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It is known that rare-earth-based pyrochlore oxide may accommodate the well-defined two-in-two-out spin ice state with its tetrahedral unit. Low-energy excitation is argued to favor the highly concerned monopole state which attracts essential attention. However, such an excitation cannot be directly tracked and imaged using advanced characterizations, raising challenges to our understanding of the physics of monopoles. In this work, we propose an improved two-dimensional artificial spin ice structure on the Shastry–Sutherland lattice to restore the degeneracy of realistic pyrochlore systems. Such a structure avoids the deficiency of inequivalent nearest and next-nearest exchanges in the planar quadrate unit, which, however, is equivalent to the tetrahedral unit of realistic pyrochlore oxides. Therefore, this spin ice model restores state degeneracy that is lost in conventional planar artificial spin ice structures, representing an improved simulator of real spin ice systems. Our careful investigations of such improved structures reveal the rich physics of spin ice excitations, including the phase diagram, which allows different ordered phases and interesting critical phase transitions between spin ice phase I and phase II. Energy spectrum analysis suggests that restoration of state degeneracy substantially reduces monopole excitation energy, resulting in a striking monopole emergency at the critical point. Furthermore, the emergent spin dimer phase in this improved model allows high-density monopole excitations and exhibits high-correlated monopole fluid states. [ABSTRACT FROM AUTHOR]

Achieving the formation of target open crystalline lattices from colloidal particles is of paramount importance for their potential application in photonics. Examples of such desired structures are the diamond, tetrastack, and pyrochlore lattices. Here, we demonstrate that the self-assembly of tetravalent patchy particles results in the selective formation of cubic tetrastack crystals, both in the bulk and in the systems subjected to external fields exerted by the solid substrate. It is demonstrated that the presence of an external field allows for the formation of well-defined single crystals with a low density of defects. Moreover, depending on the strength of the applied external field, the mechanism of epitaxial growth changes. For weakly attractive external fields, the crystallization occurs in a similar manner as in the bulk, since the fluid does not wet the substrate. Nonetheless, the formed crystal is considerably better ordered than the crystals formed in bulk, since the surface induces the ordering in the first layer. On the other hand, it is demonstrated that the formation of well-ordered cubic tetrastack crystals is considerably enhanced by the increase in external field strength, and the formation of the thick crystalline film occurs via a series of layering transitions. [ABSTRACT FROM AUTHOR]

Rare-earth titanate oxides are believed to be prospective functional materials for photocatalytic and photoluminescent applications because of their excellent optical properties and thermal stability of their physical properties. However, the relationships between optical properties and photoelectron trapping mechanisms are unclear. Herein, the structure, electronic, and optical properties of pyrochlore-structure Re2Ti2O7 (Re = Sm and Eu) were investigated using the first-principles approach with the Hubbard parameter U (GGA + U). The calculated bandgap is 2.5 eV for Sm2Ti2O7 and 2.4 eV for Eu2Ti2O7, which is in good agreement with the experimental observation. The results indicate that the strongly localized f states at the top of valence band are charge-trapping sites for photoexcitation of Re2Ti2O7, where electrons can absorb photon energy and transfer from the valence band to the conduction band, resulting in the photocatalytic and/or fluorescent effects in the visible and early UV regions. The important optical parameters, dielectric function ε (ω) , refractive index n (ω) , extinction coefficient k (ω) , reflectivity R (ω) , absorption coefficient I (ω) , optical conductivity σ (ω) , and electron energy-loss L (ω) were studied in detail, indicating that these optical parameters of Sm2Ti2O7 and Eu2Ti2O7 are insensitive to the ultra-violet (UV) radiation, but both Sm2Ti2O7 and Eu2Ti2O7 exhibit excellent optical properties in the visible and early UV regions. This work provides a clear understanding on the photoelectron trapping mechanism of pyrochlore-structure Re2Ti2O7, which will help to improve the photocatalytic and photoluminescent performance of Re2Ti2O7 and broaden their applications. [ABSTRACT FROM AUTHOR]

Magnetic refrigeration technology is regarded as one of the ideal solutions for cryogenic refrigeration, while magnetocaloric materials are the crucial ones. A series of polycrystalline RE2Ti2O7 (RE = Gd, Tb, and Ho) compounds were prepared by a simple one-step solid-phase reaction method in the atmosphere. The crystal structure, magnetic properties, and magnetocaloric effect (MCE) of these compounds were systematically investigated. Crystallographic research indicates that these compounds crystallized in a pyrochlore structure. Meanwhile, magnetic measurements illustrate that this class of pyrochlore oxides is highly frustrated magnetic materials and exhibits complex magnetic behavior. In addition, under the field change of 0–1 T, the values of the maximum magnetic entropy change (− Δ S M max ) and the refrigeration capacity are calculated to be 0.9 and 5.8 J/kg for Gd2Ti2O7, 9.0 and 32.9 J/kg for Tb2Ti2O7, 9.9 and 29.9 J/kg for Ho2Ti2O7, respectively. Therefore, RE2Ti2O7 (RE = Tb and Ho) pyrochlores exhibit excellent MCEs under low magnetic fields, providing candidate materials for the application of cryogenic magnetic refrigeration technology. [ABSTRACT FROM AUTHOR]

