共查询到20条相似文献,搜索用时 31 毫秒
1.
J. Dec W. Kleemann Th. Woike R. Pankrath 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,14(4):627-632
The complex dielectric susceptibility of Sr
0.61
Ba
0.39
Nb
2
O
6
:Ce
3+
(SBN61:Ce) has been measured at frequencies and temperatures before and after poling. The relaxor behaviour with large polydispersivity observed above the ferroelectric phase transition
temperature, T
c
= 360 and 340 K for x
(Ce) = 0 and 0.0066, respectively, is perfectly modeled within the framework of Chamberlin's dynamically correlated domain approach.
Below T
c
the dynamic nanodomain state crosses over into a ferroelectric state with polydispersive domain wall dynamics at very low
frequencies. Presumably SBN61:Ce belongs to the three-dimensional random field Ising rather than to the dipole glass universality
class.
Received 1 October 1999 相似文献
2.
W. Boujelben A. Cheikh-Rouhou J.C. Joubert 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,24(4):419-423
Deficiency effects in the A site upon the structural, magnetic and electrical properties in the lacunar perovskite manganite
oxides Pr0.7Sr0.3-x
xMnO3 ( 0 ?
x
? 0.3) and Pr0.7-x
xSr0.3MnO3 ( 0 ?
x
? 0.23) have been investigated. This study focuses on the different parameters which govern the magnetic and electrical properties
in such samples. The powder X-ray diffraction patterns for all samples could be indexed either with a rhombohedral perovskite
structure and R
c space group for x
? 0.2 in strontium deficient samples and for x
? 0.1 for praseodymium deficient ones. For other values of x the samples could be indexed in the orthorhombic structure with Pbnm space group. Magnetic and electrical investigations
show that praseodymium and strontium vacancies do not have similar effects on the lacunar compounds. Magnetization measurements
versus temperature show that all our samples exhibit a magnetic transition when the temperature decreases. All the praseodymium
deficient samples exhibit a paramagnetic-ferromagnetic transition when the temperature decreases while the strontium deficient
ones exhibit this transition only for low x values. The magnetic transition temperature shifts to lower values as the strontium deficiency increases (from 265 K for
x
= 0 to 90 K for x
= 0.3) and to higher values with the praseodymium deficiency increase (from 265 K for x
= 0 to 315 for x
= 0.23). Resistivity measurements as a function of temperature show a semiconducting-metallic transition for all x values in the praseodymium lacunar samples and only for low x values ( 0 ?
x
? 0.1) in the strontium lacunar ones when the temperature decreases.
Received 12 April 2000 and Received in final form 8 January 2001 相似文献
3.
P. Lehnen W. Kleemann Th. Woike R. Pankrath 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,14(4):633-637
The linear birefringence (LB) of Sr
0.61-x
Ba
0.39
Nb
2
O
6
:Ce
3+
x (SBN61:Ce) has been measured as a function of temperature within the range of . Large tails have been observed above the ferroelectric phase transition temperatures T
c
= 350, 328, 320 and 291 K for the concentrations x
= 0, 0.0066, 0.0113 and 0.0207, respectively. Within an Ornstein-Zernike analysis the critical exponents , and are determined. It suggests that pure SBN61 belongs to the 3D Ising universality class. Doping with Ce
3+
ions, which seem to act as random fields, enhances the relaxor properties. The critical exponents and of SBN61:Ce shift against those of the three-dimensional random-field Ising model.
Received 1 October 1999 相似文献
4.
M. Gaudry J. Lermé E. Cottancin M. Pellarin B. Prével M. Treilleux P. Mélinon J.-L. Rousset M. Broyer 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):201-204
Optical properties of mixed clusters (AuxAg
1 - x
)
n
and (NixAg
1 - x
)
n
, produced by laser vaporization and embedded in an alumina matrix, are reported. The size effects are investigated for different
concentrations (x
= 0.25, 0.5 and 0.75) in the diameter range 2-4 nm. For alloyed clusters (AuxAg
1 - x
)
n
of a given size an almost linear evolution of the surface plasmon frequency ω
s
with the concentration is observed (between those of pure gold and pure silver clusters). Moreover the blue-shift and the
damping of the resonance with decreasing size is all the more important as the gold concentration in the particles increases.
