No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
A mechanical spectrum study of bilayer cuprate La1.82Sr0.18CaCu2O6+δ
Abstract
The mechanical spectrum of bilayer cuprate La1.82Sr0.18CaCu2O6+delta (La2126) was measured using the vibrating reed method from 30 K to room temperature at kilohertz frequency. A clear modulus softening was observed at 223 K accompanied by a sharp internal friction peak, which evidences a phase transition. Another broad internal friction peak around 250 K was observed, accompanied by a large modulus change. This contrasts with the broad internal friction peak of Ca doped Y Ba2Cu3O7-delta (Y123) for which no clear modulus change was observed. The main contribution to the broad internal friction peak of La2126 is expected to be from the glass transition of the interstitial oxygen atoms.
... More recently, multiferroicity was reported in YBaCuFeO 5+δ samples [7], while the detailed information on the interstitial oxygen was not addressed. Mechanical spectrum is a well-known probe for the study of the phase transition and the relaxation of micro-units such as point defects, dislocations, grain boundaries, and domain walls in solids [11][12][13][14]. It is sensitive to the mobility of atoms on an atomic scale. ...
... Consequently P1 peak is suggested to be the stress induced relaxation of the interstitial oxygen. Due to the possible presence of a 3x3x1 superstructure [14], the relaxation process of P1 peak should come from those interstitial oxygen, which do not form the superstructure, that is to say, only a small portion of the interstitial oxygen contributes to P1 peak. ...
Double perovskite oxide YBaCuFeO5+delta samples (labeled as "as-prepared") were sintered by a solid-state reaction technique. Mechanical spectra of as-prepared sample were measured under vacuum condition from room temperature up to 720K by the reed vibration method. In the first heating run, two internal friction peaks were observed around 380 and 620K (labeled as P1 and P2, respectively) in YBaCuFeO5+delta. In the subsequent cooling run, both of them disappeared and a small step-like decrease of the internal friction around 500K was found. This step-like change was reproduced in the following thermal cycles. Thermogravimetric analysis (TGA) was also performed in order to monitor the oxygen content of the sample. It showed that the interstitial oxygen concentration decreased in the first heating run. The interstitial oxygen relaxation is suggested to be the origin of P1 peak. In dielectric measurements, a dielectric loss peak appeared around the temperature of the P2 internal friction peak and the peak temperature was independent on the measuring frequency. It is expected that P2 is associated with some kind of transitions of the interstitial oxygen. Further mechanical loss measurement of the annealed sample and scanning electron microscopy characterizing the as-prepared and annealed samples, provided more information on the interstitial oxygen in YBaCuFeO5+delta samples.
... More recently, multiferroicity was reported in YBaCuFeO 5+δ samples [7], while the detailed information on the interstitial oxygen was not addressed. Mechanical spectrum is a well-known probe for the study of the phase transition and the relaxation of micro-units such as point defects, dislocations, grain boundaries, and domain walls in solids [11][12][13][14]. It is sensitive to the mobility of atoms on an atomic scale. ...
... Consequently P1 peak is suggested to be the stress induced relaxation of the interstitial oxygen. Due to the possible presence of a 3x3x1 superstructure [14], the relaxation process of P1 peak should come from those interstitial oxygen, which do not form the superstructure, that is to say, only a small portion of the interstitial oxygen contributes to P1 peak. In the cooling route of the first thermal cycle, a drop of internal friction platform around 500K was observed as shown in Fig. 2. ...
The internal friction (Q−1), electric resistance (R), frequency (f), and zero position shift (ε) as functions of temperature are measured on Ti-rich NiTi alloys. A new internal friction (IF) peak beside the lower side of the original IF peak of the martensitic phase transition appearing in quenched specimens is observed in the aged specimen. Further study by SEM and X-ray diffraction indicates that the Ti-rich precipitation appears in the aged specimen. It is suggested that the new IF peak is also associated with the martensitic phase transition, but with a lower Ms point in the region near the Ti-rich precipitation.
