The electrical behavior of copper oxide (CuO) ceramics sintered at 920 °C has been characterized by a combination of fixed, radio frequency (rf) capacitance measurements, and impedance spectroscopy (IS). Fixed rf capacitance measurements on ceramics with sputtered Au electrodes revealed a temperature- and frequency-dependent high effective permittivity of ∼104 in the temperature range of 150–320 K. The response is similar to that observed for relaxor-ferroelectrics, however, the magnitude of the effect can be suppressed by thermal annealing of the ceramics with Au electrodes in air at 300 °C or by changing the work function of the electrode material by using In–Ga as opposed to Au. IS data analysis revealed the ceramics to be electrically heterogeneous semiconductors with a room temperature dc resistivity <104 Ω cm, consisting of semiconducting grains with relative permittivity, er, <10 and slightly more resistive grain boundaries with “effective” permittivity, eeff, of ∼110. Samples with Au electrodes ex...

Relaxor ferroelectric-like high effective permittivity in leaky dielectrics/oxide semiconductors induced by electrode effects: A case study of CuO ceramics

Abnormal high dielectric constant in SmFeO3 semiconductor ceramics

Mn3O4 nanoparticles were prepared by a simple chemical route using cetyltetramethylammonium bromide (CTAB) as a template agent. Mn3O4 nanocrystals present an octahedral shape, and their crystallite size varies between 20 and 80 nm. They were characterized by XRD, SEM, DTA/TG, and IR spectroscopy. XRD studies confirm the presence of a highly crystalline Mn3O4 phase. The Rietveld refinement of the X-ray diffraction data confirms that Mn3O4 nanoparticles crystallize in the tetragonal system with space group I41/amd. DTA/TG and XRD measurements demonstrate the phase transition toward a spinel structure between 25 and 700∘C. The electrical conductivity increases between 80 and 300∘C, suggesting a semiconducting behaviour of Mn3O4. Both dielectric dispersion (e′) and dielectric loss (e′′) were investigated from 80 and 300∘C in the frequency range of 10 Hz–13 MHz. The dielectric properties showed typical dielectric dispersion based on the Maxwell-Wagner model.

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Mn3O4 Nanoparticles: Synthesis, Characterization, and Dielectric Properties

Single-phase cubic (La0.4Ba0.4Ca0.2)(Mn0.4Ti0.6)O3 (LBCMT) was reported by Jha et al. [J. Solid State Chem. 177, 2881 (2004)] to exhibit an extraordinarily high effective permittivity (eeff∼6980 and 590 at 1 and 100kHz, respectively) at room temperature. According to x-ray-diffraction analysis, the structure of this perovskite can be fully described on the centrosymmetric space-group Pm3¯m, which precludes the occurrence of ferroelectricity. In the present work, impedance spectroscopy has shown that LBCMT exhibits a bulk permittivity, er∼40–45, in accordance with that expected for a cubic, centrosymmetric perovskite. LBCMT is a semiconductor with a bulk resistivity of ∼3kΩcm at 300K and an activation energy for conduction of ∼0.20eV which is consistent with an electron hopping conduction mechanism. Finally, it is demonstrated that the high effective permittivity eeff reported previously is not an intrinsic bulk effect arising from hopping conduction between Mn+3 and Mn+4, but is ultimately associated with...

Origin of the high permittivity in (La0.4Ba0.4Ca0.2)(Mn0.4Ti0.6)O3 ceramics

Colossal dielectric constant in PrFeO3 semiconductor ceramics

(La0.4Ba0.4Ca0.2)(Mn0.4Ti0.6)O3: A new titano-manganate with a high dielectric constant and antiferromagnetic interactions

Effect of different concentrations of naturally occurring admixture in the form of fine powder of black gram pulse (BGP) on the hydration of Portland cement was studied by isothermal calorimetry and 57Fe Mossbauer spectroscopy. The spectra were recorded for anhydrous cement and the hydration products at room temperature and 77 K. In the presence of BGP, the spectra showed superparamagnetic doublets at room temperature and the sextet at 77 K, due to the presence of fine particles of iron containing component. Mossbauer studies of hydration products confirmed the formation of nanosize hydration products containing Fe3 + . The isomer shift (δ) and the quadrupole splitting (ΔE Q) values of C4AF in the cement confirmed iron in an octahedral and tetrahedral environment with +3 oxidation state. The high value of quadrupole splitting showed the high asymmetry of the electron environment around the iron atom. The overall mechanism of the hydration of cement in presence of BGP is discussed.

Sarita Rai

Papers

(La0.4Ba0.4Ca0.2)(Mn0.4Ti0.6)O3: A new titano-manganate with a high dielectric constant and antiferromagnetic interactions

Mössbauer and calorimetric studies of portland cement hydration in the presence of black gram pulse