Structural and Magnetic Properties of B-Site-Ordered RE2CuTiO6 (RE = Dy, Ho, and Er) Double-Perovskite Oxides with Significant Cryogenic Magnetocaloric Performance

The magnetocaloric effect (MCE) is currently intensively investigated in various rare earths (RE)-containing magnetic solids, not only for developing appropriate magnetocaloric materials (MCMs) for cryogenic magnetic cooling but also for deepening our understanding into the inherent physical properties of these materials. Here, we provide a systematic experimental investigation into a series of new RE2CuTiO6 (RE = Dy, Ho, Er) double-perovskite (DP) oxides regarding the structural and magnetic properties, especially for their cryogenic MCE and magnetic-phase transition (MPT). All of these RE2CuTiO6 oxides crystallize in a B-site-ordered hexagonal DP-type structure with the symmetry of the crystallographic space group P6̅m2. These DP oxides exhibit magnetic ordering, with MPT temperatures of approximately 2.7, 2.2, and 2.7 K for Dy2CuTiO6, Ho2CuTiO6, and Er2CuTiO6, respectively. The magnetocaloric performances of the RE2CuTiO6 DP oxides were characterized by the peak values of magnetic entropy change, the temperature-averaged magnetic entropy change (5K-lift), and relative cooling powers. These magnetocaloric parameters were deduced to be 18.7/17.9 J/kgK and 298.2 J/kg for Dy2CuTiO6, 12.5/12.2 J/kgK and 273.9 J/kg for Ho2CuTiO6, and 13.8/12.9 J/kgK and 188.4 J/kg for Er2CuTiO6 under a magnetic field change of 0-5 T. These values are comparable to those of most reported RE-containing magnetocaloric materials, indicating that these RE2CuTiO6 DP oxides are promising candidates for cryogenic magnetic cooling applications.

CaCu3Ti4O12 Perovskite Materials for Advanced Oxidation Processes for Water Treatment

The many pollutants detected in water represent a global environmental issue. Emerging and persistent organic pollutants are particularly difficult to remove using traditional treatment methods. Electro-oxidation and sulfate-radical-based advanced oxidation processes are innovative removal methods for these contaminants. These approaches rely on the generation of hydroxyl and sulfate radicals during electro-oxidation and sulfate activation, respectively. In addition, hybrid activation, in which these methods are combined, is interesting because of the synergistic effect of hydroxyl and sulfate radicals. Hybrid activation effectiveness in pollutant removal can be influenced by various factors, particularly the materials used for the anode. This review focuses on various organic pollutants. However, it focuses more on pharmaceutical pollutants, particularly paracetamol, as this is the most frequently detected emerging pollutant. It then discusses electro-oxidation, photocatalysis and sulfate radicals, highlighting their unique advantages and their performance for water treatment. It focuses on perovskite oxides as an anode material, with a particular interest in calcium copper titanate (CCTO), due to its unique properties. The review describes different CCTO synthesis techniques, modifications, and applications for water remediation.

Recent advances in the development of europium(III) and terbium(III)-based luminescent supramolecular metallogels

In the recent past, special attention has been paid to the development of metallogels as novel luminescent materials from rationally designed gelators with lanthanide ions, especially europium (Eu(III)) and terbium (Tb(III)) metal ions. Lanthanide (Ln(III)) based metallogels possess various useful properties with an extensive range of applications in the field of advanced materials, and electronic and bio-technologies. Lanthanide ions in coordination with appropriate sensitizer ligands can reproduce metal-based optical, redox, and electronic properties in soft gel materials. The optical properties of the luminescent Ln(III) based metallogels can be tuned over the complete visible spectrum (400-750 nm) including the generation of white light by mixing both Eu(III) and Tb(III) with the ligand in various stoichiometric ratios. Additionally, the dynamic nature of the lanthanide-ligand (Ln-N) coordination bond allows the Ln(III) based metallogels to respond to various external stimuli. Luminescent self-healing supramolecular gels using organic ligands as 'hosts' and Ln(III) ions as 'guests' are also a current topic of research interest. In this review, we discuss and summarize some selected recent examples of newly developed luminescent Eu(III) and Tb(III) based supramolecular metallogels with potential applications in the fields of optoelectronic devices, stimuli responsiveness, self-healing, luminescent films, and sensors.