... Recently, frequency modulation acoustic attenuation mechanical spectroscopy (FMAA-MS) has been developed, in which a rectangular sample is clamped at one end and can vibrate at the other end, and the length of the sample can be less than 30 mm. [9] In this letter, we show that the FMAA-MS can be used to investigate the order-disorder phase transition in a Ni 68 Fe 32 NC alloy where the length of the measured sample is 10 mm. ...
An investigation into the properties of nanocrystalline (NC) materials with sample lengths less than 30 mm seems to be a challenge by using conventional mechanical spectroscopy (MS). We use a newly developed frequency modulation acoustic attenuation mechanical spectroscopy (FMAA-MS) to investigate phase transition in Ni68Fe32 NC alloy (22 nm) where the length of the sample is 10 mm. An internal friction peak accompanied by an abrupt increase in resonant frequency occurs at 641 K, which originates from order-disorder phase transition, confirmed by a vibrating sample magnetometer and differential scanning calorimetry.
The internal friction of partially Sr-substituted Pr(Ba1−xSrx)2Cu3O7−δ (x = 0, 0.05, 0.1, 0.2, 0.3, and 0.4) ceramics was measured by the vibrating-reed method from liquid nitrogen temperature to room temperature at kilohertz frequencies. The intensity of the internal friction peak, which appears around 250 K, decreases upon Sr doping. The result is explained in terms of a possible combining structural freezing transition of CuO5 square pyramids and oxygen atoms in CuOx chains. Another internal friction peak around 134 K was observed in tetragonal Pr(Ba0.6Sr0.4)2Cu3O7−δ which is temporarily explained by the hopping of holes in the CuO2 layers.
The mechanical spectrum of double perovskite Y BaCuFeO5+δ was measured using the vibrating reed method from 100 K to room temperature at kilohertz frequency. A sharp internal friction peak around 203 K and a broad one around 260 K were observed in Y BaCuFeO5+δ. A deviation of the temperature dependent reduced modulus from linear behavior above 203 K is observed which is concurrent with the sharp internal friction peak. This suggests a phase transition mechanism of the sharp internal friction peak. The intensities of the two internal friction peaks were both depressed upon partial Ca substitution of Y. By comparison of the mechanical spectrum with the bilayer superconductor Y Ba2Cu3O7+δ, one kind of transition in double perovskite oxide is proposed for the sharp internal friction peak.
Double perovskite YBaCuFeO5+δ samples were prepared by two different sintering procedures. The interstitial oxygen contents of two samples are different which were estimated from thermogravimetric analysis (TGA). The mechanical spectrum below room temperature was measured using the vibrating reed method at kilohertz frequencies. Two internal friction peaks can be discerned in two samples above 200K whose intensities show a correlation with the interstitial oxygen concentration. The lower temperature peak is attributed to the freezing transition of the interstitial oxygen. Another internal friction peak observed around 150 K can be explained by the stress induced hopping of electrons in the Fe ion sites.
Internal friction of nanocrystalline nickel is investigated by mechanical spectroscopy from 360 K to 120 K. Two relaxation peaks are found when nanocrystalline nickel is bent up to 10% strain at room temperature and fast cooling. However, these two peaks disappear when the sample is annealed at room temperature in vacuum for ten days. The occurrence and disappearance of the two relaxation peaks can be explained by the interactions of partial dislocations and point defects in nanocrystalline materials.
Low-frequency (10-20 Hz) internal friction and shear modulus of superconducting YBa2Cu3O7-δ (δ = 0.1) ceramics have been studied at a temperature range from 40 to 1000 K. It is shown that in many cases the internal friction peculiarities were due to dynamics of ferroelastic twins.
