On the Mechanism of Cuprate Crystal Growth: The Role of Mixed Metal Carbonates

The mechanism of formation of the superconductor Bi2Sr2CaCu2O8+x (Bi-2212) has been an open question since its discovery in 1988. By controlling crystal growth through the use of biopolymers as multivalent cation chelating agents, it is demonstrated through X-ray diffraction and thermogravimetric analysis, that it is the formation of a mixed metal carbonate eutectic that promotes the formation of the target phase. X-ray diffraction experiments, supported by infrared spectroscopy, identify this phase as (Sr1−x Ca x )CO3. This knowledge allows to further reduce the eutectic melting point by the incorporation of a biopolymer rich in potassium ions, resulting in the scalable formation of Bi-2212 at a temperature 50 °C lower than has been achieved previously.