Polaronic charge transfer and large dielectric constant inCa₃CoRhO₆

Abstract

We report the dc electrical conductivity and ac impedance study of the spin chain compound Ca3CoRhO6. The sample shows a variable range hopping‐assisted dc conduction below 250 K, while a nearest neighbor small polaron hopping is observed at higher temperatures. A reasonably large frequency‐independent ac dielectric permittivity (∼3200) is observed around room temperature. The activation energy associated with the relaxation peaks in loss tangent below 200 K is found to be close to the variable range hopping energy of the dc resistivity data which signifies the active role of the charge carrier hopping toward the ac dielectric data. The characteristic time constant associated with the relaxation (7.2 × 10−11 s) and the value of activation energy (116 meV) suggest a polaronic charge transfer in the system. The modulus analysis suggests that the relaxation in permittivity is due to the intrinsic grain effect and it is likely to be associated with charge transfer between transition metal ions in a system where their mixed valence nature is already reported. The sample also shows dielectric anomaly close to the low‐temperature magnetic transition, although we failed to observe any ground state spontaneous electric polarization.

Colossal-Permittivity Behaviors in A-Site Distorted Double-Perovskite LiCuNb3O9 with Correlated Magnetoelectric Effect and Variable-Range Hopping

“…Such an eigen frequency f 0 is higher than that of CaCu 3 Ti 4 O 12 with f 0 = 5.02 × 10 14 Hz while lower than that of Fe–Ti-based oxides, e.g., 5.13 × 10 21 Hz in FeTiTaO 6 , 1.82 × 10 23 Hz in FeTiNbO 6 , and 1.82 × 10 33 Hz in FeTiSbO 6 . These suggest that LiCuNb 3 O 9 has slightly different hopping behaviors, which instead, are more similar to those multiferroic materials, e.g., Ca 3 CoRhO 6 , which possesses a variable-range hopping conductivity and the opening of a Coulomb gap in the d bands, giving rise to a strong magneto-dielectric effect . Therefore, in LiCuNb 3 O 9 , the intersite coulomb energy should be sufficient to resist the thermal fluctuations around relaxation temperatures.…”

“…67 These suggest that LiCuNb 3 O 9 has slightly different hopping behaviors, which instead, are more similar to those multiferroic materials, e.g., Ca 3 CoRhO 6 , which possesses a variable-range hopping conductivity and the opening of a Coulomb gap in the d bands, giving rise to a strong magneto-dielectric effect. 68 Therefore, in LiCuNb 3 O 9 , the intersite coulomb energy should be sufficient to resist the thermal fluctuations around relaxation temperatures. The localized charge carriers from Cu 3d can hop a larger distance to an energetically favorable site.…”

Magnetization, dielectric and thermal studies in the double perovskite polycrystalline compound Tm2CoMnO6

“…(T ) becomes independent of T below 200 K, whereas above that a sharp rise is occurred indicating towards some kind of relaxation behaviour. Such type of DP primarily shows Maxwell-Wagner type of relaxation which is may be due to the inhomogeneous grain-grain boundary effect, very common for polycrystalline oxides [43,54]. Besides that, the magnitude of activation energy and time constant found from the T variation of lnτ (whereas, τ is obtained from tanδ vs T plot) indicates towards some hopping mechanism where the charge carrier is heavier than normal electronic mass.…”

“…6(a)]. This type of compounds are considered to be high dielectric materials [42,43]. Interestingly, a hump like anomaly is observed at 53 K that is shown in the inset of fig.…”

“…From the fitting of lnτ vs 1000/T peak , we have obtained E = 354.5 meV and τ 0 = 1.94 × 10 −12 s. The value of τ 0 is too large for normal electronic conduction (∼ 10 −16 s) [46], and therefore indicates towards a different charge carrying mechanism. The activation energy is also a bit higher, which signifies some kind of long range hopping in the system [43].…”