Optical Response of High-Dielectric-Constant Perovskite-Related Oxide

Abstract

Optical conductivity measurements on the perovskite-related oxide CaCu3Ti4O12 provide a hint of the physics underlying the observed giant dielectric effect in this material. A low-frequency vibration displays anomalous behavior, implying that there is a redistribution of charge within the unit cell at low temperature. At infrared frequencies (terahertz), the value for the dielectric constant is approximately 80 at room temperature, which is far smaller than the value of approximately 10(5) obtained at lower radio frequencies (kilohertz). This discrepancy implies the presence of a strong absorption at very low frequencies due to dipole relaxation. At room temperature, the characteristic relaxation times are fast (less than or approximately 500 nanoseconds) but increase dramatically at low temperature, suggesting that the large change in dielectric constant may be due to a relaxor-like dynamical slowing down of dipolar fluctuations in nanosize domains.

Temperature dependent total scattering structural study of CaCu3Ti4O12

“…Furthermore, if this happens in a locally correlated fashion, within some sort of nanodomain structure, it could possibly be relevant for the anomalous increase of far-infrared ǫ F IR observed in studies of the optical properties. 3 In this view, upon increasing temperature, the local order on Ca sites is destroyed, and this leads to the decrease of the intrinsic (high frequency) dielectric constant. Small volume fraction polarizable defects, be they intrinsic or extrinsic, would then give the required amplification of the low-frequency dielectric constant through the mechanism described in Ref.…”

“…Relaxor-like dynamical slowing down of dipolar fluctuations in nanosize domains has been proposed by Homes et al from the optical conductivity measurements. 3 It has been argued that the high dielectric constant may arise from local dipole moments associated with off-center displacements of Ti atoms. 3 The structure does not exhibit a long range structural distortion, as typically observed in perovskite compounds.…”

“…3 It has been argued that the high dielectric constant may arise from local dipole moments associated with off-center displacements of Ti atoms. 3 The structure does not exhibit a long range structural distortion, as typically observed in perovskite compounds. Within this model the absence of a structural phase transition is explained by the premise that the tilts of the TiO 6 octahedra are large enough to uncouple the local titanium distortions from each other, effectively decoupling the ferroelectric order parameter and the long-range crystal structure.…”

In situ high temperature X-ray diffraction studies of mixed ionic and electronic conducting perovskite-type membranes

“…Perovskites (ABO 3 ) are a prominent topic of research in materials science (high-T c -electric conductor [1], ferroelectric [2] or high k dielectric [3], or magnetoresistance [4] material). Doping of these perovskites with multivalent cations on the A-and B-sites can lead to the simultaneous occurrence of ionic and electronic conductivities.…”

Composite-Hydroxide-Mediated Approach for the Synthesis of Nanostructures of Complex Functional-Oxides

“…[1][2][3][4][5][6] Nanostructures (nanoparticles, nanowires, and nanobelts) of complex oxides have attracted much attention because of their size-induced novel properties. Although some synthesis methods are successful for fabricating single-cation oxide nanocrystals, [7][8][9][10][11][12][13][14] only a limited amount of work is available for synthesizing nanostructures of complex oxides (with two or more types of cations) because of difficulties in controlling the composition, stoichiometry, and/or crystal structure.…”