共查询到20条相似文献,搜索用时 32 毫秒
1.
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
2.
Yu. F. Markov E. M. Roginskii 《Bulletin of the Russian Academy of Sciences: Physics》2011,75(10):1317-1323
The Raman spectra of mixed Hg2(Br,I)2 and Hg2(Cl,Br)2 crystals were investigated. The multimode behavior of optical vibrations induced by presence of three types of molecules
(Hg2
Hal′2, Hg2
Hal″2 and Hg2
Hal′Hal″) in the crystals was observed experimentally and is discussed theoretically. Phase transition effects such as soft modes,
density of states, IR vibration branches, and anti- and ferroelectric nanoclusters induced by polar Hal′-Hg-Hg-Hal″ molecules and their immediate environment, were observed in the Raman spectra. 相似文献
3.
S. I. Vorob’ev E. I. Golovenchits V. P. Koptev E. N. Komarov S. A. Kotov V. A. Sanina G. V. Shcherbakov 《JETP Letters》2010,91(10):512-517
The magnetic properties of the EuMn2O5 multiferroic (samples consisting of single crystals and ceramic samples) have been investigated by the muon-spin-relaxation
(μSR) method in the temperature range of 10–300 K. Below the magnetic ordering temperature T
N = 40 K, the loss of the polarization of muons and the effect of the external magnetic field have been observed. Both phenomena
can be explained by an additional channel of the depolarization of muons owing to the appearance of muons in a medium with
a low electron density due to the charge separation process (the redistribution of the electron density in the phase transition
process). The “memory” phenomenon has been revealed in a sample in the external magnetic field; the memory relaxation time
depends on the size of the structure units of the samples (single crystals or ceramic grains). 相似文献
4.
I. V. Ovchinnikov T. A. Ivanova A. N. Turanov R. R. Garipov 《Physics of the Solid State》2009,51(10):2058-2063
Significant differences in the manifestation of spin-crossover properties of the mesogen compounds [FeL
2]X with oxysalicylidene-N′-ethyl-N-ethylenediamine ligands L and anions X = PF6− and SCH− have been found by means of electron paramagnetic resonance. The electron paramagnetic resonance data and the quantum-chemical
calculation within the density functional theory enables us to establish that the observed specific features are associated
with the incorporation of the SCH− ion into the first coordination sphere of the Fe(III) ion. The role of the transition of the material to the liquid-state
phase in the formation of a low-dimensional (two-dimensional) structure with stronger intermolecular interactions has been
revealed. 相似文献
5.
The fundamental and diffuse x-ray reflections from Brillouin zone-edge X points of the paraelastic phase of Hg2Cl2 crystals (whose integrated intensity is related to the order parameter and its fluctuations) were studied. Information was obtained on the temperature dependence of the order parameter and of diffuse scattering, and the critical exponents were determined. The conclusion is drawn that the ferroelastic phase transition in these crystals is close to the tricritical point. 相似文献
6.
Precision measurements of the real and imaginary parts of the microwave surface impedance Z ac(T) = R ac(T) + iX ac(T) of the conducting ac layers of the k-(BEDT-TTF)2Cu[N(CN)2]Br crystals in the temperature interval of 0.5 < T < 100 K have demonstrated a series of features: (i) the temperature course of the field penetration depth is close to linear Δλac(T)∞ΔX ac(T) in the superconducting state at T T c ∼ 11.5 K; (ii) the curves R ac(T) = X ac(T) coincide at T c < T < 40 K; (iii) the X ac(T) value at T > 40 K increases in comparison with R ac(T); (iv) the dependence R ac(T) at T > 40 K is nonmonotonic in thin crystals. These features of the impedance Z ac(T) with increasing T are interpreted in terms of (i) the d-type symmetry of the superconducting order parameter, (ii) normal skin effect, (iii) manifestations of the antiferromagnetic fluctuations, and (iv) the size effect. The electrodynamic parameters of k-(BEDT-TTF)2Cu[N(CN)2]Br have been determined. 相似文献
7.