Ionizing events having a wide variety of radiation‐induced effects can radically affect the kinetics of defect production or structural transformation in the pyrochlore structured oxides (A2B2O7). Therefore, a thorough understanding of the kinetics associated with cation ordering and disordering is required for various technological applications. The structural responses of Gd2Ti2‐yZryO7 (y = 0.4, 1.2, 1.6) pyrochlore series irradiated by 120 MeV Au9+ ions were investigated using in situ synchrotron x‐ray diffraction (SR‐XRD), micro‐Raman spectroscopy, and scanning electron microscopy (SEM). Each pyrochlore composition irradiated at the highest fluence, where structural modifications occur, was subsequently isochronally annealed from room temperature to 1000°C. The SR‐XRD results indicate that Ti‐rich composition (y = 0.4) retains its pre‐irradiated pyrochlore structure (Fd3¯$\bar{3}$m) at 1000°C. In contrast, Zr‐rich compositions exhibit recrystallization to an intermediate defect‐fluorite phase (Fm3¯$\bar{3}$m) above 500°C, and the pre‐irradiated pyrochlore superstructure does not recover even on annealing at 1000°C. These results reveal that recrystallization temperature strongly depends on the accumulated radiation damage, generally described with the cationic radius ratio (rA/rB). Thus, investigation of the thermal annealing behavior of irradiated pyrochlores helps better understanding the general mechanisms of radiation damage and recovery of pyrochlores, which is important for their use in nuclear applications. [ABSTRACT FROM AUTHOR]

This study presents the successful synthesis of Sr2Ta2O7 with a pyrochlore crystal structure, which was previously unreported. Traditionally, Sr2Ta2O7 is synthesized in an orthorhombic layered perovskite‐type structure using traditional solid‐state reaction and batch‐type subcritical hydrothermal methods. Here, we utilize a continuous‐flow supercritical hydrothermal method, a technique primarily applied for nanoparticle synthesis and minimally explored for the synthesis of metastable crystals. Through detailed evaluations employing X‐ray diffraction and scanning electron microscopy, we confirmed the synthesis of the pyrochlore phase, characterized by particles with a diameter of less than 100 nm, synthesized at 633 K. Notably, the synthesized pyrochlore structure demonstrated remarkable stability, even after thermal treatment at 773 K for 1 h. Pyrochlore Sr2Ta2O7 stands out as a rare exception to the traditional tolerance factor approach among 278 known A2B2O7 compositions. Systematic evaluation of formation energies through first‐principles calculations revealed that the pyrochlore Sr2Ta2O7 synthesized in this study is located 0.06 eV/atom above the convex hull. This achievement underscores the potential of the continuous‐flow supercritical hydrothermal method in automating the exploration and discovery of novel crystal structures, suggesting a systematic pathway for advancing the field of material synthesis. [ABSTRACT FROM AUTHOR]

Helium (He) exerts significant influence on the physicochemical, structural, and electronic properties of pyrochlores. This paper reviews recent advancements in computer simulations aimed at stabilizing nuclear waste, focusing on disordered structures of pyrochlores, zirconate pyrochlores, and high‐entropy pyrochlores. Using Pu‐La2Zr2O7 as a case study, we demonstrate how a first‐principles approach facilitates the understanding of how He modifies the structural and electronic properties of this system. The incorporation of He interstitials in Pu‐La2Zr2O7 typically leads to an expansion in lattice constant and volume swelling. Analysis of the formation energies in this system reveals that octahedral interstitial sites or zirconium (Zr) vacancy sites are favored for He occupation, resulting in the formation of substitutional He atoms. The low concentration of He atoms in Pu‐La2Zr2O7 reduces the formation energy of cation antisite defects. Bader charge analysis indicates that the < Zr‐O > bond exerts a greater influence on the irradiation resistance of the He‐Pu‐La2Zr2O7 system compared to the < La‐O > bond. Moreover, the capacity for He interstitials increases with higher Pu concentration in the octahedrons. [ABSTRACT FROM AUTHOR]

