Abstract
We describe a material, cubic CaCu
3Ti
4O
12, which exhibits a large dielectric response, the temperature-dependence of which has not been seen, to our knowledge, in any existing material. This compound possesses a low-frequency dielectric constant,
ε∼10
4
[1], which is only weakly varying in the temperature range 100–400
K. Below
T∼100
K
, however, there is an abrupt 100-fold reduction in the value of
ε. X-ray diffraction and thermodynamic data argue against an explanation in terms of ferroelectricity, i.e. the collective ordering of local dipole moments. Both the low-frequency dielectric response as well as Raman scattering data suggest the existence of highly polarizable relaxational modes with a characteristic gap energy of 28
meV.