Such results are in agreement with theoretical calculations carried out in the frame of the time-dependent local-density-approximation
(TDLDA) including an inner skin of ineffective screening and the porosity of the matrix. The optical response of (NixAg
1 - x
)
n
clusters exhibits a surface plasmon resonance in the same spectral range as the one observed for pure silver clusters, but
considerably damped and broadened. For a given mean cluster size 3.0 nm, a blue-shift of the resonance is observed when increasing
the nickel concentration (between x
= 0.25 and x
= 0.75). The results are in good qualitative agreement with classical predictions in the dipolar approximation, assuming a core-shell
geometry.
Received 21 November 2000 相似文献
5.
D. Vignolles A. Audouard L. Brossard S. Pesotskii R. Lyubovskii M. Nardone E. Haanappel R. Lyubovskaya 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,31(1):53-61
Interlayer magnetoresistance and magnetisation of the quasi-two dimensional organic metal (BEDT-TTF)8Hg4Cl12(C6H5Br)2 have been investigated in pulsed magnetic fields extending up to 60 T and 33 T, respectively. About fifteen fundamental frequencies,
composed of linear combinations of only three basic frequencies, are observed in the oscillatory spectra of the magnetoresistance.
The dependencies of the oscillation amplitude on the temperature and on the magnitude and orientation of the magnetic field
are analyzed in the framework of the conventional two-dimensional Lifshitz-Kosevitch (LK) model. This model is implemented
by damping factors which accounts for the magnetic breakthrough occurring between electron and hole orbits yielding conventional
Shubnikov-de Haas closed orbits (model of Falicov and Stachowiak) and quantum interferometers. In particular, a quantum interferometer
enclosing an area equal to the first Brillouin zone area is evidenced. The LK model consistently accounts for the temperature
and magnetic field dependence of the oscillation amplitude of this interferometer. On the contrary, although this model formally
accounts for almost all of the observed oscillatory components, it fails to give consistent quantitative data in most other
cases.
Received 4 September 2002 / Received in final form 14 November 2002 Published online 27 January 2003
RID="a"
ID="a"e-mail: audouard@insa-tlse.fr
RID="b"
ID="b"UMR 5830: Unité Mixte de Recherche CNRS - Université Paul Sabatier - INSA de Toulouse
RID="c"
ID="c"UMS 5642: Unité Mixte de Service CNRS - Université Paul Sabatier - INSA de Toulouse 相似文献
6.
A.M. Balagurov V.Yu. Pomjakushin D.V. Sheptyakov V.L. Aksenov N.A. Babushkina L.M. Belova O.Yu. Gorbenko A.R. Kaul 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,19(2):215-223
The atomic structure of (
La
1 - y
Pr
y
)
0.7
Ca
0.3
MnO
3
compound with 0.5≤
y
≤1 has been systematically studied by neutron powder diffraction in the temperature range from 15 to 293 K. For composition
with y
= 0.75, the structural analysis was performed on two samples, one containing the natural mixture of oxygen isotopes and the other
one 75% enriched by
18
O. The room temperature structural characteristics of the series, including cell volume, average Mn-O bond distance, and average
Mn-O-Mn bond angle, are the linear functions of the <
r
A
>. Temperature dependencies of these parameters are quite smooth, except for the point T
=
T
FM
, where a jump like changes occur. The isotope enriched samples have been found identical in crystal and magnetic structure
down to the temperature of transition of the sample with
16
O into the metallic ferromagnetic phase. It confirms that different transport and magnetic properties of the samples with
16
O and
18
O at low temperature are driven by the different oxygen atoms dynamics solely. Temperature dependencies of the CO and AFM diffraction
peak intensities and of the peak widths for compositions close to the metal-insulator boundary ( y
≈ 0.75) indicate the macroscopically phase separated AFM-dielectric + FM-metallic state below T
FM
.
Received 28 April 2000 相似文献
7.
F.S. da Rocha G.L.F. Fraga D.E. Brand?o C.M. Granada C.M. da Silva A.A. Gomes 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,25(3):307-311
The magnetic moment of the Mn impurities was obtained from magnetization measurements of Y
(
Ni
1 - x
Mn
x
)
2
B
2
C as a function of the concentration x less than 0.15. Using the coherent potential approximation and starting from 3
d density of states, obtained from the first principles calculations, the magnetic moments are obtained within a two sublattice
model. For adequately estimated values of the Coulomb interactions U, the position of the energy level of Mn and adopting values for the intersublattice hybridization term, a qualitative agreement
with the observed experimental data is obtained.
