Water-assisted densification and broadband dielectric response of cold-sintered CaCu3Ti4O12-SnF2 composites

Miniaturization of electronic devices is one of the great challenges faced by the scientific and engineering community; hence extensive research has focused on novel materials, devices and technologies to implement the same. Calcium copper titanate (CCTO), a unique electro-ceramic material with a complex perovskite structure and reasonably high temperature-stable relative permittivity, is a potential candidate for the miniaturization of capacitors. In the present work, cold sintering is used to synthesize xCCTO-(1 - x)SnF2 (x = 0.5-0.8 vol fraction) composites at ultra-low temperature (<150 degrees C) in 30 min at a pressure of 500 MPa, which has not been reported earlier. The effect of the liquid phase (water) on the densification and microstructure of these composites is also investigated. X-ray diffraction (XRD) analysis confirms the co-existence of CCTO and SnF2 phases in the composites. As the volume fraction of SnF2 increases in the presence of the liquid phase, an evolution of microstructure showing the enhancement in densification is observed. A high relative density (>90%) is obtained for SnF2-based, cold-sintered systems, which can be due to the melting of SnF2, thus forming a liquid phase during cold sintering that enhances the dissolution-precipitation mechanism. Microstructural studies reveal that a certain amount of SnF2 and water enhances the densification in the composite through dissolution-precipitation followed by melting of SnF2. The relative permittivity (epsilon(r)), dielectric loss (tan delta) and micro-hardness of the xCCTO-(1 - x) SnF2 composite increase from 21.6 to 25.3, from 0.026 to 0.039 and from 3.6 to 5.1 GPa, respectively, with increasing SnF2 content. Further, a comparison of sintering temperature, relative permittivity, dielectric loss and micro-hardness of this system reveals that the 0.8CCTO-0.2SnF(2) composite cold-sintered at 150 degrees C achieves moderate relative permittivity (25.3 at 950 MHz), low dielectric loss (0.039 at 950 MHz) and good micro-hardness (3.6 GPa).