Synthesis, dielectric, magnetic, and photoluminescence properties of two new hybrid rare-earth double perovskites

Two new organic–inorganic hybrid double perovskites (R3HQ)₄CsSm(NO₃)₈ (1) (R3HQ = (R)-(-)-3-quinuclidinol) and (R3HQ)₄CsEu(NO₃)₈ (2) were synthesized and characterized. Compounds 1 and 2 exhibit obvious phase transitions at 379 and 375 K, respectively, confirmed by differential scanning calorimetry (DSC) and variable temperature powder X-ray diffraction. The rapid switching between high- and low-dielectric states makes it a typical dielectric material with a switchable dielectric constant for thermal stimulus response. Furthermore, 1 and 2 show attractive photoluminescence and paramagnetic behavior, and the fluorescence quantum yield of 2 reached 14.6%. These results show that compounds 1 and 2 can be used as excellent candidates for multifunctional intelligent materials, which also provides a new way for development of multifunctional materials.

Double Perovskite Ba2LaTaO6 for Ultrafast Fiber Lasers in Anomalous and Normal Net Dispersion Regime

Double perovskites (DPs) have been attracting attention in an assortment of optoelectronic applications, for they hold advantages such as high quantum efficiency, long carrier migration distance and strong linear and nonlinear absorptions. As specific kinds of perovskites (PVKs), DPs are gifted with orthorhombic crystal structures which provide rich conversion combinations and broaden the space for research and application. However, few works have been reported about DPs in ultrafast photonics applications. In this article, a DP with chemical formula of Ba₂LaTaO₆ (BLT) was successfully synthesized by high-temperature solid phase method. The microstructures and morphologies were observed, and the linear and nonlinear absorption were characterized. By first using BLT as a novel saturable absorber in both normal and anomalous dispersion region fiber lasers, dual-wavelength soliton and dissipative soliton were successfully operated at C-band. This study affirms BLT’s nonlinear optical properties, lays the foundation for optical research on BLT, and meanwhile provides a meaningful reference for future development of pulsed lasers based on DPs.

Cation Substitution Effects on the Structural, Electronic and Sun-Light Absorption Features of All-Inorganic Halide Perovskites

All-inorganic perovskites (such as CsPbI3) are emerging as new candidates for photovoltaic applications. Unfortunately, this class of materials present two important weaknesses in their way to commercialization: poor stability and...

A first-principles study on the phase stability and physical properties of a B-site ordered Nd2CrFeO6 double perovskite

Here, the first-principles predictions on the structural stability, magnetic behavior and electronic structure of B-site ordered double perovskite Nd₂CrFeO₆ have been reported. Initially, the ground state of the parent single perovskites NdCrO₃ and NdFeO₃ has been studied to determine the relevant Hubbard U parameter to investigate the properties of Nd₂CrFeO₆. The thermodynamic, mechanical, and dynamic stability analyses suggest the possibility of the synthesis of the Nd₂CrFeO₆ double perovskite at ambient pressure. The compound shows a ferrimagnetic nature with 2 μ_B net magnetic moment and the magnetic ordering temperature has been estimated to be ∼265 K. The electronic structure indicates a higher probability of direct photon transition over the indirect transition with a band gap of ∼1.85 eV. Additional effects of Nd (4f) spin and spin-orbit coupling on the band edges have been found to be negligible for this 4f-3d-3d spin system. This first-principles investigation predicts that due to the ferrimagnetic nature and a significantly lower band gap compared to those of its antiferromagnetic parent single perovskites, the B-site ordered Nd₂CrFeO₆ double perovskite could be a promising material for spintronic and visible-light driven energy applications.

