The structural, microstructural, non-ohmic and dielectric properties of perovskite-type CaCu3Ti4O12 (CCTO) with Ca/Cu stoichiometries of 1/3, 1/1 and 3/1 are discussed. The 1/3 Ca/Cu ratio system presents very high dielectric permittivity (∼9000 at 10 kHz) and a low non-ohmic property (α = 9), whereas the 1/1 Ca/Cu ratio system shows the opposite effect, i.e. the dielectric permittivity decreases (2740 at 10 kHz) and the non-ohmic property increases (α = 42), indicating that these properties are not directly correlated. The results of this work reinforce the idea that the greatest contribution to the very high permittivity is caused by the presence of planar defects inside the CCTO grains, generating internal nanometric domains associated with stacking faults, according to the nanoscale barrier layer capacitance model proposed very recently in the literature [1]. The non-ohmic property is related to the presence and distribution of phases such as CaTiO3 (CTO) and CuO, segregated or precipitated at the grain boundary, which generate large numbers of electrically active interfaces.

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.

Results on the characterization of photoluminescent CaCu3Ti4O12‐based films, prepared from a sol–gel precursor and heat treated at 700°C, are reported for the first time. The samples showed two emission bands at 554 and 800 nm when excited with a 488 nm Ar‐ion laser. The photoluminescent emission measured at room temperature in thin films was attributed to complex vacancy clusters. The films consisted of CaCu3Ti4O12 with traces of TiO2, CuO, and CaTiO3 and showed porous structures with an average particle size of 50 nm under atomic force microscopy resolution.

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Highly aligned CaCu(3)Ti(4)O(12) nanorod arrays were grown on Si/SiO(2)/Ti/Pt substrates by radio-frequency sputtering at a low deposition temperature of 300 °C and room temperature. Structural and morphological studies have shown that the nanostructures have a polycrystalline nature and are oriented perpendicular to the substrate. The high density of grain boundaries in the nanorods is responsible for the nonlinear current behavior observed in these arrays. The current-voltage (I-V) characteristics observed in nanorods were attributed to the resistive memory phenomenon. The electrical resistance of microcapacitors composed of CaCu(3)Ti(4)O(12) nanorods could be reversibly switched between two stable resistance states by varying the applied electric field. In order to explain this switching mechanism, a model based on the increase/decrease of electrical conduction controlled by grain boundary polarization has been proposed.