The effects of quenching and lead substitution on the ultrasonic wave velocity and attenuation in bismuth cuprate high T_csuperconductors

Abstract

The velocity and attenuation of longitudinal and shear ultrasonic waves propagated in ceramic specimens of single phase Bi(Pb)2223, Bi(Pb)2212 and lead-free Bi2212 have been measured between 10 and 295 K. The anomalous elastic effects and hysteresis in the range about 190-240 K reported by other workers have been found in samples of Bi(Pb)2223 and lead-free Bi2212. However, for the Bi(Pb)2212 phase, in which some Bi is substituted by Pb, these anomalies and hysteresis are suppressed. Quenching a sample of the Bi2212 phase from 800 degrees C into liquid nitrogen removes these anomalies, which have therefore been shown to be strongly dependent on chemical composition: either oxygen content or lead substitution for bismuth. The elastic stiffnesses of these bismuth cuprates are unusually small due largely to (i) their open microstructure on the macroscopic level but also in part as a result of (ii) their rather open layer-like structure with weak interlayer binding forces and (iii) the intermediate valence state of the copper ions. It is known that quenching the Bi2212 phase from just below the melting temperature (about 880 degrees C) into liquid nitrogen results in the reduction in oxygen content that is necessary to optimize the superconducting properties of this phase. The authors have now established that quenching also results in substantial longitudinal acoustic mode softening whilst enhancing Tc.

Effect of Ba-site substitution by Sr on ultrasonic velocity and electron–phonon coupling constant of DyBa2−xSrxCu3O7−δ superconductors

“…The increase in absolute longitudinal and shear velocities at 80 K with x may be related to the decrease of cell volume as a result of substitution of smaller Sr 2+ (ionic radius: 1.25 Å) for Ba 2+ (ionic radius: 1.42 Å). This volume change may have caused changes in interatomic length and bonding strength which were detected by both longitudinal and shear phonons and are reflected by the increase in velocity for both modes with increasing Sr [21]. Interestingly, the substitution of Sr for Ba which caused a decrease in T c has also caused an increase in  D (Table 3).…”

“…The ultrasonic method, which is sensitive to lattice instabilities and phase transitions, was found to be very useful to probe bulk property changes of ceramic materials such as glasses [8][9][10][11], magnetoresistance materials [12][13][14][15], and also high-temperature superconductors [16-24 and references therein]. In the latter, step-like velocity anomalies above 200 K indicating sudden or unexpected elastic hardening taking place in superconducting samples have been observed in several RE123 [16,17], RE1113 [20] and Bi-based samples [18,21]. The step-like anomalies were found to be oxygen related but its relationship to superconductivity is still not clear [23].…”

Testing and modelling of inductive superconducting fault current limiters

“…Inhomogeneous temperature distributions introduce thermal stresses in the materials. Assuming that the the hot zone is spherical, the stresses induced at the interfaces of hot and cold zones can be calculated as [ 131 where (5, is the compressive stress in radial direction, oee and oqp9 are the tensile stresses on the surface of the sphere, a is radius of the sphere, r is the distance to the centre of the sphere, E (41 GPa [14]) is Young's modulus, ' U (assume 0.2) is Poisson's ratio and a is the thermal expansion coefficient [15]; q 8 and ovv are plotted in Fig. 11.…”

Effects of Cd2+ substitution on elastic properties and step-like anomalies in Tl0.9Bi0.1Sr1.8Yb0.2Ca1−Cd Cu1.99Fe0.01o7− superconductors

“…Amongst the normal state peculiarities being investigated are the pseudogap, superconducting fluctuation behavior (SFB) and elastic anomalies which occurs above the critical temperature T c . The elastic anomalies can be studied using velocity measurements and several reports have suggested that the anomalies correspond to lattice instabilities and phase transition around the critical temperature and between 180 K and 230 K [1][2][3][4][5][6][7]. Although the discovery of D-wave superconductivity in high-temperature superconductors concludes that the superconductivity mechanism of HTSC does not involve phonons, the continued observation of a number of elastic anomalies in the normal state remains intriguing as they may influence other material properties an act as precursor to physical changes at much lower temperatures.…”

“…For REBa 2 Cu 3 O 7 À δ (RE¼Y, Ho, Gd, Eu, Dy and Er) systems, a number of elastic anomalies have been reported in the temperature range of 200-260 K [3,4,6,[8][9][10][11][12][13] which were characterized by step-like slope change showing sudden hardening below certain temperature. Interestingly, previous work has also shown that the step-like elastic anomalies can also be influenced by elemental substitution.…”