The mechanical relaxation spectra of superconducting and non-superconducting
MgC1−xNi3
samples were measured from liquid nitrogen temperature to room temperature at kilohertz
frequencies. There are two internal friction peaks (at 300 K, labelled as P1, and 125 K, P2)
for the superconducting sample. For the non-superconducting one, the position of P1 shifts
toward 250 K, while P2 is almost completely suppressed. It is found that the peak position
of P2 shifts towards high temperature with an increase of the measuring frequency.
The calculated activation energy is about 0.18 eV. We propose an explanation
relating P2 to the carbon atoms jumping among the off-centre positions. And
further we expect the behaviours of carbon atoms to perhaps correspond to the
normal state crossovers around 150 and 50 K observed by many other experiments.
The growing body of experimental evidence for the existence of complex textures of charges and spins in the high-temperature superconductors has drawn attention to the so-called 'stripe-phase' models as a possible basis for the mechanism of superconductivity in these materials. Such observations have until now been restricted to systems where the texture dynamics are slow or suppressed altogether, and do not include the important case of YBa2Cu3O(7-delta). It seems likely that the dynamic behaviour of stripes, which has been suggested to undergo several phase transitions as a function of temperature, should also be reflected in the lattice properties of the host materials, and this forms the motivation for our present experiments. Specifically, we use MeV helium ion channelling, an ultrafast real-space probe of atomic displacements (with sub-picometre resolution), to probe incoherent lattice fluctuations in YBa2Cu3O(7-delta) as a function of temperature and oxygen doping. We detect lattice fluctuations that are larger than the expected thermal vibration component, and which show anomalies characteristic of the phase transitions anticipated for a dynamic stripe phase. Comparison of our lattice results with single-particle-tunnelling and photoemission data highlights the importance of spin-charge separation phenomena in the copper oxide superconductors.
Modules of neurons sharing a common property are a basic organizational feature of mammalian sensory cortex. Primary visual cortex (V1) is characterized by orientation modules--groups of cells that share a preferred stimulus orientation--which are organized into a highly ordered orientation map. Here we show that in ferrets in which retinal projections are routed into the auditory pathway, visually responsive neurons in 'rewired' primary auditory cortex are also organized into orientation modules. The orientation tuning of neurons within these modules is comparable to the tuning of cells in V1 but the orientation map is less orderly. Horizontal connections in rewired cortex are more patchy and periodic than connections in normal auditory cortex, but less so than connections in V1. These data show that afferent activity has a profound influence on diverse components of cortical circuitry, including thalamocortical and local intracortical connections, which are involved in the generation of orientation tuning, and long-range horizontal connections, which are important in creating an orientation map.
We present neutron scattering data on two single crystals of the high
temperature superconductor La2-x(Ca,Sr)xCaCu2O6+delta. The Ca0.1-doped crystal
exhibits a long-range antiferromagnetically ordered ground state. In contrast,
the Sr0.15-doped crystal exhibits short-range antiferromagnetic order as well
as weak superconductivity. In both crystals antiferromagnetic correlations are
commensurate; however, some results on the Ca0.1-doped crystal resemble those
on the spin-glass phase of La2-xSrxCuO4, where magnetic correlations became
incommensurate. In addition, both crystals show a structural transition from
tetragonal to orthorhombic symmetry. Quite remarkably, the temperature
dependence and correlation length of the magnetic order is very similar to that
of the orthorhombic distortion. We attribute this behavior to an orthorhombic
strain-induced inter-bilayer magnetic coupling, which triggers the
antiferromagnetic order. The large size of the crystals made it also possible
to study the magnetic diffuse scattering along rods perpendicular to the CuO2
planes in more detail. For comparison we show X-ray diffraction and
magnetization data. In particular, for the Ca0.1-doped crystal these
measurements reveal valuable information on the spin-glass transition as well
as a second anomaly associated with the Neel transition.
