CoO3 Cobaltite Research Articles

Comprehensive analysis of Nd0.5Ba0.5CoO3 cobaltite: Unveiling electrical, optical and magnetic characteristics for optoelectronic applications

In this study, we successfully synthesized the perovskite cobaltite Nd0.5Ba0.5CoO3 (NBCO) using the sol-gel method and thoroughly characterized its optical and magnetic properties. Optical measurements, using UV absorption, the Tauc model, and diffuse reflectance spectroscopy (DRS), revealed multiple direct bandgap energies, with the most significant values being 5.23 eV (Tauc method), 5.1 eV (DRS), and 4.9 eV (reflectance). The high bandgap energies highlight NBCO's suitability for UV and optoelectronic applications. The refractive index varied between 2.48 and 3.55, while the Urbach energy was measured at 2.32 eV, indicating a moderate level of localized disorder. Magnetic characterization demonstrated a ferromagnetic-to-paramagnetic transition at 125 K, with strong molecular field effects influencing the exchange interactions. The dielectric analysis revealed an exceptionally low loss factor (tan δ ≈ 0.0012), underscoring NBCO's potential for efficient energy storage and electronic applications. These results show that NBCO offers a unique combination of high optical bandgaps, strong magnetic properties, and low dielectric loss, making it a promising candidate for advanced optoelectronic and magnetic devices.

Enhanced Electrical, Optical and Thermodynamics Proprieties of Pr0.5Ce0.5CoO3 Cobaltite Prepared Using Sol–Gel Route for Electrical and Optical Applications

Enhanced Electrical, Optical and Thermodynamics Proprieties of Pr0.5Ce0.5CoO3 Cobaltite Prepared Using Sol–Gel Route for Electrical and Optical Applications

Microstructural Analysis, Magnetic Properties, and Critical Behavior of La0.7Ba0.15Sr0.15CoO3 Perovskite

We have reported the sol-gel synthesis and microstructural, magnetic, magnetocaloric, and critical behaviors of La0.7Ba0.15Sr0.15CoO3 cobaltite. The XRD data refined by Rietveld technology confirms that a sample has a pure perovskite phase with rhombohedral structure. We tested the magnetization curve near the phase transition temperature (TC) from ferromagnetic (FM) to paramagnetic (PM), and made the Arrott diagram which confirmed the existence of the secondary phase transition. The obtained magnetic constants from hysteresis loop offer to the sample the possible use in some interesting technological applications. The M(μ0H, T) isothermal magnetizations have been analyzed to estimate the critical exponents (β, γ, and δ). We found that β exponent is close to that of the mean-field model; however, γ and δ exponents belong to an unconventional model. The reliability of the estimated critical exponents was checked from the magnetic field variations of the magnetic entropy change (− ΔSm) and the relative cooling power (RCP).

Structural, magnetic and dielectric studies on half-doped Nd0.5Ba0.5CoO3 perovskite

We have investigated in detail the structural, magnetic, and dielectric properties of half-doped Nd0.5Ba0.5CoO3 perovskite cobaltite synthesized by the auto-combustion method. The Rietveld structure refinement from X-ray diffraction pattern reveals that a polycrystalline sample of Nd0.5Ba0.5CoO3 crystallizes into an orthorhombically distorted crystal structure with space group Pmmm along with a minor distorted tetragonal phase with P4/mmm space group. The temperature dependence of magnetization measurements show paramagnetic to ferromagnetic phase transition at Curie temperature TC around 147 K for H = 200 Oe. The value of TC strongly depends on the applied magnetic bias field, and TC decreases with an increasing magnetic field. The polycrystalline sample of Nd0.5Ba0.5CoO3 cobaltite exhibits Griffiths’ phase in the temperature range 147 K ≤ T ≤ 235 K for H = 200 Oe. Investigation of the isothermal magnetic field measurements on Nd0.5Ba0.5CoO3 reveals that it exhibit antiferromagnetic, ferromagnetic and paramagnetic behaviors, at T = 2 K, 100 K and 150 K, respectively. The negative slope of the isothermal Arrott’s plots (i.e., H/M versus M2) in the low magnetic field region suggests a first-order magnetic phase transition while the positive slope in high magnetic field region reveals a second-order magnetic transition. The dielectric constant and electrical resistivity of the synthesized Nd0.5Ba0.5CoO3 cobaltite material decrease with increasing temperature as well as frequency. Bulk Nd0.5Ba0.5CoO3 cobaltite shows insulator/semiconductor to metal transition at 76 °C.

