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1.
The structural phase transition from orthorhombic (T) phase to tetragonal (T′) phase in substituted La2−x
R
x
CuO4 (R = Pr, Nd, Sm, Eu and Gd) and T′ to T-phase in Pr2−x
M
x
CuO4−y
(M = Sr, Ca) has been studied by X-ray diffraction technique. The T-phase of La2CuO4 is transferred to T′ phase abruptly atx=0.8, 0.4, 0.4, 0.3 and 0.4 respectively for substitution of Pr, Nd, Sm, Eu and Gd for La in La2CuO4 without evidence of the T* phase. The T′ structure of Pr2CuO4 (x = 0.0) gets transformed to the T* structure at 30% Ca doping (x=0.6) and then to the T structure at 50% Ca doping (x=1.0), while for Sr-contentx=0.0, 0.4 and 1.0 it shows T′, T* and T structure respectively. 相似文献
2.
C. Politis J. Geerk M. Dietrich B. Obst 《Zeitschrift für Physik B Condensed Matter》1987,66(2):141-146
High-T
c superconductivity withT
c onsets up to 42 K (midpoint: 37 K, zero resistance: 34 K) is observed in X-rays homogeneous single phase La1.8Sr0.2CuO4. The quarternary compounds La2–x
Ba
x
CuO4 and La2–x
Sr
x
CuO4 (0x0.3 for Ba and 0x<1 for Sr, depending on the heating conditions) are mixed-valence oxygen defect oxides, characterized by the presence of Cu2+ and Cu3+ simultaneously. These oxides have a tetragonal symmetry (space group:I 4/mmm) similar to that of K2NiF4. We report the synthesis, characterization, and superconducting properties of various high-temperature superconducting La–Ba–Cu–O and La–Sr–Cu–O compounds. Through the substitution of Sr for Ba in these oxygen defect compounds an increasing superconducting transition temperature onset from 28 K to 35 K for La1.8Sr0.1Ba0.1CuO4 was observed. A positive initial pressure coefficient ofdTc/dp=290 (mK/kbar) has been found for La1.8Sr0.2CuO4 with a magnetic susceptibility change consistent with the 100% diamagnetic expectation value. 相似文献
3.
L. S. Fomenko S. V. Lubenets V. S. Bobrov A. N. Izotov 《Physics of the Solid State》1998,40(3):453-457
The microhardness of La2CuO4 and La1.85Sr0.15CuO4 crystals is measured in the temperature range 81–292 K, and the influence of various factors on it is investigated. The thermal
activation parameters of the plastic deformation process in the vicinity of the indenter impression are estimated. The change
of the phase state of the compound La1.85Sr0.15CuO4 at the temperature T
0=180 K and the appearance of domain (twin) boundaries formed in the ferroelastic tetraortho transition are not seen in the
temperature dependence of the microhardness. The results of the study are compared with previously published results for YBa2CuO7−x
crystals.
Fiz. Tverd. Tela (St. Petersburg) 40, 493–497 (March 1998) 相似文献
4.
Study on the in—plane electrical resistivity and thermoelectric power in single crystals of La2—xBaxCuO4 下载免费PDF全文
The in-plane electrical resistivity and thermoelectric power have been measured on single crystals of La2-xBaxCuO4 at around x=0.125. The room temperature resistivity and thermopower have their maximum values at x=0.125, indicating that the carrier concentration is the minimum and the carriers are most strongly localized at x=0.125. The observed semiconductor-like behaviour can be well described by the weak-localized quasi-two-dimensional state. The steep rise in electric resistivity of the sample at x=0.125 below 70K is attributed to the formation of static stripe-order of holes and spins, which are pinned by the low-temperature tetragonal (LTT) structure, as discovered in La1.48Nd0.4Sr0.12CuO4. The temperature dependence of electric resistivity below 70K is still well described by the formula ρ∝ lnT. A definite change in the slope of thermopower is observed at the low-temperature orthorhombic-LTT structural phase transition temperature. The origin of the 1/8 anomaly is discussed in the text. 相似文献
5.
