アパタイト型構造を有するLn_<9.33+x/3>Si_<6-x>Al_xO_<26>焼結体(Ln=La, Nd, Sm, M=Al, Gd)の伝導度における前指数因子と活性化エネルギーの関係(<特集>希土類系物質の精密合成,形態制御および機能物性)

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Electrical conductivity of a series of Ln_<9.33 +x/3>Si_<6-x>M_xO_<26> (Ln=La, Nd and Sm, M=Al and Ga) sinters was examined. The pre-exponential factor and activation energy of the ionic conduction were well related by Meyer-Neldel rule, i.e., G=G_<00> exp (ΔE/kT_0) exp (-ΔE/kT). Most of the sinters were composed with an apatite-like phase in major and sub-products such as LnSi_O5 and Ln_2O_3 in minor proportions. The single phases with apatite-like structure were obtained for the composition of x=1.5. At this composition, the activation energy increased with a decrease in the ionic radius of Ln. The lowest activation energy and highest pre-exponential factor were observed for the combination of Ln=La and M=Al. This result was interpreted by considering the formation of the 4e sites for oxygen with under occupancy and oxygen ion interstitials surrounded with six 6h(La) sites.
社団法人日本セラミックス協会の論文
2007-10-01