Cation-stoichiometry of functional oxides modified by oxygen vacancy through growth kinetics control

Abstract

Among all functional perovskite oxides, LRE-Ba-Cu-O (LREBCO, LRE123, LRE: light rare earth = Sm, Nd, et al.) superconductors possess outstanding properties of higher critical transition temperature (Tc) and higher critical current density (Jc) than YBCO superconductors. However, cation off-stoichiometry caused by the substitution of LRE elements for Ba sites could deteriorate superconducting properties. Here, we develop a new approach for fabricating high performance superconductors crystal of nearly ideal stoichiometric Sm1+xBa2-xCu3Oy (i.e. low x value) in air through oxygen vacancy control. In the peritectic reaction of Sm211 (solid) + Ba–Cu–O (liquid) + O2 (gas) → Sm1+xBa2-xCu3Oy (solid), the higher growth rate (achieved via the high cooling rate during growth) leads to the less absorbed-oxygen in Sm1+xBa2-xCu3Oy (i. e. low y value), which could balance the whole valence of cations to gain a low x value, equivalent to a low substitution level of Sm3+/Ba2+. As a result, by using the normal precursor (Sm123 + Sm211), SmBCO bulks with the high performance (Tcmid over 94 K with the sharp transition) are successfully grown in air. Thus this path effectively realizes the control of cation stoichiometry for SmBCO by oxygen vacancy modification, which could be applicable in synthesizing other functional oxides with desirable performance.