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1.
Backscattering yields in the <001> axial channeling mode using D+ ions have been measured for YBa2Cu3O7–y single crystals with Tc=59K. 68K and 91K at temperatures between 40K and 295K. In 60 K-class YBa2Cu3O7–y with significant anomalies associated with the spin gap, it is found that the channeling anomalies are observed at 130–140 K(Tpa) in addition to anomalies at Tc. The channeling anomalies at Tc follow to the shift of Tc, suggesting the phonon anomalies induced by the superconducting-gap opening. On the other hand, Tpa is found to be almost unchanged for varying Tc, although Tpa appears near the temperature where the spin gap is opened. This leads a question whether the channeling anomalies at Tpa is directly related to the phonon anomalies induced by the spin-gap opening. The existence of lattice instability is suggested as one of possible explanations for the anomalies at Tpa. 相似文献
2.
In this paper we have shown that polycrystalline films corresponding to Tl-2223 phase can be grown by employing high thalliation
temperatures and short thalliation times. Ultrasonically deposited precursor films corresponding to Ba2Ca2.2Cu3.3Ox(Agy) have been thalliated under high vacuum (∼ 10-5 torr) at 890°C to obtain single phase Tl-2223 films. An off-stoichiometric and unreacted pellet of composition Tl2.05Ba2Ca2Cu3Oz has been used as source of Tl. We have shown that oxygen ambient is not necessary for the growth of Tl-2223 phase. The as-thalliated
films have Tc’s in the range 123 K ±0.70 K. TheT
c
has been found to be independent of the addition of AgNO3 to the precursor. The zero field transportJ
c
has been observed to be > 1.2 X 105 A/cm2 at 77 K. NearT
c
(110 K-122 K),J
c
has been observed to follow the power lawJ
c
∞ (1-T/T
c
)p,p 2. A power law withp tt 1.4 has been observed for the temperature range 70 K-110 K. An optimum doping of Ag has been observed to induce about
25% increase inJ
c
and it also leads to uniform and enlarged grain growth. The surface morphology of Ag free samples contains plate like grains
having arbitrary shapes. In contrast to this 0.35 Ag doped sample exhibits nearly rectangular plate like grains 相似文献
3.
H. Keiber H. Wühl G. P. Meisner G. R. Stewart 《Journal of Low Temperature Physics》1984,55(1-2):11-15
The specific heat of a new orthorhombic structure modification of ZrRuP has been measured. The superconducting transition temperatureT
c
of this new phase, 3.76 K, is concluded to be much lower than that of the hexagonal modification (T
c
=13.0 K) due to the 30% stiffer lattice of the orthorhombic phase as determined by the Debye temperature. The high- and low-T
c
phases of ZrRuP are found to have nearly identical densities of states at the Fermi energy. 相似文献
4.
Atomistic simulation has been performed with interatomic potentials to investigate the effect of negative hydrostatic pressure on the superconducting transition temperature (Tc) of MgB2. The calculation reveals that Tc can be greatly enhanced by applying negative pressure and it can reach up to 52.2 K at ?13 GPa, about 13 K higher than that at ambient pressure. The mechanism for the enhancement of Tc is attributed to that negative pressure reduces high-frequency phonon vibrations of B and thus dramatically enhances the electron–phonon coupling. Our result seems to open up a possible way for the enhancement of Tc in MgB2. 相似文献
5.
A great number of oxyfluorides with a chiolite related structure have been prepared. They show all a ferroelastic, ferroelectric-prototype, paraelectric transition. The highest Curie temperature (Tc = 800 K) has been obtained for the tungsten compound Na5W3O9F5. The value of Tc is found to vary as a function of the substitutions from Na5W3O9F5. The largest decrease is observed for the composition Na4Lu (WNb2)O9F5 with Tc = 88K. Pyroelectric and piezoelectric applications are expected. The influence of the composition on other transitions observed in these materials has been determined. 相似文献
6.
V.M. Pan V.P. Gorishnyak E.M. Rudenko V.E. Shaternik M.V. Belous S.A. Koziychuk F.I. Korzhinsky 《低温学》1983,23(5):258-262
Niobium nitride films with a value for Tc of up to 17.3 K have been prepared by reactive magnetron and diode sputtering in Ar and N2 gas mixture. Alteration of Tc and N2 ion implantation into NbN films was studied. It is shown that small doses of implanted ions cause an abrupt decrease of Tc to 12.8 K. Annealing at 900°C restores the high Tc By the tunnel effect, the magnitude of the energy gap is 3.05 Me V at 1.56 K for NbN with Tc = 17.1 K and . The existence of an undersurface layer has been discovered, whose width is of the order of the coherence length, with a lower Tc, of 12.0–12.8 K. The superconductivity of this layer above Tc is due to the proximity effect. NbN tunnel junctions are made with a density of the Josephson current i=(1.7-2.87) · 103 A cm?2. 相似文献
7.
