  We report far-infrared dielectric properties of powder form ferroelectric
SrTiO3. Terahertz time-domain spectroscopy (THz-TDS) measurement reveals that
the low-frequency dielectric response of SrTiO3 is a consequence of the lowest
transverse optical (TO) soft mode TO1 at 2.70 THz (90.0 1/cm), which is
directly verified by Raman spectroscopy. This result provides a better
understanding of the relation of low-frequency dielectric function with the
optical phonon soft mode for ferroelectric materials. Combining THz-TDS with
Raman spectra, the overall low-frequency optical phonon response of SrTiO3 is
presented in an extended spectral range from 6.7 1/cm to 1000.0 1/cm.
