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1.
The rapid solidification of Sb60Ag20Cu20 ternary alloy was realized by high undercooling method, and the maximum undercooling is up to 142 K (0.18TL). Within the wide undercooling range of 40-142 K, the solidified microstructures are composed of (Sb), θand ε phases. High undercooling enlarges the solute solubility of (Sb) phase, which causes its crystal lattice to expand and its crystal lattice constants to increase. Primary (Sb) phase grows in two modes at small undercoolings non-faceted dendrite growth is the main growth form; whereas at large undercoolings faceted dendrite growth takes the dominant place. The remarkable difference of crystal structures between (Sb) and θphases leads to (θ Sb) pseudobinary eutectic hard to form, whereas strips of θform when the alloy melt reaches the (θ Sb) pseudobinary eutectic line. The cooperative growth of θand ε phases contributes to the formation of (ε θ) pseudobinary eutectic easily. In addition, the crystallization route has been determined via microstructural characteristic analysis and DSC experiment. 相似文献
2.
Z. A. Kazei V. V. Snegirev A. S. Andreenko L. P. Kozeeva 《Journal of Experimental and Theoretical Physics》2011,113(2):245-250
The elastic properties of rare-earth cobaltites RBaCo4O7 (R = Y, Tm-Lu) have been experimentally studied in the temperature range of 80–300 K. The strong softening of the Young modulus
ΔE(T)/E
0 ≈ −(0.1–0.2) of cobaltites with Lu and Yb ions has been revealed, which is due to the instability of the crystal structure
upon cooling and is accompanied by an inverse jump at the second-order structural phase transition. The softening of the Young
modulus and the jump at the phase transition decrease by an order of magnitude and the transition temperature T
s and hysteresis ΔT
s increase from a compound with Lu to that with Tm. A large softening of the Young modulus at the structural transition in
Lu- and Yb cobaltites indicates that the corresponding elastic constant goes to zero, whereas this constant in Tm cobaltite
is not a “soft” mode of the phase transition. It has been found that the structural phase transition in Lu- and Yb cobaltites
is accompanied by a large absorption maximum at the phase transition point and an additional maximum in the low-temperature
phase and absorption anomalies in Tm cobaltite is an order of magnitude smaller. 相似文献
3.
V. D. Fokina E. V. Bogdanov M. V. Gorev M. S. Molokeev E. I. Pogorel’tsev I. N. Flerov N. M. Laptash 《Physics of the Solid State》2010,52(4):781-788
The thermal and dielectric properties of the (NH4)2NbOF5 oxyfluoride have been investigated. It has been established that the structural phase transitions Cmc21 → C2 → Ia observed at the temperatures T
1 = 258.0 K and T
2 = 218.9 K exhibit a nonferroelectric nature. The hydrostatic pressure, which stabilizes the initial phase and destabilizes
the low-temperature phase, hardly affects the temperature range of stability of the intermediate phase. The model of sequential
ordering of the structural elements due to phase transitions has been analyzed using experimental data on the entropies of
the phase transitions. 相似文献
4.
S. Pacetti 《The European Physical Journal A - Hadrons and Nuclei》2007,31(4):665-671
We define a general procedure, based on analyticity and dispersion relations, to estimate low-energy amplitudes for processes
like: φ→e
+
e
-
M and φ→γM, starting from cross-section data on e
+
e
-→φM, where M is a generic light scalar or pseudoscalar meson. In particular this procedure is constructed to obtain predictions on the
radiative decay rate which are crucially linked on the assumed quark structure for the meson M under consideration. Three cases are analyzed: M = η, M = f
0(qˉ) and M = f
0(qqˉ). While in the η case the estimate of the branching fraction for the radiative decay φ→ηγ is in agreement with the data, in the case of f
0, such agreement is obtained only under the hypothesis of a tetraquark scalar meson. 相似文献
5.
A. U. Sheleg V. G. Hurtavy S. N. Mustafaeva E. M. Kerimova 《Physics of the Solid State》2011,53(3):472-475
The temperature dependences of the electrical conductivity and the permittivity of TlInSe2 and TlGaTe2 crystals unirradiated and irradiated with 4-MeV electrons at a doze of 1016 cm−2 have been investigated. It has been established that electron irradiation leads to a decrease in the electrical conductivity
σ and the permittivity ɛ over the entire temperature range under study (90–320 K). It has been revealed that the TlInSe2 and TlGaTe2 single crystals undergo a sequence of phase transitions characteristic of crystals of this type, which manifest themselves
as anomalies in the temperature dependences σ = f(T) and ɛ = f(T). Electron irradiation at a doze of 1016 cm−2 does not affect the phase transition temperatures of the crystals under investigation. 相似文献
6.