Received 23 April 2001 and Received in final form 29 October 2001 相似文献
8.
D. Barba S. Jandl A.A. Martin C.T. Lin M. Cardona T. Wolf 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,22(3):277-281
Infrared reflectance, and transmission measurements as well as Raman scattering have been used to study the RE1+xBa2-xCu3O6 (RE = Nd, Sm) and YBa2Cu3O6 absorption bands in the 1100-1500 cm-1 infrared range as a function of temperature and beam polarization. In addition to two-phonon absorption between 1100 and
1170 cm-1, we observe excitations around 1400 cm-1, occurring in oxygen rich enclosures within the samples, and assign them to an excitation involving two-phonons plus the
270 cm-1 local mode related to Cu-O broken chains. Thus, the previously reported possible magnetic origin of the 1436 cm-1 sharp absorption band in YBa2Cu3O6 is contested.
Received 14 February 2001 and Received in final form 12 April 2001 相似文献
9.
N. Petit V. Garnier V. Ta Phuoc R. Caillard A.-M. Frelin A. Ruyter I. Laffez J.-C. Soret A. Maignan F. Gervais 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,25(4):423-429
The reflectivity spectra of an oriented ceramic of Bi-2223 has been investigated by polarized infrared reflectivity spectroscopy
in the energy range 0.005-2.2 eV. It is shown that the data for the polarization parallel to the c axis cannot be fitted with a one-component Drude or extended-Drude model. The conductivity spectrum is then obtained from
the best fit of a “double-damping Drude” model to reflectivity spectra, itself derived from the factorized form of the dielectric
function, and by a Kramers-Kronig inversion as well. The data and their analysis give a new insight of the 2D character of
the system.
Received 26 April 2001 and Received in final form 28 August 2001 相似文献
10.
Unconventional antiferromagnetic correlations of the doped Haldane gapsystem Y 2 BaNi 1 - x Zn x O 5
V. Villar R. Mélin C. Paulsen J. Souletie E. Janod C. Payen 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,25(1):39-51
We make a new proposal to describe the very low temperature susceptibility of the doped Haldane gap compound Y2BaNi1-xZnxO5. We propose a new mean field model relevant for this compound. The ground state of this mean field model is unconventional
because antiferromagnetism coexists with random dimers. We present new susceptibility experiments at very low temperature.
We obtain a Curie-Weiss susceptibility χ(
T
) ∼
C
/(Θ +
T
) as expected for antiferromagnetic correlations but we do not obtain a direct signature of antiferromagnetic long range order.
We explain how to obtain the “impurity” susceptibility
(
T
) by subtracting the Haldane gap contribution to the total susceptibility. In the temperature range [1 K, 300 K] the experimental
data are well fitted by T
(
T
) =
C
imp
1 +
T
imp
/
T
. In the temperature range [100 mK, 1 K] the experimental data are well fitted by T
(
T
) =
A
ln(
T
/
T
c
), where T
c
increases with x. This fit suggests the existence of a finite Néel temperature which is however too small to be probed directly in our experiments.
We also obtain a maximum in the temperature dependence of the ac-susceptibility
(
T
) which suggests the existence of antiferromagnetic correlations at very low temperature.
Received 17 July 2001 相似文献
11.
T. Nzeyimana E.A. Naji X. Urbain A. Le Padellec 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,19(3):315-325
Total cross-sections have been measured for the associative ionisation of C
+
+
O
-
, N
+
+
O
-
and O
+
+
O
-
by means of a merged-beam set-up operating with keV beams. These original measurements might be relevant to the understanding
of some astrophysical objects or laboratory-made plasmas (flames and etching plasmas). The magnitude of these cross-sections
is particularly large whatever the associating system, as these are in the range of 1×10
-14
cm2 at thermal energies. Their behaviour as a function of energy significantly differs from one system to another, and is characterised
by the Wigner law at low energy, and a rapid fall-off at higher energy due to competition with non-associative ionisation
processes.
Received 10 December 2001 and Received in final form 12 March 2002 相似文献
12.
