Nanoscale electromechanical properties of CaCu3Ti4O12 ceramics

Abstract

Piezoresponse Force Microscopy (PFM) is used to characterize the nanoscale electromechanical properties of centrosymmetric CaCu 3 Ti 4 O 12 ceramics with giant dielectric constant. Clear PFM contrast both in vertical (out-of-plane) and lateral (in-plane) modes is observed on the ceramic surface with varying magnitude and polarization direction depending on the grain crystalline orientation. Lateral signal changes its sign upon 180 rotation of the sample thus ruling out spurious electrostatic contribution and confirming piezoelectric nature of the effect. Piezoresponse could be locally reversed by suitable electrical bias (local poling) and induced polarization was quite stable showing long-time relaxation ($3 hrs). The electromechanical contrast in unpoled ceramics is attributed to the surface flexoelectric effect (strain gradient induced polarization) while piezoresponse hysteresis and ferroelectric-like behavior are discussed in terms of structural instabilities due to Ti off-center displacements and structural defects in this material.

Electrical properties and Mössbauer spectra of rutile-type Fex/2Ta(Nb)x/2Ti1-xO2 (x = 0.05, 0.1) ceramics

“…A further candidate is perovskite-type CaCu 3 Ti 4 O 12 (CCTO) ceramic. A large number of investigations analysed the giant ε(ω) values of these ceramics, observed in broad frequency and temperature ranges, for which in part an intrinsic mechanism was thought to be responsible [1][2][3][4][5], but also domain and/or grain boundary (GB) processes [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] and partially or fully sampleelectrode (SE) effects [21][22][23][24]; high-temperature work showed relaxor-like ε(ω) peaks [3,20,25,26]. On monocrystalline CCTO samples, high ε (ω) values were ascribed in the majority of cases to spatial inhomogeneities and/or planar defects [27][28][29][30][31][32][33], but also electrode effects were proposed to be the origin [34].…”

Polaronic phase transitions and complex permittivity of solid polar insulators with gigantic dielectric response

“…Several experimental studies indicate a probable polaronic contribution to polarizability in different GDR materials: codoped NiO and AB 3 Ti 4 O 12 compounds . At the same time, the significance of the polaronic response and actual mechanisms behind the polaronic contribution to GDR are still not established convincingly.…”

“…At the same time, the significance of the polaronic response and actual mechanisms behind the polaronic contribution to GDR are still not established convincingly. For instance, the polaron involvement in GDR could be understood either as dipolar or ferroelectric‐like contributions to dielectric permittivity or as polaron hopping through localized electron levels within the bandgap with a Drude‐like dielectric response . The former two mechanisms are typical for solid semiconductors and insulators with a positive real part of the dielectric permittivity ( ϵ ′ > 0) while the latter is archetypical for metallic‐like systems with ϵ ′ < 0 .…”

Flexocoupling impact on the kinetics of polarization reversal

“…The impact of flexoelectric effect ("flexoeffect"), which appears as elastic strain in response on the polarization gradient (and vice versa) [1,2,3], is of great importance for understanding and describing electrophysical and elastic properties of ferroics at nanoscale [4,5,6], such as ferroelectric thin films [7,8,9,10], thin-film-based multilayer structures [11], nanoparticles [12,13,14], nanograin ceramics [15,16] and nanocomposites [17]. This dependence is caused by a strong influence of electro-elastic field gradients on the nanoferroic properties [4][5][6], in contrast to macro-ferroics, where the gradients are pronounced only near surfaces and domain boundaries [18,19,20,21,22,23].…”