Nanoscale disorder and local electronic properties ofCaCu3Ti4O12: An integrated study of electron, neutron, and x-ray diffraction, x-ray absorption fine struct

Abstract

We report a combined experimental and theoretical study of CaCu 3 Ti 4 O 12 . Based on our experimental observations of nanoscale regions of Ca-Cu antisite defects in part of the structure, we carried out densityfunctional theory ͑DFT͒ calculations that suggest a possible electronic mechanism to explain the gigantic dielectric response in this material. The defects are evident in atomically resolved transmission electron microscopy measurements, with supporting evidence from a quantitative analysis of the electron diffraction and DFT which suggests that such defects are reasonable on energetic grounds. To establish the extent of the defects, bulk average measurements of the local structure were carried out: extended x-ray absorption fine structure ͑EXAFS͒, atomic pair-distribution function analysis of neutron powder-diffraction data, and singlecrystal x-ray crystallography. The EXAFS data are consistent with the presence of the nanoclustered defects with an estimate of less than 10% of the sample being disordered while the neutron powder-diffraction experiments place an upper of ϳ5% on the proportion of the sample in the defective state. Because of the difficulty of quantifying nanoscale defects at such low levels, further work will be required to establish that this mechanism is operative in CaCu 3 Ti 4 O 12 but it presents a nontraditional plausible avenue for understanding colossal dielectric behavior.

Role of intrinsic disorder in the structural phase transition of magnetoelectric EuTiO3

“…On the contrary, total scattering methods, such as the pair distribution function (PDF), have been successfully applied to similar problems in Ti-based perovskites. 35,36 …”

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

“…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].…”

High-temperature colossal dielectric response in RFeO3 (R=La, Pr and Sm) ceramics

“…Among all of such materials, CaCu 3 Ti 4 O 12 with extraordinarily high dielectric constant of $ 10 5 at room temperature and weak temperature dependence over a wide temperature range (from 100 to 400 K), has been extensively studied [4]. For purpose of understanding the unusual dielectric response in this ceramic, various theoretical models are proposed, such as intrinsic local dipole fluctuation model [5], Cu deficiency model [6], internal domains model [7], nanoscale disorder model [8]. Among them, one of the leading explanations should be the internal barrier layer capacitor (IBLC) model [9,10], which is composed of semiconducting grains and insulating grain boundaries.…”