Semiconductor–Conductor Transition Analysis by Low-Frequency Impedance in Ultrasonically Synthesized Al-Doped Sodium Tantalate

Strontium cobalt oxide (SrCoO3-δ) nanoparticles were successfully synthesized using; composite mediated hydrothermal (CMHM), without water and surfactants (WOWS) sol-gel and co-precipitation methods. The probable electrical conduction mechanism of synthesized strontium cobaltite was investigated via complex impedance analysis. Characterization techniques were employed to study the dependence of structure, homogeneity, physical parameters and electrical properties on synthesis procedures. After heat treatment, X-Ray Diffraction (XRD) confirmed the formation of phase pure SrCoO3-δ powders synthesized with CMHM, WOWS sol-gel and co-precipitation methods. Fourier Transform Infrared Spectroscopy (FTIR) spectra indicated the presence of fingerprint region of perovskite (ABO3-δ) structure. Raman spectroscopy revealed the internal motion of oxygen inside the CoO6 octahedra of SrCoO3-δ perovskite structure. A Raman phonon mode under 600 cm−1 position was identified which is commonly observed for such perovskite oxide. Scanning Electron Microscopy (SEM) images showed uniformly diffused, microporous and agglomerated sphere like morphology. Differential Thermal Analysis (DTA) and Thermogravimetry (TGA) verified formation of intermediate metal carbonates that decomposed to final product. Complex impedance spectroscopic plots (Nyquist plots) against frequency (20 Hz–3 MHz) discovered single semi-circular arcs in the low frequency region. These arcs showed that, grain boundary contribution is dominated over grain contribution to the total electrical conduction behavior. Modulus analysis disclosed non-Debye type conductivity relaxation in hydrothermally synthesized samples. The AC conductivity graphs followed Jonscher’s power law and hopping model. Hydrothermally synthesized samples exhibited minimum impedances and maximum AC conductivity, which makes them excellent candidate for cathode material in intermediate temperature range solid oxide fuel cells (IT-SOFCs) applications.

La0.5Eu0.2Ba0.3−x□xMnO3 (x = 0.00, 0.05 and 0.15) samples were prepared using sol–gel method and annealed at Ts = 750 and 950 °C. The X-ray diffraction technique shows that all samples crystallize in the rhombohedral structure with R-3c space group. Electrical properties of the prepared compounds were investigated using impedance spectroscopy technique in a wide temperature range (80–440 K). The results show a semiconductor behavior for all samples. From dc-conductivity (σdc) analysis, it is observed that increasing barium-deficiency content and sintering temperature improves the electrical conductivity. It is also found that the conduction mechanism is governed by hopping process. Ba-deficiency and sintering temperature affects the activation energy (Ea). From σdc, in the temperature range of 250–480 K and at Ts = 750 °C, it is found that Ea1 decreases from 190 meV for x = 0.00 to 164 meV for x = 0.15. Also, for x = 0.00, Ea1 decreases from 165 meV at Ts = 750 °C to 145 meV at Ts = 950 °C. Complex impedance analysis indicates the presence of non-Debye type relaxation. Such analysis confirms the contribution of grain boundary on the conduction. The activation energy Ea2 deduced from dc-conductivity matches very well with the value estimated from relaxation time (Eaτ) indicating that relaxation and transport mechanisms are related to the same defect.

In the present study polycrystalline Ba1−xLaxTi1−x/4O3 (x = 0.00, 0.015, 0.025, 0.035, 0.045 and 0.055) powders were synthesized using sol–gel route at 850 °C for 4 h. Calcined powders were sintered in air at 1300 °C for 6 h to make dense ceramics. XRD studies confirmed the tetragonal crystal structure of the x = 0.00–0.035 compositions at room temperature of the Ba1−xLaxTi1−x/4O3 ceramic samples. A cubic symmetry (Pm3m) was observed for the x > 0.035 compositions around room temperature. SEM studies showed that the average grain size was decreased with an increase in La content. The dielectric constant (ɛr) and dielectric loss (tan δ) of the Ba1−xLaxTi1−x/4O3 ceramics were investigated in the frequency regime (10 kHz–1 MHz). The highest magnitude of ɛr and tan δ around room temperature at 10 kHz was recorded for the x = 0.025 composition as 14,468 and 0.07, respectively. The Curie temperature (Tc) was shifted to low temperatures with an increase in La content. Complex impedance analysis confirmed the grain boundary and bulk contribution in the conduction mechanism for the x = 0.00 composition. The x ≥ 0.015 compositions showed only grain boundary contributions. The total resistance of sintered samples was decreased with an increase in temperature for the Ba1−xLaxTi1−x/4O3 ceramics, showing a typical ceramic behavior.

