共查询到20条相似文献,搜索用时 31 毫秒
1.
L. Khusravbekov E. V. Charnaya S. D. Vasil’kov I. K. Rakhimov M. I. Salakhutdinov A. Kholov 《Physics of the Solid State》2007,49(3):516-518
This paper reports on the results of acoustic investigations of a NaBi(MoO4)2 crystal in the temperature range from 20 to 70°C. The temperature dependences of the velocity of longitudinal ultrasonic waves propagating along the crystallographic axes z and x are measured at a frequency of 4 MHz. The results obtained demonstrate that a structural phase transition occurs in the NaBi(MoO4)2 crystal at a temperature of 309 K. The experimental findings are consistent with the assumption that the observed phase transition is either a second-order ferroelastic transition or a first-order ferroelastic transition that is very close to being a second-order phase transition. 相似文献
2.
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
3.
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
4.
D. P. Kozlenko T. A. Chan S. E. Kichanov Z. Jirák L. S. Dubrovinsky B. N. Savenko 《JETP Letters》2011,92(9):590-594
The crystal structure and Raman spectra of Pr0.7Ca0.3MnO3 manganite at high pressures of up to 30 GPa and the magnetic structure at pressures of up to 1 GPa have been studied. A structural
phase transition from the orthorhombic phase of the Pnma symmetry to the high-pressure orthorhombic phase of the Imma symmetry has been observed at P ∼ 15 GPa and room temperature. Anomalies of the pressure dependences of the bending and stretching vibrational modes have
been observed in the region of the phase transition. A magnetic phase transition from the initial ferromagnetic ground state
(T
C = 120 K) to the A-type antiferromagnetic state (T
N = 140 K) takes place at a relatively low pressure of P = 1 GPa in the low-temperature region. The structural mechanisms of the change of the character of the magnetic ordering
have been discussed. 相似文献
5.
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
6.
D. P. Kozlenko T. A. Chan S. E. Kichanov A. V. Trukhanov S. V. Trukhanov B. N. Savenko 《Physics of Particles and Nuclei Letters》2011,8(10):1063-1065
The crystal and magnetic structures of manganite Pr0.7Ba0.3MnO3 have been studied at high pressures of up to 5.1 GPa and temperatures from 10 to 300 K by means of the neutron diffraction.
At normal pressure and a temperature T
C = 200 K, a ferromagnetic state forms in Pr0.7Ba0.3MnO3. At high pressures P ≥ 1.9 GPa and T < T
N ≈ 153 K, a new antiferromagnetic state of A-type have been observed. Under high pressure, the Curie temperature T
C increases with the characteristic quantity dT
C/dP ≈ 2.4 K/GPa. A possible reason for the appearance of an A-type antiferromagnetic phase in Pr0.7Ba0.3MnO3 at high pressures may be anisotropic uniaxial compression of oxygen octahedra along the b axis of the orthorhombic structure. 相似文献
7.
S. G. Jabarov D. P. Kozlenko S. E. Kichanov A. V. Belushkin B. N. Savenko R. Z. Mextieva C. Lathe 《Physics of the Solid State》2011,53(11):2300-2304
The crystal structure of lead titanate PbTiO3 was investigated by energy dispersive X-ray diffraction at high pressures up to 4 GPa in a temperature range of 300–950 K.
At the ambient conditions, the PbTiO3 structure is tetragonal with the space group P4mm (ferroelectric phase). A structural phase transition into the cubic phase with a space group Pm[`3]mPm\bar 3m is observed at T = 747 K. It was found that the phase transition temperature decreases upon applying the high pressure with the coefficient
dT
C
/dP = -65 K/GPa. Dependences of parameters and volume of the unit cell on the pressure and temperature was found, and the bulk
modulus and thermal expansion coefficients for the tetragonal and cubic phases of lead titanate have been calculated. 相似文献
8.
R. I. Zainullina N. G. Bebenin V. V. Ustinov D. A. Shulyatev 《Physics of the Solid State》2017,59(2):283-286
The temperature dependences of the velocity of longitudinal sound waves and the internal friction in a La0.82Ca0.18MnO3 single crystal with the Curie temperature T C = 181 K have been studied. As temperature decreases, the single crystal is shown to undergo the transition from the pseudocubic O* to the Jahn–Teller O’ phase at T ~ 254 K and the reverse transition from O’ to O* phase at T ~ 84 K. The velocity of sound and the internal friction in the O’ phase are found to be significantly smaller than those in the O* phase. 相似文献
9.
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
10.
