Formation mechanism and roles of oxygen vacancies in melt-grown Al2O3/GdAlO3/ZrO2 eutectic ceramic by laser 3D printing

Abstract

Laser three-dimensional (3D) printing has become a significant technique to fabricate high-performance Al2O3-based eutectic ceramics based on melt growth. However, oxygen vacancies are inevitable crystal defects during this process, and their formation mechanism and roles in the as-deposited ceramics are still unclear. In this paper, Al2O3/GdAlO3/ZrO2 ternary eutectic ceramics were prepared by laser 3D printing, and the formation mechanism of the oxygen vacancies was revealed by conducting a well-designed annealing experiment. In addition, the effects of the oxygen vacancies on the structure and mechanical property of the as-solidified eutectic ceramic were investigated. The formation of oxygen vacancies is revealed to be a result of the transfer of oxygen atoms from the oxide ceramic to the oxygen-deficient atmosphere by means of vacancy migration mechanism. Besides, the presence of oxygen vacancies has no obvious effects on crystalline structure and microstructure of the additively manufactured eutectic ceramic. However, the chemical bond property changes to some extent due to the formation of these crystal defects, which may affect the mechanical property of the as-deposited eutectic ceramic. It is found that the hardness decreases by 3.9%, and the fracture toughness increases by 13.3% after removing the oxygen vacancies. The results may provide a potential strategy to regulate the mechanical property of the oxide ceramic materials.

Cracking mechanism in laser directed energy deposition of melt growth alumina/aluminum titanate ceramics

“…The microstructure morphology and stress level determine the crack propagation ability, whereas the solidification defects determine the crack nucleation difficulty. [44][45][46] The microstructure morphology of MGCs-LDED is closely related to the scanning speed, as shown in Figure 12A-D. With the increase of scanning speed, the phase size gradually decreases, whereas the number of solidification defects such as pores increases significantly, which is consistent with the conclusion of Wu et al 47 In addition, the scanning speed also has an important influence on the solidification conditions in the LDED process.…”

“…The technical characteristic of rapid melting‐solidification gives MGCs‐LDED a fine and unique microstructure, but also brings common solidification defects such as pores and intergranular voids. The microstructure morphology and stress level determine the crack propagation ability, whereas the solidification defects determine the crack nucleation difficulty 44–46 …”

The origin of microstructural inhomogeneity in vacuum‐sintered ZrO2‐doped Lu2O3 transparent ceramics

“…In general, the oxygen atoms on the surface of metal oxide are easier to escape during high‐temperature nonoxygen‐rich sintering 44,45 . During high‐temperature sintering process of Lu 2 O 3 ceramics, the oxygen‐deficient state near the surface facilitates gradual transformation of lattice oxygen on the sample's surface into oxygen (O 2 ) and oxygen vacancy ($${{\mathrm{O}}}_{\mathrm{o}} \to {\mathrm{V}}_{\mathrm{o}}^{{\mathrm{ \bullet \bullet }}}{\mathrm{ + 1/2}}{{\mathrm{O}}}_{\mathrm{2}} \uparrow {\mathrm{ + 2e^{\prime}}}$$) 19,46 .…”

“…In general, the oxygen atoms on the surface of metal oxide are easier to escape during high-temperature nonoxygen-rich sintering. 44,45 During high-temperature sintering process of Lu 2 O 3 ceramics, the oxygen-deficient state near the surface facilitates gradual transformation of lattice oxygen on the sample's surface into oxygen (O 2 ) and oxygen vacancy (O o → V •• o +1∕2O 2 ↑ +2e ′ ). 19,46 When more oxygen vacancies accumulate on the sample's surface, long-time high-temperature sintering promotes the migration of oxygen vacancies to the sample's interior, and the lattice oxygen in the interior migrates to the surface.…”

All‐Direct Laser Patterning Zinc‐Based Microbatteries

“…With the precise photothermal effect of the laser, we can create a patterned MnO 2 /rGO cathode by in situ oxidation of the Mn 2+ ions into MnO 2 nanoparticles accompanied by generation of abundant oxygen vacancies, and reduction of GO. The in situ induced oxygen vacancies could introduce more electrochemical active sites into electrode material so as to enhance the charge storage capacity, [22,23] which is hardly achieved by using other processing methods. Additionally, we can make a patterned GO-Zn anode by transferring Zn nanoparticles from glass substrates to the GO film through photothermal effect of the laser.…”