Relationship of solubility parameter (x), powder properties and phase formation in the Nd_1+xBa_2-xCu₃O_6.5+x/2+δ system

The relationship between the solubility parameter, x, in the solid solutions Nd_1+xBa_2-xCu₃O_6.5+x/2+δ (Nd123SS) and XRD patterns, powder surface area (SA), particle size, morphology and melting points was investigated. An efficient way to determine the value of x and residual BaCuO₂ content during Nd123SS powder synthesis is presented. The method is based on calculation of the orthorhombic splitting (OS) factor from the unit cell parameters obtained from XRD data. The final phase in the Nd123SS system is formed through a diffusion controlled reaction between BaCuO₂ and Nd123SS and a kinetic model is developed to describe the formation of the Nd123 (x = 0) superconducting powder. Finally, high values of T_c (measured by DC magnetization) were found in the powders. The highest T_c of 98.7 K was measured for the x = 0 case. This value is the highest ever reported for the Nd-Ba-Cu-O system. The T_c was found to be insensitive to the value of x, ranging between 98.7 and 94 K for x between O and 0.25, respectively. This data is in contrast to published results on samples synthesized at higher temperatures, where T_c fell to 40 K at x = 0.25.