O6 Double Perovskites Research Articles

Investigation of physical properties of Ba2NdX(X=Nb, Ta)O6 double perovskites for renewable energy applications

Alkali metals at the A site, coupled with rare earth transition metals featuring partly filled 4f and d orbitals at B and B’ sites in A2BB’O6 structure of double perovskites, induce complex d-f electron interactions. Present study explores the rare earth-based double perovskites Ba2NdNbO6 and Ba2NdTaO6, investigating their structural, optoelectronic, magnetic, and thermoelectric characteristics using first principles method. Computational analyses confirm the stable cubic symmetry and ferromagnetic ground state of both compounds. Negative formation enthalpies underline their thermodynamic stability. Spin polarized electronic band structures reveal direct–indirect degeneracy near the Fermi level, dominated by Nd-4f electrons. Optical investigations indicate absorption onset edges at 4.0 eV and significant absorbance peaks in the 6–10 eV range. Furthermore, the investigation into thermoelectric figure of merit reveals capability of Ba2NdNbO6 and Ba2NdTaO6 to efficiently convert heat energy in thermoelectric devices. These findings provide information for potential applications of investigated compounds in thermoelectric (TE) and optoelectronic devices; e.g., in optical absorbers, TE coolers and generators, and photonic devices.

DFT investigation of optoelectronic and thermoelectric features of Ba2Ce(Sn,Pt)O6 double perovskites

This study explores the geometric and thermodynamic stability, optoelectronic, and thermoelectric attributes of Ba2Ce(Sn,Pt)O6 double perovskites (DPs) through first-principles calculations. Both DPs exhibit stable cubic structures. Ba2CeSnO6 displays a bandgap of approximately 2.1 eV, indicating semiconductive behavior, while Ba2CePtO6 features a narrower bandgap of around 0.41 eV. This electronic behavior of both DPs is mainly influenced by the emergence of Ce-4f flat bands. Analysis of optical properties reveals absorption peaks at 3.4 eV for Ba2CeSnO6 and 1.2 eV for Ba2CePtO6, suggesting potential applications in visible and ultraviolet light optoelectronics. Additionally, the thermoelectric (TE) investigation demonstrates promising results, with high Seebeck coefficients (S) of 170 for Ba2CeSnO6 and 221 μV/K for Ba2CePtO6 at room temperature. The computed thermoelectric figure of merit (zT) exhibits a relatively stable trend for temperatures greater than 300 K, reaching 0.66 for Ba2CeSnO6 and 0.74 for Ba2CePtO6 at 800 K. This research provides valuable insights into the potential applications of these double perovskites in emerging technologies including visible light photonics and thermoelectric generators.

Engineering Ba2Bi2O6 Double Perovskite with La3+ for High Current Density Visible Light Photoelectrochemical Hydrogen Evolution.

A Lanthanum ion (La3+) incorporation strategy is implemented to modify Ba2Bi2O6-based double perovskite photoelectrodes. X-ray diffraction (XRD) characterization shows that highly crystalline Ba2La0.4Bi1.6O6 double perovskites with the space group I2/m are successfully prepared. UV-vis absorption spectra and the Tauc-plot reveal an optical band gap Eg ≈1.57 ± 0.01eV. A thickness dependence of the photoelectrodes photoelectrochemical (PEC) performance shows that the submicron (≈1µm) 4-times spin-coated thin film photoelectrode displays strong p-type conductivity, which delivers an encouraging photocurrent density of 0.88mAcm-2 at 0.25VRHE under AM 1.5G illumination. 10-times coated and 20-times coated medium thick (125.8-197µm) photoelectrodes that exhibit moderate p-type conductivity, show further enhanced photocurrent densities of 1.5mAcm-2 at 0VRHE. In contrast, charge recombination centers existing in a standard thick pellet (≈500µm) Ba2La0.4Bi1.6O6 photoelectrode can quench photo-generated charge carriers and greatly undermine PEC activities. The approach to doping at the Bi(III) sites contrasts with earlier efforts that focus on doping at the Bi(V) sites and thus paves the way for further tailoring a family of novel promising photocathode materials for efficient solar-water conversion devices.