M. Anselmino M. Boglione A. Prokudin C. Türk 《The European Physical Journal A - Hadrons and Nuclei》2007,31(3):373-381
We consider the azimuthal and PT-dependence of hadrons produced in unpolarized Semi-Inclusive Deep Inelastic Scattering (SIDIS) processes, within the factorized
QCD parton model. It is shown that at small PT values, P
T ≲ 1GeV/c, lowest-order contributions, coupled to unintegrated (transverse-momentum-dependent) quark distribution and fragmentation
functions, describe all data. At larger PT values, P
T ≳ 1GeV/c, the usual pQCD higher-order collinear contributions dominate. Having explained the full PT range of available data, we give new detailed predictions concerning the azimuthal and PT-dependence of hadrons which could be measured in ongoing or planned experiments by HERMES, COMPASS and JLab Collaborations. 相似文献
7.
T.M. Aliev K. Azizi A. Ozpineci 《The European Physical Journal C - Particles and Fields》2007,51(3):593-599
Using three point QCD sum rule methods, the form factors relevant to semileptonic Bs→DsJ(2460)ℓν decay are calculated. The q2 dependences of these form factors are evaluated and compared with the heavy quark effective theory predictions. The dependence
of the asymmetry parameter α, characterizing the polarization of the DsJ meson, on q2 is studied. The branching ratio of this decay is also estimated, and it is shown that it can easily be detected at LHC. 相似文献
8.
A. M. Balagurov I. A. Bobrikov V. Yu. Pomjakushin E. V. Pomjakushina D. V. Sheptyakov I. O. Troyanchuk 《JETP Letters》2011,93(5):263-268
The magnetic and crystal structures of the Pr0.5Sr0.5CoO3 metallic ferromagnet have been studied by the neutron diffraction technique. It is demonstrated that below 150 K, the compound
is mesoscopically separated into two crystalline phases with different spatial symmetries and with different directions of
the magnetic anisotropy. The phase separation exists down to 1.5 K, and at temperatures below 90 K, the low-symmetry phase
occupies about 80% of the sample volume. The main structural difference between the phases is the configuration of oxygen
atoms around praseodymium and, to a certain extent, around cobalt. The ferromagnetic structure with the magnetic moment lying
in the basal plane of the structure (μCo ≈ 1.7 μ
B
at 1.5 K) arises at 234 K, whereas the component directed along the long axis of the unit cell appears at 130 K. The formation
of the new structural phase and change in the orientation of the magnetic moment give rise to the anomalies of the physical
and magnetic characteristics of this compound observed earlier at temperatures about 120 K. 相似文献
9.
D. P. Kozlenko N. T. Dang Z. Jirák S. E. Kichanov E. V. Lukin B. N. Savenko L. S. Dubrovinsky C. Lathe C. Martin 《The European Physical Journal B - Condensed Matter and Complex Systems》2010,77(3):407-411
The crystal and magnetic structures of Pr0.15Sr0.85MnO3
manganite have been studied by means of powder X-ray and neutron diffraction
in the temperature range 10–400 K at high external pressures up to 55 and 4 GPa, respectively. A structural phase transition
from cubic to tetragonal
phase upon compression was observed, with large positive pressure
coefficient of transition temperature dT
ct
/dP = 28(2) K/GPa. The C-type
antiferromagnetic (AFM) ground state is formed below T
N
≈ 260 K
at ambient pressure. While at ambient pressure the structural and magnetic
transition temperatures are close, T
ct
~ T
N
, upon compression
they become decoupled with T
N
≪ T
ct
due to much weaker
T
N
pressure dependence with coefficient dT
N
/dP = 3.8(1) K/GPa. 相似文献
10.
