correlatively decreases dramatically. The comparison of
the two series Pr0.7Ca0.3−xSrxMnO3−δ and Pr0.66Ca0.34−xSrxMnO3−δ shows also the crucial role of the hole carrier density: for a same mean ionic radius of the interpolated cation Tmax is decreased of about 50 K by introducing 0.034 hole per Mn mole. 相似文献
10.
Composite materials used for electrode and electrolyte materials have been intensely studied in view of their advantages such
as higher conductivity and better operational performance compared to their single-phase counterparts. The present work aims
at studying the electrical and structural characteristics of a new composite electrolyte namely, (PbI2)
x
− (Ag2O–Cr2O3)100−x
where x = 5, 10, 15, 20, and 25 mol%, respectively, prepared by the melt quenching technique. The room temperature X-ray diffraction
spectra revealed certain crystalline phases in the samples. AC conductivity analysis for all the prepared samples was carried
out over the frequency range 1 MHz–20 Hz and in the temperature window 297–468 K. The room temperature conductivity values
were calculated to be in the order of 10−5–10−3 Scm−1. An Arrhenius dependence of temperature with conductivity was observed, and the activation energies calculated were found
to be in the range 0.27–0.31 eV. Furthermore, the total ionic transport number (t
i) values obtained for all these indicated the ionic nature of this system.
Paper presented at the Third International Conference on Ionic Devices (ICID 2006), Chennai, Tamilnadu, India, Dec. 7–9, 2006. 相似文献
11.
We present a variational method for solving the two-electron Dirac-Coulomb equation. When the expectation value of the Dirac-Coulomb
Hamiltonian is made stationary for all possible variations of the different components of a well-behaved trial function one
obtains solutions representative of the physical bound state wave functions. The ground state wave function is derived from
the application of a minimax principle. Since the trial function remains well-behaved, the method remains safe from the twin
demons of variational collapse and continuum dissolution.
The ground state wave function thus derived can be interpreted as a linear combination of different configurations. In particular,
the admixing of intermediate states having one (two) electron(s) deexcited to a negative-energy orbital (orbitals) contributes
a second-order level shiftE
0−
(2)
which can be identified with the second-order shift due to the Pauli blocking of the production of one (or two) virtual electron-positron
pair(s). Thus the minimax solution corresponds to the renormalized ground state in quantum electrodynamics, with deexcitations
to negative-energy orbitals taking the place of the avoidance of virtual pairs.
If one extends the relativistic configuration interaction (RCI) treatment by additionally including negative-energy and mixed-energyeigenvectors of the Dirac-Hartree-Fock hamiltonian matrix in the two-electron basis, the calculated energy will be shifted from the conventional
RCI value by an amount that is much smaller thanE
0−
(2)
. For two-electron atoms, we have derived expressions for the all-spinor limit (δE) and thes-spinor limit (δE
s) of this shift in leading orders. The all-spinor limit (δE) is of orderα
4
Z
4 1/3 whereas thes-spinor limit (δE
s) is of orderα
4
Z
3 2/3. leading components are related to the 1-pair component ofE
0−
(2)
in a simple way, and the relationships offer the possibility of computing energy due to virtual pairs. Numerical results
are discussed. 相似文献
12.
A. V. Dvurechenskii A. A. Karanovich R. Grötzschel F. Herrmann R. Kegler A. V. Rybin 《Physics of the Solid State》1998,40(2):195-199
Electron spin resonance has been used to study the depth distribution of point defects in Si samples bombarded by N5+ (E=16 MeV) and Si5+ (E=26.8 MeV) ions at 175 and 300 K in the dose range (4–8)×1015 cm−2. It was established that unlike the implantation of moderate-energy Si ions (E ∼ 100 keV), the depth distributions of planar tetravacancies in samples bombarded by ions at 300 K under these conditions
have two maxima. The experimental results indicate that the tetravacancy density maximum closer to the surface is formed as
a result of secondary defect formation processes. No continuous amorphous layer was observed in the bulk of any of the Si
samples. This experimental observation is evidence of defect annealing which takes place when high-energy ions are implanted
in Si.
Fiz. Tverd. Tela (St. Petersburg) 40, 217–222 (February 1998) 相似文献
13.