Effect of Mg doping at Fe/Cr site on magnetic and optical properties of Gd2FeCrO6 double perovskite

The influence of Mg doping on structural, magnetic and optical characteristics of Gd2FeCrO6, Gd2Fe0.75Mg0.25CrO6 and Gd2FeCr0.75Mg0.25O6 double perovskites has been systematically investigated. The monoclinic crystal structure with the P21/n space group is confirmed by powder X-ray diffraction data. From the scanning electron microscopy graphs, we noticed few nearly spherical and dumbbell-shaped grains for all compounds with an average grain size of about 76 - 85 nm. The magnetic studies demonstrated the presence of a weak ferromagnetic transition with antiferromagnetic background at low temperatures for all the samples. A decrement in the transition temperature of Gd2FeCrO6 (TC = 8.14 K) is observed on Mg doping, which is due to the smaller ionic radii of Mg at the Fe/Cr site in Gd2Fe0.75Mg0.25CrO6 and Gd2FeCr0.75Mg0.25O6 double perovskites. By analyzing the UV–visible spectroscopic absorption data, direct band gaps around 3 eV are concluded for pure and Mg doped Gd2FeCrO6 double perovskites, validating their application in wastewater photocatalysis.

Synthesis, structural and optical properties of a novel double perovskite for LED applications

Amidst growing concerns for environmental sustainability and green ecology, the utilization of Light Emitting Diodes (LEDs) for indoor plant cultivation has emerged as an influential area of research. Nonetheless, the growth of indoor plants is often constrained by inadequate lighting. Consequently, designing novel LEDs to create an appropriate light environment has emerged as a focal point in research. As a new type of photocatalytic material with excellent optical properties and light stability, double perovskite has broad application prospects in LEDs manufacturing. In this context, this article aims to synthesize a new Ca2Lu(Nb,Mn)O6 double perovskite and study its optical properties in LEDs lighting for indoor plant growth. A new Ca2Lu(Nb,Mn)O6 double perovskite were synthesized using the traditional high-temperature solid-phase method. The crystal structure and luminescence properties of the double perovskite were characterized in detail using powder X-ray diffraction (XRD), Rietveld refinement, excitation and emission spectra, decay lifetimes, quantum efficiency (QE), electron paramagnetic resonance (EPR) spectra, temperature-dependent emission spectra, and the Commission International de l’Eclairage (CIE) color coordinates. The photoelectric properties of Ca2Lu(Nb,Mn)O6 and Ca2LuNbO6 double perovskite have been explored through first-principles investigations. The absorption spectra from 270 to 600 nm indicates that it can be effectively excited by ultraviolet (UV) light. The emission spectra show a strong broad red emission peak at 684 nm. The luminescence mechanism has been studied using the Tanabe-Sugano diagram. In addition, the internal UV emission ratio β1, crystal field strength Dq, and Racah parameters B and C were evaluated. The thermal stability of the sample was studied through emission spectra at heating temperatures from 303 to 573 K. The results indicate that Ca2Lu(Nb,Mn)O6 double perovskite provides a new solution for indoor plant growth.

Structural, optical, and photocatalytic properties of rare-earth free double-perovskite oxides Ba2Bi[formula omitted](Bi[formula omitted]Sb[formula omitted])O6

