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La0.4Pr0.25Ca0.35-xAgxMnO3 samples were elaborated using sol–gel method. X-ray diffraction study indicates that the investigated compounds exhibit an orthorhombic structure with Pbnm space-group sy...

Characterization of the electrical properties of Pr0.65Ca0.25Pb0.1MnO3 ceramic, prepared by the solid-state method, is conducted using the impedance spectroscopy technique. Ac-conductivity measurements reveal the presence of two electrical behaviors. A semiconductor character obtained at low-temperature ranges of 80–160 K, and a metallic behavior found at high-temperature ranges of 180–400 K. The temperature dependence of the exponent s confirms the contribution of two conduction processes in the transport mechanism. In the range of T 140 K, the conduction process is governed by the correlated barrier hopping (CBH) model. Finally, beyond T = 250 K, the dc-conductivity is characterized by the appearance of a saturation region.

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.

We have prepared a 20% Pr doped Sm0.55Sr0.45MnO3 sample by using the solid-state reaction and studied the magnetic and electrical properties. Arrott plots confirm the occurrence of a first-order phase transition. All the signatures of the FM first-order transition disappear above a critical magnetic field. Based on dc-electrical conductivity, a metal semi-conductor transition has been observed at TM-Sc = 180 K. Temperature-dependent conductivity measurement has been carried out to probe the electrical conduction mechanism, which revealed the change of conduction mechanism from the variable range hopping to the small polaron hopping around 180 K. The temperature dependence of e’ indicates a dielectric anomaly, implying a possible ME coupling in the vicinity of FM transition. The modulus spectra and complex impedance of the reported sample undoubtedly showed the non-Debye type relaxation process. We have obtained different activation energies values calculated from the conduction and relaxation mechanism. An electrical equivalent circuit model was suggested to explain the impedance contributions.

Pr0.65Ca0.25Cd0.1MnO3 ceramic was elaborated using the conventional solid-state reaction technique. The polycrystalline sample was subjected to investigate by ac impedance spectroscopy. From the main results, the electrical conductivity analysis confirms the semiconductor behavior and indicates that the hopping process governs the electrical conductivity. From ac-conductivity, two distinct mechanisms are observed. Indeed, the conduction mechanism is attributed to the correlated barrier hopping model in the middle of the frequency region and the overlapping large polaron tunneling in the high-frequency one. The analyzed impedance and modulus confirmed the presence of non-Debye-type relaxation phenomenon. Different electrical equivalent circuits were used to analyze the Nyquist plots. The obtained results confirm the contribution of grain boundary on the conduction. The increase in dielectric constant and the rate of its increase at low frequency were related to the disorder of the cation sublattices.

The solid-state reaction method was used to fabricate Pr0.65Ca0.25X0.1MnO3 manganite compounds with X = Cd, Sr, and Pb. X-ray diffraction (XRD), magnetometry, and impedance spectroscopy technique are used to study the structural, magnetic, electrical, and dielectric properties. The X-ray diffraction reveals that all samples crystallize in the orthorhombic system. The magnetic measurements on all samples show the presence of charge ordering transition at high temperature followed by an antiferromagnetic transition. From dc-conductivity analysis, all samples display the presence of semiconductor behavior. It is observed that the lowest obtained value of the activation energy (Ea) corresponds to the Pb-doped sample. The activation energy deduced from the dc-conductivity (Ea)σ matches very well with that estimated from relaxation time (Ea)relax, indicating that the relaxation process and the electrical conduction are related to the same origin. For each X dopant, the ac-conductivity is obeyed to the Jonsher law. The analysis of the impedance spectra highlights the presence of non-Debye relaxation phenomenon. Dielectric results show that the Pb doped sample has better dielectric properties than Cd and Sr doped ones. The dielectric properties are strongly dependent on both temperature and frequency. Dielectric constants decrease with frequency, and their behaviors have been interpreted based on space charge polarization according to Maxwell-Wagner’s two-layer model. The observed high conductivity and high dielectric permittivity values suggest that our compounds may be suitable for applications in electronic devices.