Impedance studies of La0.6Gd0.1Sr0.3Mn0.9In0.1O3 manganite prepared by the sol-gel method

An La0.6Gd0.1Sr0.3Mn0.75Si0.25O3 ceramic was prepared via a solution-based chemical technique. X-ray diffraction study confirms the formation of the compound in the orthorhombic structure with the Pnma group space. Dielectric properties have been investigated in the temperature range of 85–290 K with the frequency range 40 Hz to 2 MHz. The conductivity spectra have been investigated by the Jonscher universal power law: σ(ω) = σdc + Aωn, where ω is the frequency of the ac field, and n is the exponent. The deduced exponent ‘n’ values prove that a hopping model is the dominating mechanism in the material. Based on dc-electrical resistivity study, the conduction process is found to be dominated by a thermally activated small polaron hopping (SPH) mechanism. Complex impedance analysis (CIA) indicates the presence of a relaxation phenomenon and allows us to modelize the sample in terms of an electrical equivalent circuit. Moreover, the impedance study confirms the contribution of grain boundaries to the electrical properties.

Effect of exceeding the concentration limit of solubility of silver in perovskites on the dielectric and electric properties of half doped lanthanum–calcium manganite

Studies on electrical properties of Fe doped ZnO nanostructured oxides synthesized by sol–gel method

Structural, magnetic and dielectric properties of Ni0.6Mg0.4Fe2O4 ferromagnetic ferrite prepared by sol gel method

La2/3Cu3Ti4O12 (LCTO) precursor powders were synthesized by the sol–gel method. Effect of sol conditions and sintering process on microstructure and dielectric properties of LCTO powders or ceramics were investigated systematically. The optimum sol conditions for the synthesis of precursor powders were as follows: the Ti4+ concentration of 1.00 mol/L, the molar ratio of water and titanium of 5.6:1 and the sol pH of 1.0, respectively. After sintered at 1105 °C for 15 h, the LCTO ceramics exhibited more homogeneous microstructure, much higher dielectric constant (ca 09–1.6 × 104) and lower dielectric loss (ca 0.057). The higher dielectric constant of the LCTO ceramics might be due to the internal barrier layer capacitor effect. The LCTO ceramics showed two kinds of conductivity activation energy for grain boundary conductivity from complex impedance analysis. The transition temperature of two activation energy values occured between 170 and 210 °C. The temperature range of 170–210 °C was critical pseudocritical region of the dielectric constant, dielectric loss and activation energy. Furthermore, it was concluded that the grain boundary play an important role for electrical properties.

This study presents the electrical properties, complex impedance analysis and dielectrical behavior of La0.5Ca0.5-xAgxMnO3 manganites with compositions below the concentration limit of silver solubility in perovskites (0 ≤ x ≤ 0.2). Transport measurements indicate that all the samples have a semiconductor-like behavior. The metal-semiconductor transition is not observed across the whole temperature range explored [80 K-700 K]. At a specific temperature, a saturation region was marked in the σ (T) curves. We obtained a maximum σdc value at ambient temperature with the introduction of 20% Ag content. Two hopping models were applied to study the conduction mechanism. We found that activation energy (Ea) related to ac-conductivity is lower than the Ea implicated in dc-conductivity. Complex impedance analysis confirms the contribution of grain boundary to conductivity and permits the attribution of grain boundary capacitance evolution to the temperature dependence of the barrier layer width. From the temperature dependence of the average normalized change (ANC), we deduce the temperature at which the available density of trapped charge states vanishes. Such a temperature is close to the temperature at which the saturation region appears in σ(T) curves. Moreover, complex impedance analysis (CIA) indicates the presence of electrical relaxation in materials. It is noteworthy that relaxation species such as defects may be responsible for electrical conduction. The dielectric behavior of La0.5Ca0.5-xAgxMnO3 manganites has a Debye-like relaxation with a sharp decrease in the real part of permittivity at a frequency where the imaginary part of permittivity (ε'') and tg δ plots versus frequency demonstrate a relaxation peak. The Debye-like relaxation is explained by Maxwell-Wagner (MW) polarization. Experimental results are found to be in good agreement with the Smit and Wijn theory.

