共查询到20条相似文献,搜索用时 31 毫秒
1.
R. Clérac M. Fourmigué J. Gaultier Y. Barrans P.A. Albouy C. Coulon 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,9(3):445-459
The physical properties of paramagnetic Mo(V) organometallic radical cation salts, , are investigated through the study of two series of solid solutions incorporating two kinds of anions ( or ). The combination of EPR and X-ray diffraction is used to specify the nature of the structural phase transitions which occur
in the paramagnetic phase and to determine the corresponding (
T
,
x
) phase diagrams. Finally, antiferromagnetic resonance is studied to probe the low temperature antiferromagnetic ground state.
In the last part of the paper, the observed complex phase diagram is analyzed by considering a compressible model with at
least two independent modes of compression. We conclude that the larger compressibilities are associated with the smaller
anions.
Received 5 August 1998 相似文献
2.
D. Ď. Obadović A. Vajda M. Stančić S. Jovanović-šanta J. Petrović D. Lazar 《Phase Transitions》2013,86(4):509-519
The synthesis of new chiral seco-estrone derivatives is presented, as well as their influence on the phase transition of binary mixtures of cholesteryc liquid crystals. The new chiral derivatives do not posses any liquid crystalline phases and were synthesized in several synthetic steps, starting from estrone. We have studied the mixtures of cholesteryl non-anoate (40%) with cholesteryl myristate (40%) and addition of new chiral derivatives 3 4, or 5 (20%). It was concluded that the addition of chiral derivative 3 to the binary mixture stabilizes smectic A and cholesteric phase and shifts the phase transition temperature with respect to pure binary mixture for about 5°C towards lower temperatures. The extension of the temperature range of the cholesteric phase from 5°C to 15°C was established in the case when the derivatives 3 and 4 are added to the binary mixture of cholesteryl nonanoate with cholesteryl myristate. The phase diagrams of investigated compounds are formed on the basis of data obtained by the optical microscopy. Using X-ray diffraction on the crystalline powder of unoriented samples we have determined the molecular parameters: the thickness of smectic and cholesteric layers and average distance between the long axes of neighboring molecules. 相似文献
3.
Z. Kvitek J. Bornarel 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,30(2):153-160
The phase front during the 218 K transition in KD2PO4 crystals under a thermal gradient perpendicular to the c ferroelectric axis is observed to have a factory-roof shape. This shape is studied versus the magnitude of Ge in samples cut with faces in (100), (010), (001) planes or in (
0), (110), (001) ones. A geometric approach as well as the calculation of the elastic-strain energy caused by lattice misfits
along the phase front demonstrate the incoherent interface nature of the phase front. Furthemore, the results and their interpretation
allow to predict the sign of the lattice deformation u
xx
( > 0).
Received 25 April 2002 Published online 29 November 2002 相似文献
4.
E.I. Efremova A.A. Shiryaev Z.A. Kydryashova L.A. Nosikova S.A. Syrbue V.V. Chernyshev 《Phase Transitions》2015,88(5):503-512
The system of hydrogen-bonded liquid crystals formed from binary mixtures p-n-heptyloxybenzoic (I) acid and p-n-undecloxybenzoic (II) acid has been investigated by polarizing optical microscopy, differential scanning calorimetry, X-ray diffraction, and scattering and dielectric measurements. The T–X phase diagram was obtained for this system. All mixtures show enantiotropic smectic and nematic phases. The crystalline phase represents a (α, β) solid solution. At the 2:1 ratio of I to II, an intermediate phase – co-crystal γ – is formed. The co-crystal γ possesses a much wider mesophase range than the corresponding initial components. In contrast to mixtures based on the solid solutions having a positive anisotropy, the co-crystal shows a negative dielectric anisotropy in the mesophase. 相似文献
5.
E. García-Matres N. Stüßer M. Hofmann M. Reehuis 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,32(1):35-42
The magnetic structures of Mn1-xFexWO4 with x
= 0.0, 0.16, 0.21, 0.225, 0.232, 0.24, 0.27, 0.29, and 1.0 were refined from neutron powder diffraction data. The magnetic phase
diagram could be completed in the coexistence range of different magnetic structures up to x
= 0.29. For the magnetic state at 1.5 K a commensurate antiferromagnetic structure with a propagation vector
= (±1/4, 1/2, 1/2) was found for x
⩽ 0.22 while the magnetic spins order with
= (1/2, 0, 0) for x
≥ 0.22. In the latter phase, additionally, weak magnetic reflections indexed to an incommensurate ordering with
= (- 0.214, 1/2, 0.457) occur in the diffraction pattern up to x
= 0.29 indicating the occurence of a reentrant phase. For 0.12 ⩽
x
⩽ 0.29 the low temperature phases are separated from a magnetic high temperature phase showing only magnetic reflections indexed
to a spin arrangement with
= (1/2, 0, 0). The magnetic phase diagram is discussed qualitatively considering random superexchange between the statistically distributed
Mn2+- and Fe2+-ions in the coexistence range 0.12 ⩽
x
⩽ 0.29 of different magnetic structures related to those of pure MnWO4 and FeWO4.
