A low-temperature internal friction study of Y124 superconductors

Abstract

A ceramic sample of Y Ba2Cu4O8 (Y124) was synthesized at atmospheric pressure with the addition of NaNO3 as an enhancer. The internal friction was measured from liquid nitrogen temperature to room temperature at kilohertz frequency using the vibrating reed method. Instead of a broad internal friction peak around 220 K observed in Y Ba2Cu3O7−δ (Y123) a small step in the internal friction spectrum was observed around 200 K with increase of temperature in Y124. This internal friction behaviour is similar to that of Sr-substituted Y Ba0.8Sr1.2Cu3O7−δ. We expect that the internal friction step in Y124 originates from charge carrier crossover. The small size of the change in internal friction around 200 K in Y124 is due to suppression of the lattice response compared with that in undoped Y123.

Field-induced log(1/T) diverging resistivity deviation from normal state in superconducting cuprates

“…At zero field it exhibits superconductivity with a transition temperature (T c ) of 22 K. At higher temperature, it shows temperature dependence of T 2 above T c (as shown by the dotted curve in the inset). At temperatures higher than about 200 K the temperature dependence of the resistivity deviates from T 2 , and it shows a temperature dependence of (T / T F ) 2 ln(T F / T ) above 150 K (as shown by the dotteddashed curve in figure 2), as found previously [14,15]. It should be noted that T c of this sample is lower than the maximal T c (25 K) in this system, which may suggest that the oxygen content in this sample has not been reduced completely to achieve the best superconductivity.…”

“…Single crystals of Nd 2−x Ce x CuO 4−δ (NCCO) grown by the flux method [14] were used in our study. The actual Ce concentrations were determined by energy dispersive x-ray analysis (EDX).…”

A low temperature internal friction study of Y0.85Ca0.15Ba2Cu3O7−δ with different oxygen content

“…The carrier transition scene gets further support from heliumion channeling experiment [1] and ultrafast spectroscopy [14]. In our recent internal friction study of Sr substituted Y123 [6] and Y124 [7], it also shows a strong correlate of the phase transition in Y123 to an electronic crossover around 180 K in YBa 2 Cu 4 O 8 (Y124) indicated by NMR and NQR experiments [8]. It is accepted that Cu NQR frequency at the Cu(2) site in the CuO 2 plane is roughly equal to carrier density at the local Cu(2) site [15].…”

“…This peak has been extensively studied among different frequency ranges [2 -5] and no consistent conclusion has been given now. In our recent internal friction study of Sr substituted Y123 [6] and Y124 [7], it shows a strong correlation of this phase transition in Y123 to an electronic crossover around 180 K in YBa 2 Cu 4 O 8 (Y124) indicated by nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) experiments [8]. Then it seems much meaningful to the intensive study of P3 peak for the completely understanding the normal-state behavior of HTSC.…”

Effects of Nano-Al Doping on Superconductivity and Microstructure of MgB₂ Bulk Superconductors

“…A simple effective method to increase pinning properties of the superconductor is the process of chemical doping. For example, the doping of SiC [4], TiB 2 [5], Zr [6] and carbon [7] has resulted in improvements of J c properties, respectively. Al is a good candidate for the substitution since AlB 2 has the same crystal structure as MgB 2 .…”