Crystal of composition Li0.02Na0.98NbO3 is ferroelectric at room temperature (space group Pc2m, Tc = 640 K). Two kinds of domain walls parallel to (101) or (141) planes have been observed at 300 K. The birefringence na-nc and the domain pattern have been investigated from 300 to 950 K. Four transitions have been detected at T2 = 540 K, T3 = Tc = 640 K, T4 = 825 K and T5 = T′c = 940 K. The transition at T′c is of ferroelastic-prototype type. The switching of the polarization associated with the disappearing of the domain walls is in good agreement with a ferroelectric-ferroelastic coupling. 相似文献
8.
The discovery of a new superconductor, LaFeAsO1?xFx with a superconducting critical temperatureT,c, of 26 K in 2008, has quickly renewed interest in the exploration of iron‐based superconductors. More than 70 new superconductors have been discovered within several months, with the highest Tc of up to 55 K being observed in the SmFeAsO1?x compound. High Tcs have previously only been observed in cuprates; these new iron‐based superconductors have been added as second members of the high‐Tc family. The crystal structure of these compounds contains an almost 2D Fe–As layer formed by FeAs4 tetrahedrons, which can be separated by an oxide or metal layer that provides extra electrons to the Fe–As layer, and the itinerant iron 3d electrons form an antiferromagnetic (AFM) order state in the undoped parent compounds at around 100–200 K. Superconductivity can be induced by carrier doping, which destroys the AFM ground state. In this Review, the most recent findings on and basic experimental facts about this class of high‐Tc materials will be presented, including the various superconducting structures, the synthesis methods, the physical properties of the parent compounds, the doping methods that could produce superconductivity, pressure effects, and the prospects for this new iron‐based high‐Tc family. 相似文献
9.
Yuan‐Yuan Tang Yong Ai Wei‐Qiang Liao Peng‐Fei Li Zhong‐Xia Wang Ren‐Gen Xiong 《Advanced materials (Deerfield Beach, Fla.)》2019,31(29)
A ferroelectric with a high phase‐transition temperature (Tc) is an indispensable condition for practical applications. Over the past decades, both strain engineering and the isotope effect have been found to effectively improve the Tc within ferroelectric material systems. However, the former strategy seems to prefer working in inorganic ferroelectric thin films, while the latter is also limited to some certain systems, such as hydrogen‐bonded ferroelectrics. It is noted that a mono‐fluorinated molecule is geometrically very similar to its parent molecule and the substitution of H by an F atom can introduce a chiral center on the molecule to template or stabilize polar structures. Significantly, the barrier of rotation of the fluorinated organic molecules is raised, resulting in a remarkable increase in Tc. Herein, by applying the molecular design strategy of H/F substitution to the organic–inorganic perovskite ferroelectric (pyrrolidinium)CdCl3 with a low Tc of 240 K, two high‐Tc chiral perovskite ferroelectrics, (R)‐ and (S)‐3‐F‐(pyrrolidinium)CdCl3 are successfully synthesized, for which the Tc reaches 303 K. The significant enhancement of 63 K in Tc extends the ferroelectric working temperature range to room temperature. This finding provides a new effective way to regulate the Tc in ferroelectrics and to design high‐Tc molecular ferroelectrics. 相似文献
10.
Balvinder Gogia Subhash C Kashyap D K Pandya K L Chopra 《Bulletin of Materials Science》1991,14(2):217-222
The role of preparation conditions and the effect of addition of Pb in Bi-Sr-Ca-Cu-O (BSCCO) superconductor, on theT
c,J
c and grain orientation have been studied. Calcination at a temperature higher than the melting point of Bi2O3 after the prereaction at 800°C leads to formation ofc-axis oriented nearly single phase material. The presence of lead yields a nearly highT
c phase (2223) exhibiting a maximum transition temperatureT
c=110 K and ΔT
c=2 K. The addition of lead and grain orientation together result in an increase inJ
c by nearly two orders of magnitude. The degradation behaviour was studied in terms of changes inT
c,J
c and structure on exposure to atmosphere up to 250 days. Samples with 0.6 Pb were found to be superconducting withT
c=97 K even after 250 days. The highT
c phase was stable against degradation. Our studies indicate that the degradation of leaded BSCCO is a surface phenomenon rather
than bulk phenomenon. 相似文献
11.