The critical behaviour of Pr0.5Sr0.5−xAgxMnO3 (0 ≤ x ≤ 0.2) samples around the paramagnetic–ferromagnetic phase transition is studied based on isothermal magnetization measurements. The assessments based on Banerjee's criteria reveal the samples undergoing a second-order magnetic phase transition. Various techniques such as modified Arrott plot, Kouvel–Fisher method, and critical isotherm analysis were used to determine the values of the ferromagnetic transition temperature TC, as well as the critical exponents of β, γ and δ. The values of critical exponents, derived from the magnetization data using the Kouvel–Fisher method, are found to be (β = 0.43 ± 0.002, 0.363 ± 0.068 and 0.328 ± 0.012), (γ = 1.296 ± 0.007, 1.33 ± 0.0054 and 1.236 ± 0.012) for x = 0.0, 0.1 and 0.2, respectively. This implies that the Pr0.5Sr0.5−xAgxMnO3 with 0 ≤ x ≤ 0.2 systems does not belong to a single universality class and indicates that the presence of magnetic disorder in the system must be taken into account to fully describe the microscopic interaction of these manganites. With these values, magnetic-field dependences of magnetization at temperatures around TC can be well described following a single equation of state for our samples. From magnetic entropy change (ΔSM), it was possible to evaluate the critical exponents of the magnetic phase transitions. Their values are in good agreement with those obtained from the critical exponents using a modified Arrott plot (MAP). We used the scaling hypotheses to scale the magnetic entropy change and heat capacity changes to a universal curve respectively for Pr0.5Sr0.5−xAgxMnO3 samples.

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.

In the present study, Sm0.55Sr0.45MnO3 manganite was elaborated using the conventional solid-state reaction method. Electrical and dielectric measurements carried out using impedance spectroscopy technique. The direct current study shows that the compound exhibits semiconductor behavior. Then, a saturation in the DC conductance is observed at around 360 ​K. Conductance spectra are discussed in the outline of single and double Jonscher power laws. In the intermediate frequency range, the AC conductance is governed by the activation of a correlated barrier hopping (CBH) conduction mechanism. Hence, the overlapping large polaron tunneling (OLPT) process dominates the transport properties at high frequencies. Finally, the dielectric response confirms the contribution of the grain, grain boundary, and the electrode polarization on the dielectric properties of the Sm0.55Sr0.45MnO3 compound.

The present study aimed to elucidate the causal factor of tentacular malformations observed in Stramonita haemastoma. For this purpose, an annual, spatial and interspecific survey of the tentacular malformations was conducted in addition to the experimental semi-amputation of the tentacles of S. haemastoma. This study reports, for the first time, the occurrence of tentacular malformations in S. haemastoma collected for one year from the Bizerta Channel. Tentacle malformations were detected in 12 out of 17 Mediterranean and Atlantic coastal sites. Besides S. haemastoma, two sympatric muricid species (Hexaplex trunculus and Bolinus brandaris) also showed the occurrence of tentacular malformations. The experimental semi-amputation of the tentacles of S. haemastoma confirmed the capacity of regeneration in this gastropod; however, the process was often deficient and the neo-formed anterior segment was usually shorter, thinner and provided with a small ocellus. Sometimes, individuals were unable to regenerate a number of structures like the posterior segment and the ocellus, which may explain the tentacular malformations observed previously in S. haemastoma. This study provided new data about the incidence of tentacular malformations in marine gastropods. Our results further demonstrate the capacity of regeneration in S. haemastoma, which can be used as a new model in regeneration studies.

The present study was aimed at determining bioaccumulation and cell and tissue distribution of Pb and Cd in the green garden snail, Cantareus apertus (Born, 1778), exposed to different nominal dietary concentrations of Pb (25, 100 and 2500 mg Pb/kg), Cd (5, 10 and 100 mg Cd/kg) and their combination (25mg Pb+10 mg Cd/kg and 2500 mg Pb+100 mg Cd/kg) for 1 and 8 wk. Pb and Cd were bioaccumulated in the digestive gland in a dose-dependent manner and the degree of effects on growth was related to the level of exposure, though metal-metal interactions were observed after treatment with mixtures of Pb and Cd. The present results are absolutely comparable to those obtained in other terrestrial pulmonates in other regions and therefore they absolutely support that C. apertus is suitable as biomonitor for the assessment of the Pb and Cd levels and their biological effects in soil ecosystems in Northern Africa.

