共查询到20条相似文献,搜索用时 234 毫秒
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E.V. Boldyreva Yu.A. Chesalov T.N. Drebushchak E.N. Kolesnik Yu.A. Kovalevskaya I.E Paukov 《Phase Transitions》2013,86(7):497-506
The crystals and the powder samples of β-alanine were studied in the wide temperature range by adiabatic calorimetry, differential scanning calorimetry, IR- and Raman spectroscopy and X-ray diffraction. No phase transitions could be observed. A small anomaly observed at about 256 K in the Cp(T) dependences measured for the samples re-crystallized from water was shown to be due to the presence of a small (about 0.14% of the total sample mass) amount of solvent inclusions. This anomaly was not observed in the solvent-free samples, either powders or single crystals. 相似文献
3.
Q.S. Hu H. Zheng 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,28(3):255-262
A new perturbation approach is developed for single- and many-electron Holstein model in one-, two-, and three-dimension.
The results show that this approach has a good agreement with the Migdal theory in the adiabatic regime when the coupling
is moderate (λ < 1), but with the Lang-Firsov theory in the antiadiabatic regime ( ω/W≫ 1). In the intermediate region, our approach can describe the transition from a large-polaron Fermi-liquid to the small-polaron,
and this transition may be discontinuous in adiabatic regime, which means a phase transition appears in many-electron system.
In single-electron case, we eliminate the abrupt transition using the degenerate perturbation theory, and the calculated ground
state energy and effective mass are successfully compared with those of previous authors. Besides, the method has the advantage
of requiring little computational effort.
Received 27 December 2001 / Received in final form 8 April 2002 Published online 31 July 2002 相似文献
4.
《Solid State Communications》1986,59(5):257-259
Dielectric constant and differential scanning calorimetry measurements have shown a transition to a new phase in both KOH (at 233 K) and KOD (at 257 K); the shape of the dielectric anomaly suggests electrical ordering at low temperature. Structural parameters obtained from high resolution neutron powder diffraction data demonstrate the ordering to be antiferroelectric. A preliminary account is given of the structures at 293 K and 77 K. 相似文献
5.
Mariager SO Pressacco F Ingold G Caviezel A Möhr-Vorobeva E Beaud P Johnson SL Milne CJ Mancini E Moyerman S Fullerton EE Feidenhans'l R Back CH Quitmann C 《Physical review letters》2012,108(8):087201
We use time-resolved x-ray diffraction and magneto-optical Kerr effect to study the laser-induced antiferromagnetic to ferromagnetic phase transition in FeRh. The structural response is given by the nucleation of independent ferromagnetic domains (τ(1)~30 ps). This is significantly faster than the magnetic response (τ(2)~60 ps) given by the subsequent domain realignment. X-ray diffraction shows that the two phases coexist on short time scales and that the phase transition is limited by the speed of sound. A nucleation model describing both the structural and magnetic dynamics is presented. 相似文献
6.
High-energy x-ray diffraction study on phase transition asymmetry of plastic crystal neopentylglycol
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As a prototype material of colossal barocaloric effects, neopentylglycol is investigated by combining high-precision differential scanning calorimetric measurement and high-energy x-ray diffraction measurement. The diffraction data at constant temperatures indicate a first-order phase transition with thermal hysteresis as well as the phase transition asymmetry, specifically, the phase transition is completed faster at cooling than at heating. The analysis of resulting pair distribution function confirms the intermolecular disorder in the high-temperature phase. The phase transition asymmetry is quantitatively characterized by time-resolved x-ray diffraction, which is in agreement with the thermal measurement. Also, such an asymmetry is observed to be suppressed at high pressures. 相似文献
7.
Badro J Fiquet G Struzhkin VV Somayazulu M Mao HK Shen G Le Bihan T 《Physical review letters》2002,89(20):205504
We present a new method to separate the crystallographic and electronic phase transitions in hematite using x-ray emission spectroscopy and x-ray diffraction. Our observations, based on the behavior of a metastable high-pressure phase in the stability domain of the low-pressure phase, show that the electronic transition is preempted by the crystallographic transition. The former occurs only afterwards in the high-pressure phase, possibly as a result of a Mott transition. The idea that the electronic transition drives the transition in hematite is therefore invalidated. Such methods should help elucidate the mechanics and the driving forces behind a number of first-order high-pressure phase transitions. 相似文献
8.
《中国物理快报》2016,(9)
The in situ high-pressure behavior of the semiconductor antimony trioxide(Sb_2O_s) is investigated by the Raman spectroscopy techniques and angle-dispersive synchrotron x-ray powder diffraction in a diamond anvil cell up to31.5 and 30.7 GPa,respectively.New peaks observed in the external lattice mode range in the Raman spectra at 13.5 GPa suggest that the structural phase transition occurs.The group mode(140 cm~(-1)) in Sb_2O_3 exhibits anomalous pressure dependence;that is,the frequency decreases gradually with the increasing pressure.High pressure synchrotron x-ray diffraction measurements at room temperature reveal that the transition from the orthorhombic structure to high-pressure new phase occurs at about 14.2 GPa,corresponding to the softening of the group optic mode(140 cm~(-1)). 相似文献
9.