Ruiting Sun Xiaoli Wang Jing Shi Le Wang 《Applied Physics A: Materials Science & Processing》2011,104(1):129-133
New perovskite solid solution ceramics of (1−x)BaTiO3-xBi(Mg1/2Ti1/2)O3 ((1−x)BT-xBMT, x≤0.09) were synthesized by the solid-state reaction technique. X-ray diffraction studies have revealed a stable single perovskite
structure for all samples. Dielectric measurements were carried out at different frequencies and temperatures. The polarization
evolutions with temperatures were measured to investigate the ferroelectric properties. All the compositions show features
of ferroelectrics with diffuse phase transition, though the temperature T
m
of their dielectric constant maximum ε
m
is frequency dependent. The dielectric constant peak ε(T) of (1−x)BT-xBMT ceramics become broad with increasing BMT content. During the temperature range of ε(T) peak summit, (1−x)BT-xBMT ceramics present quasi-linear dielectric phenomenon under high electric field with very high dielectric constant. 相似文献
11.
A method for preparing thin films of CsPbI3 and Cs4PbI6 complex compounds has been developed. Their absorption spectrum is investigated in the energy range of 2–6 eV at temperatures
from 90 to 500 K. It is found that the CsPbI3 compound is unstable and passes to the Cs4PbI6 phase upon heating at T ≥ 400 K. 相似文献
12.
The narrow D
s0
* (2317) and broad D
0
* (2300-2400) charmed scalar mesons and their radial excitations are described in a coupled-channel quark model that also reproduces
the properties of the light scalar nonet. All two-meson channels containing ground-state pseudoscalars and vectors are included.
The parameters are chosen fixed at published values, except for the overall coupling constant λ, which is fine-tuned to reproduce the D
s0
* (2317) mass, and a damping constant α for subthreshold contributions. Variations of λ and D
0
* (2300-2400) pole postions are studied for different α values. Calculated cross-sections for S-wave DK and Dπ scattering, as well as resonance pole positions, are given for the value of α that fits the light scalars. The thus predicted radially excited state D
s0
*′(2850), with a width of about 50MeV, seems to have been observed already. 相似文献
13.
Elemental mixtures of Al, Cu, Fe powders with the nominal composition of Al70Cu20Fe10 were mechanically alloyed in a planetary ball mill for 80 h. Subsequent annealing of the as-milled powders were performed
at 600–800°C temperature range for 4 h. Structural characteristics of the mechanically alloyed Al70Cu20Fe10 powders with the milling time and the heat treatment were investigated by X-ray diffraction (XRD), differential scanning
calorimeter (DSC) and differential thermal analysis (DTA). Mechanical alloying of the Al70Cu20Fe10 did not result in the formation of icosahedral quasicrystalline phase (i-phase) and a long time milling resulted in the formation
of β-Al(Cu,Fe) solid solution phase (β-phase). The i-phase was observed only for short-time milled powders after heat treatment above 600°C. The β-phase was one of the major phases in the Al70Cu20Fe10 alloy. The w-Al7Cu2Fe1 phase (w-phase) was obtained only after heat treatment of the short-time milled and unmilled samples. The present investigation
indicated that a suitable technique to obtain a large amount of quasicrystalline powders is to use a combination of short-time
milling and subsequent annealing. 相似文献
14.
A. G. Gamzatov A. M. Aliev K. Sh. Khizriev I. K. Kamilov A. S. Mankevich I. E. Korsakov 《Physics of the Solid State》2011,53(11):2271-2274
The heat capacity of the manganite La0.87K0.13MnO3 has been measured in the temperature range 80–350 K. The nature of the ferromagnetic phase transition and the critical properties
of heat capacity near the Curie temperature have been studied. The regularities of variations in the universal critical parameters
near the phase transition point have been established. The calculated critical exponent and amplitudes of the heat capacity
with allowance for corrections on the scaling (α = −0.13 and A
+/A
− = 1.178) correspond to the critical behavior of the 3D Heizenberg model. 相似文献
15.
We present the results a study of structure by neutron diffraction and data on the magnetic properties (linear and nonlinear
(second and third order) susceptibilities) of polycrystalline La0.88MnO2.95. This compound exhibits an insulator-metal (IM) phase transition at T
IM
≈ 253 K (above the Curie temperature, T
C
≈ 244 K) and reveals colossal magnetoresistance. The crystal structure is found to be rhombohedral, and the space group is
R3c. Analysis of magnetic properties shows that at T* ≈ 258 K > T
C
, isolated paramagnetic clusters occur in the paramagnetic matrix; their concentration increases upon cooling. We observed
no noticeable differences between the temperature evolution of the clustered state of this manganite with its insulator-metal
transition and in the insulator La0.88MnO2.91. Possible scenarios of the paramagnet-ferromagnet and I-M transitions in a self-organized clustered structure are discussed. 相似文献
16.
