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1.
First-principles calculations reveal that the fcc-to-hcp pressure-induced transformation in solid xenon proceeds through two mechanisms between 5 and 70 GPa. The dynamics of the phase transition involves a sluggish stacking-disorder growth at lower pressures (path I) that changes to a path involving an orthorhombic distortion at higher pressures (path II). The switchover is governed by a delicate interplay of energetics (enthalpy of the system for the structural stability) and kinetics (energy barrier for the transition). The two types of martensitic transformations involved in this pressure-induced structural transformation are a twinned martensitic transition at lower pressures and a slipped martensitic transition at higher pressures. 相似文献
2.
《Physica A》1988,150(1):159-171
By using recent Padé approximations for the Coulombic contribution and hard-core, Van der Waals and polarisation approximations for the atomic contribution, the thermodynamic functions for the nonideal xenon plasma are constructed. These formulae cover a large range of pressure and temperature. Single ionisation is studied by minimising the free energy with respect to the particle numbers. A second critical point is predicted. The coexistence line for the corresponding first order phase transition (weakly ionised plasma - strongly ionised plasma), the lines indicating the soft transition to a higher degree of ionisation at overcritical temperatures, as well as the border of the coexistence area are presented. The influence of the different interactions on the critical data is discussed. 相似文献
3.
The dependence of the martensite structure on the volume fraction of coherent inclusions inherited from aged austenite has been studied. An explanation for the considerable martensite lattice tetragonality in the case of thin martensite twins in comparison with their inclusion diameter is suggested. A reason for surface relief height decreasing for alloys with narrow temperature hysteresis of transformation has been discovered. 相似文献
4.
G. Fritsch V. V. Kokorin V. A. Chernenko A. Kempf I. K. Zasimchuk 《Phase Transitions》2013,86(4):233-240
Single crystals of different compositions in shape memory alloys Ni-Mn-Ga have been studied by electron and low temperature X-ray diffraction as well as by differential scanning calorimetry. It is shown that the cooling-induced martensitic phases are long-periodic ones modulated along the (110) directions by a transverse wave of atomic shifts with 5 and 7 atomic layers periodicity for the alloys studied exhibiting a martensitic transformation at 180 K and 446 K, respectively. The transformation heats appeared to be about 10 times different for both alloys. 相似文献
5.
6.
Jun-Hua Hao Zhi-Qiang Wu Zheng Wang Qing-Hua Jin Bao-Hui Li Da-Tong Ding 《Physica B: Condensed Matter》2009,404(20):3671-3673
First principles calculations of the total energy of CaTe as a function of unit cell volume have been carried out for the NaCl, MnP and CsCl structures on the basis of density functional theory (DFT). All these calculations are performed with the CRYSTAL06 program package. The sequence of high-pressure phases for CaTe transforms from NaCl phase to an intermediate state with a mixture of NaCl and MnP phases and then to the CsCl phase is obtained, which is in good agreement with the previous experimental results. Several structural properties (equilibrium lattice constant, bulk modulus, etc.) of NaCl structure have been calculated, which are also in agreement with the previous experimental results. 相似文献
7.
The influence of laser irradiation on the photoluminescence spectra of perfect C60 crystals in the orientationally disordered phase is investigated. It is shown that irradiation of the crystals with low-power
light for short durations at T=200 K produces radical changes in the luminescence spectrum. The pressure dependences of the spectral bands of the phototransformed
and initial (without irradiation) spectra differ significantly, indicating a photoinduced structural transformation of the
X centers responsible for the luminescence of C60. The phototransformed C60 crystals are stable against further exposure to light irradiation and pressure.
Pis’ma Zh. éksp. Teor. Fiz. 70, No. 12, 784–788 (25 December 1999)
Deceased. 相似文献
8.
T. Goryczka J. Lelatko B. Górka-Kostrubiec P. Ochin H. Morawiec 《The European physical journal. Special topics》2008,158(1):131-136
Off-stoichiometric Ni-Mn-Ga alloys, with various chemical compositions, were produced by melt-spinning technique. Transformation
behavior was studied by means of differential scanning calorimetery (DSC). Ribbons and bulks reveal reversible martensitic
transformation which occurs, dependently on chemical composition, in the range of temperatures: between 100°C and -150°C.
Transmission electron microscope and X-ray diffractometer were used for structure examination. Dependently on chemical composition
five-layered (10 M) or seven-layered (14 M) martensite was observed, whereas the parent phase shows the B2 structure. Due
to high cooling rate realized in melt-spinning technique some amount of amorphous phase was found. For all ribbons magnetization
was measured versus change of temperature as well as magnetic field. Due to relatively high density of dislocations lower
value of magnetization were obtained. 相似文献
9.
10.
利用第一性原理计算方法,探讨了体相CrI_3在低温斜方六面体结构(■,BiI_3-type)及高压单斜结构(C2/m,AlCl_3-type)的相变、电子结构和光学性质.计算结果显示,半导体CrI_3当压强增加到26.1GPa时,高压导致的晶格畸变致使CrI_3从相■变化到相C2/m;原子之间的错位位移,使导带处的能带发生下移,价带处的能带发生了一定程度的上移,导致带隙减小.两种相的光学性质进一步验证了这些特性. 相似文献
11.
A. Bulou A. Gibaud M. Debieche J. Nouet B. Hennion D. Petitgrand 《Phase Transitions》2013,86(1-4):47-53
Abstract The structural phase transition observed at ?13°C in KAlF4 is shown to be martensitic. The results of an investigation of the phonon spectrum by inelastic neutron scattering are reported. It is shown that the transition is preceded by the softening of a flat phonon branch. A model is proposed to explain how such a softening is related to the martensitic transition. 相似文献
12.
