A THEORETICAL-STUDY OF ANOMALOUS ELASTIC BEHAVIOR OF NA-DOPED Y-1-2-3 HIGH-T(C) SUPERCONDUCTOR

In view of enhancing the T(c) value of Y-1-2-3 samples, Na is doped at the yttrium site. Ultrasonic longitudinal velocity studies have been carried out over the temperature range 80-300 K by the pulse transmission technique. The Young's modulus, leaving the temperature region 200-110 K, is found to increase continuously with decreasing temperature. However, in the temperature region 200-110 K, the modulus of elasticity is found to increase in an unprecedented manner exhibiting a peak value at 140 K. A qualitative explanation based on the ordering of oxygen atoms is given. The elastic moduli of this sample at various temperatures have also been generated by using Watchman's and Varshni's theoretical equations by employing a standard least-squares method and are found to predict the values of C(ij)(T) - C(ij)(0) easily up to 50 K.