Sets of multiple biomarkers can be applied to achieve a comprehensive assessment of the biological impact of the chemical pollutants in contaminated soils. This approach requires the integration of diverse biomarker data into indices that provide early signs of ecosystem health disturbance. Within this context, this study aims at integrating multiple biomarkers in green garden snail, Cantareus apertus, on the basis of data obtained in preceding laboratory and field studies. In the laboratory, snails had been treated with dietary Pb, Cd and their mixture. Prompt (1 wk) and long-lasting (8 wk) response profiles were characterized and the biomarkers integrated as Integrated Biomarker Response (IBR/n) index. The response profiles were dose and treatment time dependent in quantitative terms and also qualitatively different along the treatment time. Yet, IBR/n was sensitive to provide early (1 wk) signs of health disturbance caused by the metals, and remained sensitive in the long term (8 wk). In the field study, soil metal pollution was investigated along a distance gradient from a main roadside. Both metal levels in the soil–plant-snail system and a set of biomarkers in snails were recorded. The IBR/n revealed that disturbance in soil ecosystem health was restricted to short distances (at 20 m but not at 150 m). Therefore, IBR/n was a suitable approach also in the complexity of the field. Moreover, together with the IBR/n index, recently developed indices of bioavailability (SET) and risk (ERITME) were applied in the field study. In accordance with the IBR/n index, the SET index also revealed an excess transfer of metals to snails limited to a short distance from the roadside and identified Cd as the priority target for soil pollution management. Likewise, the ERITME classification rank confirmed that environmental risk was the highest at 20 m away from the roadside and then decreased at 150 m and beyond. Therefore, the application of the IBR/n index together with existing indices of the bioavailability (excess transfer) and risk of contaminants represents a challenging approach for the integrated environmental risk assessment of contaminated soils.

Structural, magnetic and dielectric properties of La0.5Eu0.2Ba0.3−x□xMnO3 (x = 0.00, 0.05 and 0.15) perovskites are investigated. Nano-polycrystalline samples prepared using sol-gel wet chemical method were subjected to annealing in two different temperatures and investigated by powder X-ray diffraction (XRD), magnetometry, and ac impedance spectroscopy. XRD characterizations indicated that all samples exhibited a single rhombohedral phase. The temperature-dependent magnetizations indicate the ferromagnetic transition. The resistivity decreased and the magnetic ordering temperature increased as Ba-deficiency increased. The dielectric constant dependent on frequency shows normal behavior. The samples with a lower sintering temperature show the highest resistivity and dielectric constant. Dielectric anomaly dependent on temperature was observed close to the magnetic ordering temperature, indicating the possibility of ferroelectricity and further magnetoelectric coupling. The dielectric behaviors have been interpreted based on space charge polarization according to Maxwell-Wagner’s two-layer model and hopping of charge between Mn3+ and Mn4+ ions.

The magnetic properties and magnetocaloric effect (MCE) in Pr

The lacunar La 0.5 Eu 0.2 Ba 0.2 □ 0.1 MnO 3 nanoparticles where □ is a barium deficiency has been prepared using the sol-gel method. The M-T data suggests that the sample undergoes a paramagnetic (PM) to ferromagnetic (FM) transition upon cooling. Deviation of the temperature dependence of inverse susceptibility curves from the Curie Weiss law and less than unity susceptibility exponents indicating the existence of a Griffiths singularity. The magnetocaloric effect and the critical behavior of the sample are systematically studied using bulk magnetization M ( H, T ) in the vicinity of the Curie temperature. The critical exponents have been obtained using different methods such as modified Arrott plot, critical isotherm analysis and field dependence of magnetocaloric effect. Though the self-consistency and reliability of obtained critical exponents of β = 0.581 ± 0.022, γ = 0.165 ± 0.008 and δ = 3.12 ± 0.03 are verified by the Widom scaling law and scaling equations, the critical parameters do not obey magnetocaloric effect scaling laws, indicating that the nanometer size effect play a significant role on the magnetic phase transition for La 0.5 Eu 0.2 Ba 0.2 □ 0.1 MnO 3 nanocrystalline.