H. Lehmann G. Nimtz L. D. Haas T. Jakobus 《Applied Physics A: Materials Science & Processing》1981,25(3):291-295
The dielectric properties of epitaxial Pb1−x
Sn
x
Te layers are investigated at 9 GHz in a composition range betweenx=0 and 0.225. The samples are characterized by fairly low carrier concentrations between 1.4×1016 and 32×1016 cm−3. Data of the static dielectric constant (ε
s
) are obtained at temperatures of 77 and 300 K. The results of ε
s
are 25% to 100% higher compared to previous measurements in bulk material from other authors. The observed higher values
of ε
s
in the investigated samples may be due to the reduced number of point defects in epitaxially grown Pb1−x
Sn
x
Te layers. The model of Kawamura which predicts a dependence of ε
s
on the effective band gap cannot be verified. 相似文献
14.
We find the unusual vortex dynamics in the low-temperature liquid phase of amorphous MoxSi1−x films by measuring the fluctuating component of the flux-flow voltage δV(t) about the average voltage. For the thick film, in which the quantum vortex liquid (QVL) phase has been well-determined in
the field-temperature plane, δV(t) originating from the vortex motion is clearly visible in the QVL phase, where the distribution of δV(t) is anomalously asymmetric, implying large velocity and/or number fluctuations of driven vortices. For the thin film, in
which the QVL phase has not been determined from the static transport measurements, similar unusual vortex motion is observed
in nearly the same reduced-temperature regime. We suggest that vortex dynamics in the low-temperature liquid phase of thick
and thin films is dominated by common physical mechanisms related to quantum-fluctuation effects. 相似文献
15.
La2 − x
Sr
x
NiO4 +
δ
materials were investigated as cathodes for the electrochemical reduction of oxygen on a Ce1.9Gd0.1O1.95 (CGO10) electrolyte using cone-shaped electrodes together with electrochemical impedance spectroscopy. The area-specific
resistance (ASR) of the La2 − x
Sr
x
NiO4 +
δ
nickelates towards the reduction of oxygen is equal to the ASR of perovskites; however, it is not as low as for the best
Fe–Co-based perovskites. The lowest ASR is found for the compound La1.75Sr0.25NiO4 +
δ
with an ASR of 23.8 Ωcm2 measured on a cone-shaped electrode in air at 600 °C. It is suggested that difference in oxide ionic conductivity of the
nickelates is the main cause for the different activity of the nickelates towards the electrochemical reduction of oxygen. 相似文献
16.
I. O. Troyanchuk M. V. Bushinsky D. V. Karpinsky V. Sirenko V. Sikolenko V. Efimov 《The European Physical Journal B - Condensed Matter and Complex Systems》2010,73(3):375-381
The Bi1−xAxFeO3−
δ (A = Sr, Pb)
systems have been studied using the X-ray, neutron powder
diffraction and magnetization measurements in a magnetic field up to
14 T. It was found that around x ∼ 0.06 the crystal symmetry
changes from a rhombohedral (space group R3c) to
pseudo-tetragonal. In the composition range
0.07 ≤ x ≤ 0.14 the phases with different symmetry of
the unit cell coexist independent of synthesis conditions. The
neutron powder diffraction shows that the iron ions have average
oxidation state close to 3+. The magnetic structure for
Bi0.5Sr0.5FeO3−
δ is found to be G-type
antiferromagnetic with magnetic moment of about
3.8 μB/Fe3+. The weak ferromagnetic state due to
magnetoelectric interactions was revealed in the lightly doped
rhombohedrally distorted compositions. No evidence for a spontaneous
magnetization was observed for the pseudo-tetragonal phases. These
compositions show irreversible nonlinear magnetization vs. field
behavior apparently due to small local deviations from the
collinearity of the magnetic moments. 相似文献
17.