La0.75Ba0.25−xSrxFeO3 perovskite compounds with different strontium concentrations were synthesized via the sol–gel method. X-ray diffraction (XRD) data indicated that all obtained samples crystallize in the orthorhombic structure with the Pnma space group. The dielectric properties of these samples, using complex impedance spectroscopy technique have been carried out as function of frequency and temperature as well. An adequate electrical equivalent circuit has been used to evaluate the grain and grain boundary contributions in complex impedance results. Furthermore, the AC conductivity spectra obey to Jonscher’s universal power law. The behavior of the exponent “S” suggests that the conduction mechanism follows the overlapping large polaron tunneling (OLPT) process for x = 0.05, while for both compounds x = 0.10 and x = 0.15 the non-overlapping small polaron tunneling (NSPT) is the applicable model. The behavior of e″ as a function of both frequency and temperature has been described by Giuntini model.

Study of electrical properties of nickel doped SnO 2 ceramic nanoparticles

In this work, we report the synthesis of undoped ZnO and In-doped ZnO nanoparticles by sol–gel method from 0 to 5 wt% of In amount. The effect of indium incorporation on structural and electrical properties of these samples was investigated. X-ray diffraction analysis confirms the formation of undoped ZnO and In-doped ZnO nanopowders with a hexagonal wurtzite crystalline structure and the average crystallite size varies between 31 and 55 nm. The morphological study shows that the shape of the crystallites is hexagonal and it changes into cylindrical prismatic after doping. Further, the study of electrical response was carried out by impedance spectroscopy. The electrical properties of these samples are dependent on temperature and frequency. We find that the conductivity increases with increasing In dopant. It has been found that the highest conductivity corresponds to the concentration 3% of indium content. Concerning the complex impedance analysis, the equivalent circuit of grain consists of resistance and constant phase element in parallel. These results contribute to various technological applications.

Manganese doped tin oxide nanoparticles with manganese content varying from 0 to 15 mol % were synthesized using sol-gel method. The structural and compositional analysis was carried out using x-ray diffraction (XRD), scanning electron microscope (SEM), and energy dispersive x-ray analysis (EDAX). Dielectric and impedance spectroscopy was carried out at room temperature to explore the electrical properties of Mn doped SnO2. XRD analysis indicated the formation of single phase rutile type tetragonal structure of all the samples. The crystallite size was observed to vary from 16.2 to 7.1 nm as the Mn content was increased. The XRD, SEM, and EDAX results corroborated the successful doping of Mn in the SnO2 matrix. Complex impedance analysis was used to distinguish the grain and grain boundary contributions to the system, suggesting the dominance of grain boundary resistance in the doped samples. The dielectric constant ε′, dielectric loss tan δ and ac conductivity σac were studied as a function of frequency and composition and the behavior has been explained on the basis of Maxwell–Wagner interfacial model. All the dielectric parameters were found to decrease with the increase in doping concentration. Moreover, it has been observed that the dielectric loss approaches to zero in case of high dopant concentration (9%, 15%) at high frequencies.

The orthorhombic Pr0.8Na0.2MnO3 ceramic was prepared in polycrystalline form by a Pechini sol–gel method and its structural, magnetic, electrical and dielectric properties were investigated experimentally. A structural study confirms that the sample is single phase. Magnetic measurements show that the sample is a charge ordered manganite. The sample undergoes two successive magnetic phase transitions with the variation of temperature: a charge ordering transition occurred at TCO = 212 K followed by a paramagnetic (PM) to ferromagnetic (FM) transition around TC = 115 K. From an electrical point of view, a saturation region was marked in the conductivity as a function of temperature σ(T) curves at a specific temperature. The dc-conductivity (σdc) reaches a maximum value at 240 K. The obtained results are in good agreement with the temperature dependence of the average normalized change (ANC). We found that the conduction mechanism was governed by small polaron hopping (SPH) in the high temperature region and by variable range hopping (VRH) in the low temperature region. Complex impedance analysis indicates the presence of a non-Debye relaxation phenomenon in the system. Also, the compound was modeled by an electrical equivalent circuit. Then, the contribution of the grain boundary in the transport properties was confirmed.