We present the structural, optical, and photocatalytic properties of rare-earth free double-perovskite compounds Ba2Bi3+(Bi1−2x5+Sb2x5+)O6 (x= 0, 0.1, 0.2, 0.3, 0.4, and 0.5). All samples prepared by the solid-state reaction method were formed in the single-phase monoclinic and rhombohedral perovskite oxides. Using the First Principle calculations of density functional theory, the effect of Sb substitution on band gap broadening was examined and a reasonable correlation was found with the experimental results. The photocatalytic activities were studied from the MB and IPA decomposition experiment. It was observed that Ba2Bi3+(Bi1−2x5+Sb2x5+)O6 exhibited better MB degradation performance under Sb substitution accompanied by the formation of nanoparticles. IPA decomposition result supports this finding and suggested that smaller particles in the Sb substituted samples reasonably affect the CO2 evolution performance.The maximum MB decomposition rate (about 50%) was found for the 20% Sb-incorporated sample. In contrast to the previously reported rare-earth-based double perovskite photocatalyst, a comparable performance was obtained in this research. The excellent surface morphology associated with the smaller particle sizes and better crystallinity for the Sb substituted sample promoted more active sites that facilitated improved photocatalytic activities of Ba2Bi3+(Bi1−2x5+Sb2x5+)O6 double perovskite.

Functional properties of A-site cation ordered phases derived from La[formula omitted]MnNiO[formula omitted] double perovskites

Starting from a room temperature parent La2MnNiO6 double perovskite as a prototype example, we ventured ferroelectricity and metal–insulator transition in the AA′BB′O6 double perovskites. Using first-principles density functional calculations guided by symmetry, we have shown that by appropriate A-site substitution i.e., by forming AA′ combinations, La2MnNiO6 within Mn and Ni in rock-salt ordering can be transformed into both ferroelectric insulating or polar metallic phase. We found that the charge difference between the cations and the radius mismatch between A and A′ are the key factors for deciding a particular ordering. The layered ordering becomes more stable when both charge difference and radius mismatch are large. The energy gain is more pronounced when the charge difference at the A-site is large. Further, we have identified and discussed the key structural distortions responsible for driving functional properties into the system. Our proposed mechanism is valid for other similar A2BB′O6 systems within 3d-3d double perovskites architecture with B and B′ sublattices in the rock-salt ordering.

Machine learning for imbalanced datasets: Application in prediction of 3d-5d double perovskite structures

3d-5d double perovskite is one kind of the most promising materials due to its novel properties and excellent performance with strong spin-orbit coupling. We used machine learning (ML) to search new 3d-5d perovskites. Three new methods derived from rescaling strategy in training models are used to solve the imbalanced problem which is more effective and more accurate than conventional machine learning models. Out of 664 scanned candidates of A2BB'O6 double perovskite (A is nonmagnetic metal, B and B' are 3d and 5d transition metals, respectively), we find 166 compounds can be stable 3d-5d double-perovskite structures, where A cations have to be +3 or +2 changed. Our results may throw light on the development of perovskite-based devices with strong spin-orbital couplings.

Structural, dielectric, electrical and optical properties of Li/Fe modified barium tungstate double perovskite for electronic devices

In this communication, the synthesis (solid-state reaction route) and characterization (structural and electrical properties) of Li/Fe modified barium tungstate BaWO4 of chemical formula (BaLi)(FeW)O6 double perovskite have been reported. Analysis of room temperature X-ray diffraction data shows the formation of a new single-phase (double perovskite) of tetragonal symmetry. The calculated average crystallite size and lattice strains are found to be 42 nm and 0.111% respectively. The scanning electron micrograph shows that grains are distributed uniformly with less porosity in the material. Detailed studies of field (frequency) and thermal (temperature) dependence of capacitive (dielectric) and resistive (impedance and conductivity) characteristics of the prepared material have shown the dielectric dispersion, relaxation, and non-Debye type of conduction mechanism respectively of the material. The existence of a non-Debye type of relaxation process and thermally activated relaxation process in the material has been analyzed by using impedance spectroscopy and conductivity techniques respectively. The presence of the depressed semicircular arcs in both Nyquist and Cole-Cole plots confirms the semiconductor nature of the material, which is well supported from ZSIMPWIN fitted impedance data. Study of room temperature Raman spectra supports the incorporation of Li/Fe of LiFeO2 in BaWO4 to produce new double perovskite of a composition BaLiFeWO6 of tetragonal symmetry. Further, as the temperature dependence of resistance shows a good stability factor, sensitivity factor, and thermistor constant, the material may be useful for thermistor-related devices. The nature of I–V characteristics confirms the presence of the Ohmic type of conductivity of the material. The energy bandgap of 2.85 eV, obtained from the UV–visible spectrum, suggests the material may also be used for optoelectronic devices.

