Abstract
Relatively pure YBCO was first synthesized by heating a mixture of metal carbonates at temperatures between 1,000 and 1,300 K, resulting in the reaction: 4BaCO3+Y2(CO3)3+6CuCO3+(1/2-x)O2 → 2YBa2Cu3O7-x+1/3CO2. Modern syntheses of YBCO use the corresponding oxides and nitrates. The superconducting properties of YBa2Cu3O7-x are sensitive to the value of x, i.e., its oxygen content. Only those materials with 0≤x≤0.65 are superconducting below Tc, and when x ~ 0.07, the material superconducts at the highest temperature, i.e., 95 K, or in the highest magnetic fields, i.e., 120 T and 250 T when B is perpendicular and parallel to the CuO2 planes, respectively. In addition to being sensitive to the stoichiometry of oxygen, the properties of YBCO are influenced by the crystallization methods applied. YBCO is a crystalline material, and the best superconductive properties are obtained when crystal grain boundaries are aligned by careful control of annealing and quenching temperature rates. However, these alternative methods still require careful sintering to produce a quality product. New possibilities have arisen since the discovery of trifluoroacetic acid, a source of fluorine that prevents the formation of undesired barium carbonate (BaCO3). This route lowers the temperature necessary to obtain the correct phase at around 700℃. This, together with the lack of dependence on vacuum, makes this method a very promising way to achieve a scalable YBCO bulk.
