Elastic moduli and step-like elastic anomalies in Ce-substituted Tl_0.9Bi_0.1Sr_2−xCe_xCa_0.9Y_0.1Cu_1.99Fe_0.01O_7−δ (x = 0–0.20) superconductors

Abstract

Ultrasonic velocity measurements have been performed on polycrystalline Tl_0.9Bi_0.1Sr_2−xCe_xCa_0.9Y_0.1Cu_1.99Fe_0.01O_7−δ superconductor to study the influence of Ce substitution on elastic properties of the samples. Ce was observed to influence elastic moduli at 80 K which showed the largest value obtained at x = 0.10 where, coincidentally, the highest superconducting temperature T_c among samples was also shown. A longitudinal velocity anomaly was observed at around 260 K for the unsubstituted sample (x = 0). Ce substitution caused the temperature of the elastic anomaly to shift to 250 K (x = 0.1) and 262 K (x = 0.2). The existence of the step-like elastic anomaly was suggested to be due to oxygen ordering taking place in Tl–O planes. The analysis of elastic behavior in the vicinity of the elastic anomalies using the Landau free-energy model suggests that the anomaly is due to a phase transition which involves oxygen ordering.

Keywords:

• elastic anomaly
• elastic properties
• phase transitions
• Landau model
• high-temperature superconductors
• oxygen ordering

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the Malaysian Ministry of Education under Research Acculturation Grant Schemes (RAGS) [grant number. 600-RMI/RAGS 5/3 (142/2014)].