Site-Selective d10/d0 Substitution in an S = 1/2 Spin Ladder Ba2CuTe1-xWxO6 (0 ≤ x ≤ 0.3).

Isovalent nonmagnetic d10 and d0 B″ cations have proven to be a powerful tool for tuning the magnetic interactions between magnetic B′ cations in A2B′B″O6 double perovskites. Tuning is facilitated by the changes in orbital hybridization that favor different superexchange pathways. This can produce alternative magnetic structures when B″ is d10 or d0. Furthermore, the competition generated by introducing mixtures of d10 and d0 cations can drive the material into the realms of exotic quantum magnetism. Here, Te6+ d10 was substituted by W6+ d0 in the hexagonal perovskite Ba2CuTeO6, which possesses a spin ladder geometry of Cu2+ cations, creating a Ba2CuTe1–xWxO6 solid solution (x = 0–0.3). We find W6+ is almost exclusively substituted for Te6+ on the corner-sharing site within the spin ladder, in preference to the face-sharing site between ladders. The site-selective doping directly tunes the intraladder, Jrung and Jleg, interactions. Modeling the magnetic susceptibility data shows the d0 orbitals modify the relative intraladder interaction strength (Jrung/Jleg) so the system changes from a spin ladder to isolated spin chains as W6+ increases. This further demonstrates the utility of d10 and d0 dopants as a tool for tuning magnetic interactions in a wide range of perovskites and perovskite-derived structures.

Double Double to Double Perovskite Transformations in Quaternary Manganese Oxides.

Control of cation ordering in ABX3 perovskites is important to structural, physical and chemical properties. Here we show that thermal transformations of AA'BB'O6 double double perovskites, where both A and B sites have 1:1 cation order, to (A0.5 A'0.5 )2 BB'O6 double perovskites with fully disordered A/A' cations can be achieved under pressure in CaMnMnWO6 and SmMnMnTaO6 , enabling both polymorphs of each material to be recovered. This leads to a dramatic switch of magnetic properties from ferrimagnetic order in double double perovskite CaMnMnWO6 to spin glass behaviour in the highly frustrated double perovskite polymorph. Comparison of double double and double perovskite polymorphs of other materials will enable effects of cation order and disorder on other properties such as ferroelectricity and conductivity to be explored.

Double Double to Double Perovskite Transformations in Quaternary Manganese Oxides

AbstractControl of cation ordering in ABX3 perovskites is important to structural, physical and chemical properties. Here we show that thermal transformations of AA′BB′O6 double double perovskites, where both A and B sites have 1:1 cation order, to (A0.5A′0.5)2BB′O6 double perovskites with fully disordered A/A′ cations can be achieved under pressure in CaMnMnWO6 and SmMnMnTaO6, enabling both polymorphs of each material to be recovered. This leads to a dramatic switch of magnetic properties from ferrimagnetic order in double double perovskite CaMnMnWO6 to spin glass behaviour in the highly frustrated double perovskite polymorph. Comparison of double double and double perovskite polymorphs of other materials will enable effects of cation order and disorder on other properties such as ferroelectricity and conductivity to be explored.

Rare earth double perovskites: a fertile soil in the field of perovskite oxides

This review summarizes the compositions, syntheses, and applications of rare earth A2B′B′′O6 double perovskites.

