共查询到20条相似文献,搜索用时 15 毫秒
1.
《Journal of Physics and Chemistry of Solids》2001,62(5):897-902
The internal friction of KOH-doped ice single crystals has been measured as a function of temperature in the frequency range from 0.1 to 20 Hz and compared with data on dielectric relaxation. There are two damping peaks, namely the α peak at around 85 K and the β peak at around 170 K. The Arrhenius relation of the α peak is almost equivalent to that for dielectric relaxation at the same temperatures. However, a relaxation corresponding to the β peak is not found in the dielectric measurements. The α peak is attributed to the rotation of water molecules by OH− ions, which occupy H2O sites. The β peak arises from the presence of the KOH, but no mechanism is offered at this stage. 相似文献
2.
We consider phase transitions in 2D XY-like systems with long-range dipole-dipole interactions and demonstrate that BKT-type
phase transition always occurs separating the ordered (ferroelectric) and the disordered (paraelectric) phases. The low-temperature
phase corresponds to a thermal state with bound vortex-antivortex pairs characterized by linear attraction at large distances.
Using the Maier-Schwabl topological charge model, we show that bound vortex pairs polarize and screen the vortex-antivortex
interaction, leaving only the logarithmic attraction at sufficiently large separations between the vortices. At higher temperatures
the pairs dissociate and the phase transition similar to BKT occurs, though at a larger temperature than in a system without
the dipole-dipole interaction. 相似文献
3.
Victor I. Sokolov Sergey F. Dubinin Vitaliy D. Parkhomenko Vladimir V. Gudkov Alexander V. Tkach Nikita B. Gruzdev 《Solid State Communications》2004,129(8):507-510
Neutron diffraction and ultrasonic experiments as well as measurements of heat conductivity in ZnSe and Zn1−xNixSe (x=0.0025) semiconductors have been carried out. As a result, a structural transition induced by Ni impurity has been found at 相似文献
4.
G Briganti V Mazzacurati M.A Ricci G Signorelli M Nardone 《Solid State Communications》1982,42(7):493-496
High resolution Raman spectra of ice Ih single crystal in the frequency range 0–30 cm?1 are reported, at various temperatures. For the first time evidence is given for the existence of a Lorentzian central component in all scattering configurations. A polarization analysis of the spectra clearly shows that the central mode cannot be ascribed to the high frequency tails of the Brillouin doublet, nor to the disorder induced phonon background even accounting for renormalization of the phonon propagator. The epectral features indicate the existence of a direct coupling between the light and some relaxation mechanism of the crystal.A model is suggested to account for the excess scattering and for the activation of the acoustic phonon density of states. 相似文献
5.
6.
Previous work on Ba2TiGe2O8 crystals has shown an unusual low-temperature (~ 223 K on cooling, ~ 273 K on heating) phase transition. Precession x-ray photographs on Ba2TiGe2O8 single crystals show an incommensurate modulation along b*, and, for the first time, also along a*. Single crystal intensity data confirm the average structure in space group Cmm2. There is positional disorder in the pyrogermanate groups, and this is the probable cause for the modulated structure. The low-temperature phase transition is proposed to be a lock-in transition, with the modulation along a* locking in at a value of 1/3. Several properties, as well as other unusual features of the low-temperature phase transition, are discussed in light of the proposed lock-in transition. Domain studies show that the ferroelastic domains are unstable in the low-temperature phase. 相似文献
7.
Roy SB Perkins GK Chattopadhyay MK Nigam AK Sokhey KJ Chaddah P Caplin AD Cohen LF 《Physical review letters》2004,92(14):147203
First order ferromagnetic (FM) to antiferromagnetic (AFM) phase transition in doped CeFe2 alloys is studied with the micro-Hall probe technique. Clear visual evidence of magnetic phase coexistence on micrometer scales and the evolution of this phase coexistence as a function of temperature, magnetic field, and time across the first order FM-AFM transition is presented. Such phase coexistence and metastability arise as a natural consequence of an intrinsic disorder-influenced first order transition. The generality of these phenomena involving other classes of materials is discussed. 相似文献
8.
Abstract Optical effects of the first and second order with respect to the order parameter (1 is antiferromagnetic vector) have been studied in Cr2O3 around its phase transition at TN = 306 K from the antiferromagnetic to paramagnetic state. The magnetic linear birefringence is characterized by a rather large magnitude Δn sp ? 10?3 and by a large contribution of fluctuations of the order parameter to the birefringence. The study of the nonreciprocal optical rotation induced by an electric field has shown that the phase transition has a well defined first-order character. This result is also supported by the observation of a nonlinear (quadratic in the electric field) nonreciprocal rotation in a narrow temperature region ΔT = 0.15 K around TN . The temperature variation of the order parameter l(T) below TN is well described by a power low l where τβ = (TN - T)/TN and β = 0.355. We also observed a very reproducible effect of the rotation of the optical indicatrix in opposite directions for two types of antiferromagnetic domains. The possible explanation of this effect could be related to the so-called gyrotropic birefringence, an effect related to kili terms in the dielectric permeability. 相似文献
9.
The diffusion of He through both H2O and D2O amorphous solid water (ASW) has been measured between 55 and 110 K. We find the diffusion rate is dependent on the isotopic composition of the ASW lattice. This lattice isotope effect is the "inverse" of a normal isotope effect in that diffusion is faster in the heavier (D2O) isotope. Transition state theory calculations show that the inverse isotope effect is due to a tight transition state and predominantly arises from the zero-point vibrational energy associated with the frustrated rotational modes of water in the lattice. 相似文献
10.
