The microwave characteristics of the BaTi4O9-BaPr2Ti4O12 system were i
nvestigated, including its microstructure and infrared reflection spec
troscopy. It was found that this system is entirely composed of two ph
ases, BaTi4O9 and BaPr2Ti4O12, and it is suggested that the lattices o
f each phase are well matched obliquely at the interface in the sinter
ed ceramics. The dielectric properties are compared with calculated va
lues deduced from the mixing relations of the two components. Furtherm
ore, the infrared reflection spectra of this system were analysed with
the factorized form of the dielectric function, for the purpose of st
udying the applicability of the reflection analysis technique to this
mixed phase system.