V. Ghanbarian M. R. Mohammadizadeh 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,61(3):309-318
Electric-field gradient (EFG) and asymmetry parameter (η) at all
oxygen and copper sites of nonsuperconducting PrBa2Cu3O7
(Pr123) compound were calculated using the full-potential
(linearized)-augmented-plane-wave plus local orbitals method. Exchange and
correlation effects were treated by LSDA+U for Cu(3d) and Pr(4f) electrons.
The effects of changing screened Coulomb parameters UPr, UCu1, and
UCu2 on the results were individually studied. The calculated EFG of O2
site is close to the EFG of O3 site at variance with the experimental
result. It was shown that by increasing superconducting holes in O2 and O3
sites the EFG at these sites increase and vice versa. The most famous
theories which have been proposed to explain the suppression of
superconductivity in perfect (without any mis-substitution or other defects)
Pr123 compound are not consistent with the experimental EFG at O2 and O3
sites. By replacing one Pr atom at the Ba site on unit cell of Pr123
(PrBa), it was shown that PrBa mis-substitution reduces the
superconducting holes in both O2 and O3 sites and could be responsible for
the suppuration of superconductivity in Pr123 samples. It is very probable
that the unusual behaviors of experimental EFG at O2 and O3 sites of Pr123
are related to oxygen defects which are produced with PrBa
mis-substitution. 相似文献
13.
R. Beuc H. Skenderovi T. Ban D. Vea G. Pichler W. Meyer 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,15(2):209-214
We measured a very distinct satellite band at 875.2 nm between two resonance lines of cesium. Spectral simulation using Spies
and Meyer [#!ref1!#] ab initio potential curves and an appropriate transition dipole moment function was compared with experimental profile. Implications
of the investigated satellite band at 875.2 nm in the field of ultracold cesium atom collisions are discussed with a special
emphasize to new possibilities of the photoassociation of two ground state atoms leading to the formation of ultracold intermediate
long-range molecules.
Received 07 March 2001 and Received in final form 14 May 2001 相似文献
14.
The electrical and magnetoresistant properties of La0.67(Ca0.65Ba0.35)0.33MnO3/Agx (abbreviated by LCBMO/Agx) have been studied. The results show that Ag addition causes a decrease of resistivity dramatically and especially induces a large enhancement of room temperature magnetoresistance (MR). The room temperature MR ratio for x=0.27 sample in 10 kOe magnetic field is 41%, almost 20 times larger than that for x=0 sample. This enhancement is related to that the Curie temperature (Tc) of the sample is near room temperature, as well as the significant reduction of resistivity. The good fits of experimental results for x=0.27 sample to Brillouin function indicate that the MR behavior in the Ag added LCBMO is induced by the spin-dependent hopping of the electrons between the spin clusters, which is an intrinsic property of the CMR materials. 相似文献
15.
M. AminA. El-Korashy S.S. IbrahimM. Dabour S. Arafa 《Journal of Physics and Chemistry of Solids》2002,63(5):869-874
DC electrical conductivity for a virgin and poled annealed (NH4)2ZnCl4b-axis single crystal shows a defect controlled property. A Schottky mechanism is a probable mechanism of conduction in regions of strong structural transitions. The rise of conductivity in the incommensurate and paraelectric phases is linked to an increase in discommensurations density. The activation energies (ΔE) in the three phases region were calculated. DTA measurements shows that the crystal is stable up to 200 °C and the phase transition temperatures were observed at 42, 94.8 and 137 °C. The effective activation energy (Ee) was obtained using Kissinger and Mahadevan equations. It was found to be equal to 0.49 eV. This correlates with the value obtained through DC conductivity. 相似文献
16.
Z.C. Xia Y. Wang H.R. Zeng Q.X. Zhou M.T. Hu B. Dong G. Liu X.N. Feng L. Liu S.L. Yuan C.Q. Tang 《Solid State Communications》2006,137(4):216-220
The electrical transport and magnetic properties of high Bi doped (La0.73Bi0.27)0.67Ca0.33MnO3 are studied at the temperature and magnetic field ranges from 10 to 300 K and 0 to 3 T. Significant temperature and magnetic field hystereses are observed in both resistivity and magnetization measurements. Meanwhile, an enhanced magnetoresistance effect, within a wide temperature window, is obtained in the (La0.73Bi0.27)0.67Ca0.33MnO3. The hysteresis and enhanced magnetoresistance are discussed based on an inhomogeneous metastable structure related to the Bi dopant. 相似文献
17.