Magnetic and magnetocaloric properties of La0.55Bi0.05Sr0.4CoO3 and their implementation in critical behaviour study and spontaneous magnetization estimation

In this work, we present the results of the magnetic, critical, and magnetocaloric properties of the rhombohedral-structured La0.55Bi0.05Sr0.4CoO3 cobaltite. Based on the modified Arrott plot, Kouvel–Fisher, and critical isotherm analyses, we obtained the values of critical exponents (β, γ, and δ) as well as Curie temperature (TC) for the investigated compound. These components were consistent with their corresponding values and they were validated by the Widom scaling law and scaling theory. The obtained critical exponents were close to the theoretical prediction of the mean-field model values, revealing the characteristic of long-range ferromagnetic interactions. The magnetic entropy, heat capacity, and local exponent n(T, μ0H) of the La0.55Bi0.05Sr0.4CoO3 compound collapsed to a single universal curve, confirming its universal behaviour. The estimated spontaneous magnetization value extracted through the analysis of the magnetic entropy change was consistent with that deduced through the classical extrapolation of the Arrott curves. Thus, the magnetic entropy change is a valid and useful approach to estimate the spontaneous magnetization of La0.55Bi0.05Sr0.4CoO3.

A systematic study on effect of electron beam irradiation on electrical properties and thermopower of RE0.8Sr0.2CoO3 (RE=La, Pr) cobaltites

The effect of electron beam (e-beam) irradiation on the crystal structure and transport properties of polycrystalline samples of La0.8Sr0.2CoO3 (LSCO) and Pr0.8Sr0.2CoO3 (PSCO) cobaltites is reported in this communication. The of X-ray diffraction data reveals that the pristine and irradiated compounds of LSCO and PSCO samples are single phased having rhombohedral structure with R-3C space group. It is noticed that the crystal structure is preserved even after irradiation. Nonetheless the unit cell parameters are slightly altered when exposed to e-beam. The resistivity patterns of LSCO and PSCO samples demonstrate the occurrence of semiconducting behavior over the measured temperature range of 10–300 K. From the analysis of the temperature dependent resistivity data on the bulk samples, it is seen that small polaron hopping (SPH) mechanism is more dominating in the high temperature region of the pristine sample as compared to e-beam irradiated samples of LSCO and PSCO. The Seebeck coefficient (S) data of all the batches of LSCO and PSCO samples predominantly display positive values over a vast temperature region, indicating that holes are the dominant charge carriers. The investigation of S measurements confirms the validity of SPH mechanism in the high temperature region.

Effect of thermoelectric material of Ca or Fe-doped LaCoO3

As the Perovskite-type Lanthanum Cobalt Oxide of LaCoO3 is nontoxic and thermally stable even at high temperature, this material is expected as a candidate for thermoelectric applications. The thermoelectric performance of a material is often evaluated by the dimensionless figure-of-merit, ZT (=S[Formula: see text]T/[Formula: see text]), or S[Formula: see text] in the ZT equation. S[Formula: see text] shows the electrical characteristic as a Power factor (PF). It has been reported Seebeck coefficient of LaCoO3 is higher than other oxide materials at room temperature even though electrical conductivity and ZT are lower values. In this study, calcium-doped lanthanum cobaltite La[Formula: see text]Ca[Formula: see text]CoO3 (x = 0.00, 0.05, 0.10 and 0.15) and iron-doped lanthanum cobaltite LaCo[Formula: see text]Fe[Formula: see text]O3 (y = 0.05, 0.10 and 0.15) have been prepared by solid-phase process. The X-ray diffraction patterns of the calcium-doped samples and iron-doped samples show cubic perovskite structure. Electric conductivities were improved by Ca or Fe substitution and showed a tendency to increase with increasing the temperature. The sample substituted with Fe 5 mol.% showed the maximum PF, 0.510 ([Formula: see text] W/K2m) at 548 K, and the sample substituted with Ca 15 mol.% showed the maximum PF, 0.152 ([Formula: see text] W/K2m) at 498 K.