Received 9 October 2002 Published online 14 March 2003 相似文献
6.
Y. Liu J. Dong D.Y. Xing 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,3(2):185-188
Minimizing total free energy by numerical calculations, we obtain the magnetic phase diagram of perovskite Mn oxides, such
as with , Ca, Sr, etc. in the whole doping region from x
=0 to x
=1 at temperature T
=0. It is discovered that a spiral state is stable in a low concentration of X ions while a canted state is stable in a high
concentration of X ions, and a ferromagnetic phase can exist in the intermediate concentrations when the antiferromagnetic
interaction is weak. The energy difference between spiral and canted states is found to be small when the Hund coupling is
large. Magnetic field induced spiral/canted phase transition is considered as a possible mechanism of the colossal magnetoresistance
(CMR) in the Mn oxides.
Received: 11 July 1996 / Revised: 7 December 1996 / Accepted: 24 July 1997 相似文献
7.
P. Zieliński W. Schranz D. Havlik A.V. Kityk 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,24(2):155-165
A four-state pseudospin model is constructed for the isomorphous phase transition hcp-2↦hcp-1 in pure C70 and in C70-rich mixed crystal C
70(1 - x)
C60x. With the specific anisotropic pseudospin interactions adapted to the C70 crystal the model is equivalent to a two-state Ising model in a temperature-dependent field. Replica symmetric state of the
model is shown to approach the critical point when the width of distribution of random fields and/or of random bonds increases.
The temperature of the phase transition and the phase equilibrium temperature then are practically constant, whereas the experiment
shows their strong decrease with x. The main effect of dilution resides in an x-dependence of the model parameters. Dilatometric data on the hexagonal C
70(1 - x)
C60x are used to fit these parameters. A metastable disordered phase subsisting below the phase transition is discovered in a
range of the model parameters and is shown to be responsible for the macroscopic behaviour of the system. A good agreement
with experimental data is obtained for the spontaneous strain and for the x-dependence of the hysteresis.
Received 20 April 2001 and Received in final form 26 September 2001 相似文献
8.
Rajeev Ahuja 《高压研究》2013,33(1-6):131-138
Abstract We have investigated the structural phase transitions in sodium and silver halides theoretically under high compressions by means of first-principles self-consistent total-energy calculations within the local-density approximation using the full-potential linear-muffin-tin-orbital (FPLMTO) method. Our results confirm the recent high pressure experimental observations of crystallographic phase transformations in sodium halides (Leger et al. (1998) J. Phys.: Condens. Matter, 10, 4201) and silver halides (Hull and Keen (1999) Phys. Rev., B59, 750. The calculated transition pressures agree with the experimental data. 相似文献
9.
Ravindra Dhar 《Phase Transitions》2013,86(3):175-199
Twisted-grain-boundary (TGB) phases shown by some liquid-crystalline materials have properties common to those of both smectic and cholesteric phases. Following analogy between liquid crystals and super conductors proposed by de Gennes [Solid State Commun., 10, 753 (1972)], Renn and Lubensky [Phys. Rev. A, 38, 2132 (1988)] theoretically predicted a chiral analog of the smectic A (SmA*) phase, which is now known as TGBA phase. The TGBA phase was experimentally observed for the first time by Goodby et al. [Nature, 337, 449 (1989)] in the chiral homologous series of ferroelectric liquid-crystal material R- and S-1-methylheptyl 4′-[(4′′-n-alkoxyphenyl)propionoyloxy]-biphenyl-4-carboxylates (nP1M7), with n?=?13,14,15. Since then, more than a hundred pure and mixed systems showing TGBA phase have been found. Later, Renn derived a mean-field phase diagram based on the chiral Chen-Lubensky model, and predicted two more TGB phases, namely TGBC and TGBC?. These two phases have also been experimentally observed in many systems, and in a few, the phase diagram is similar to that predicted by Renn. Unlike the TGBA phase, several theoretical models have been proposed for TGBC and TGBC? phases, and it remains to be ascertained whether all the types of proposed TGBC/TGBC? structures experimentally exist. A review of the theoretically predicted and experimentally observed TGB phases is given in the present article. Some recently observed novel optical textures of the TGB phases are also reported. 相似文献
10.