Ch. Niedermayer C. Bernhard T. Blasius A. Decker A. Golnik 《Hyperfine Interactions》1997,105(1-4):131-137
We have studied the magnetic phase diagram for the bilayer compound Y1-x Cax Ba2 Cu3 O6 in the regime of low doping (hole concentration within a CuO2 plane, psh < 0.1). For psh < 0.03, the data demonstrate the freezing of the spin degrees of freedom associated with the doped holes into a spin‐glass‐like
state which is superimposed on the preexisting long range order of the Cu2+ spins. Only a single spin‐glass like transition at a temperature Tg is observed for samples in the hole concentration range 0.03 < psh < 0.1. While the threshold for the occurrence of superconductivity is almost the same (psh > 0.06) for the Y1-x Cax Ba2 Cu3 O6 and the La2-x Srx CuO4 systems, the magnetic correlations that coexist with superconductivity are considerably stronger in the bilayer Y1-x Cax Ba2 Cu3 O6 system as indicated by significantly increased transition temperatures Tg.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
6.
The significance of heterovalent, substitutional disorder for the distribution of charge carriers in La2−x
Sr
x
CuO4 has been investigated. Disorder is shown to cause strong variations of binding energies of the ions ranging to some eV for
Sr contentsx=0.1. Balancing the energy for a hole transport, Cu3++O2−→Cu2++O−, and taking binding energy variations into account, the process is realized to become possible without consuming energy for
a subset Θ for allx Cu3+ in one formula unit of La2−x
Sr
x
CuO4. The functions Θ(x) are presented for hole transports to apex and in-plane oxygens, respectively. The delocalization of charge carriers is interpreted
to be caused by valency disorder on metal lattice sites. 相似文献
7.
Z. Z. Akselrod G. A. Denisenko B. A. Komissarova L. N. Kryukova G. K. Ryasny A. A. Sorokin L. G. Shpin’kova 《Hyperfine Interactions》1990,61(1-4):1147-1150
Results of TDPAC studies of hyperfine interaction in high temperature superconducting ceramics are reported. The γ-ray cascade
of 329–487 keV in140Ce excited in the decay of140La in La2-xSrxCuO4 samples (x=0 and 0.15), and 133–482 keV cascade in181Ta excited in the decay of181Hf in YBa2Cu3O7-δ samples were used. The procedure of introducing radioactive181Hf into the ceramics is described and indirect evidence for the occupation of Cu sites by the181Hf-181Ta probe is presented. 相似文献
8.
K. V. Mitsen O. M. Ivanenko 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,52(2):227-231
An model of La2-xSrxCuO4 explaining the
features of incommensurate spin textures without any assumption of stripe
formation is proposed. The foundations of this model are the mechanism of
negative-U center formation proposed earlier and the concept of specific
ordering of doped ions. It is shown that within the framework of the
proposed model the features of “stripe” textures of
La2-xSrxCuO4 reflect exclusively the geometrical relations
existing in a square lattice and the competition between different types of
doped hole ordering. 相似文献
9.
A nonuniform electron density distribution is observed in La1−x− y
NdySrxCuO4 and La1−x−y
EuySrxCuO4, and long-lived magnetic fluctuations in these compounds are studied. The dynamics of the magnetic fluctuations depends strongly
on the magnetic properties of the rare-earth ions, which stabilize the low-temperature tetragonal phase.
Pis’ma Zh. éksp. Teor. Fiz. 67, No. 5, 344–349 (10 March 1998) 相似文献
10.
Ch. Niedermayer M. Ro manith A. Golnik E. Recknagel A. Weidinger J. I. Budnick B. Chamberland c. Baines 《Hyperfine Interactions》1989,50(1-4):593-597
Muon-spin-rotation (μSR) experiments were performed on superconducting La1.90Sr0.10CuO4 in zero external field. Below 2 K, a fast depolarization of the muon signal is observed, indicating that internal magnetic
fields are present at the muon site. The average magnitude of the magnetic field in La1.90Sr0.10CuO4 is in the order of 3 mT and thus approximately 14 times smaller than the corresponding field in antiferromagnetic La2CuO4. The present data support theoretical models of superconductivity in which magnetic correlations are responsible for pairing. 相似文献
11.
