Role of oxygen vacancies in the magnetic and dielectric properties of the high-dielectric-constant systemCaCu3Ti4O12: An electron-spin resonance study

Abstract

We report experiments of electron spin resonance ͑ESR͒ of Cu 2+ in polycrystalline samples of CaCu 3 Ti 4 O 12 post-annealed in different atmospheres. After being synthesized by solid state reaction, pellets of CaCu 3 Ti 4 O 12 were annealed for 24 h at 1000°C under air, Ar or O 2 . Our temperature dependent ESR data revealed for all samples nearly temperature independent g value ͑2.15͑1͒͒ and linewidth for T ӷ T N Ϸ 25 K. However, the values of ESR linewidth are strongly affected by the oxygen content in the sample. For instance, argon post-annealed samples show a much larger linewidth than the O 2 or air post-annealed samples. We attribute this broadening to an increase of the dipolar homogeneous broadening of the Cu 2+ ESR lines due to the presence of oxygen vacancies which induce an S =1/2 spin inside the TiO 6 octahedra. Correlation between a systematic dependence of the ESR linewidth on the oxygen content and the high dielectric constant of these materials is addressed. Also, ESR, magnetic susceptibility, and specific heat data for a single crystal of CaCu 3 Ti 4 O 12 and for polycrystals of CdCu 3 Ti 4 O 12 are reported.

Effect of Cd Dopant on Dielectric Properties of CaCu₃Ti₄O₁₂

“…6. This conclusion is consistent with a previous dielectric measurement of pure CdCu 3 Ti 4 O 12 (ε ～9 × 10 3 at room temperature (100 kHz)) by Zuo et al [28], in contrast to the first report, ε=409, for pure CdCu 3 O-Cu-O. [29,30] In typical perovskite ferroelectrics, the dipole moment induced by the distortion of TiO 6 octahedron from its regular configuration plays an important role for the appearance of ferroelectricity.…”

“…[2] Furthermore an antiferromagnetic phase transition was observed at 25 K by magnetic susceptibility and specific heat measurements. [3] Compared with typical perovskite-type ferroelectrics such as BaTiO 3 and PbTiO 3 , the nature of this perovskite-related compound is very peculiar in exhibiting high dielectric constants over the wide range of temperature. The giant dielectric behavior seems to originate from an extrinsic origin.…”

“…Although extensive works have been done to understand the anomalous dielectric behavior, the origin of the novel high dielectric response is still unclear. In this paper, we prepared Cd-doped CCTO and studied the role of Cd ions in ACu 3 The calcined samples were milled and pressed into pellets of 20 mm in diameter and about 1 mm in thickness. Then the pellets were sintered in air at 1373 K for 12 h. X-ray powder diffraction data were recorded on an X-ray diffractometer with MoKα radiation and a diffracted-beam graphite monochromator operated at 50 kV and 100 mA.…”

Quasi-two-dimensionalS=12magnetism ofCu[C6H2(<

“…9. Calibration of the intensity data using CaCu 3 Ti 4 O 12 as reference, 40 revealed that indeed all copper spins contribute to the ESR signal. The ESR intensity shows a pronounced broad maximum at around 6 K similar to the χ(T) data.…”

Magnetic properties of (La 0.7 Sr 0.3 MnO 3 ) x (CaCu 3 Ti 4 O 12 ) 1−x nanostructured composites

“…The broadening of the paramagnetic line may occur due to an additional internal magnetic field from the ferromagnetic LSMO component. In pure CCTO the ESR linewidth varies considerably with the change in the oxygen content while the absolute value of g-factor is independent of the annealing atmosphere: air, argon, or oxygen [39].…”