Coexistence of the phonon and relaxation soft modes in the terahertz dielectric response of tetragonal BaTiO3.
The dielectric response to infrared waves polarized along the tetragonal axis of a ferroelectric single-domain crystal of BaTiO3 was determined by time-domain THz spectroscopy and Fourier-transform infrared reflectivity techniques. In addition to the three well-known polar lattice modes, the experiment shows an additional mode of the relaxation type in the THz spectral region, which accounts for the Curie-Weiss behavior of the c-axis dielectric constant. A comparison of experimental results with ab initio based effective-Hamiltonian simulations allows us to elucidate its relation to the order-disorder model of Comes, Lambert, and Guinier [Solid State Commun. 6, 715 (1968)10.1016/0038-1098(68)90571-1].
Hlinka
J
J
Institute of Physics, Academy of Sciences of the Czech Republic, Na Slovance 2, Prague 8, Czech Republic.
Ostapchuk
T
T
Nuzhnyy
D
D
Petzelt
J
J
Kuzel
P
P
Kadlec
C
C
Vanek
P
P
Ponomareva
I
I
Bellaiche
L
L