Fabrication of Fine-Grained Functional Ceramics by Two-Step Sintering or Spark Plasma Sintering (SPS)

The majority of functional materials today are based on ceramic materials which find use in a wide range of applications that include magnetic, electronic, optical, thermoelectric (TE) and piezoelectric energy. The properties and reliability of functional ceramic materials are highly depended on the density, grain size and existence of heterogeneities in the microstructure. It is a well-known fact that there is property enhancement at finer grain sizes for most functional materials through a multitude of mechanisms depending on the application. However, what remains a challenge is the success in maintaining fine-grained microstructures using conventional sintering methods. The use of such methods results in uncontrollable grain growth and coarse microstructures which negate the benefits of fine-grained related properties. The use of spark plasma sintering (SPS) technique offers an opportunity to produce fine-grained microstructures with minimum grain growth. However, grain refinement is not always guaranteed during SPS sintering especially under high-temperature sintering conditions. Therefore, sintering conditions that allow densification with minimal grain growth are well suited for microstructural refinement. A modified two-step sintering (TSS) methodology in SPS has proven to yield promising results and has potential use in the production of functional ceramic materials with controlled microstructures