T. Shinjo S. Nasu T. Mizutani K. Shintaku N. Hosoito K. Matsukuma T. Takabatake 《Hyperfine Interactions》1990,55(1-4):1379-1386
Mössbauer absorption measurements were carried out for119Sn and57Fe impurities in La2CuO4, La1.85Sr0.15CuO4 and La1.6Sr0.4CuO4. For all cases,57Fe spectra at 4.2 K show magnetic hyperfine splittings. On the other hand, a magnetic hyperfine field at Sn nucleus is observed only in the case of La1.85Sr0.15CuO4. The results indicate that the Cu magnetic spins are collectively fluctuating in the superconducting sample. 相似文献
12.
I. Souza Azevedo E. Baggio Saitovitch M. Hücker B. Büchner H. Micklitz 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,6(3):313-315
57Fe M?ssbauer effect studies of La1.65Eu0.20Sr0.15CuO4 doped with 0.5 at% 57Fe performed in the temperature region 300 K >
T
> 4.2 K give an onset temperature for magnetic ordering of K. This temperature practically is the same as that found in Nd doped La2-xSrxCuO4. It indicates that the magnetic ordering temperature in the LTT phase of rare earth (RE) doped La2-xSrxCuO4 is independent of the RE moment. The direction of the 57Fe magnetic moment in the magnetically ordered state is within the CuO2 plane, while it has been found to be parallel to the c-axis in Nd doped La2-xSrxCuO4.
Received: 23 June 1998 / Accepted: 14 July 1998 相似文献
13.
E. Torikai K. Nishiyama K. Kojima K. Nagamine H. Kitazawa I. Tanaka H. Kojima 《Hyperfine Interactions》1993,79(1-4):879-883
In order to investigate the electronic structure around oxygen in superconducting La2–x
Sr
x
CuO4 (x=0.10 and 0.14), precise measurements were carried out on the paramagnetic Knight shifts in the spin rotation frequency of the negative muon bound to the oxygen with reference to antiferromagnetic La2–x
Sr
x
CuO4 (x=0.05). Remarkable temperature as well as crystalline-axis dependence was observed for the highT
c case with a divergence character towardsT
c. Possible mechanisms to explain the observed results are given. 相似文献
14.
G. M. Luke L. P. Le B. J. Sternlieb Y. J. Uemura J. H. Brewer R. Kadono R. F. Kiefl S. R. Kreitzman T. M. Riseman C. E. Stronach M. Davis S. Uchida H. Takagi Y. Tokura Y. Hidaka T. Murakami E. A. Early J. T. Markert M. B. Maple C. L. Seaman 《Hyperfine Interactions》1991,63(1-4):311-317
We report muon spin relaxation/rotation measurements on sintered powder samples of Nd2−x
Ce
x
CuO4−y
and a large single crystal of Nd2CuO4−y
. We find an electronic phase diagram which is quite similar to that of hole-doped superconductors such as La2−x
Sr
x
CuO4−y
, although the doping of electrons into the system is less efficient in destroying the static moments on the copper spins.
Static magnetic order in Nd2CuO4−y
appears below about 250 K, and two spin reorientations are seen atT=75 K andT=35 K. Measurements of the magnetic field penetration depth have been unsuccessful due to the rare-earth paramagnetism of
these materials. 相似文献
15.
Y. Takahashi 《Zeitschrift für Physik B Condensed Matter》1987,68(4):411-416
The frequency dependence of the reflectivity spectra of doped La2–x
Sr
x
CuO4 in a high frequency region is analyzed based on a picture of correlated hole hopping within a lower Hubbard subband. It is shown that experimental trends are fairly well accounted for by this model, suggesting that the normal state of this compound is quite different from the metallic state. 相似文献
16.