Single crystals of the high pressure phase of the 'spin-chain-compound' (VO) 2 P 2 O 7 could be grown from the melt, but crystal size is limited so far. As an alternative to melt growth, we suggest to prepare single crystals of the high pressure phase by a phase transformation of previously grown single crystals of the ambient pressure phase. 相似文献
11.
ObjectiveTo quantitatively evaluate induced phase errors in fast spin echo (FSE) signals due to low frequency electromagnetic inference (EMI).MethodsSpecific form of Bloch equation is numerically solved in time domain for two different FSE pulse sequences (ETL = 8) with two different bandwidths. A single spin is modeled at x = 10 cm, EMI frequencies are simulated from 1 to 1000 Hz and phase errors at different echo times are calculated.ResultsPhase errors in the received echo signals induced by EMI are significantly higher at low frequencies (< 200 Hz) than at high frequencies and the phase errors at low frequencies can be effectively reduced by using high receiving bandwidth.ConclusionPulse sequence bandwidth can be used to control the phase errors in the FSE signals due to low frequency EMI. 相似文献
12.
K. S. Aleksandrov S. V. Misyul T. I. Ivanova V. P. Sakhnenko G. M. Chechin 《Phase Transitions》2013,86(1-4):245-255
A group-theoretical analysis is performed for the complete condensation of order parameters at structural phase transitions (SPT's) in the high-temperature superconductors belonging to the D 17 4h -14/mmm space group in the high-symmetry phase. As a rule, such transformations are due to a successive softening of phonons with wave vectors k 1 = 1/2 b 3 and k 2 = 1/2 (b 1 - b 3) belonging to the K13(X) star of the Brillouin zone of a tetragonal body-centered Bravais cell. SPT's in system La2-x Ba x CuO4 are considered in detail. 相似文献
13.
I. V. Kalinin E. I. Kats M. Koza V. V. Lauter H. Lauter A. V. Puchkov 《Journal of Experimental and Theoretical Physics》2010,111(2):215-219
The results of recent neutron scattering studies of solid helium in silica aerogel are discussed. Previously I.V. Kalinin
et al., Pis’ma Zh. éksp. Teor. Fiz. 87 (1), 743 (2008) [JETP Lett. 87 (1), 645 (2008)], we detected the existence of a superfluid phase in solid helium at a temperature below 0.6 K and a pressure
of 51 bar, although, according to the phase diagram, helium should be in the solid state under these conditions. This work
is a continuation of the above studies whose main goal was to examine the detected phenomenon and to establish basic parameters
of the existence of a superfluid phase. We have determined the temperature of the superfluid transition from solid to superfluid
helium, T
C = 1.3 K, by analyzing experimental data. The superfluid phase excitation parameters (lifetime, intensity, and energy) have
a temperature dependence similar to that of bulk helium. The superfluid phase coexists with the solid phase in the entire
measured temperature range from T = 0.05 K to T
C and is a nonequilibrium one and disappears at T
C. 相似文献
14.
Yu.A. Nastishin M. Kléman J. Malthête H.T. Nguyen 《The European physical journal. E, Soft matter》2001,5(3):353-357
We have shown that cholesteryl nonanoate, a thermotropic compound which is well known to exhibit pretransitional effects at
the smectic A (SmA) cholesteric (N*) transition (W.L. McMillan, Phys. Rev. A 4, 1238 (1971); 6, 936 (1972)), has in fact a TGBA phase in between. Our arguments rely on the observation of new TGBA defects, either in Robinson
spherulites cooled from the N* phase or in free-standing films. The same new defects can be obtained in a well-documented
TGBA phase of a tolane compound. We analyze qualitatively the TGBA defects in both geometries, in particular their relation
to the disclination radius of the N* Robinson spherulites.
Received 12 February 2001 相似文献
15.
Nanocrystalline rutile Titanium dioxide has been studied by X-ray diffraction at ambient temperature up to 47.4 GPa. The material is found to transform to the monoclinic baddeleyite structure between 20 and 30 GPa, which is higher than the corresponding pressure range for bulk material. Upon decompression, the baddeleyite phase transforms to the f -PbO 2 phase at about 4-2 GPa. The experimental bulk moduli are 211(7) GPa for the rutile phase, 235(16) for the baddeleyite type and 212(25) GPa for the f -PbO 2 type phase. The results are compared with previous measurements of bulk rutile Titanium dioxide. 相似文献
16.