M. Scavini M. Brunelli C. Ferrero C. Mazzoli P. Ghigna 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,65(2):187-190
High resolution synchrotron radiation X-ray powder diffraction was used to investigate the melting of the cooperative Jahn-Teller
distortion (cJTd) in a perovskite of composition KCu0.8Mg0.2F3. A first order phase transition relaxing the cJTd is observed at T ∼ 600 K. From the transition temperature, an estimation of kT is derived (kT = 0.05 eV) for the cJTd in the doped compound. This is the very first observation of cJTd melting in a compound of the series
KCu1−x
Mg
x
F3. A structural phase diagram for the Cu rich zone of the series is proposed. In principle, the extension of this experimental
investigation could be used to disentangle the orbital order (OO) and cJTd energy scales in the parent compound KCuF3, a test system for OO theories. 相似文献
17.
The [N(CH3)4][N(C2H5)4]ZnCl4 compound has been synthesized by a solution-based chemical method. The X-ray diffraction study at room temperature revealed
an orthorhombic system with P21212 space group. The complex impedance has been investigated in the temperature and frequency ranges 420–520 K and 200 Hz–5 MHz,
respectively. The grain interior and grain boundary contribution to the electrical response in the material have been identified.
Dielectric data were analyzed using the complex electrical modulus M
* for the sample at various temperature. The modulus plots can be characterized by full width at half height or in terms of
a non-exponential decay function ϕ(t) = exp[(−t/τ)
β
]. The detailed conductivity study indicated that the electrical conduction in the material is a thermally activated process.
The variation of the AC conductivity with frequency at different temperatures obeys the Almond and West universal law. 相似文献
18.
D. M. Zashchirinskii L. I. Koroleva A. S. Morozov Yu. V. Dolzhenkova 《Physics of the Solid State》2011,53(2):316-319
The magnetocaloric effect ΔT has been studied by a direct method in two samples of the manganite Sm0.55Sr0.45MnO3, namely, a single crystal (sample A) and a ceramic sample (sample C). The temperature dependences of the ΔT effect of both samples exhibit a maximum at T
max = 143.3 K for the sample A and T
max = 143 K for the sample C. In these maxima, the values of the ΔT effect are 0.8 and 0.4 K in the magnetic field H = 14.2 kOe for the samples A and C, respectively. In addition, the ΔT(T) curve of the sample A has a minimum at T
min = 120 K, in which ΔT = −0.1 K. The maximum value of the ΔT effect increases with an increase in the magnetic field H in the range of magnetic fields up to 14.2 kOe, and the rate of this increase at H > 8 kOe is higher than that at H < 8 kOe. These features of the ΔT effect are explained by the presence of ferromagnetic and antiferromagnetic A- and CE-type clusters in the samples. 相似文献
19.
The phase transition during chemical lithium insertion into α-MoO3 was investigated by chemical analysis, X-ray diffraction (XRD) and electrochemical characterisation. The samples have been
prepared by reaction of various amounts of water-free lithium iodide with fine-particulate orthorhombic molybdenum trioxide
in n-hexane (non-aqueous media), which yielded materials with different Li/Mo ratio. XRD investigations of these materials proved
that the crystal structure of the layered α-MoO3 has been changed after the chemical lithiation. The phase transition ranged from 0.25 < x < 0.5 in Li
x
MoO3 upon chemical lithium insertion into α-MoO3. The XRD lines of lithium inserted phase Li
x
MoO3 grew at the expense of the XRD lines of the pristine α-MoO3 as lithium ions were chemically inserted until the disappearance of lines related to α-MoO3. The electrochemical performance of the lithiated samples is improved in comparison with the starting material (non-lithiated
α-MoO3). 相似文献
20.
The double perovskite Sr2NiMoO6 powders and ceramics were prepared by two different (conventional and precursor) solid-state reaction methods. The phase
structure was characterized by XRD and TEM techniques. It has been indicated that single-phase perovskite powders were obtained
when calcined in air at 1300°C. However, nano-particles of the size 30–60 nm have been found in powders prepared with the
precursor method, while those from the conventional route exhibit large irregular shaped particles with aggregation. The dielectric
properties (ε
r
and tanδ) were also examined in the sintered ceramics. The results showed the transition point at 280°C for conventional route, while
no clear phase change was observed in ceramics from the precursor route. These observations clearly indicate that the different
starting processes affected the phase formation behavior and the electrical properties of Sr2NiMoO6 ceramics. 相似文献