V. I. Pudov A. S. Sobolev Y. P. Sukhorukov N. M. Chebotaev S. V. Naumov 《Journal of Superconductivity and Novel Magnetism》2010,23(2):269-273
A method for evaluation of the critical temperature T c and the width of the superconducting transition ΔT c in HTSC single crystals has been developed. By this method, the first derivative of the temperature dependence of the resistivity, \(\frac{\partial \rho (T)}{\partial T}\), is constructed. A technique for synthesis of YBa2Cu3O7?x single crystals with highly reproducible physical-mechanical properties has been described. A standard sample with T c=94 K and ΔT c=0.25 K has been synthesized and certified. 相似文献
12.
Experimental data of the temperature dependence of the thermoelectric power S(T) for differently doped HTSC-samples recently found renewed interest in the context of the van Hove scenario as well as the spin gap behavior. Furthermore, a universal relation between S(290K) and the hole concentration p has been reported. On the other hand, ion irradiation of HTSC- films with ions of medium energy (typically 350 ke V) is known to produce defects leading to a strong increase in normal-state resistivity and a depression of the superconducting transition temperature Tc. The idea of the present work is to combine both techniques to test whether the ion-induced defects are predominantly oxygen vacancies within the CuO-chains, reducing p as monitored by S(290K). For this purpose, c-axis oriented YBa2Cu3O7-films on (100)-SrTiO3 substrates were irradiated with 350 ke V He+-ions. After each irradiation step an XRD analysis and an S(T)-measurement for Tc < T < 295 K is performed. It is shown that for small fluences the ioninduced S(T)-changes can be attributed to oxygen displacements destroying the CuO-chains, while for higher fluences additional defects within the CuO2-planes have to be taken into account. The corresponding S(T) behavior is comparable to what has been reported for Zn-substituted underdoped HTSC-samples. 相似文献
13.
Lin Li Bai-ru Zhao Ping Zhou Shou-quan Guo You-xiang Zhao 《Journal of Low Temperature Physics》1981,45(3-4):287-294
The dependence of Tc on sputtering conditions, chemical composition, and phase structure for Nb-Ge films has been studied. It was found that Tc varied with composition, but was not dependent on exact stoichiometry of the film; the Nb/Ge ratio was <3 for very high Tc 23 K films and 4 for films with Tc 20 K. X-ray results showed that the films with Tc 23 K contained a certain amount of tetragonal Nb5Ge3 with a lattice parameter of A15 phase 5.14 Å. The depth profile of very high Tc films showed no increase of oxygen concentration at the film-substrate interface; no correlation of high Tc and impurities was found. 相似文献
14.
Yoshiya Akagi Hiroyuki Sasakura Satoru Noguchi Shigeki Tsukui Takashi Oka Motoaki Adachi 《Journal of Superconductivity》2004,17(3):449-453
The Ru-1232 compounds have been synthesized in the (Ru1–xNb
x
)Sr2(GdCe1.8Sr0.2)Cu2O
z
system, and effects of Nb substitution for Ru on superconductivity and ferromagnetism of the Ru-1232 compounds have been investigated. First, X-ray powder diffraction study shows that nearly the single 1232 phase samples can be obtained in the x composition range from 0.0 to 0.3. Then, from the electrical resistivity study, it is found that each of the samples shows resistivity dropping phenomenon at two temperatures of T
c
l and T
c
h, which originates from superconductivity of the Ru-1232 phase and the Ru-1222 one, respectively. Both of the starting temperatures are lowering with increasing Nb content x. Lastly, from the magnetic susceptibility study, it is found that superconducting transition temperature T
c is 20 K for the Ru-1232 sample with x = 0.0 and the ferromagnetic transition temperature T
m is about 90 K. This study also shows that both of the values of T
c and T
m become low with increasing x from 0.0 to 0.3. 相似文献
15.
K K Saini C P Sharma S N Ekbote Pavas Asthana D K Suri Kant Chander S A Agnihotry Subhas Chandra 《Bulletin of Materials Science》1991,14(2):235-239
EnhancedT
c in calcium-free Tl compounds of the series Tl
m
Ba2Ca
n−1Cu
n
O
x
(2201) has been reported. Three different starting compositions (2201, 1201 and 2202) were studied extensively with varying
conditions of preparation. Under optimized conditions (sintering temperature 970°C and duration 3–10 min) the highestT
c(onset) ranges from 103 K to ∼ 115 K andT
c (zero) ∼ 95 K was found. XRD studies showed the transformation of all the three nominal compositions into 2201 phase with
differentT
cs. 相似文献
16.
