Thomas E. Karis, C. Mark Seymour, et al.
Rheologica Acta
We report careful right-angle Raman measurements, in the tetragonal phase of BaTiO3, of the lowest overdamped "soft" E(TO) mode. The measurements are from 22°C to the tetragonal-to-cubic phase transition, which occurs at Tc=135°C. We fit the data to the usual damped-harmonic- oscillator form, and obtain the harmonic frequency o and the damping constant. The results are in reasonable agreement with other measurements (which, however, have not gone as high in temperature). Unexpectedly, we find that 0 increases up to Tc, which means that the dielectric constant perpendicular to the ferroelectric axis, a, decreases right up to Tc. However, this result agrees with capacitance measurements of a to T=Tc-8°C. We also comment on the results of the A1 modes and reemphasize that all the A1 and E modes disappear abruptly above Tc and thus obey the appropriate selection rules. There are, however, broad features at about 270 and 520 cm-1 that can be observed above as well as below Tc. These broad features are not any of the 3n-3=12 optical modes at the center of the Brillouin zone. © 1978 The American Physical Society.
Thomas E. Karis, C. Mark Seymour, et al.
Rheologica Acta
Kafai Lai, Alan E. Rosenbluth, et al.
SPIE Advanced Lithography 2007
K.N. Tu
Materials Science and Engineering: A
Lawrence Suchow, Norman R. Stemple
JES