Critical Behavior Near the Paramagnetic-Ferromagnetic Phase Transition in La1−x Sr x CoO3 (x = 0.3 and x = 0.5) Cobaltites

In this work, we present the study of structural, magnetic and critical behavior of La1−x Sr x CoO3 (x = 0.3 and 0.5) cobaltites. X-ray diffraction analysis using the Rietveld refinement shows that the sample La0.7Sr0.3CoO3 crystallizes in a rhombohedral distorted perovskite structure with $R\overline {3} c$ space group, while La0.5Sr0.5CoO3 exhibits both phases rhombohedric and cubic, with $R\overline {3} c$ and $Pm\overline {3} m$ space groups. Our samples exhibit thermo-magnetic irreversibility behavior in the magnetization data under a magnetic applied field of 0.05 T. The temperature dependence of magnetic susceptibility at higher temperatures for La0.7Sr0.3CoO3 sample reveals the presence of the Griffiths’ phase above the Curie temperature, while it follows the Curie–Weiss law perfectly for La0.5Sr0.5CoO3. Different techniques including the modified Arrott plot, the Kouvel-Fisher method and the critical isotherm analysis have been used to analyze the paramagnetic-ferromagnetic phase transition. The values of the critical exponents associated to this transition were close to those expected in the mean-field model. The validity of the calculated critical exponents has been confirmed by the scaling equation of state. The determined critical exponents using various methods are found to follow the scaling equation with the magnetization data scaled into two different curves below and above the critical temperature.

Studies on the structure, critical behavior and magnetocaloric effect in (LaBi)SrCoO cobaltite

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.

Spin state and magnetic ordering of half-doped [formula omitted] cobaltite

Cobaltites show intriguing magnetic and transport properties, when compared with manganites for instance, as they exhibit an additional degree of freedom: the spin state of the Co ions. For Nd0.5Sr0.5CoO3 this spin configuration is not well-established, as well as the magnetic ordering below the Curie temperature. Thus, in the present effort, magnetization measurements and a mean-field theoretical model were developed in order to understand in detail these aspects of the half-doped Nd0.5Sr0.5CoO3 cobaltite. These results show that the Co and Nd magnetic sub-lattices couple antiferromagnetically below Curie temperature Tc=215K down to very low temperature. These findings clarify the presence of the plateau observed at 80K on M(T) curve, which is erroneously attributed, in the literature, to the onset of an antiferromagnetic ordering. Magnetization data also clearly shows that Co3+ and Co4+ are in an intermediate spin state. In addition, experimental and theoretical magnetic entropy changes were determined and a comparative analysis among these two leads to ratify the results above claimed. Finally, from all those results, a magnetic phase diagram for Nd0.5Sr0.5CoO3. could be drawn.

Critical behavior and magnetocaloric study in La0.6Sr0.4CoO3 cobaltite prepared by a sol–gel process

The structure, magnetic properties, critical exponents and magnetocaloric effect (MCE) of La0.6Sr0.4CoO3 cobaltite are studied.

Suppression of the antiferromagnetic state in La0.82Ba0.18CoO3 cobaltite at high pressure

The crystal and magnetic structure of La0.82Ba0.18CoO3 complex cobalt oxide is studied by the neutron diffraction technique at high pressure (up to 4 GPa) within the temperature range of 10–290 K. At normal pressure, the crystal structure of La0.82Ba0.18CoO3 corresponds to the rhombohedral symmetry described by the space group R3c. At temperatures below T N = 100 K, the onset of a noncollinear antiferromagnetic (AFM) phase is observed. This phase is characterized by the wave vector k = (0, -0.5, 0.5). The applied high pressure leads to the rapid suppression of the AFM phase, which completely vanishes at P > 2 GPa. In La0.82Ba0.18CoO3, the degree of instability of the AFM phase with respect to the high pressure is appreciably higher than that in the related compounds with the ferromagnetic ground state. The correlation between the instability of the AFM state in La0.82Ba0.18CoO3 at high pressure and the changes in the electron configuration of Co3+ ions is also analyzed.

Effect of Eu doping and partial oxygen isotope substitution on magnetic phase transitions in (Pr1 − y Eu y )0.7Ca0.3CoO3 cobaltites

We study experimentally and theoretically the effect of Eu doping and partial oxygen isotope substitution on the transport and magnetic characteristics and spin-state transitions in (Pr$_{1-y}$Eu$_y$)$_{0.7}$Ca$_{0.3}$CoO$_3$ cobaltites. The Eu doping level $y$ is chosen in the range of the phase diagram near the crossover between the ferromagnetic and spin-state transitions ($0.10 < y < 0.20$). We prepared a series of samples with different degrees of enrichment by the heavy oxygen isotope $^{18}$O, namely, containing 90%, 67%, 43%, 17%, and 0% of $^{18}$O. Based on the measurements of ac magnetic susceptibility $\chi(T)$ and electrical resistivity $\rho(T)$, we analyze the evolution of the sample properties with the change of Eu and $^{18}$O content. It is demonstrated that the effect of increasing $^{18}$O content on the system is similar to that of increasing the Eu content. The band structure calculations of the energy gap between $t_{2g}$ and $e_g$ bands including the renormalization of this gap due to the electron-phonon interaction reveal the physical mechanisms underlying such similarity.

