K. Khirouni

Electric–dielectric properties and complex impedance analysis of La0.5Ca0.5−xAgxMnO3 manganites

The electric and dielectric properties of La0.5Ca0.5−xAgxMnO3 (LCMO–Ag with x = 0 and x = 0.4) were investigated using the impedance spectroscopy technique. For the free compound, conductivity analysis proved the absence of a metal–semiconductor transition in the temperature range of 80 K to 700 K. When silver was introduced, such transition appears at around TMS = 200 K. 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. Several results were deduced from the complex impedance analysis (CIA). First, a non-Debye relaxation phenomenon in the system was observed. Second, the CIA permitted us to model the compounds in terms of an electrical equivalent circuit. Moreover, this study confirmed the contribution of the grain boundary in the transport properties. It was found that the activation energy deduced from the conductivity, the relaxation time and the grain boundary were close to each other. The dielectric constant and dielectric loss were investigated. For the free compound, the dielectric transition was not observed in the investigated temperature range but, for the doped compound, the dielectric transition appeared at Td = 200 K. The Td value was close to the TMS value. The thermal evolution of the real part of dielectric permittivity is described by the Curie–Weiss law. From the variation of the imaginary part of the dielectric permittivity and the dielectric loss versus temperature at different frequencies, we found that the free compound had a typical behavior of a relaxor but the doped one had a typical behavior of a normal dielectric.

Effect of erbium concentration on the structural, optical and electrical properties of a Bi4Ti3O12 system

We have studied the influence of erbium doping on the optical and electrical properties of a Bi4Ti3O12 compound. Bi4−xErxTi3O12 (x = 0.0, 0.1, 0.2 and 0.3) samples are prepared by the solid state reaction method. X-ray diffraction (XRD) revealed that our samples are homogenous and crystallize in the orthorhombic system with the Fmmm space group. Absorbance measurement reveals that the peak intensity increases with increasing erbium concentrations and this behavior confirms the good homogeneity of the samples. DC-conductivity measurements show that all samples are characterized by a semiconductor behavior. It is found that electrical conductivity is reduced considerably with increasing erbium content up to x = 0.3. This is due to the decrease in oxygen vacancy density. For the free compound, dc-conductivity is characterized by the appearance of a saturation region at a specific temperature (Tsat = 480 K). For Er doped compounds, Tsat goes beyond 600 K. An AC-conductivity study shows that the conductivity is governed by the jump relaxation model (JRM) and conduction through grain boundaries. We found that the conductivity spectrum of the investigated materials obeys the Jonscher universal double power law. The deduced activation energy increases when increasing the erbium content from Ea = 467 meV for x = 0 to Ea = 670 meV for x = 0.3. Increasing the Er substitution reduces the frequency dispersion of the real part of the dielectric constant e′. Also, the tan δ plot indicates that the investigated samples exhibit the characteristics of a relaxor dielectric.

Electrical conductivity analysis and magnetic properties of Pr0.7Ca0.3Mn0.95Co0.05O3 oxide

The structural, electrical, magnetic and magnetocaloric properties of Pr0.7Ca0.3Mn0.95Co0.05O3 have been studied. The X-ray diffraction refinement results indicate that the sample is single phase and crystallizes in the distorted orthorhombic system with Pnma space group. The investigation of the temperature and frequency dependence of conductance indicates that the sample exhibits a semi-insulator character and the conduction mechanism is explained using hopping model. Complex impedance analysis confirms the contribution of grain boundary in the transport properties in the Pr0.7Ca0.3Mn0.95Co0.05O3 system. Magnetocaloric effect and transition order are investigated by using magnetization measurements. The field dependence of magnetic entropy change and relative cooling power are analyzed and showing the power law dependence. The Landau theory for phase transitions framework is applied to describe the magnetocaloric effect in Pr0.7Ca0.3Mn0.95Co0.05O3 manganite. The obtained results are discussed in terms of magnetoelastic and electron interaction contribution to the magnetic entropy.

Study of magnetic and electrical properties of Pr0.65Ca0.25Ba0.1MnO3 manganite

The magnetic properties and magnetocaloric effect (MCE) in Pr0.65Ca0.25Ba0.1MnO3 have been investigated supplemented by electrical data. X-ray diffraction shows that the sample crystallizes in the distorted orthorhombic system with the Pnma space group. Pr0.65Ca0.25Ba0.1MnO3 undergoes paramagnetic–ferromagnetic (PM–FM) phase transition at TC ∼ 85 K. For a magnetic field change of 5 T, the maximum value of the magnetic entropy change (−ΔSmaxM) is estimated to be 4.4 J kg−1 K−1 around TC with a large relative cooling power (RCP) value of 263.5 J kg−1. While the modified Arrott plots suggested that the magnetic transition belongs to the second order phase transitions, the universal curves of the rescaled magnetic entropy (ΔSM) proved the opposite. The electrical properties of Pr0.65Ca0.25Ba0.1MnO3 have been investigated using impedance spectroscopy techniques. The dc-resistivity (σdc) study shows the presence of semiconductor behavior. Ac-conductivity (σac) analysis shows that the conductivity is governed by a hopping process. From the analysis of the alternating regime, the exponent s variation obtained is in good agreement with Mott theory. The impedance spectrum analysis reveals the presence of a relaxation phenomenon. Based on these analyzes, the sample can be modeled by an electrical equivalent circuit.

Correlation of crystal structure and optical properties of Ba0.97Nd0.0267Ti(1-x)WxO3 perovskite

The Ba0.97Nd0.0267Ti(1−x)WxO3 (BNTx) pervoskite with a single phase tetragonal structure was prepared at 900 °C using the Molten salt method. Raman spectra, Fourier transform infrared spectra (FT-IR), absorption spectra (Vis-NIR) and photoluminescence spectra (PL) in the temperature range from 10–300 K were used to investigate the correlations between the crystal structure and the optical properties of BNTx ceramics. Raman analyses and FT-IR indicated that the W6+ ions are incorporated sufficiently into into the BNTx lattice. The optical absorption spectra were recorded in the wavelength range of 400–1000 nm. The optical band gap (Eg) and Urbach energy (Eu) values were calculated from the absorption spectra. The emission spectra exhibited three prominent peaks located at 880, 1058 and 1340 nm corresponding to the 4F3/2 → 4I9/2,11/2,13/2 transition levels, respectively. They also showed a decrease in the intensity of emission spectra following the addition of W6+ ions. This decrease is due to the slight changes in the crystal environment around Nd3+ and the non-radiative energy transfer. According to the PL measurements, the study of power-excitation density confirmed that two photons at low energy are required to create the down-conversion (DC) emissions, implying that they may also have important applications as DC materials.

Reply to “Electrical properties analysis of materials with ferroic order”

We thank the authors for the interest they have given to our paper (M. Smari et al., RSC Advances, 2015, 5, 2177), but we find that their comment is oriented according to their previous work and to their own vision of data analysis.