Development mechanism of Ce-doped red zirconia ceramics prepared by a high-temperature reduction method

Red zirconia ceramics is unstable at high temperature and the saturate degree of color is very poor. To broaden the application especially in colorful backsheet of mobile phone, a red zirconia ceramics based on Ce-doped yttria stabilized zirconia (YSZ) was sintered at 1450 °C. Then, the red zirconia ceramics were prepared by a high-temperature reduction method. As the reduction temperature and the doping of CeO₂ increased, the value of a* (a < 0 indicates green, and a>0 indicates red) first increased and then decreased. The redness of the ceramic sample reached the highest value of 32.5. The maximum fracture toughness reached was 9.6 MPa m^1/2. According to first principle calculations, it is shown that the Ce 4f state appears near the Fermi level after Ce₂O₃ doping. During the electronic transition from 4f states of Ce atoms to 4d states of Zr and Y atoms, it combines with the oxygen vacancies generated during the reduction to form a color center. The appearance of the color centers causes a band gap of about 2.0 eV in the crystal. The corresponding absorption wavelength is 480–500 nm, and thus the observed color is red. This work provides a way to prepare stable high-temperature red zirconia ceramic with high saturate degree of color. The color centers development mechanism was considered to be the formation of red.