Terbium induced glassy magnetism in La,Ca-based cobaltites

The La0.8–xTbxCa0.2CoO3 cobaltites of orthoperovskite Pbnm structure were investigated by the X-ray and neutron diffraction, specific heat, and magnetization measurements. The terbium doping has two important effects, it increases the size disorder on perovskite A-sites and influences the magnetic properties due to large Ising-type moments (∼8.9 Bohr magnetons per Tb). The compounds show a bulk magnetic moment below TC = 82 K, 53 K, and 30 K for x = 0.1, 0.2, and 0.3, respectively. The neutron diffraction evidences a long-range ferromagnetic arrangement of cobalt moments, combined below ∼20 K with ordering of terbium moments in a canted arrangement. A homogeneous magnetic phase is proved for the x = 0.1 sample, while x = 0.2 and 0.3 are in an intrinsically non-homogeneous magnetic state with long-range ordering only comprising 55% and 30% of the sample volumes. The ac susceptibility experiments prove a glassy character of the terbium doped samples and provide arguments for the short-range ordering above TC and wide distribution of relaxation times.

Pressure enhanced ferromagnetism and suppressed exchange bias in La0.9Ba0.1CoO3 cobaltite

Pressure effect on magnetic properties of La0.9Ba0.1CoO3 cobaltite, exhibiting the ferromagnetic (FM) cluster-glass behavior and exchange bias (EB) effect at low temperatures, was investigated up to 10 kbar. It was found that an applied pressure increases the temperature TCcl ≈ 190 K, below which the FM clusters appear, and enlarges the FM phase volume in the sample. Positive value of dTCcl/dP coefficient suggests a wide eg-electron bandwidth for Co ions sited inside the Ba-rich regions (FM clusters). The EB field HE increases sharply with decreasing temperature below the spin-glass (SG) like transition temperature Tf ≈ 38 K, in a consequence of the exchange coupling at the FM/SG interfaces. Applied pressure was found to suppress strongly the EB, in particular, HE reduces by a factor of ∼3 under pressure of 10 kbar at 30 K. It appears that under pressure, HE varies oppositely to the changes in FM phase volume that is very similar to the behavior observed for phase-separated FM/antiferromagnetic manganites. Overall, the pressure-induced diminution in HE is explained by considering an increase of the FM cluster size and by concomitant decrease of distance between clusters. The results show that for phase-separated FM/SG cobaltites, the EB effect may be controlled by external pressure.

Ground state and the metal-insulator transition in (Pr1−y Y y )1−x Ca x CoO3 (0.45 ≤ x ≤ 0.55) cobaltites

Pr0.5Ca0.5CoO3 exhibits a non-conventional metal-insulator transition (MIT) in which the insulating state is due toa volume contraction (∼2%) and electron transfer from Pr to Co sites. Pr1−x Ca x CoO3cobaltites with Ca doping around x ∼ 0.5 (0.45 ≤ x ≤ 0.55) have been investigated. Different ground states and phase transitions are reported in samples at both sides of the half-doped composition. The relevance of the Pr/Ca ratio around half-doping and the amplitude of the changes observed at the MIT are analyzed. Besides the expected variation in the transition temperature, we report an enhanced Pr3+/Pr4+ transformation at the MIT in Pr0.45Y0.05Ca0.50CoO3[0.25(5) e−/Pr ion and T MI = 120 K] with respect to Pr0.5Ca0.5CoO3[0.15(5) e−/ Pr ion and T MI = 75 K].