Inelastic neutron scattering investigations on optimally doped YBCO revealed a very pronounced temperature dependence of the Cu–O in-plane bond-stretching vibrations along the (0 1 0)-direction: a downward shift of spectral weight with decreasing temperature by at least 10 meV in a narrow range of wave vectors halfway to the zone boundary. The temperature evolution starts around 200 K, well above the superconducting transition temperature. This phonon anomaly provides strong evidence for large electron–phonon coupling. It also indicates an incipient charge density wave instability within the CuO2 planes reminiscent of dynamical charge stripes. The magnetic fluctuations have been investigated in great detail on the same sample. Incommensurate spin fluctuations have been observed for energies both below and above the energy of the resonance peak at E=41 meV. However, the dispersive nature of these fluctuations as well as their apparent isotropy in the basal plane speak against an interpretation of the spin fluctuation spectrum in the framework of the classical stripe phase picture.
The ceramic sample of Y0.85Ca0.15Ba2Cu3O7−δ was prepared by standard solid-state reaction method, and samples with different oxygen concentration were obtained by quenching from high temperature. The internal friction was measured using the vibrating reed method from liquid-nitrogen temperature to room temperature at kilohertz frequency. An internal friction peak was observed around 250 K in Y0.85Ca0.15Ba2Cu3O7−δ quenched from 1023 K. The peak is related to the one observed around 220 K (labeled as P3 peak) in undoped YBa2Cu3O7−δ (Y123). This result shows the dependence of P3 peak on carriers density and P3 peak has a strong correlation to the abnormal behavior of Y123 in the underdoped range. The variation of two low temperature thermal activated relaxation peaks (P1 and P2) on oxygen content were also investigated. And consistent explanations were given based on all recent researches.
The internal friction of YSr2Cu3−xFexO7−δ (x=0.35, 0.5 and 1) ceramics was measured by the vibrating-reed method from liquid nitrogen temperature to room temperature at kilohertz frequencies. Two mechanical energy dissipation peaks appeared around 200 and 250 K (labeled as P4 and P3, respectively) for x=0.35 sample. With increasing Fe content, P4 shifts toward higher temperature and P3 is depressed. These results provide more information on their origin of them in YBa2Cu3O7−δ (Y123) and show a crucial relationship between P4 peak and the CuOx chain layers.
We measure the internal friction Q−1 in YBa2Cu3O7−x and Bi2Sr2CaCu2O8+x samples. At temperatures near 35K for KHz frequencies we observe an attenuation peak. In the case of YBa2Cu3O7−x, assuming a thermally activated relaxation behaviour, we are able to show that it corresponds to the same process as other peaks observed at higher frequencies. For Bi2Sr2CaCu2O8+x this is not the case, and the origin of the peak, found in all the measured samples, remains unknown.
In HTS ceramic samples of the 2201-, 2212-, 2223-BSCCO and 123-, 124-YBCO systems, the temperature dependences of lattice parameters and dc-magnetic susceptibility were measured in the temperature range 80-300 K as well as those of acoustic properties and ac-magnetic susceptibility were investigated in the temperature range 5-300 K. The peculiarities in the lattice parameter temperature dependences, such as the maxima or kinks at T1 in the temperature range 190 K < T1 < 270 K and the minima at T0 ≈ Tc + 15 K, correlate with the internal friction peaks observed in both temperature ranges. The absence of the peculiarities in the non-superconducting samples suggests that they are associate with the characteristics of the sample responsible for the superconductivity in HTS ceramics.