The dependencies of ac susceptibility on the superimposed dc magnetic fields for the stripe-ordered La1.45Nd0.4Sr0.15CuO4 single crystal with two superconducting transitions have been studied in the 3D and 2D superconducting ranges for the fields along different orientations of the crystal. The results show that with increasing fields the interlayer Josephson coupling and the in-plane superconductivity are suppressed orderly for the fields perpendicular to CuO2 planes. The influences of the field parallel to CuO2 planes on the 3D and 2D superconductivity are much weaker than those of the field parallel to the c-axis. The irreversibility lines for the 3D and 2D superconducting states are also studied. 相似文献
17.
Floating-zone growth and property characterizations of high-quality La2-хSrхCuO4 superconductor crystals 下载免费PDF全文
We have grown underdoped(x=0.11,0.12) and optimally doped(x=0.16) La2 x SrxCuO4 single crystals by the traveling-solvent floating-zone technique.In order to prepare good quality cuprate crystals,we have made much effort to optimize the preparation procedures.For example,we haveadopted the sol-gel route to prepare a highly fine and homogeneous La2xSrxCuO4 precursor powder for fabricating a very dense ceramic feed rod used for the floating-zone growth,and we have also used quite a slow growth rate.The high quality of the grown crystals has been verified by double-crystal x-ray rocking curves,with the full-width-at-half-maximum being only 113-150 arcseconds,which are the best data reported so far for La2xSrxCuO4 crystals.The superconducting critical temperatures of the grown crystals are 30,31 and 38.5 K for x=0.11,0.12 and 0.16 samples,respectively,according to magnetic measurements. 相似文献
18.
Ken-ichi Kumagai Kenji Kawano Kenji Fujiwara Isao Watanabe Kusuo Nishiyama Kanetada Nagamine 《Hyperfine Interactions》1993,79(1-4):929-935
Muon spin rotation (SR) is applied to La2–x
Ba
x
CuO4 aroundx=0.12 where the superconductivity (SC) is suppressed remarkably. The magnetic ordering of Cu-moments appears below 35 K in the narrow range ofx where a lattice instability from the low temperature orthorhombic (LTO) to the low-temperature tetragonal (LTT) structure exists. The present study suggests strongly that the magnetic ordering of Cu-moments is an important factor in the suppression of high-T
c superconductivity aroundx=0.12 in La2–x
Ba
x
CuO4. Similar results are obtained for the La2–x
Sr
x
CuO4 and La2–x–y
Sr
x
Nd
y
CuO4 systems. 相似文献
19.
M. V. Eremin S. G. Solov’yanov S. V. Varlamov 《Journal of Experimental and Theoretical Physics》1997,85(5):963-970
We solve the problem of the effect of strong electron correlations on the homogeneous spin susceptibility of current carriers
in CuO2 planes. We show that the dependence of the spin susceptibility χ(T) of high-T
c superconductors of the La2−x
SrxCuO4 type on temperature and the doping index x can be explained fairly well by the two-band model suggested earlier (the singlet-correlated oxygen band plus the lower Hubbard
band of copper). The model has features in common with the phenomenological t-J model but cannot be reduced to the latter completely. In contrast to the t-J model, the density of states of the oxygen holes has a peak near the bottom of the band. It is the presence of this peak
together with the non-Fermi-liquid properties that explain the unusual behavior of the spin susceptibility of La2−x
SrxCuO4.
Zh. éksp. Teor. Fiz. 112, 1763–1777 (November 1997) 相似文献
20.
Three valency models for orthorhombic La2-x
Sr
x
CuO4 were investigated for increasing Sr concentrationsx (0x0.21): 1. Cu2+Cu3+, 2. apex O2–O– and 3. in-plane O2–O–. All calculations were done by using structural parameters valid for the temperature range from 10 to 22 K. We thereby calculated the electrostatic interaction energy which, next to ionization potentials and electron affinities, comprises a major of the binding energyE
B
of crystals. Second-order effects were accounted for by calculating the strength of ionic dipole moments induced by crystal electric fields at relevant lattice sites. Their largest strengths are comparable to the dipole moment of the water molecule. Three out of five dipoles in La2-x
Sr
x
CuO4 vanish during the transition from the orthorhombic to the tetragonal phase. The binding energy differences between the different models suggest that the system is in a state of model 1. However, the differences are very small, being in the order of 0.3 to 0.76 eV atx=0.13. 相似文献