Phase transition in Pr0.5Ca0.5CoO3 and related cobaltites

We present an extensive investigation (magnetic, electric and thermal measurements and X-ray absorption spectroscopy) of the Pr0.5Ca0.5CoO3 and (Pr1−y Y y )0.7Ca0.3CoO3 (y = 0.0625 − 0.15) perovskites, in which a peculiar metal-insulator (M-I) transition, accompanied with pronounced structural and magnetic anomalies, occurs at 76 K and 40 − 132 K, respectively. The inspection of the M-I transition using the XANES data of Pr-L 3-edge and Co-K-edge proofs the presence of Pr4+ ions at low temperatures and indicates simultaneously the intermediate spin to low spin crossover of Co species on lowering the temperature. The study thus definitively confirms the synchronicity of the electron transfer between Pr3+ ions and Co3+/4+O3 subsystem and the transition to the low-spin, less electrically conducting phase. The large extent of the transfer is evidenced by the good quantitative agreement of the determined amount of the Pr4+ species, obtained either from the temperature dependence of the XANES spectra or via integration of the magnetic entropy change over the Pr4+ related Schottky peak in the low-temperature specific heat. These results show that the average valence of Pr3+/Pr4+ ions increases (in concomitance with the decrease of the formal Co valence) below T MI for (Pr0.925Y0.075)0.7Ca0.3CoO3 up to 3.16+ (the doping level of the CoO3 subsystem decreases from 3.30+ to 3.20+), for (Pr0.85Y0.15)0.7Ca0.3CoO3 up to 3.28+ (the decrease of doping level from 3.30+ to 3.13+) and for Pr0.5Ca0.5CoO3 up to 3.46+ (the decrease of doping level from 3.50+ to 3.27+).

Effect of Partial Oxygen Isotope Substitution on the Phase Diagram of (Pr&lt;sub&gt;1-y&lt;/sub&gt;Eu&lt;sub&gt;y&lt;/sub&gt;)&lt;sub&gt;0.7&lt;/sub&gt;Ca&lt;sub&gt;0.3&lt;/sub&gt;CoO&lt;sub&gt;3&lt;/sub&gt; Cobaltites

Effect of the partial oxygen isotope substitution on (Pr1-yEuy)0.7Ca0.3CoO3 cobaltites was studied in detail for the crossover region (0.12&lt;у&lt;0.26) of the phase diagram. We prepared a series of the cobaltite samples with the different degrees of enrichment by the heavy oxygen isotope 18O, namely, containing 90%, 67%, 43%, 17%, and 0% of 18O. The Eu doping of the samples was chosen to be near and on the both sides of the crossover doping level ycr. Based on measurements of the ac magnetic susceptibility χ(Т) and electrical resistivity ρ(Т), we were able to analyze the evolution the sample properties with the change Eu and 18O content.

Comparative study of heterogeneous magnetic state above TC in La0.82Sr0.18CoO3 cobaltite and La0.83Sr0.17MnO3 manganite

The magnetic, transport and structural properties are studied for La0.83Sr0.17MnO3 and La0.82Sr0.18CoO3 single crystals with nearly the same doping and the metallic ground state. Their comparisons have shown that ferromagnetic clusters originate in the paramagnetic matrix below Т⁎>TC in both samples and exhibit similar properties. This suggests the possible universality of such phenomena in doped mixed-valence oxides of transition metals with the perovskite-type structure. The cluster density increases on cooling and plays an important role on the physical properties of these systems. The differences in cluster evolutions and scenarios of their insulator–metal transitions are related to different magnetic behaviors of the matrixes in these crystals that is mainly due to distinct spin states of the Mn3+ and Co3+ ions.

Size-dependent spin state and ferromagnetism in La0.8Ca0.2CoO3 nanoparticles

Magnetic and structural properties of nanocrystalline low-doped La0.8Ca0.2CoO3 cobaltites with particle size of 8, 13, 23, and 50 nm, prepared by the glycine-nitrate method, were investigated in temperature range 5–320 K, magnetic field up to 50 kOe and under hydrostatic pressure up to 10 kbar. With particle downsizing, a noticeable expansion of unit cell, with concomitant changes in the rhombohedral structure toward the cubic one was observed. It was found that the increased surface-disorder effect strongly suppresses the ferromagnetic state in La0.8Ca0.2CoO3 nanoparticles leading to a decrease, by factor of about 2, both in spontaneous magnetization, MS, and Curie temperature, TC, when particle’s size decreases from 23 to 8 nm. The effective magnetic moment μeff was found also to decrease distinctly due to the strong interdependence between Co–O–Co interactions and Co spin state. The size-induced magnetic disorder drives the La0.8Ca0.2CoO3 nanoparticles to a dominant glassy behavior for 8 nm particles. This is evidenced by the fact that the freezing temperature varies with magnetic field in a strict conformity with the de Almeida–Thouless law for spin glasses and also by the observation of characteristic slowing down in the spin dynamics. The applied pressure suppresses TC, MS, and coercive field HC, like it is observed for bulk La0.8Ca0.2CoO3. Nevertheless, in nanoparticles the pressure effect on TC is noticeably stronger, while HC diminishes with pressure much slower then in bulk material.