A. Bhattacharyya S. Chatterjee S. Giri S. Majumdar 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,70(3):347-351
The magnetotransport and magnetic properties of the binary intermetallic compound Ho2In have been investigated. Clear signature of long range ferromagnetic order in the resistivity and the magnetization data
at TC = 85 K is observed. A further spin reorientation type transition is also apparent in our measured data at around Tt = 32 K. The sample exhibits negative magnetoresistance (peak value of –14% at 5 T) over a wide temperature range that extends
well above TC. Substantially large magneto-caloric effect is also observed in the sample (maximum value of –8.5 J kg-1K-1 for 0 → 5 T), which peaks around the TC of the sample. The observed magnetoresistance and magnetocaloric effect are related to the suppression of spin disorder by
an external magnetic field. Ho2In can be an interesting addition to the list of rare-earth based magnetic refrigerant materials showing magneto-caloric effect
across a second order phase transition. 相似文献
11.
Vladimir A. Kulbachinskii Boris M. Bulychev Vladimir G. Kytin Alexey V. Krechetov Valeriy P. Tarasov Elizaveta A. Konstantinova Yuriy A. Velikodnyi Yuriy B. Muravlev Andrey V. Zoteev 《Central European Journal of Physics》2010,8(1):101-112
Sodium fullerides Na
n
C60 (n = 2, 3) have been synthesized by a liquid phase reaction and investigated with X-ray diffraction (XRD), nuclear magnetic
resonance (NMR), electron paramagnetic resonance, and differential thermal analysis. XRD data indicate that the crystal structure
of Na2C60 at 300 K is face centered cubic (FCC). A phase transition from primitive cubic to FCC crystal structure has been observed
in this work in Na2C60 fulleride at 290 K. The transition is accompanied by the step-like change of paramagnetic susceptibility. The crystal structure
of Na3C60 is more complicated than, and different from, what has been reported in the literature. A nearly seven-fold increase of paramagnetic
susceptibility with increasing temperature has been observed in the Na3C60 fulleride at 240–260 K. In the same temperature range, a new line at about 255 ppm appears in the 23Na NMR spectrum, indicating a significant increase of electron density near the Na nucleus. The observed effect can be explained
by a metal-insulator transition caused by a structural transition. 相似文献
12.
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
13.
K. A. Shaykhutdinov S. I. Popkov A. N. Lavrov L. P. Kozeeva M. Yu. Kameneva V. V. Val’kov D. M. Dzebisashvili A. D. Fedoseev 《JETP Letters》2010,92(5):332-337
The behavior of the low-temperature specific heat C(T) for YBa2Cu3O6 + x
single crystals with the doping level corresponding to the normal phase has been studied by the relaxation technique at different
values of the applied magnetic field. It has been found that the C(T)/T plot exhibits such an anomaly as a steep increase with decreasing temperature from T about 4 K down to T ≤ 2 K (the minimum temperature value accessible in the experiment). The applied magnetic field as high as 9 T inverts this
anomaly and leads to a sharp drop in C(T)/T during cooling within the same temperature range. A model involving the Schottky-type centers formulated in this work and
the data on spin correlation functions has allowed us to calculate the temperature dependence of the specific heat, which
fits the experimental curves quite well. 相似文献
14.
A model of a crystal with a strong electron-phonon interaction that initiates a second-order phase transition has been considered.
The purpose of the study is to determine the temperature dependence of the thermodynamic potential of the symmetric phase
in the temperature range in the immediate vicinity of the transition temperature T
C for this model. The problem has been solved using the quantum Matsubara Green’s function approach, which takes into account
the influence of both thermal and quantum fluctuations. It has been demonstrated that fluctuation coherent deformations of
the crystal lattice with the same symmetry as in the ordered phase appear to be energetically favorable at T > T
C due to the interaction with the electronic subsystem. The results obtained have made it possible to construct the model of
the second-order phase transition near the Curie point T
C. 相似文献
15.
T. V. Drokina G. A. Petrakovskii L. Keller J. Schefer A. D. Balaev A. V. Kartashev D. A. Ivanov 《Journal of Experimental and Theoretical Physics》2011,112(1):121-126
The magnetic structure of the NaFeGe2O6 monoclinic compound has been experimentally investigated using the elastic scattering of neutrons. At a temperature of 1.6
K, an incommensurate magnetic structure has been observed in the form of an antiferromagnetic helix formed by a pairs of the
spins of the Fe3+ ions with helical modulation in the ac plane of the crystal lattice. The wave vector of the magnetic structure has been determined and its temperature behavior
has been studied. The analysis of the temperature dependences of the specific heat and susceptibility, as well as the isotherms
of the field dependence of the magnetization, has revealed the existence of not only the order-disorder magnetic phase transition
at the point T
N = 13 K, but also an additional magnetic phase transition at the point T
c = 11.5 K, which is assumingly an orientation phase transition. 相似文献
16.