Recent Advances in the Catalytic Applications of Lanthanide-Oxo Clusters

Lanthanide-oxo/hydroxo clusters (LOCs) in this mini-review refer to polynuclear complexes featuring a polyhedral metal-oxo/hydroxo cluster core of lanthanide ions exclusively or with coexisting 3d metal ions. We summarize herein the recent works using this unique family of cluster complexes for catalysis; this aspect of research stands in stark contrast to their extensively studied synthetic and structural chemistry as well as the much-researched magnetic properties. Following a brief introduction of the synthetic strategies for these clusters, pertinent results from available literature reports are surveyed and discussed according to the types of catalyzed reactions. Particular attention was paid to the selection of a cluster catalyst for a specific type of reactions as well as the corresponding reaction mechanism. To the end, the advantages and challenges in utilizing LOCs as multifunctional catalysts are summarized, and possible future research directions are proposed.

Structural, dielectric, magnetic and optical properties of double perovskite oxide Sm2NiMnO6nanoparticles synthesized by a sol-gel process

Here we report on the structural, dielectric, magnetic and optical properties of double perovskite Sm₂NiMnO₆(SNMO) nanoparticles synthesized by a sol-gel method. Structural Reitveld refinements on x-ray powder diffraction data revealed that the SNMO nanoparticles crystallized in a monoclinic crystal structure withP2₁/nspace group. SEM and (HR)TEM images revealed the phase purity and single-crystalline nature of the SNMO nanoparticles. XPS spectra confirmed the presence of Sm³⁺, Ni²⁺and Mn⁴⁺ions in the SNMO nanoparticles and oxygen in the forms of lattice oxygen and the hydroxyls species. SNMO ceramics exhibited relaxor-type dielectric behavior, well fitted by modified Curie-Weiss law. Such dielectric behavior originated from the interactions of random dipoles arisen from the B-site cations disorder accompanied with the variations in local electric fields and local strain fields due to the different radii of B-site cations, and/or the virtual electrons hopping between the Ni²⁺and Mn⁴⁺cations. Magnetic data demonstrate the variations of the magnetic transitions at low temperatures and the spin glass-like behavior below 11 K, which is attributed to the spin fluctuations induced by the competing interactions between the ferromagnetic (FM) and antiferromagnetic phases. Large positive Curie-Weiss temperature (θ_p) indicates the dominant FM super-exchange interactions in the SNMO samples. The SNMO nanoparticles have a direct optical band gap of 1.42 eV, close to 1.34 eV in a single junction solar cell. That enables the SNMO nanoparticles to be useful for solar cell absorbers.

Rare earth elements based oxide ion conductors

Rare-earth-elements-based oxide ion conductors with various structures and their structure-property relationships were systematically presented and summarized, which can provide new insight and guidance for the development of new oxide ion conductors.

Bi Alloying into Rare Earth Double Perovskites Enhances Synthesizability and Visible Light Absorption

A high throughput combinatorial synthesis utilizing inkjet printing of precursor inks was used to rapidly evaluate Bi-alloying into double perovskite oxides for enhanced visible light absorption. The fast visual screening of photo image scans of the library plates identifies 4-metal oxide compositions displaying an increase in light absorption, which subsequent UV-vis spectroscopy indicates is due to bandgap reduction. Structural characterization by X-ray diffraction (XRD) and Raman spectroscopy demonstrates that the visually darker composition range contains Bi-alloyed Sm₂MnNiO₆ (double perovskite structure), of the form (Bi,Sm)₂MnNiO₆. Bi alloying not only increases the visible absorption but also facilitates crystallization of this structure at the relatively low annealing temperature of 615 °C. Investigation of additional seven combinations of a rare earth (RE) and a transition metal (TM) with Bi and Mn indicates that Bi-alloying on the RE site occurs with similar effect in the family of rare earth oxide double perovskites.