Raman Scattering Study of SrTi18O3

Antiferrodistortive and ferroelectric soft modes of isotoped ferroelectric SrTi 18 O 3 x 16 O 3(1- x ) were observed for a single crystal of x =0.87 with Raman scattering. The frequency of one of the antiferrodistortive modes exhibits a gradual change near the ferroelectric transition point at 24 K ( T c ) induced as the isotope effect. The spectral forms characteristic of the ferroelectric microscopic regions were also observed in both phases. The ferroelectric soft mode does not exhibit any softening behavior even just at T c . The transition mechanism of the isotopically induced ferroelectric phase is discussed.