Synthesis, characterization, and thermostability of bis(2,2,6,6- tetramethyl-3,5-heptanedionato)barium(II)

The metal-organic chemical vapor deposition (MOCVD) technique is a promising process for high-temperature superconductor YBa₂Cu ₃O_7-δ (YBCO) preparation. In this technique, it is a challenge to obtain barium precursors with high volatility. In addition, the purity, evaporation characteristics, and thermostability of adopted precursors in whole process will decide the quality and reproducible results of YBCO film. In the present report, bis(2,2,6,6-tetramethyl-3,5-heptanedionato)barium(II) (Ba(TMHD)₂) was synthesized, and its structure was identified by FTIR, ¹H NMR, ¹³C NMR, and ESI-MS spectroscopy. Subsequently, the thermal properties and the kinetics of decomposition were systematically investigated by nonisothermal thermogravimetric analysis methods. Based on the average apparent activation energy evaluated by the Ozawa, Kissinger, and Friedman methods, the volatilization process was discussed, and all results show that Ba(TMHD)₂ is unstable and highly sensitive to the change of temperature during the whole evaporation process. Therefore, it is very important to choose suitable volatilization technology and conditions for avoiding Ba(TMHD)₂ breakdown (or thermal aging) during MOCVD process. Subsequently, the possible conversion function is estimated through the Coats-Redfern method to characterize the evaporation patterns and follows a phase boundary reaction mechanism by the contracting surface equation with average activation energy of 118.7 kJ·mol^-1.