Sintering mechanisms in YBa2Cu3O7−x superconducting ceramics

Abstract

The densification of ceramic compacts of YBa2Cu3O7−x (123) was studied with a vertical dilatometer. The runs effected under isothermal conditions (ISO) covered the 920–970∘C range and were performed under static air atmosphere. Also, controlled heating rate (CHR) runs, from about 800 to 1050∘C, were conducted at 5∘C/min under either flowing oxygen or static air. The ISO data could be satisfactorily fitted by the solution-precipitation (SP) model giving an activation enthalpy of 221 kJ/mol. Furthermore, the CHR data for 920–970∘C was also fitted with the same model giving 207 kJ/mol as the activation energy. From analysis of CHR data, the initial stage sintering is driven by solid state sintering between 827–894∘C (823–908∘C in O2). Then, in the interval 902–920∘C (914–934∘C in O2) the intermediate stage driven by grain growth (GG), competes with the rearrangement process associated to the presence of a liquid phase. This last process applied because the next sintering stage in the range 922–970∘C (938–990∘C in O2 flow) could be fitted by the SP model with an activation enthalpy of 207 kJ/mol (229 kJ/mol in O2). In the range 972–995∘C (990–1014∘C in O2), the solid state (GG) intermediate stage mechanism and/or viscous flow competes with the SP process.