層状化合物A_nNb_<n+3m>O_<3n+3m>[(ANbO_3)_n(NbO)_<3m>](A=Ba, Sr)の形成に及ぼすANbO_3(ペロブスカイト型)ブロックの格子サイズ・対称性の影響

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The factors which influence the formation of layer structured A_nNb_<n+3m>O_<3n+3m>[(ANbO_3)_n(NbO)_<3m>](A=Ba, Sr), consisting of m-NbO blocks and n-ANbO_3 (perovskite type) blocks, were discussed. In the Ba_nNb_<n+3m>O_<3n+3m> system, compounds with a larger value of n/m ratio were synthesized at lower temperature than that with a smaller value of n/m ratio. Lattice constant of a-axis of these compounds decreased with increasing n/m ratio (Ba_2Nb_5O_9 (n/m= 2/1) [a= 0.4172 nm], BaNb_4O_6 (n/m= 1/1) [a= 0.4182 nm], BaNb_7O_9 (n/m= 1/2) [a= 0.4195 nm]). This tendency was also the same for the Sr_nNb_<n+3m>O_<3n+3m> system (Sr_2Nb_5O_9 (n/m=2/1) [a=0.4141 nm], Sr_2Nb_8O_<12> (n/m=2/2) [a=0.4166 nm]). On the other hand, when the amount of Ca substitution for Ba or Sr increased, (Ba, Ca)Nb_4O_6 (n/m= 1/1) and (Sr, Ca)_2Nb_8O_<12 >(n/m= 2/2) were formed instead of (A, Ca)_2Nb_5O_9 (n/m=2/1) at 1573 and 1673 K, respectively. These different tendencies can be explained in terms of matching of NbO block and ANbO_3 block. : Not only the difference of lattice sizes between NbO block and ANbO_3 block, but also the symmetric property in ANbO_3 block have large effects on the formation of A_nNb_<n+3m>O_<3n+3m>.
社団法人日本セラミックス協会の論文
2001-12-01