We report a pressure-dependent investigation of KMnF(3) by x-ray diffraction up to 30 GPa. The results are discussed in the framework of Landau theory and in relation to the isostructural phase transition in SrTiO(3). The phase transition temperature near 186 K in KMnF(3) shifts to room temperature at a critical pressure of P(c) = 3.4 GPa; the pressure dependence of the transition point follows ΔP(c)/ΔT(c) = 0.0315 GPa K(-1). The transition becomes second order under high pressure, close to the tricritical point. The phase transition is determined by the rotation of MnF(6) octahedra with their simultaneous expansion along the rotation axis. The rotation angle was found to increase to 10.5° at 24 GPa. An additional anomaly was observed at higher pressure around 25 GPa, suggesting a further phase transition. 相似文献
10.
The magnetocaloric properties of the Gd 5 Ge 2.025 Si 1.925 In 0.05 compound have been studied by x-ray diffraction,magnetic and heat capacity measurements.Powder x-ray diffraction measurement shows that the compound has a dominant phase of monoclinic Gd5Ge2Si2-type structure and a small quantity of Gd 5(Ge,Si) 3-type phase at room temperature.At about 270 K,this compound shows a first order phase transition.The isothermal magnetic entropy change(△SM) is calculated from the temperature and magnetic field dependences of the magnetization and the temperature dependence of MCE in terms of adiabatic temperature change(△Tad) is calculated from the isothermal magnetic entropy change and the temperature variation in zero-field heat-capacity data.The maximum S M is 13.6 J·kg-1·K-1 and maximum △Tad is 13 K for the magnetic field change of 0-5 T.The Debye temperature(θD) of this compound is 149 K and the value of DOS at the Fermi level is 1.6 states/eV·atom from the low temperature zero-field heat-capacity data.A considerable isothermal magnetic entropy change and adiabatic temperature change under a field change of 0-5 T jointly make the Gd5Ge2.025Si1.925 In 0.05 compound an attractive candidate for a magnetic refrigerant. 相似文献
11.
B. A. Strukov E. P. Ragula S. V. Arkhangel’skaya I. V. Shnaidshtein 《Physics of the Solid State》1998,40(1):94-95
Using precise vacuum adiabatic calorimetry it is shown that the specific heat of the model ferroelectric crystal TGS does
not exhibit the logarithmic singularity predicted by theory above the transition temperature. This discrepancy with the available
specific heat data in the literature, obtained by dynamical measurements, is discussed with allowance for the maximum attainable
measurement accuracy (0.3%) in the static adiabatic experiment.
Fiz. Tverd. Tela (St. Petersburg) 40, 106–108 (January 1998) 相似文献
12.
Rouquette J Haines J Al-Zein A Papet P Damay F Bourgeois J Hammouda T Doré F Maignan A Hervieu M Martin C 《Physical review letters》2010,105(23):237203
The electronic ferroelectric lutetium ferrite (LuFe(2)O(4)) was studied by x-ray diffraction as a function of pressure. Pressure is shown to induce an irreversible rhombohedral to orthorhombic transition leading to a supercell determined by the combination of electron and synchrotron x-ray diffraction. This new configuration is proposed to be charge ordered in agreement with the results of resistivity measurements. 相似文献
13.
A. S. Paranjpe 《Phase Transitions》2013,86(3):115-126
Abstract Differential scanning calorimetric investigations have been conducted on sucrose solutions for temperatures T<?100°C and in the sucrose concentration range 74 < c < 97. A novel method is adopted for sample preparation. For c > 92, the room temperature phase is amorphous, as indicated by its x-ray diffraction pattern. A melting transition is reported for the first time for these concentrations. A second-order phase transition is recorded for T < 0°C, which is clearly observed only during heating cycles, indicating a continuous phase transition during cooling. These transitions have not been reported so far, suggesting that the phase formed due to the procedure adopted for sample preparation may be different from that reported in the literature. 相似文献
14.
A large amount of toluene can be absorbed into the 1-dimensional tunnels in copper(II) trans-1,4-cyclohexane dicarboxylate (Cu(trans-1,4-OOCC6H10C)) at room temperature, and it can be desorbed by evacuation at elevated temperatures. The reversible absorption/desorption behavior of toluene was studied by magnetic susceptibility measurements using SQUID magnetometer and by powder X-ray diffractometry with high-energy synchrotron radiation at SPring-8, Japan. The first order phase transition was observed at 160 K in the magnetic susceptibility curve for the empty (non-absorbed or desorbed) sample, and the structural difference between the low and high temperature phases was detected in the powder X-ray diffraction patterns. On the other hand, no phase transition was observed in fully toluene-absorbed sample, and the structure was similar to that of the low temperature phase of the empty sample. The absorption/desorption behavior observed in the present study coincides with the results of heat capacity measurements by adiabatic calorimetry reported previously. 相似文献
15.