L.?K.?Aminov I.?N.?Kurkin R.?M.?Rakhmatullin R.?B?ttcher A.?P?ppl S.?Sen 《Physics of the Solid State》2009,51(11):2282-2285
This paper reports on the results of EPR studies of mixed CeO2-Y2O3 crystals (including nanosized crystals) doped by gadolinium ions. It is revealed that the width of the line corresponding
to the allowed transition 1/2 ↔ −1/2 between the Kramers-conjugated states |±1/2〉 of the Gd3+ ion decreases with a decrease in the powder size from macrosizes to nanosizes. The observed dependence can be due to the
increase in the unit cell size during grinding of the samples. 相似文献
8.
A. I. Gusev 《Journal of Experimental and Theoretical Physics》2011,113(1):96-105
Symmetry analysis of the Pd6B monoclinic superstructure (space group C2/c) formed in the cubic (with the B1 structure) solid solution of boron in palladium (PdB
y
) has been carried out. The formation of this superstructure proceeds as a first-order phase transition via the disorder-order
channel including nine nonequivalent superstructure vectors of four stars {k
10}, {k
4}, {k
3}, and {k
0}. For the Pd6B monoclinic super-structure (space group C2/c), the distribution function for boron atoms is calculated and the interval of admissible values of the long-range order parameters
is defined. It is shown that the transition channel determined in this way coincides with the channel in which the M6X monoclinic superstructure (space group C2) is formed; therefore, the Pd6B superstructure can also be described in space group C2 to the same degree of accuracy. The higher symmetry of the monoclinic model (space group C2/c) suggests that it describes the structure of the Pd6B phase (Pd6B□5), as well as of mutually inverse phases M6X□5 and M6X5□, more adequately than the model with space group C2. It is shown that superstructures of the M6X□5 type (space groups C2/c, C2, C2/m, and P31) and inverse superstructures of the M6X5□ type with the same space groups have the positions of the nearest surrounding of metal atoms by two types of nonmetallic
sublattice sites located in the first and second coordination spheres. 相似文献
9.
The effects accompanying the ferroelastic phase transition in Hg2Br2 polycrystalline samples are compared in an x-ray diffraction study with similar effects observed to occur in Hg2Br2 single crystals. In particular, an analysis is made of the “orthorhombic” splitting of the basal plane reflections and the behavior with temperature of the Bragg and diffuse reflections from the X points of the Brillouin zone, which characterize the behavior of the order parameter and its fluctuations, respectively. Polycrystalline samples exhibit strong smearing of the phase transition effects originating from the existence of damaged surface layers and elastic and plastic strain fields which induce order parameter fluctuations over a wide temperature range. 相似文献
10.
The Bragg and diffuse reflections from different X points of the Brillouin zone boundary of the Hg2Br2 crystal in the paraphase are studied. The intensities of these reflections are related to the order parameter and its fluctuations. The temperature dependence of the order parameter and its fluctuations is analyzed, and the values of the critical exponents indicating closeness of the phase transition in these crystals to the tricritical point are determined. 相似文献
11.
V.M. Sreekumar R.M. Pillai B.C. Pai M. Chakraborty 《Applied Physics A: Materials Science & Processing》2008,90(4):745-752
The present study analyzes the morphological transformations of reaction products i.e., MgO, MgAl2O4 occurring during the reaction between SiO2 and Al-Mg alloy in Al-Mg-SiO2 composite processed by the liquid metallurgy technique. Different phases of platelet and hexagonal morphologies are detected
and their composition analysis by EDS has confirmed them as being transition phases existing between MgO, MgAl2O4 and Al2O3. This study has also revealed the gradual transformation of (i) MgO needles to octahedral MgAl2O4 through Mg-Al-Si-O and Mg-Al-O transition phases having platelet morphologies and (ii) MgAl2O4 to Al2O3 through hexagonal transition phases on holding of Al-5Mg-SiO2 and Al-1Mg-SiO2 composites respectively at 1023K. Fully developed α-Al2O3 crystals are not observed under the present experimental conditions, wherein the Mg content is well above the equilibrium
Mg content required for the formation of stable Al2O3 (<0.05 wt. %).