L. M. Volkova S. A. Polyshchuk S. A. Magarill F. E. Herbeck 《Journal of Superconductivity》2001,14(6):693-700
We establish the empirical correlation for diborides (AB2) between T
c and crystal chemical parameters of a simpler structural fragment—sandwich A2(B2) where the superconductivity appears—like that found in high-T
c cuprate superconductors. Our results suggest that in the absence of vacacies in B2 plane, T
c of diborides can be higher, that is, 77 K, the evaporation temperature of liquid nitrogen. We discuss critical crystal chemistry parameters controlling T
c and ways to achieve higher transition temperatures in diborides, based on this correlation. 相似文献
17.
Yoshiya Akagi Hiroyuki Sasakura Satoru Noguchi Shigeki Tsukui Takashi Oka Motoaki Adachi 《Journal of Superconductivity and Novel Magnetism》2004,17(3):449-453
The Ru-1232 compounds have been synthesized in the (Ru1?xNb x )Sr2(GdCe1.8Sr0.2)Cu2O z system, and effects of Nb substitution for Ru on superconductivity and ferromagnetism of the Ru-1232 compounds have been investigated. First, X-ray powder diffraction study shows that nearly the single 1232 phase samples can be obtained in the x composition range from 0.0 to 0.3. Then, from the electrical resistivity study, it is found that each of the samples shows resistivity dropping phenomenon at two temperatures of T c l and T c h, which originates from superconductivity of the Ru-1232 phase and the Ru-1222 one, respectively. Both of the starting temperatures are lowering with increasing Nb content x. Lastly, from the magnetic susceptibility study, it is found that superconducting transition temperature T c is 20 K for the Ru-1232 sample with x = 0.0 and the ferromagnetic transition temperature T m is about 90 K. This study also shows that both of the values of T c and T m become low with increasing x from 0.0 to 0.3. 相似文献
18.
N. A. Borovoi Yu. P. Gololobov G. L. Isaenko N. B. Stepanishchev 《Inorganic Materials》2009,45(1):1-6
The existence of two polytypes at room temperatures, C-TlInS2 and 2C-TlInS2, with different monoclinic cell parameters, c and 2c, has been revealed. Significant differences in crystal lattice dynamics of these polytypes have been found. In particular, two phase transitions (PTs) have been detected for the polytype C-TlInS2 as the temperature varies: a second-order PT from paraphase to incommensurate phase at T i = 215 K and a first-order ferroelectric PT accompanied by a quadrupling of the parameter c at T c = 197 K. No PT accompanied by an increase in unit cell parameter c has been found in the polytype 2C-TlInS2, but a global temperature hysteresis characteristic of crystals with an incommensurately modulated structure has been detected at T = 180–230 K. 相似文献
19.
Various ceramic samples of Hg x Ba2CuO4+δ have been synthesised by the quartz ampoule method with previously prepared Ba2CuO3+y as a precursor. By tuning the mercury content x < 1 and controlling the synthesis of Ba2CuO3+y , we have prepared samples which show sharp superconducting transitions with different T c-values for different samples. The temperature of the onset of diamagnetism varies between 80 K and 96 K. For two samples, each with T c = 95 K, the specific heat c p(T) has been measured between 60 and 110 K with a continuous heating method. An O2-annealed sample A reveals a broad magnetic superconducting transition, whereas the transition of the as-synthesised sample B is narrow. The specific heat anomaly of the superconducting transition can clearly be identified for sample B and is broadened in applied magnetic fields. It cannot be resolved in the O2-annealed sample A, most likely because of a broad distribution of T c-values as indicated by the broad transition. 相似文献
20.
Single crystals of some new ternary stannides in the systems (M)CoSn, (M)RuSn and (M)OsSn, where M = rare earth, Y. Sc, Ca, Sr, or Th have been grown from a tin solvent in vacuo. We find the new compounds to be isomorphous to the published rare earth rhodium tin compounds. The ternary, TmOsxSny, has been found to be a reentrant superconductor with Tc = 1.1K and Tm = 0.6K. Superconducting and/or magnetic transition temperatures and lattice parameters are given. A tabular summary of identified phases and their lattice constants for all the ternary stannides prepared so far is included for comparative purposes. 相似文献