Acoustic measurements from 10-2 to 107 Hz show that phase-like transitions (PLTs) characterized by a small jump of lattice parameters in the range 100-300 K always exist in high-Tc (near 100 K) superconducting Y-Ba-Cu-O, Bi-Sr-Ca-Cu-O and Tl-Ba-Ca-Cu-O. Ferroelastic loops associated with the elastic softening of C'=((C11+C22)/2-C12)/2 and C66 invariably occur at the PLT temperatures, and in some cases the shape memory effect may be observed. For various samples of Bi-Sr-Ca-Cu-O and Tl-Ba-Ca-Cu-O with different Tc, the acoustic attenuation (Q-1, alpha ) from the kilohertz to megahertz range reveals a plateau (Qp-1, alpha p) above Tc and drops obviously below Tc with the turning point at Tc. This kind of anomaly has not been observed for non-superconducting samples. Qp-1 is found to be closely related to the carrier density for YBa2Cu3O7- delta , Y1-xPrxBa2Cu3O7 and Gd1-xPrxBa2Cu3O7, and the drop of Q-1 and a below Tc is considered to be caused by superconducting condensation. The energy dissipation (Qp-1 and alpha p) related to carriers can be explained reasonably by using a coupling model of carriers with local dynamic distortion. Furthermore, taking account of the smearing of the superconducting gap structure and by using the modified Bardeen-Cooper-Schrieffer (BCS) relative jump rate, S(E, E', Gamma )=Re(1- Delta 2/((E-i Gamma )(E'-i Gamma ))), the calculated results of acoustic attenuation below Tc are in fairly good agreement with the experimental data. The superconducting gap Delta and the damping rate Gamma for both Bi-Sr-Ca-Cu-O and TI-Ba-Ca-Cu-O have also been obtained.
We have studied the relationship between structural defects and superconductivity in La1.8SrxCa1.2-xCu2O6-δ (0≤x≤0.8). The samples were prepared by synthesis under different oxygen pressures, P(O2)=50, 250, and 400 atm. Six of the seven samples were found to be superconducting with 22≤Tc≤58 K. The structural properties were determined by neutron powder diffraction. The inter-CuO2-plane spacing, dCu-Cu, increases as Ca on the M(1) site between these planes is replaced by the larger Sr and La ions. The metal-site ordering is influenced by the oxygen pressure during synthesis. We have used the inter-CuO2-plane spacing, neutron-diffraction measurements of the scattering from the metal sites, and chemical constraints to determine the occupancies of La, Sr, and Ca at the M(1) site. For the same overall composition, higher oxygen pressure leads to a larger fraction of La on the M(1) site. Oxygen occupancy of the vacant O(3) site in the M(1) plane increases sharply when dCu-Cu exceeds 3.5 Å. The superconducting transition temperature Tc decreases systematically as the occupancy of O(3) increases for samples that would otherwise be expected to be superconducting.
The existing measurements of elastic energy dissipation and modulus on RBa2Cu3O6+x have been reviewed and the possible mechanisms have been discussed taking into account the whole range of temperatures and O stoichiometries. Most of the processes have been correlated with the dynamics of O in the CuOx planes: those above room temperature to jumps of O bound in chains and ordered domains, and those at low temperature with hops between off-centre positions within the chains. Free oxygen in the diluted tetragonal phase has a mobility which is anomalously high for an oxide. Phase transformations are observed both above and below room temperature, and have been discussed in connection with the relaxation processes.
The internal friction of Ca partially substituted Y1−xCaxBa2Cu3O7−δ ceramics was measured using the vibrating reed method from liquid-nitrogen temperature to room temperature at kilohertz frequency. There are two thermally activated relaxation peaks (called P1 and P2 at 95 K and 120 K, respectively). The intensity of P1 almost remains unchanged with Ca substitution, while that of P2 decreases. Another internal friction peak appears around 220 K (called P3). With the increase of Ca content, the intensity of P3 decreases and the peak position shifts toward low temperature. We also have observed that Zn substitution affects P3 much less and Fe substitution seems to result in another contribution to the internal friction around 250 K. We expect that the P3 peak originates from a charge-carrier crossover and possibly has some relationship with the occurrence of the dynamic stripe at low temperature.