L. I. Koroleva D. M. Zashchirinski T. M. Khapaeva L. I. Gurski N. A. Kalanda V. M. Trukhan R. Szymczak B. Krzumanska 《Physics of the Solid State》2008,50(12):2298-2302
This paper reports on a study of the effect of oxygen deficiency on the magnetic and electrical properties of the La1 − x
Sr
x
MnO3 − δ manganites (x = 0, 0.2, 0.4; δ = 0, 0.13, 0.2). In compositions with x = 0 and δ = 0.13 and 0.2, the temperature dependence of the magnetization M (T) can be approximated by the Langevin function with the moment of superparamagnetic clusters μ = 77μB (δ = 0.13) and 86μB (δ = 0.2) at temperatures of 25 K ≤ T ≤ 250 K, with the exception of a small temperature range near 132 K in which a maximum characteristic of the LaMnO3 antiferromagnet is seen. These compositions, as well as Sr-doped compositions with δ ≠ 0, reveal a difference between the
magnetizations of the sample cooled in a weak magnetic field and in zero field. At T = 6 K in a magnetic field of 16 kOe, the compositions with x = 0.2 and 0.4, δ = 0.13 possess a magnetic moment per formula unit lower than that with δ = 0, as well as reveal an anomalous
relation between the Curie temperature T
C and the Curie paramagnetic point gJ, namely, T
C > gJ. The magnetization of compositions with x = 0.2 and 0.4, δ = 0.2 follows the Langevin function with μ = 40μB and 130μB, respectively. The electrical resistivity of samples with x = 0.4 and δ = 0.13 and 0.2 is one to two orders of magnitude larger than that of the composition with x = 0.4, δ = 0, which evidences partial or complete compensation of acceptor defects (Sr2+ ions) by donor defects (doubly charged O2− vacancies). The above properties of oxygen-deficient compositions suggest that they contain an insulating ferro-antiferromagnetic
magnetically double-phase state. The magnetoresistance and volume magnetostriction in samples with x = 0.4 and δ = 0, 0.13, and 0.2 are small; indeed, in a magnetic field of 8 kOe, they do not exceed 1.4% and 6 × 10−6, respectively. On this basis, it is concluded that the unbalanced doubly charged donors (O vacancies) are in the state with
antiparallel spins and, thus, do not initiate the formation of ferron-type ferromagnetic clusters. The significance of both
compensated and unbalanced doubly charged donors consists in that they give rise to the formation of fractured Mn-O-Mn bonds,
which bring about lowering of the magnetic moment per formula unit in compositions with x = 0.2 and 0.4 and δ = 0.13 and the transition to superparamagnetism in compositions with x = 0.2 and 0.4, δ = 0.2.
Original Russian Text ? L.I. Koroleva, D.M. Zashchirinskiĭ, T.M. Khapaeva, L.I. Gurskiĭ, N.A. Kalanda, V.M. Trukhan, R. Szymczak,
B. Krzumanska, 2008, published in Fizika Tverdogo Tela, 2008, Vol. 50, No. 12, pp. 2201–2205. 相似文献
18.
The difference of the energies of levels Δ
n
= E
lev(2+0
n
) − E
lev(0+0
n
) at n = 1, 2, and 3 and the multipole-mixture parameter δ for (2+02−2+01) and (2+03−2+01) transitions are contrasted against the structure of the K
π
= 02+ and 03+ rotational bands that was calculated on the basis of the quasiparticle-phonon model. The values of (Δ2 − Δ1), (Δ3 − Δ1), and (Δ2 − Δ3) are found to correlate with the sign of the parameter δ and with the calculated structure of the K
π
= 02+ and 03+ bands.
Original Russian Text ? A.M. Demidov, L.I. Govor, V.A. Kurkin, I.V. Mikhailov, 2009, published in Yadernaya Fizika, 2009,
Vol. 72, No. 2, pp. 236–240. 相似文献
19.
A. S. Emelyanov S. I. Raevskaya F. I. Savenko I. P. Raevski M. A. Malitskaya E. I. Sitalo 《Bulletin of the Russian Academy of Sciences: Physics》2009,73(1):123-124
It is established that, as a result of application of even a small (∼0.5 kV cm−1) bias field E, the maximum of the piezoelectric coefficient d
31 in (1 − x)Pb(Mg1/3Nb2/3)O3 − xPbTiO3(x = 0.06, 0.13) crystals shifts from the Vogel-Fulcher temperature to the critical point in the E-T phase diagram of a given composition. The field dependence of the d
31(T) peak magnitude has a maximum near the E values corresponding to the critical point.
Original Russian Text ? A.S. Emelyanov, S.I. Raevskaya, F.I. Savenko, I.P. Raevski, M.A. Malitskaya, E.I. Sitalo, 2009, published
in Izvestiya Rossiiskoi Akademii Nauk. Seriya Fizicheskaya, 2009, Vol. 73, No. 1, pp. 132–133. 相似文献
20.
Melt-spinning Nd
x
Fe100-x
alloys over a wide composition range: 10≤x≤90, has lead to the identification of three metastable phases. Two of these correspond to phases which are stable in late
rare earth-iron alloy systems, the third is related to the fcc grain boundary phase observed in sintered Nd−Fe−B permanent
magnets. Structural and magnetic data are presented. 相似文献