Charge carriers and small-polaron migration as the origin of intrinsic dielectric anomalies in multiferroic TbMnO₃polycrystals

Abstract

Temperature-dependent and frequency-dependent dielectric investigations have been performed in TbMnO3 polycrystals sintered in either oxidative or reductive atmospheres. The results revealed the occurrence of two dielectric anomalies above 100 K, which are caused by the thermal activation of charge carriers and their motion in grain cores and grain boundaries. The temperature dependence of the bulk dc conductivity was also analysed and indicates that charge carriers move between inequivalent sites according to a variable-range-hopping mechanism. Also, a strong correlation between dielectric properties and crystalline structure was observed. Furthermore, a low-temperature dielectric relaxation, commonly reported in rare-earth manganite crystals, was observed in both samples. This relaxation follows the empirical Cole-Cole model and was attributed to small-polaron tunnelling. Polaron motion was observed to be affected by the magnetic transitions, structural properties and intrinsic anisotropies in TbMnO3. It is also worth mentioning that the dielectric anomaly due to motion of charge carriers in grain boundaries is the only one of extrinsic origin, while the anomalies related to carrier motion in grain cores and small-polaron tunnelling are intrinsic to TbMnO3.

Effect of internal electric field on ferroelectric polarization in multiferroic TbMnO3

“…1(b)where the dielectric constant and loss data show anomaly at T C . The inset of this figure shows the dielectric data up to 130 K where the two step-like feature above 30 K can be explained by small polaron tunneling and Maxwell-Wagner-type dielectric relaxation28,29 . a) shows pyro-current (I P yro ) data recorded while warming the sample at 4 K/min from 10 K to 130 K, after poling the sample from 130 K to 10 K (T P ole ) with E ext = − 4…”

Dielectric response of Al-substituted multiferroic TbMnO3 at high temperatures

“…The dielectric permittivity was calculated from the impedance data, employing the relation ε 0 r ¼ Z 00 /ωC 0 (Z 02 þ Z 002 ). The dielectric response of the samples is due to the motion of charge carriers, and a strong correlation between the dielectric properties and the crystalline structure should exist in polycrystalline ceramics [22]. The dielectric constant shows a dispersive nature at low frequencies and is considerably affected by the temperature.…”

Physical properties of Nano Crystalline Ceramic HoBaCrO

“…In fact, at low temperatures, the thermal energy is not sufficient to allow the electron hopping between the nearest neighbour sites but is possible to hop further to find a localized state with a smaller potential difference. The conductivity data were fitted using Mott's law [68]:…”

“…The hopping distance R hop and hopping energy W hop can be written at a given temperature as [68,69]:…”