Preparation and properties of high-density Bi₂O₃ ceramics by cold sintering

High-density Bi₂O₃ ceramics were prepared via a three-step cold sintering process (TS-CSP) at an ultra-low temperature. In the first step, the relative density of the Bi₂O₃ ceramic, subjected to 155 °C and 300 MPa for 25 min, is 96.23%, with the majority of the crystals inside the ceramic. The Bi₂O₃ ceramic was further densified with a corresponding increase in the relative density to 98.52%, after processing at 210 °C and 300 MPa for 25 min, in the second step. Finally, in the third stage of the processing, the temperature was raised from 210 °C to 270 °C and isothermally held for 25 min, which enabled the Bi₂O₃ ceramic grains to fully grow to yield a grain size of 4.02 μm, having a relative density of 99.13%. The densification mechanism of the TS-CSP Bi₂O₃ ceramics is via a dissolution-recrystallization-growth process. The relative permittivity, quality factor and grain size of the Bi₂O₃ ceramics are 33.44, 16,218 GHz and 4.02 μm, respectively. The materials and their preparation described herein provide a novel approach for the preparation of ultra-low temperature ceramics.