V. A. Ryzhov P. L. Molkanov A. V. Lazuta V. V. Runov V. P. Khavronin I. O. Troyanchuk 《Bulletin of the Russian Academy of Sciences: Physics》2010,74(10):1477-1480
We present the results from studying the magnetic properties (linear and nonlinear susceptibilities and the depolarization
of polarized neutrons) of Nd1 − x
Ba
x
MnO3 manganite, x = 0.3, with Curie temperature T
C ≈ 140 K and dielectric-to-metal transition temperature T
DM ≈ 129 K. Its critical behavior corresponds to that of an isotropic 3-D ferromagnet at temperatures above T*≈ 144 K, but a strong nonlinear response in weak magnetic fields and depolarization are observed at temperatures below T*. It is shown that this nontraditional behavior is related to the generation of ferromagnetic clusters in the paramagnetic
matrix that form a conducting percolative network at temperatures near T
DM. 相似文献
17.
The Cr3+ EPR spectra of Li2Ge7O15 (LGO) crystals are analyzed in the temperature range of the ferroelectric phase transition. The temperature dependence of the local order parameter is determined from the measured splittings of the EPR lines in the polar phase. The experimental critical exponent of the order parameter β=0.31 in the range from the phase transition temperature T C to (T C -T) ~ 40 K corresponds to the critical exponent of the three-dimensional Ising model. Analysis of the available data demonstrates that, away from the phase transition temperature T C , the macroscopic and local properties of LGO crystals are characterized by a crossover from the fluctuation behavior to the classical behavior described in terms of the mean-field theory. The temperature dependence of the local order parameter for LGO: Cr crystals does not exhibit a crossover from the Ising behavior (β=0.31) to the classical behavior (β=0.5). This is explained by the defect nature of Cr3+ impurity centers, which weaken the spatial correlations in the LGO host crystal. The specific features of the critical properties of LGO: Cr3+ crystals are discussed within a microscopic model of structural phase transitions. 相似文献
18.
The parameters of the long-wavelength exciton band for Rb2CdI4 films are investigated in the temperature range 90–410 K. It is found that the Rb2CdI4 films undergo a sequence of phase transitions at temperatures Tc1=380 K (paraphase → incommensurate phase), Tc2=290 K (incommensurate phase → ferroelastic phase I), and Tc3 = 210 K (ferroelastic phase I → ferroelastic phase II). The parameters of the exciton band (such as the spectral position and the half-width) measured during heating and cooling of the Rb2CdI4 film differ significantly. This is especially true for the incommensurate phase. Upon heating of the incommensurate phase, the domain boundaries become frozen, whereas the cooling of this phase is accompanied by the generation of solitons and their pinning, which, in turn, results in a first-order phase transition at the temperature Tc2. It is revealed that the oscillator strength of the exciton band anomalously increases in the range of existence of commensurate phase I (Tc3<-T<-Tc2) due to ordering of the Rb2CdI4 crystal lattice. 相似文献
19.
A. V. Goltsev K. V. Dyakonov N. F. Kartenko L. A. Kulakova V. V. Popov É. Z. Yakhkind Ya. M. Mukovskii V. P. Dyakonov 《Physics of the Solid State》2005,47(11):2102-2105
The acoustical, resistive, and magnetic properties of a La0.75Sr0.25MnO3 lanthanum manganite single crystal are investigated in the temperature range involving the second-order magnetic phase transition. The acoustical measurements are performed by the pulse-echo method in the frequency range 14–90 MHz. It is found that, as the temperature decreases, the velocity of a longitudinal acoustic wave propagating along the [111] axis in the single crystal drastically increases at temperatures below the critical point of the magnetic phase transition. No dispersion of the acoustic velocity is revealed. A sharp increase in the acoustic velocity is accompanied by the appearance of an acoustical absorption peak. The observed effects are discussed with due regard for the interaction of acoustic waves with the magnetic moments of the manganese ions. 相似文献
20.
Aditya M. Vora 《Central European Journal of Physics》2008,6(2):253-262
The theoretical investigations of the superconducting state parameters (SSP) viz. electron-phonon coupling strength λ, Coulomb pseudopotential μ*, transition temperature T
C
, isotope effect exponent α and effective interaction strength N
O
V of six binary La100-C
Ga
C
(C = 16, 20, 22, 24, 26 and 28 at. %) metallic glasses have been reported using Ashcroft’s empty core (EMC) model potential
for the first time. Five local field correction functions proposed by Hartree (H), Taylor (T), Ichimaru-Utsumi (IU), Farid
et al. (F) and Sarkar et al. (S) are used in the present investigation to study the screening influence on the aforesaid properties. It is observed that
the electron-phonon coupling strength λ and the transition temperature T
C
are quite sensitive to the selection of the local field correction functions, whereas the Coulomb pseudopotential μ*, isotope effect exponent α and effective interaction strength N
O
V show weak dependences on the local field correction functions. The T
C
obtained from H-local field correction function are found in qualitative agreement with available experimental data and show
almost linear nature with the concentration (C) of ‘Ga’ element. A linear T
C
equation is proposed by fitting the present outcomes for H-local field correction function, which is in conformity with other
results for the experimental data. Also, the present results are found to be in qualitative agreement with other such earlier
reported data, which confirms the superconducting phase in the metallic glasses.
相似文献