Figure 4

(a) Curves of mean grain size vs. sintering temperature for Na1/2Eu1/2Cu3Ti4O12 and Na1/2Sm1/2Cu3Ti4O12 ceramics. (b) Relationship between the atomic ratio of Cu+/Cu2+ or Ti3+/Ti4+ and sintering temperature for these samples. Solid dots and hollow dots in (b) correspond to the ratio of Ti3+/Ti4+ and the ratio of Cu+/Cu2+, respectively.