N. Shramchenko F. Dénoyer 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,29(1):51-59
A detailed investigation of the Fourier space of several Al-Pd-Mn samples with composition Al-72.6 at. %, Pd-22.9 at. %, Mn-4.5
at. % is reported. In the phase diagram of the Al-Pd-Mn ternary alloy, this composition corresponds to the so-called ξ' phase which was described as an icosahedral quasicrystalline approximant. By re-examining the Fourier space by means of
X-ray diffraction (powder patterns and single crystal precession patterns), complex structures in close relation with the
ξ'-phase have been observed. These long-range order complex structures are described as resulting from a periodic perturbation
of the ξ' structure along the c direction. Two states with periodicities c
(3 + τ) and c
(5 + τ) have been observed in this study (τ: golden mean). Structural models based on periodic arrangements of “defects” layers separating layers of phase are proposed. These two states are certainly intermediate states between the phase and the metastable decagonal quasicrystalline phase.
Received 11 April 2002 / Received in final form 24 June 2002 Published online 17 September 2002 相似文献
17.
T. Vuletić P. Auban-Senzier C. Pasquier S. Tomić D. Jérome M. Héritier K. Bechgaard 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,25(3):319-331
The phase diagram of the organic superconductor (TMTSF)2PF6has been revisited using transport measurements with an improved control of the applied pressure. We have found a 0.8 kbar
wide pressure domain below the critical point (9.43 kbar, 1.2 K) for the stabilisation of the superconducting ground state
featuring a coexistence regime between spin density wave (SDW) and superconductivity (SC). The inhomogeneous character of
the said pressure domain is supported by the analysis of the resistivity between T
SDW
and T
SC
and the superconducting critical current. The onset temperature T
SC
is practically constant ( 1.20±0.01 K) in this region where only the SC/SDW domain proportion below T
SC
is increasing under pressure. An homogeneous superconducting state is recovered above the critical pressure with T
SC
falling at increasing pressure. We propose a model comparing the free energy of a phase exhibiting a segregation between
SDW and SC domains and the free energy of homogeneous phases which explains fairly well our experimental findings.
Received 3 September 2001 and Received in final form 9 November 2001 相似文献
18.
S. A. Gridnev L. P. Safonova O. N. Ivanov T. N. Davydova 《Physics of the Solid State》1998,40(12):1998-2001
The anomalous changes of the low-frequency elastic and inelastic properties of single-crystal (NH4)2SO4 accompanying the phase transition from the paraelectric to the ferroelectric phase have been studied by the reverse torsion-pendulum
method at 223 K and in the temperature region where the spontaneous polarization changes sign.
Fiz. Tverd. Tela (St. Petersburg) 40, 2202–2205 (December 1998) 相似文献
19.
G. K. Chepurnykh V. S. Ivanii O. G. Medvedovskaya O. A. Nikitina 《Physics of the Solid State》1999,41(11):1877-1879
Properties of phase transitions in a magnetic field H parallel to the easy axis have been investigated, and it has been shown, in particular, that the nature of the transition
of the magnetic subsystem from the antiferromagnetic phase to the angular phase depends on the “sign” of the Dzyaloshinskii
interaction. The conditions for orientation of the antiferromagnetism vector l in the basis plane in fields larger than the threshold field have been determined. It is shown that the transition from the
angular phase to the state where the resulting magnetic moment m is parallel to the easy axis takes place in the field corresponding to a spin-flip transition. From an analysis of the configuration
of the magnetic subsystem for arbitrary orientation of the external magnetic field, it follows that the values of the critical
angle (ψ
cr
) for which a first-order phase transition takes place satisfy the condition
in the case in which the anisotropy constant f in the basis plane is of the order of the first anisotropy constant b. Usually
so that the tricritical point in the phase diagram H
y
,H
z
satisfies the condition H
y
∼H
z
.
Fiz. Tverd. Tela (St. Petersburg) 41, 2044–2046 (November 1999) 相似文献
20.
V.V. Savkin A.N. Rubtsov T. Janssen 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,31(4):525-531
The classical two-dimensional discrete frustrated φ
4
model is studied by Monte Carlo simulations. The correlation function is obtained for two values of a parameter d that determines the frustration in the model. The ground state is a ferro-phase for d
= - 0.35 and a commensurate phase with period N
= 6 for d
= - 0.45. Mean field predicts that at higher temperature the system enters a para-phase via an incommensurate state, in both cases. Monte Carlo data for d
= - 0.45 show two phase transitions with a floating-incommensurate phase between them. The phase transition at higher temperature
is of the Kosterlitz-Thouless type. Analysis of the data for d
= - 0.35 shows only a single phase transition between the floating-fluid phase and the ferro-phase within the numerical error.
Received 16 December 2002 / Received in final form 17 January 2003 Published online 6 March 2003
RID="a"
ID="a"e-mail: vladimir@shg.ru 相似文献