The heat capacity of thallium dihydrogen phosphate was measured from 12 to 300 K. A lambda anomaly with a small first order discontinuity was found at 229.76 K with the integrated enthalpy and entropy changes equal to 370 J mol-1 and 1.8 J K-1 mol-1, respectively. The entropy discontinuity at the first order transition is 0.25 J K-1 mol-1. The Landau theory of phase transitions of the second kind reproduces closely the temperature dependence of the anomalous heat capacity. This, together with the small discontinuity in the entropy, implies that the phase transition is close to a classical critical point of higher order. The relative dielectric permittivity ?r(b) along the b-axis at 1 kHz is anomalously large and strongly temperature dependent, while the ?r(a1) and ?r(c) are not. A broad absorption centered at 1700 cm-1 was observed in the infrared absorption spectrum, indicating presence of hydrogen bonding of the length ~ 0.25 nm. Occurrence of a phase transition at 127 ± 2 K was suggested by differential thermal analysis of thallium dideuterium phosphate. 相似文献
11.
12.
13.
K. E. Kamentsev A. A. Bush E. A. Tishchenko S. A. Ivanov M. Ottoson R. Mathieu P. Nordblad 《Journal of Experimental and Theoretical Physics》2013,117(2):320-326
The results of thermogravimetric, X-ray diffraction, and electrical studies of LiCu2O2 single crystals in the temperature range 300–1100 K are presented. A reversible first-order phase transition between the orthorhombic and tetragonal phases is found to occur in these single crystals at T = 993 K. A pronounced peak on a differential thermal analysis curve and jumps in the unit cell parameters and the electrical resistivity are detected at the phase-transition temperature. The data on the crystal structure of LiCu2O2 and the phase transition-induced change in the entropy determined in this work are used to conclude that the revealed phase transition is caused by the ordering-disordering of Li+ and Cu2+ cations in their structural positions. 相似文献
14.
Yukihiro Yoshimura 《高压研究》2013,33(1):172-177
I have examined the changes in in situ Raman spectra of ice in aqueous LiOH solution as a function of pressure at liquid nitrogen temperature (77 K). Here, I have shown the possibility that ice in aqueous LiOH solution transforms to a high-density amorphous like phase at around 0.9 GPa. I have mentioned that the results show differences strongly depending on the salts dissolved in the aqueous solutions. 相似文献
15.
Brillouin spectroscopy has been used to study the local acoustic properties of the crystal grain boundary region in a naturally formed bicrystalline sample of ice Ih at - 16°C. Spectra from the boundary region show a distinct and unexpected asymmetry of the upshifted versus the downshifted longitudinal Brillouin components. 相似文献
16.
17.
《Journal of magnetism and magnetic materials》1987,66(1):17-22
The antiferromagnetic compound GeCo2O4 exhibits a magnetic phase transition characterized by thermal hysteresis of the susceptibility versus temperature curve and by a diffuse neutron scattering with a small correlation length. The data are compared to the expected first-order phase transition of the n ≥ 4 component vector models. 相似文献
18.
《Physics letters. A》2020,384(17):126375
Based on the first-principle calculations and k⋅p effective model analysis, we predicted a new topological semimetal (TSM) MgBi2O6. Without spin-orbit-coupling (SOC) and under the generalized-gradient-approximation (GGA), MgBi2O6 is a nodal-line semimetal. When the exchange-correlation energy was changed to HSE06, MgBi2O6 was trivial insulator in the equilibrium volume, but it became TSM under 7% hydrostatic tensile strain. MgBi2O6 might be an important platform to study the topological properties because of the two following advantages for measurements: (1) The nodal line, drumhead-liked surface state and Fermi Arc are very closely to the Fermi level; (2) The band structure is very “clean” (no other bulk bands except the related inverted conduction and valence bands around the Fermi level), which avoids the surface states been embedded into the bulk states. 相似文献
19.
The spinel-type LiMn$_{2}$O$_{4}$ is a promising candidate as cathode material for rechargeable Li-ion batteries due to its good thermal stability and safety. Experimentally, it is observed that in this compound there occur the structural phase transitions from cubic ($Fd\bar{3}m)$ to tetragonal ($I4_{1}/{amd}$) phase at slightly below room temperature. To understand the phase transition mechanism, we compare the Gibbs free energy between cubic phase and tetragonal phase by including the configurational entropy. Our results show that the configurational entropy contributes substantially to the stability of the cubic phase at room temperature due to the disordered Mn$^{3+}$/Mn$^{4+}$ distribution as well as the orientation of the Jahn-Teller elongation of the Mn$^{3+}$O$_{6}$ octahedron in the the spinel phase. Meanwhile, the phase transition temperature is predicted to be 267.8 K, which is comparable to the experimentally observed temperature. These results serve as a good complement to the experimental study, and are beneficial to the improving of the electrochemical performance of LiMn$_{2}$O$_{4}$ cathode. 相似文献
20.
We present a first-principles study of the structure and energetics of Bjerrum defects in ice Ih and compare the results to experimental electrical conductivity data. While the DFT result for the activation energy is in good agreement with experiment, we find that its two components have quite different values. Aside from providing new insight into the fundamental parameters of the microscopic electrical theory of ice, our results suggest the activity of traps in doped ice in the temperature regime typically assumed to be controlled by the free migration of L defects. 相似文献