V. Barci H. El-Samman A. Gizon J. Gizon T. Bengtsson Y. Gono 《Zeitschrift für Physik A Hadrons and Nuclei》1985,321(2):353-357
The collective moment of inertia ? band (2) of123Cs produced in the115In+12C reaction at 80 MeV has been measured by gamma-gamma energy correlation techniques. The variations of ? band (2) with the rotational frequency are compared to those of122Xe and analysed in the frame of a cranked Nilsson-Strutinsky model. We conclude that the addition of one proton to the triaxial (γ?30°)122Xe core gives a final prolate-type nucleus123Cs withγ?0° above a rotational frequency?ω?0.55 MeV. 相似文献
13.
通过结构和磁性测量,研究了四元哈斯勒合金Ni50-xCoxMn38Sn12(x=1, 2, 4, 6, 8)的晶体结构和相变特征.结果表明,Co原子的掺杂不但没有影响三元哈斯勒合金Ni-Mn-Sn的原有结构,而且还增强了样品在奥氏体相的铁磁交换作用.此外,通过Maxwell方程计算了其中三种成分样品(x= 2, 4, 6)的磁熵变ΔSM
关键词:
哈斯勒合金
Ni-Co-Mn-Sn
马氏体相变
磁热效应 相似文献
14.
利用电弧炉制备了Ni50-xFexMn37In13(x=1, 3, 5) 多晶样品, 通过结构和磁性测量, 系统分析了Ni50-xFexMn37In13(x=1, 3, 5)样品的晶体结构和马氏体相变. 结果表明, 三样品在室温下呈现出了不同的晶体结构. 同时, 随着Fe含量的增加, 样品的马氏体相变温度急剧下降, 而铁磁性却逐渐增强. 研究了Fe3和Fe5样品在反马氏体相变过程中的磁电阻和磁卡效应. 在外加3 T的磁场下, 两样品在反马氏体相变区域所表现出的磁电阻效应分别约为-46%和-15%, 而等温熵变则约为6 J·kg-1·K-1和9.5 J·kg-1·K-1. 然而, 伴随非常宽的相变温跨和较小的磁滞损失, Fe3样品在反马氏体相变区域的净制冷量达到96 J·kg-1. 相似文献
15.
16.
Martensitic transformations and strain variation in
amorphous-crystalline thin ribbons of Ti50Ni25Cu25,
Ti40.7Hf9.5Ni44.8Cu5 and
Ti40.7Hf9.5Ni39.8Cu10 alloys were investigated. The
amorphous-crystalline state in the samples was produced by an interruption
of the isothermal crystallization in DSC apparatus. The volume fraction of
the crystalline phase Vcryst in the samples was varied from 10 to 100%. Transformation temperatures in amorphous-crystalline thin ribbons of
Ti50Ni25Cu25 alloy depended only slightly on the crystalline
volume fraction. On the contrary, the strong dependence of the martensitic
transformation temperatures on the volume of crystalline phase was obtained
in Ti40.7Hf9.5Ni44.8Cu5 and
Ti40.7Hf9.5Ni39.8Cu10 alloys. Moreover, it was found
that the intervals of the direct transformation are extremely narrow,
whereas the intervals of the reverse transformation are unusually wide. As
the crystalline volume fraction rises, both the direct transformation
interval and the reverse one decrease, and the transformation temperatures
increase. It was shown that increase of the Cu-content in
Ti40.7Hf9.5Ni49.8 -xCux (x = 5, 10%) alloys results
in decrease of the transformation temperatures, of the temperature interval
of the reverse transformation on heating and of the hysteresis, while the
temperature interval of the direct transformation on cooling widens 相似文献
17.
This paper studies the martensitic transformation in the Cu-doped NiMnGa alloys. The orthorhombic martensite transforms to L21 cubic austenite by Cu substituting for Ni in the Ni50-xCuxMn31Ga19 (x=2--10) alloys, the martensitic transformation temperature decreases significantly with the rate of 40 K per Cu atom addition. The variation of the Fermi sphere radius (kF) is applied to evaluate the change of the martensitic transformation temperature. The increase of kF leads to the increase of the martensitic transformation temperature. 相似文献
18.
We have measured the pressure dependence of the supersolid fraction by a torsional oscillator technique. Superflow is found from 25.6 bar up to 136.9 bar. The supersolid fraction in the low temperature limit increases from 0.6% at 25.6 bar near the melting boundary up to a maximum of 1.5% near 55 bar before showing a monotonic decrease with pressure extrapolating to zero near 170 bar. 相似文献
19.
Abstract Numerous studies have demonstrated the importance to include pressure as a kinetic parameter in the elucidation of inorganic reaction mechanisms. These studies have specially led to a better understanding and a systematic classification of solvent exchange and ligand substitution reactions of octahedral complexes of transition metal elements. The mechanistic picture for substution reactions on square planar complexes is well established and involves a concurrent bimolecular attack by solvent and the nucleophile on the substrate with a considerable discrimination among different entering groups. The search for factor promoting the conversion of the normal associative mode of activation into a dissociative process has then attracted much attention. Two attempts to induce dissociation, as studied by high-pressure NMR, are presented: one is to prevent the formation by means of sterically hindered ligands, the other one is to promote bond weakening at the leaving group. 相似文献