Abstract
The complex dielectric response of cubic pyrochlore ceramics was investigated between 100 Hz and 100 THz by a combination of low-frequency capacitance bridges, a high-frequency coaxial technique, time domain transmission THz spectroscopy, and infrared spectroscopy. The data obtained between 10 K and 400 K revealed glasslike dielectric behavior: dielectric relaxation is observed over a wide frequency and temperature range, and the dielectric permittivity and loss maxima shift to higher temperature values by almost 200 K with increasing measuring frequency. The distribution of relaxation frequencies broadens on cooling and can be described by a uniform distribution. The high-frequency end of the distribution at is almost temperature independent and its low-frequency end obeys the Arrhenius Law with an activation energy of The relaxation is assigned to the local hopping of atoms in the A and O’ positions of the pyrochlore structure among several local potential minima. The barrier height for hopping is distributed between 0 and 0.2 eV. Such an anomalously broad distribution may have its origin in the inhomogeneous distribution of atoms and vacancies on sites, which gives rise to random fields and nonperiodic interatomic potential. Frequency independent dielectric losses noise) are observed at low temperatures, which seems to be a universal behavior of disordered systems at low temperatures.
- Received 18 December 2001
DOI:https://doi.org/10.1103/PhysRevB.66.054106
©2002 American Physical Society