PACS 05.70.Np 相似文献
12.
A. I. Gusev 《Physics of the Solid State》2011,53(8):1664-1671
A symmetry analysis of the monoclinic (space group C2/c) Pd6B superstructure formed in the cubic (with structure B1) boron solid solution PdB
y
in palladium has been performed. The formation of this superstructure occurs as a first-order phase transition via the disorder-order
transition channel including nine nonequivalent superstructure vectors of four stars {k
10}, {k
4}, {k
3}, and {k
0}. For the monoclinic (space group C2) Pd6B superstructure, the distribution function of boron atoms has been calculated and the interval of admissible values of long-range
order parameters has been determined. It has been shown that the found transition channel is identical to the channel of the
formation of the monoclinic (space group C2/c) M
6
X superstructure; therefore, the Pd6B superstructure can be described with the same accuracy in space group C2. The higher symmetry of the monoclinic (space group C2/c) model suggests that it more accurately describes the structure of the phase Pd6B (Pd6B□5) and mutually inverse phases M
6
X□5 and M
6
X
5□ than the model with space group C2. It has been demonstrated that there are two types of the nearest environment of metal atoms with non-metal sublattice sites
arranged in the first and second coordination spheres in M
6
X□5-type superstructures (space groups C2/c, C2, C2/m, and P31) and in inverse M
6
X
5□-type superstructures with the same space groups. 相似文献
13.
E. Z. Kuchinskii I. A. Nekrasov Z. V. Pchelkina M. V. Sadovskii 《Journal of Experimental and Theoretical Physics》2007,104(5):792-804
Pseudogap phenomena are observed for the normal underdoped phase of different high-T
c cuprates. Among others, the Bi2Sr2CaCu2O8 − δ (Bi2212) compound is one of the most studied experimentally. To describe the pseudogap regime in Bi2212, we use a novel generalized
ab initio LDA + DMFT + Σk hybrid scheme. This scheme is based on the strategy of one of the most powerful computational tools for real correlated materials:
the local density approximation (LDA) + dynamical mean-field theory (DMFT). Conventional LDA + DMFT equations are here supplied
with an additional (momentum-dependent) self-energy Σk in the spirit of our recently proposed DMFT + Σk approach taking into account pseudogap fluctuations. In the present model, Σk describes nonlocal correlations induced by short-range collective Heisenberg-like antiferromagnetic spin fluctuations. The
effective single-impurity problem of the DMFT is solved by the numerical renormalization group (NRG) method. Material-specific
model parameters for the effective x
2 − y
2 orbital of Cu-3d shell of the Bi2212 compound, e.g., the values of intra-and interlayer hopping integrals between different Cu sites, the
local Coulomb interaction U, and the pseudogap potential Δ were obtained within the LDA and LDA + DMFT schemes. Here, we report
on the theoretical LDA + DMFT + Σk quasiparticle band dispersion and damping, Fermi surface renormalization, momentum anisotropy of (quasi)static scattering,
densities of states, spectral densities, and angular-resolved photoemission (ARPES) spectra, taking into account pseudogap
and bilayer splitting effects for normal (slightly) underdoped Bi2212 (δ = 0.15). We show that LDA + DMFT + Σk successfully describes strong (pseudogap) scattering close to Brillouin zone boundaries. Our calculated LDA + DMFT + Σk Fermi surfaces and ARPES spectra in the presence of pseudogap fluctuations are almost insensitive to the bilayer splitting
strength. However, our LDA-calculated value of bilayer splitting is rather small to describe the experimentally observed peak-dip-hump
structure. The results obtained are in good semiquantitative agreement with various recent ARPES experiments.
The article was submitted by the authors in English. 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.
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
16.
Depression of the ferroelastic phase transition in LiCsSO<Subscript>4</Subscript> by uniaxial stress
Zbigniew Tylczyński 《Central European Journal of Physics》2011,9(3):722-728
In the lithium-caesium sulphate crystal in the temperature range of ferroelastic phase transition, the uniaxial stress σ
X
induced changes in velocity and attenuation of the longitudinal ultrasonic wave propagating in the direction [010] are studied.