Evaluation of Ba doped Sr2TiFe0.5Mo0.5O6 double perovskites for high temperature thermoelectric power generation

Here we reported high temperature thermoelectric properties of environmental friendly Ba doped Sr2TiFe0.5Mo0.5O6 (STFM) based double perovskites. STFM ceramics can be assumed as combination of Sr2TiFeO6 with high Seebeck coefficient and Sr2TiMoO6 double perovskite with metal like electrical conductivity. Doping of Mo in Sr2TiFoO6 increased its conductivity manifold and Seebeck coefficient showed its behavior altered from p-type to n-type. Barium doping in STFM ceramic samples further increased the Seebeck coefficient although at the expense of conductivity. Maximum thermoelectric power factor was obtained in Ba0.1Sr1.9TiFe0.5Mo0.5O6 compositions. Charge transport properties were investigated using polaron conduction theory in conjugation with defect chemistry.

Local structure, electrical and magnetic properties of Fe-doped Sr2(Ni,Mo)O6 double perovskite

Abstract Double perovskite material of 10 mol% Fe-doped Sr 2 (Ni,Mo)O 6 was prepared by solid-state reaction. The NiMoO 4 precursor was first synthesized as a starting material with calcination temperature at 1100 °C in air. Effects of FeO, Fe 2 O 3 and Fe 3 O 4 dopant on phase formation, morphology, electrical and magnetic properties of the specimens were investigated and discussed. The XRD technique was used to analyze the phase formation of the samples. It can be clearly seen that phase formation of pure Sr 2 (Ni,Mo)O 6 indicated the cubic phase structure, while the tetragonal phase was found with FeO, Fe 2 O 3 and Fe 3 O 4 dopant. All XANES spectra were collected at the ambient temperature and atmospheric pressure. The result demonstrated that the oxidation state of Fe is 3 + , indicating the occurrence of γ-Fe 2 O 3 phase for all samples. In addition, the room temperature ferroelectric and ferromagnetic properties were determined using a simple Sawyer–Tower circuit (at fixed measuring frequency of 50 Hz) and Vibrating Sample Magnetometer (VSM), respectively. The maximum ferroelectric and ferromagnetic properties were seen with Fe 2 O 3 dopant. Interestingly, the ferroelectric and ferromagnetic properties of Sr 2 (Ni,Mo) 0.9 Fe 0.1 O 6 ceramics were affected by iron oxide doping.

Design and Crystal Growth of Magnetic Double Perovskite Iridates: Ln2MIrO6 (Ln = La, Pr, Nd, Sm-Gd; M = Mg, Ni)

A series of monoclinic distorted double perovskites of the general formula Ln2MIrO6 (Ln = La, Pr, Nd, Sm–Gd; M = Mg, Ni) were grown as highly faceted single crystals from a potassium hydroxide flux. The structural distortions and the magnetic interactions in A2BB′O6 double perovskites can be “designed” via a judicious choice of A, B, and B′ cation sizes and by selecting magnetic or nonmagnetic ions to occupy the A, B, and/or B′ sites. A study of the relationship between the number of magnetic ions, the degree of monoclinic distortion, and the resulting magnetic interactions was conducted. Magnetic susceptibility and field dependent magnetization measurements were performed for all synthesized compounds. It was determined that smaller A-site lanthanide cations cause more pronounced monoclinic distortions, resulting in smaller M–O–Ir (M = Mg, Ni) bond angles that correlate with higher magnetic ordering temperatures. The magnetic susceptibility and field dependent magnetization data were both consistent with...

