Localized polarons and conductive charge carriers: Understanding CaCu3Ti4O12 over a broad temperature range

Abstract

CaCu 3 Ti 4 O 12 (CCTO) has a large dielectric permittivity that is independent of the 1 arXiv:1810.08949v3 [cond-mat.mtrl-sci] 17 Nov 2018 probing frequency near the room temperature, which complicated due to the existence of several dynamic processes. Here, we consider the combined effects of localized charge carriers (polarons) and thermally activated charge carriers using a recently proposed statistical model to fit and understand the permittivity of CCTO measured at different frequencies over the whole temperature range accessible by our experiments. We found that the small permittivity at the lowest temperature is related to polaron frozen, while at higher temperatures the rapid increase is associated with the thermal excitation of polarons inducing the Maxwell-Wagner effect, and the final increase of the permittivity is attributed to the thermally activated conductivity. Such analysis enables us to separate the contributions from localized polarons and conductive charge carriers and quantify their activation energies.

Re‐entrant dipole glass‐like behavior and lattice dynamics of 0.65Bi(Mg1/2Ti1/2)O3‐0.35PbTiO3

“…Finally, a dielectric plateau occurs above 400 K. Further increasing the temperature leads to a diffuse phase transition (DPT) around the ferroelectric to paraelectric phase transition temperature. The temperature dependence of the dielectric permittivity near room temperature is very similar to that of K 0.5 Na 0.5 NbO 3 ‐Bi 0.5 Na 0.5 TiO 3 system and the giant dielectric material CaCu 3 Ti 4 O 12 , where the Maxwell‐Wagner effect is used to explain their dielectric behavior …”

“…To understand the response of dipoles of each group dependence of temperature, P 1 ( E b , T ) and P 2 ( E b , T ) versus temperature for the re‐entrant dipole glass‐like behavior are shown in Figure B. The opposite trends with the increase in temperature and a significant change occur near 200 K. It suggests that the number of dipoles to overcome the potential confinement increases with temperature above 200 K. Temperature dependences of both P 1 ( E b , T ) and P 2 ( E b , T ) exhibit smaller change compared with those of CaCu 3 Ti 4 O 12 or Ba(Ti 1‐ x Zr x )O 3 for x < 0.3, indicating that the dipoles (polar clusters) in this system are different from the polarons of CaCu 3 Ti 4 O 12 or the ferroelectric domains of Ba(Ti 1‐ x Zr x )O 3 . The function describes the ability of dipoles to overcome potential wells at different temperature, as shown in Figure C, which is similar to the Fermi‐Dirac function.…”

“…The temperature dependence of the dielectric permittivity near room temperature is very similar to that of K 0.5 Na 0.5 NbO 3 -Bi 0.5 Na 0.5 TiO 3 system and the giant dielectric material CaCu 3 Ti 4 O 12 , where the Maxwell-Wagner effect is used to explain their dielectric behavior. 16,17 The presence of low-temperature frequency dispersion of BMT-PT in the ferroelectric phase rather than the paraelectric phase shows dipole glass-like behavior. Therefore, the relaxation process can be assigned as re-entrant dipole glasslike relaxor.…”

Multiferroic Properties and Magnetoelectric Coupling of Fe‐Doped (Ba0.7Ca0.3)TiO3‐Ba(Zr0.2Ti0.8)O3 Ceramics

“…r H can be given bywhere is the dielectric constant of materials at a high frequency, m is the mass of electron, m * is the effective mass of donor electron, and is Bohr radius. With the increase in x , oxygen vacancies increase, which not only increases the number of bound magnetic polarons but also the effective mass of donor electron, and the latter can result in the decrease in r H . Meanwhile, the ratio of the centrosymmetric cubic phase increases with increasing x , also causing the decrease in r H through the decrease in dielectric constant.…”

Influences of Sr2+ Doping on Microstructure, Giant Dielectric Behavior, and Non-Ohmic Properties of CaCu3Ti4O12/CaTiO3 Ceramic Composites

“…For the CCTO-based ceramics, the observed heterogeneous electrical microstructure, consisting of insulating grain boundaries (GBs) sandwiched by semiconducting grains, are supported the internal (GB) barrier layer capacitor (IBLC) effect [1,5,7,12]. However, the intrinsic effect of the grains cannot be ignored or illogically excluded [17]. The dielectric response and related nonlinear electrical behavior result from the Schottky potential barrier at the interface between adjacent semiconducting grains [18][19][20][21].…”