ELASTIC BEHAVIOR OF OXYGEN CONTROLLED MELT GROWTH PROCESSED NEG-123 HTSC MATERIALS

A series of superconducting materials having compositional formula, ( Nd - Eu - Gd )- Ba - Cu - O (123) + x%( Nd - Eu - Gd ) Ba - Cu - O (211) or NEG-123 + NEG-211 (where x ranges from 0–50%) were prepared by the Oxygen Controlled Melt Growth (OCMG) process. After characterizing the materials by studying their microstructure, measuring Jc and Tc values, the ultrasonic longitudinal velocity (Vl) measurements were carried out both as a function of composition (x% of 211 phase) as well as the temperature, over a temperature range 80–300 K. It has been found that the variation of ultrasonic longitudinal velocity is similar to that of Jc with increasing x values (concentration of NEG-211). These results indicate that by dispersing 40% fine NEG-211 particles in the superconducting matrix of NEG-123, both the critical current densities as well as the ultrasonic velocity values are found to exhibit highest values. It is known that the lattice defects of ceramic superconductors are manifested in the form of elastic anomalies, especially in the normal temperature region (100–250 K). In order to understand the complete scenario of elastic anomalies of HTSC materials, a systematic investigation of the ultrasonic velocities of HTSC materials prepared by the OCMG technique has been undertaken and using the results an attempt has been made to generalize the scenario of the elastic anomalies in HTSC materials.