The phase transition is close to the three-critical point and the critical exponent is κ = 0.27 ± 0.02. The stress applied drastically decreases the stepwise change in the wave velocity at T
C
up to its disappearance at 2 MPa. In the temperature range between T
C
and T
C
− 6 K, the stress leads to an increase in the wave velocity and a decrease in its attenuation. This range was interpreted
as that of co-existence of ferroelastic and incommensurate ordering, in which the stress influences the density of solitons
leading to stiffening of the crystal lattice. 相似文献
17.
Large low-field-induced magnetic entropy changes, ΔS
M, are observed in La0.67Ca0.33MnO3 and La0.67Ca0.33Mn0.96Fe0.04O3 single crystals. The peaks of ΔS
M broadened asymmetrically to high temperatures under higher magnetic fields for two materials should be attributed to the
first-order magnetic phase transition at T
c. A small amount of iron doping results in an increase in the refrigerant capacity of the material though the magnetic entropy
change decreases. The discovery of excellent magnetocaloric features of these single crystals in the low magnetic field can
provide some ideas for exploring novel magnetic refrigerants operating under permanent magnet rather than superconducting
one as magnetic field source.
Supported by the State Key Project of Fundamental Research (Grant No. 2005CB724402), and the National Natural Science Foundation
of China (Grant No. 50672126)
Contributed by CHENG ZhaoHua 相似文献
18.
A. Yu. Mollaev I. K. Kamilov R. K. Arslanov T. R. Arslanov U. Z. Zalibekov V. M. Novotortsev S. F. Marenkin 《JETP Letters》2010,91(9):478-480
The magnetic susceptibility χ/χ0 and the longitudinal Δρ
zz
/ρ0 and transverse Δρ
xx
/ρ0 magnetoresistances have been measured as functions of the hydrostatic pressure P ≤ 7 GPa at room temperature in the high-temperature ferromagnetic semiconductor Cd0.7Mn0.3GeAs2 with a chalcopyrite structure and the Curie temperature T
c = 355 K. A pressure-induced metamagnetic transition from the low-magnetization state to the high-magnetization state has
been observed in Cd0.7Mn0.3GeAs2 near the magnetic ordering temperature. This transition is accompanied by the hysteresis of the magnetic susceptibility and
magnetoresistance. 相似文献
19.
V. R. Galakhov M. Neumann D. G. Kellerman 《Applied Physics A: Materials Science & Processing》2009,94(3):497-500
X-ray absorption, resonant X-ray emission, and X-ray photoelectron spectroscopical methods have been applied for the study
of the electronic structure of defective lithium cobaltites Li
x
CoO2 (0.6≤x≤1.0). Resonant O K
α X-ray emission spectra of LiCoO2 showed localized excitonic states due to a dd transition between occupied and unoccupied Co 3d states. On the base of measurements of Co 3s X-ray photoelectron, Co 2p, and O 1s X-ray absorption spectra, it was established that in defective cobaltites the electronic holes are localized mainly in O
2p states. An evidence of phase separation in Li
x
CoO2 has been found. It was shown that the semiconductor-to-metal transition in Li
x
CoO2 (x<0.76) at about 160 K is not accompanied by changes in the Co 3d electronic configuration which remains 3d
6. 相似文献
20.
V. M. Gaba V. I. Stadnyk Z. O. Kogut R. S. Brezvin 《Journal of Applied Spectroscopy》2010,77(5):648-653
The influence of uniaxial mechanical stresses directed along the principal crystallophysical axes on refractiveindex temperature
dependences in K2ZnCl4 crystals was studied. It is established that the refractive indices ni are quite sensitive to uniaxial stresses. Significant
baric shifts of the paraphase–incommensurate–commensurate phase transition points to different temperature regions were observed,
which is due to the effect of the uniaxial stress on the K2ZnCl4 crystal structure. It is found that applying uniaxial pressure increases the value of the temperature hysteresis of the commensurate–incommensurate
phase transition. 相似文献