In the case of the Ce1−xZrxLayO2−y/2 sample, La(NO3)3 was employed instead of Bi(NO3)3. In the synthesis of the
Ce1−xZrxBiyO2−y/2 pigments, the molar ratio of bismuth was fixed to 20 mol% to maximize the Bi3+-doping effect, because the solubility limit of Bi3+ into the CeO2–ZrO2 lattice was 20 mol% [11].