B K Sadashiva 《Pramana》1999,53(1):213-222
We describe briefly some results obtained on both chiral and achiral compounds exhibiting chiral mesophases. We report the
first example of a single component system exhibiting the undulated twist grain boundary C* or UTGB
C* phase. Preliminary results concerning a few achiral compounds composed of banana-shaped molecules exhibiting a mesophase
is reported. They have been investigated by polarized light optical microscopy, differential scanning calorimetry and x-ray
diffraction studies. 相似文献
16.
Pozo-Navas B Raghunathan VA Katsaras J Rappolt M Lohner K Pabst G 《Physical review letters》2003,91(2):028101
We have observed a discontinuous unbinding transition of lipid bilayer stacks composed of phosphatidylethanolamine and phosphatidylglycerol using x-ray diffraction. The unbinding is reversible and coincides with the main (L(beta)-->L(alpha)) transition of the lipid mixture. Interbilayer interaction potentials deduced from the diffraction data reveal that the bilayers in the L(beta) phase are only weakly bound. The unbinding transition appears to be driven by an abrupt increase in steric repulsion resulting from increased thermal undulations of the bilayers upon entering the fluid L(alpha) phase. 相似文献
17.
A thermal study of the liquid crystals tridecylcyanobiphenyl and tetradecylcyanobiphenyl has been performed by means of adiabatic scanning calorimetry. Both compounds exhibit only the smectic-A mesophase between the normal liquid and the crystalline phase and their phase transitions are strongly first order. A summary of the enthalpies and transition temperatures for all the smectic homologues of the cyanobiphenyl family is given, based on high-resolution measurements of the present work and previous studies. 相似文献
18.
A new extended solid nitrogen,referred to as post-layered-polymeric nitrogen(PLP-N,or Panda-N),was observed by further heating the layered-polymeric nitrogen(LP-N) to above 2300 K at 161 GPa.The new phase is found to be very optically transparent and exhibits ultra-large d-spacings ranging from 2.8 to 4.9 A at 172 GPa,suggesting a lower-symmetry large-unit-cell 2D chain-like or OD cluster-type structure with wide bandgap.However,the observed x-ray diffraction pattern and Raman scattering data ca... 相似文献
19.
Evgueni Antipov Yuri Podolsky Nikolai Platé Manfred Stamm Erhard W. Fischer 《Journal of Macromolecular Science: Physics》2013,52(4):431-450
Abstract The structure, phase composition, and temperature behavior of two trans-1,4-polybutadienes (TPBs) were studied by means of x-ray scattering and differential scanning calorimetry (DSC) techniques. The two samples examined were (1) PB synthesized using an immobilized titanium-magnesium catalyst and (2) a random copolymer based on PB prepared with a homogeneous vanadium-containing catalyst used as a reference material. It was found that the nascent structure of the first PB involves three phases: crystalline, mesomorphic (low-temperature form), and amorphous. In the vicinity of 65°C, a first-order phase transition occurs. The system becomes biphasic and contains the high-temperature form of the mesophase, as well as the amorphous phase, component. Above 165°C, the polymer melts to form a single-phase isotropic melt with a structure typical of liquids. The lateral dimension of crystallites reversibly changes at the crystal-mesophase transition. It is suggested that during annealing of the mesophase formed by cooling of the isotropic melt, the chains acquire an extended conformation. Loss of regularity of the structure of macromolecules of TPB causes a reduction of phase transition temperatures, an increase of the imperfection of the crystalline phase, and a contraction of the temperature range of existence of the mesophase. 相似文献
20.
Wakabayashi Y Bizen D Nakao H Murakami Y Nakamura M Ogimoto Y Miyano K Sawa H 《Physical review letters》2006,96(1):017202
A novel structure of orbital ordering is found in a Nd0.5Sr0.5MnO3 thin film, which exhibits a clear first-order transition, by synchrotron x-ray diffraction measurements. Lattice parameters vary drastically at the metal-insulator transition at 170 K (= T(MI)), and superlattice reflections appear below 140 K (= T(CO)). The electronic structure between T(MI) and T(CO) is identified as A-type antiferromagnetic with a d(x2-y2) ferro-orbital ordering. The new type of antiferro-orbital ordering characterized by the wave vector (1/4 1/4 1/2) in cubic notation emerges below T(CO). The accommodation of the large lattice distortion at the first-order phase transition and the appearance of the novel orbital ordering are brought about by the anisotropy in the substrate, a new parameter for the phase control. 相似文献