We present a detailed study of the static magnetization M ( H , T ) in the vicinity of the ferromagnetic–paramagnetic (FM–PM) phase–transition temperature ( T C ) in polycrystalline Sm 0.55− x Pr x Sr 0.45 MnO 3 (0.3 ≤ x ≤ 0.4) manganites. The critical exponents β , γ , and δ are determined by using various techniques such as modified Arrott plot, Kouvel–Fisher method and critical isotherm analysis, and are found to be β = 0.255 ± 0.021 and γ = 0.957 ± 0.014 with T C = 226 K for Sm 0.25 Pr 0.3 Sr 0.45 MnO 3 and β = 0.324 ± 0.024 and γ = 1.212 ± 0.027 with T C = 254 K for Sm 0.15 Pr 0.4 Sr 0.45 MnO 3 . A careful analysis of the magnetic data recorded in Sm 0.55− x Pr x Sr 0.45 MnO 3 demonstrates the existence of a tri-critical point that separates discontinuous first-order magnetic transition (FOMT) from continuous second-order magnetic transition (SOMT).

In the present paper, we report the structure, the magnetic, the critical behavior, the magnetocaloric properties and the universal curve of La0.45Bi0.15Sr0.4CoO3 cobaltite. Polycrystalline sample was synthesized in air by the solid state reaction method at a sintering temperature of 1200 °C. Phase purity, structure, size, and crystallinity were investigated using X-ray diffractometry (XRD) and scanning electron microscopy (SEM). The Reitveld refinement of XRD pattern shows that the sample adopts a rhombohedral system with $$R\overline 3 c$$ space group. Critical exponents obtained by the modified Arrott plot technique, Kouvel–Fisher method, and critical isothermal analysis are close to the theoretical prediction of 3D Heisenberg model values, revealing the characteristic of short-range ferromagnetic interactions. With these values, the M(T,µ0H) relations below and above the curie temperature collapse into two universal branches in the asymptotic critical region following the scaling equation. Moreover, the experimental magnetic entropy changes measured for various fields collapse onto a master curve, confirming the universal behavior of the magnetocaloric effect in this system. Particularly, its magnetic-field dependence obeys a power-law fitting, where the exponent n = 0.98 is quite far from the value calculated at Curie temperature from the critical exponents. This difference is related to the magnetic inhomogeneity in the sample.

The present study was aimed at determining cell and tissue-level biomarkers and histopathological alterations in the green garden snail, Cantareus apertus (Born, 1778), exposed to different nominal dietary concentrations of Pb (25, 100 and 2500 mg Pb/kg), Cd (5, 10 and 100 mg Cd/kg) and their combination (25 mg Pb + 5 mg Cd/Kg, 100 mg Pb + 10 mg Cd/kg and 2500 mg Pb + 100 mg Cd/ kg) for 1 and 8 weeks. Lead and Cd exerted histopathological effects on the digestive gland in a dose-dependent manner and related to lysosomal and tissue-level biomarkers. The biological responses observed included digestive cell vacuolisation and numerical atrophy, calcium cell hydropic degeneration, excretory cell hypertrophy, inflammatory responses, blood vessel congestion, and disruption of the blood vessel wall and the interstitial connective tissue. Lysosomal enlargement and transient intracellular accumulation of neutral lipids and lipofuscins were also observed, together with alterations in the cell type composition and thinning of the digestive gland epithelium and with diverticular distortion. This response profile fits well with the biological effects reported after metal exposure in gastropods from other regions, as well as with data obtained in parallel studies dealing with metal bioaccumulation and intralysosomal accumulation, mortality, feeding, growth, oxidative stress and neurotoxicity exerted elicited by Pb, Cd and their mixture in green garden snails under the present experimental conditions. Consequently, C. apertus seems to be a suitable model species for the biomarker-based assessment of the biological effects of Pb and Cd, alone or in combinations, thus providing a challenging opportunity to advance in identifying suitable sentinel species for metal pollution biomonitoring and ecosystem health assessment in soil ecosystems in Northern Africa.