The internal friction of partially Sr-substituted
Y(Ba1-xSrx)2Cu3O7-δ (Y123) ceramics was
measured by the vibrating-reed method from liquid nitrogen
temperature to room temperature at kilohertz frequencies. The
intensity of the internal friction peak, which appears around 220 K,
decreases upon Sr doping while the peak position shows no systematic
change. Our results do not support the previous oxygen
order-disorder explanation; we present another approach relating
this peak to the crossover in charge-carrier dynamics, and its
evolution with Sr doping is discussed in terms of release of
internal strain and electron-phonon coupling.
This paper reports on an ultrasonic study at 85 kHz and 485 kHz of melt-textured Y123 YBa Cu O where a 2 3 7 yd possible structural change has been identified in the 220 K region. Work on oxygenated and partially deoxygenated samples has shown that the change is associated with oxygen in the samples and that the activation energy for the process is 110 meV. The conclusions are based on a qualitative and quantitative description of ultrasonic attenuation and ultrasonic velocity changes in the material as a result of slow thermal cycling and quenching experiments. q 1998 Elsevier Science B.V. All rights reserved.
The diffusion of excess oxygen atoms in La2CuO4+, (0 < 0.035)="" was="" studied="" by="" mechanical="" spectroscopy="" with="" a="" vibrating="" reed="" method="" (220="">< 1.3khz;="" 4k="">< t="">< 380k).="" for="" samples="" with="">=0.013(2) we observe a very large internal friction peak (T
max=275K, f=0.22kHz). It shifts to higher temperatures with increasing frequencies indicating a thermally activated relaxation behavior with an activation enthalpy of 0.31(3) eV. The relaxation peak vanishes after vacuum annealing the sample ( 0) leading to the conclusion that the relaxation peak is due to the diffusion of excess oxygen atoms. A relaxation peak of similar strength as in the sample with =0.013 is also detected in an oxygen enriched sample ( = 0.035). This unexpected finding of the relaxation strength is discussed in terms of the proposed phase diagrams for La2CuO4+. In addition, a shoulder at the high temperature wing of the strong relaxation peak is seen the position of which does not vary with the vibration frequencies.
A neutron-scattering study of nonsuperconducting La2-xSrxCaCu2O6 (x=0 and 0.2), a bilayer copper oxide without CuO chains, has revealed an unexpected tetragonal-to-orthorhombic transition with a doping dependent transition temperature. The predominant structural modification below the transition is an in-plane shift of the apical oxygen. In the doped sample, the orthorhombic superstructure is strongly disordered, and a glassy state involving both magnetic and structural degrees of freedom develops at low temperature. The spin correlations are commensurate.
We report ac susceptibility and 17O nuclear-magnetic-resonance (NMR) measurements on the double-CuO2-layer La2-xSrxCaCu2O6 high-temperature superconducting cuprate (HTSC) with a Tc,max of 60 K. A comparison is made with 89Y NMR measurements on YBa2Cu3O7-delta, which has a higher Tc,max of 93 K and Y0.8Ca0.2Ba2Cu3O7-delta with a slightly lower Tc,max of 87 K. We find that the hole concentration dependence of the normal-state gap and of Tc both scale with Tc,max, implying a universal scaled phase diagram for these two superconductors, and, by implication, for the wider class of HTSC. This suggests that the normal-state gap and the pairing mechanism may have a common origin.
The crystal structures of superconducting and nonsuperconducting La1.82Ca1.18Cu2O6+/-delta synthesized under O2 pressures of 400 and 2 atm were refined by Rietveld analysis of neutron-powder-diffraction data. These samples contained no impurities and their observed and calculated diffraction patterns were in excellent agreement. In both samples, Ca and La preferentially occupied, respectively, a 2a site in eightfold coordination and a 4e site in ninefold coordination; a slightly higher ordering was observed in the superconducting compound. An apical oxygen site was almost fully occupied. A trace of excess oxygen between two CuO2 planes was detected in the superconducting compound. Cu-O(1) and Cu-O(2) bond lengths differed a little between the two samples. Increases in cation ordering and in interstitial oxygen might be important factors determining superconductivity in this system.