The Fundamental Mechanism Behind Colossal Permittivity in Oxides

Abstract

Colossal permittivity materials exhibit extreme polarization in an applied electric field, providing applications in electronics and energy transmission. Understanding the atomic‐scale mechanism behind colossal permittivity remains a challenging task and is key to optimizing materials with this property. The fundamental mechanism of colossal permittivity is reported and, using CaCu3Ti4O12 as an example, it is attributed to the formation of an unusual metallic interface between the grain and grain boundary materials (CaCu3Ti4O12 and CuxO (x = 1, 2), respectively), not created by oxygen vacancies as is normally the case in oxide materials. This metallic layer around the grain forms confined shells of charge that pool on one side when under an applied field, which results in colossal permittivity. A route towards enhancing colossal permittivity is explained by means of manipulating the interface properties, as well as altering sample geometries. A methodology to artificially engineer colossal permittivity metamaterials is also shown.

Excellent Capacitor–Varistor Properties in Lead-Free CaCu3Ti4O12–SrTiO3 System with a Wrinkle Structure via Interface Engineering

“…For the practical applications of CP materials, the ideal dielectric materials should have a high permittivity and relatively low dielectric loss with weak frequency/temperature dependency . Among the CP materials listed above, the lead-free perovskite-like CP materials of the ACu 3 Ti 4 O 12 family, particularly CCTO materials, have gained comprehensive attention owing to their highly stable CP behavior over a wide frequency and temperature range and the absence of a ferroelectric phase transition. , Among different physical mechanisms for a CP response, the internal barrier layer capacitance (IBLC) model has generally been acknowledged to account for the origin of CP characteristics in pure CCTO materials, which should be ascribed to an internal barrier layer capacitor mechanism related to an obviously electrical heterogeneity of grains with n-type semi-conductivity and grain boundaries with insulativity. , Besides, the CCTO material also exhibits remarkably strong nonlinear current–voltage ( I – V ) characteristics even without adding any dopants, resulting from the presence of intrinsic electrostatic barriers at the grain boundary regions, namely, a back-to-back Schottky potential barrier model. , As a result of the fascinating nonlinear properties, the CCTO material as a varistor is therefore anticipated to have great potential for applications such as resistive-switching devices and gas sensors . Overall, the aforementioned advantages of superior dielectric and nonlinear behaviors in the CCTO system signify its potential for capacitor–varistor devices in electrical dual-function applications.…”

“…20,21 Among different physical mechanisms for a CP response, the internal barrier layer capacitance (IBLC) model has generally been acknowledged to account for the origin of CP characteristics in pure CCTO materials, which should be ascribed to an internal barrier layer capacitor mechanism related to an obviously electrical heterogeneity of grains with n-type semi-conductivity and grain boundaries with insulativity. 22,23 Besides, the CCTO material also exhibits remarkably strong nonlinear current− voltage (I−V) characteristics even without adding any dopants, resulting from the presence of intrinsic electrostatic barriers at the grain boundary regions, namely, a back-to-back Schottky potential barrier model. 17,24 As a result of the fascinating nonlinear properties, the CCTO material as a varistor is therefore anticipated to have great potential for applications such as resistive-switching devices and gas sensors.…”

Polaron Hopping Induced Giant Room‐Temperature Magnetodielectric Effect in Disordered Rutile NiNb2O6

“…The measured dielectric response at f <1k Hz is lower than the simulated grain response, because of the screening of the conducting interface (see in Table S2) which is similar to the case in CaCu 3 Ti 4 O 12 . [ 22 ] It is noteworthy that the s parameter of the UDR dipole element maximizes at T ≈ 250 K (Figure 2c‐bottom). The s parameter is considered to reflect the spin‐phonon coupling strength, which will be further illustrated in Section 2.4.…”

Colossal Permittivity Ti1–x(Eu0.5Ta0.5)xO2 Ceramics with Excellent Thermal Stability

“…As is known, the grain boundary exists on polycrystalline CP materials, which is sandwiched between semiconducting grains. The semiconducting grains and insulating grain boundary form the Schottky-type barrier and interfacial polarization, which is considered as the primary cause of the colossal dielectric response. , This is named the IBLC effect. For the secondary phase, it is introduced into the ceramics with the matrix phase of rutile TiO 2 due to solid solubility, nonisovalent substitution, and obvious ion radius differences. ,− The radius of donor ions (e.g., Nb 5+ ≈ 0.70 Å and Ta 5+ ≈ 0.69 Å) is similar to that of Ti 4+ (0.74 Å), whereas the radius of acceptor ions (In 3+ ≈ 0.94 Å and Ga 3+ ≈ 0.62 Å) usually is larger or smaller than that of Ti 4+ ions. , The obvious difference in the radius of accepter/donor ions results in the appearance of secondary phases in the co-doped TiO 2 ceramics.…”