Clediator
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I will comment only on this chapter. Copper is one of the few elements which can be found in their elemental state but barium and yttrium not. They are far too strong reducing agents to be found in their elemental state and are due to that only present in salts (Ba2+ and Y3+). The typical synthetic approach to YBCO is high temperature fusion reaction in a specific temperature range to get the mixed valency of copper right. The oxidation state of the cations can be controlled by controlling temperature and partial pressure of oxygen (constant for reactions in air). Superconductors are perfect diamagnets rejecting any magnetic field leading to the described levitation (Meißner-Ochsenfeld-Effect). All matter is diamagnetic in principle but other forms of magnetism are overpowering it. Ba2+ and Y3+ are typical diamagnetic cations due to their closed shells with completely paired electrons and only react weakly to magnetic fields.