In the context, Eu3+ (Dy3+)-doped YNbxTa1-xO4 and REVTa2O9 (RE=Y, La, Gd) phosphors have been synthesized from the hybrid precursors. Both XRD and SEM indicated the particles present
good crystalline state, whose crystalline grain sizes were in the range of 0.5 to 1 μm. Besides, XRD patterns of YNbxTa1-xO4 (x=0.1, 0.2, 0.3, 0.5, 0.9) have shown that the phase has been changed from M′-type YTaO4 to M-type YNbO4 with increasing niobium content. Furthermore, from the luminescent spectra of Eu3+-doped YNbxTa1-xO4, it was observed that the 5
D
0–7
F
2 transition of Eu3+ was predominated and its intensity increases with increasing niobium content, as well as the intensity ratio of 5
D
0–7
F
2 transition to 5
D
0–7
F
1 transition for Eu3+. The optimum concentrations of Eu3+ and Dy3+ in YNb0.5Ta0.5O4 have been found to be 6 and 5 mol %, respectively. At the same time, the luminescent properties of Eu3+ and Dy3+ in REVTa2O9 (RE=Y, La, Gd) have also been investigated that GdVTa2O9:Eu3+ (Dy3+) presents high luminescence, while LaVTa2O9:Eu3+ (Dy3+) shows weak luminescence.
PACS 78.20.-e; 78.55.-m; 61.72.Ss; 32.50.+d; 81.40 Tv 相似文献
18.
Vladimir Dmitriev Vitaly Sinitsyn Denis Machon Eugeny Ponyatovsky Hans Peter Weber 《Journal of Physics and Chemistry of Solids》2003,64(2):307-312
The effect of pressure on the phase transformations in Sm2(MoO4)3, Gd2(MoO4)3 and Eu2(MoO4)3 crystals has been studied in situ using synchrotron radiation. All three isostructural compounds undergo a structural phase transition at 2.2-2.8 GPa to a new phase, which is interpreted as a possible precursor of amorphization. Amorphization in these crystals occurs irreversibly over a wide pressure range, and its mechanism, interpreted as a chemical decomposition, is found to be weakly affected by the degree of hydrostaticity. 相似文献
19.
A. Bhattacharjee P.J. van Koningsbruggen Joel S. Miller 《Journal of Physics and Chemistry of Solids》2008,69(11):2713-2718
The 57Fe Mössbauer spectroscopy of mononuclear [Fe(II)(isoxazole)6](ClO4)2 has been studied to reveal the thermal spin crossover of Fe(II) between low-spin (S=0) and high-spin (S=2) states. Temperature-dependent spin transition curves have been constructed with the least-square fitted data obtained from the Mössbauer spectra measured at various temperatures between 84 and 270 K during a cooling and heating cycle. This compound exhibits an unusual temperature-dependent spin transition behaviour with TC(↓)=223 and TC(↑)=213 K occurring in the reverse order in comparison to those observed in SQUID observation and many other spin transition compounds. The compound has three high-spin Fe(II) sites at the highest temperature of study of which two undergo spin transitions. The compound seems to undergo a structural phase transition around the spin transition temperature, which plays a significant role in the spin crossover behaviour as well as the magnetic properties of the compound at temperatures below TC. The present study reveals an increase in high-spin fraction upon heating in the temperature range below TC, and an explanation is provided. 相似文献
20.
We investigated the temperature dependences of the line shape, spin-lattice relaxation time, T1, and spin-spin relaxation time, T2, of the 1H nuclei in (NH4)4LiH3(SO4)4 single crystals. On the basis of the data obtained, we were able to distinguish the “ammonium” and “hydrogen-bond” protons in the crystals. For both the ammonium and hydrogen-bond protons in (NH4)4LiH3(SO4)4, the curves of T1 and T2 versus temperature changed significantly near the ferroelastic and superionic phase transitions at TC (=232 K) and TS (=405 K), respectively. In particular, near TS, the 1H signal due to the hydrogen-bond protons abruptly narrowed and the T2 value for these protons abruptly increased, indicating that these protons play an important role in this superionic phase transition. The marked increase in the T2 of the hydrogen-bond protons above TS indicates that the breaking of O-H?O bonds and the formation of new H-bonds with HSO4- contribute significantly to the high-temperature conductivity of (NH4)4LiH3(SO4)4 crystals. 相似文献