Field control of multiferroic spherical core-shell nanocomposites with applications in microwave range

Muliferroic spherical nanoparticle configurations consisting of magnetostrictive core encapsulated in piezoelectric shell have been studied. The particles were simulated in a test configuration with help of the HFSS 13.0 (by Ansoft). An external magnetic field H0 was applied, which determines the apparition of dipolar electric fields of tens of milivolts around nanoparticle structures, used for tuning and control of different microstructures, at molecular level and in spintronics. The nanoparticle compounds are: an A2BB'O6 double perovskite with large piezoelectric coefficients and a MeFe2O4 spinel or a AFe12O19 M-type hexagonal ferrite with large magnetostriction, resulting in nanoparticle configurations with large magnetoeletric (ME) effect. The strength of the ME effect is also increased by the effect of the closed-packed shape of the spherical core-shell configuration. Different magnetic phases (spinel versus hexaferrite) were considered, in order to determine their influence in the interaction process with the applied magnetic field. The diameter of the piezoelectric shell did not exceeded 300 nm, starting from about 50 nm. The components of the magnetoelectric coefficient tensor and the effective electric and magnetic susceptibilities have been determined by simulation in microwave range (2 - 8 GHz for spinel compounds, respectively 12 - 28 GHz for hexaferrite compounds), for different magnetic fields applied for control (0 - 400 Oe), fields depending on particles size. The tensor components depend on the physical properties of the constituents and also on the constituents geometry and relative position. Nanoparticle configurations geometry and the applied H0 field were modified in order to obtain a convenient variation and control of the compound susceptibilities. Graphs are available for choosing the optimal configuration and parameter values for a specific application.

Large magnetization and frustration switching of magnetoresistance in the double-perovskite ferrimagnet Mn2FeReO6.

Ferrimagnetic A2 BB'O6 double perovskites, such as Sr2 FeMoO6 , are important spin-polarized conductors. Introducing transition metals at the A-sites offers new possibilities to increase magnetization and tune magnetoresistance. Herein we report a ferrimagnetic double perovskite, Mn2 FeReO6 , synthesized at high pressure which has a high Curie temperature of 520 K and magnetizations of up to 5.0 μB which greatly exceed those for other double perovskite ferrimagnets. A novel switching transition is discovered at 75 K where magnetoresistance changes from conventional negative tunneling behavior to large positive values, up to 265 % at 7 T and 20 K. Neutron diffraction shows that the switch is driven by magnetic frustration from antiferromagnetic Mn(2+) spin ordering which cants Fe(3+) and Re(5+) spins and reduces spin-polarization. Ferrimagnetic double perovskites based on A-site Mn(2+) thus offer new opportunities to enhance magnetization and control magnetoresistance in spintronic materials.

Large Magnetization and Frustration Switching of Magnetoresistance in the Double‐Perovskite Ferrimagnet Mn2FeReO6

AbstractFerrimagnetic A2BB′O6 double perovskites, such as Sr2FeMoO6, are important spin‐polarized conductors. Introducing transition metals at the A‐sites offers new possibilities to increase magnetization and tune magnetoresistance. Herein we report a ferrimagnetic double perovskite, Mn2FeReO6, synthesized at high pressure which has a high Curie temperature of 520 K and magnetizations of up to 5.0 μB which greatly exceed those for other double perovskite ferrimagnets. A novel switching transition is discovered at 75 K where magnetoresistance changes from conventional negative tunneling behavior to large positive values, up to 265 % at 7 T and 20 K. Neutron diffraction shows that the switch is driven by magnetic frustration from antiferromagnetic Mn2+ spin ordering which cants Fe3+ and Re5+ spins and reduces spin‐polarization. Ferrimagnetic double perovskites based on A‐site Mn2+ thus offer new opportunities to enhance magnetization and control magnetoresistance in spintronic materials.

Electrical Conductivity and Complex Impedance Analysis of Ba2CrMo0.8W0.2O6 Double Perovskite

Electrical properties of Ba 2CrMo0.8W0.2O6 double perovskite were investigated using admittance spectroscopy technique. According to impedance analysis, the material was modeled by an electrical equivalent circuit. Such analysis proves the presence of relaxation phenomenon in the compound. We also found that ac conductivity follows the Jonscher universal power law. Conduction process is found to be dominated by the thermally activated small polaron (SPH). The activation energy values, inferred from dc conductivity and from the temperature dependence of relaxation time, are closed to each other. Such result indicates that conduction process and relaxation phenomenon are related to the same defect.