Gadolinium zirconate (GZO) with pyrochlore phase exhibits exceptional promise for thermal barrier coatings due to its notable low thermal conductivity. Current synthesis methods for GZO, however, are frequently complex, energy-intensive, and environmentally hazardous. A more sustainable and eco-friendly synthesis route for GZO is thus imperative. This research introduces a green synthesis process for pyrochlore GZO utilizing the molten salt method. Experimental synthesis at varying temperatures revealed changes in the phase composition of GZO via the molten salt method. Fluorite GZO formed at 1200 °C, while pyrochlore GZO appeared at 1400 °C. XRD refinement, TEM, and Raman spectroscopy confirmed these results. Density Functional Theory (DFT) calculations established the minimum theoretical synthesis temperature for pyrochlore GZO at 1370 °C. Limiting factors for reactions at different temperatures during the molten salt synthesis process were identified. DFT calculations and experiments verified that the fluorite structure GZO transitions to pyrochlore GZO at temperatures exceeding 1370 °C. Property tests on pyrochlore GZO samples synthesized through two pathways showed minimal differences. This study thus lays a theoretical foundation for the eco-friendly synthesis of pyrochlore GZO material using the molten salt method and offers insights for future process development. [ABSTRACT FROM AUTHOR]

Zirconolite and pyrochlore have been considered as the potential immobilization matrix materials of minor actinides due to their high solubility, radiation tolerance and chemical durability. In this work, a series of Ca 1-x Ho 2x Zr 1-x Ti 2 O 7 (0.1 ≤ x ≤ 1.0) ceramics were prepared by solid state synthesis and sintering at 1400 °C for 48 h twice. Powder X-ray Diffraction (XRD), Backscattered Scanning Electron Microscopy with Energy-Dispersive X-ray spectroscopy (BSEM-EDX), Transmission Electron Microscopy (TEM) were employed to investigate the phase evolution, solubility, and substitution mechanism of Ho. The results displayed that zirconolite-2M would be transformed to zirconolite-4M and then to pyrochlore with increasing Ho concentration. The initial phase transformation of zirconolite-2M to zirconolite-4M, subsequently zirconolite-4M to pyrochlore were observed in x = 0.2 and 0.4 samples, respectively. Zirconolite-4M could be synthesised at x = 0.38 sample with trace perovskite. Moreover, the semi-quantitively solubility limits of Ho in zirconolite-2M and zirconolite-4M were determined to be 27 and 41.5 at.%, respectively. Single-phase pyrochlore were fabricated after 70 at.%. In addition, the novel substitution mechanism was revealed by Rietveld refinement with Ho preferentially replacing the Ca of zirconolite-2M so that some replaced Ca occupied vacant Zr site. For pyrochlore, Ho, Ca and Zr occupied A site (16d) and Ti entered in B site (16c). The findings would provide more insights into zirconolite–pyrochlore ceramic system. [ABSTRACT FROM AUTHOR]

Y2TiO5 belongs to the Ln2TiO5 (Ln = lanthanide or Y) family of ceramic materials and exhibits a range of desirable material properties such as radiation tolerance, frustrated magnetism, and large dielectric constant. However, understanding the complex crystal structure of Y2TiO5 remains elusive, given that Y2TiO5 can adopt multiple polymorphs such as cubic, orthorhombic, and hexagonal phases within the lattice. In this work, we report a detailed structural analysis of Y2TiO5 using four‐dimensional scanning transmission electron microscopy coupled with unsupervised machine learning. The pyrochlore nanodomains, characterized by the ordered arrangement of yttrium cations on the A site of their A2BO5 structure, are present within the matrix of a predominantly fluorite‐structured Y2TiO5 along with a third polymorph, the hexagonal phase. The pyrochlore phase is found to form 2 nm boundary regions around hexagonal phase stacking faults, highlighting the potential influence of the hexagonal phase on the occurrence and distribution of the pyrochlore phase. Lastly, we identify a unique pyrochlore phase with asymmetric arrangement of cation ordering along a single planar direction. Our findings provide invaluable insights into the possible mechanisms stabilizing pyrochlore nanodomains within the fluorite lattice of Y2TiO5. [ABSTRACT FROM AUTHOR]

A single high-entropy pyrochlore-type compound (A 2 B 2 O 7) was successfully synthesized, incorporating 8 different rare-earth cations at the A site and 2 different metal cations at the B site in equiatomic amounts [(8A 1/8) 2 (2B 1/2) 2 O 7 ]. Powders with a nominal composition of (La 1/8 Sm 1/8 Nd 1/8 Pr 1/8 Y 1/8 Gd 1/8 Dy 1/8 Yb 1/8) 2 (Hf 1/2 Zr 1/2) 2 O 7 were fabricated by glycine nitrate procedure (GNP). The GNP process yielded powders with low crystallinity and after subsequent calcination, a well crystalline ceramic powders were formed. The phase evolution was initially analyzed using X-ray diffraction (XRD). In situ high-pressure X-ray diffraction was employed to investigate the structural stability and high-pressure behavior of the A 2 B 2 O 7 pyrochlore up to 25.8 GPa. Theoretical investigations of the high-entropy pyrochlore systems were performed and showed good agreement with the experimentally obtained results. [ABSTRACT FROM AUTHOR]

Pyrochlore-based high-entropy ceramics can encapsulate multiple elements with different valences, making them promising for immobilizing high-level radioactive nuclides in molten salt radwaste. This approach addresses key challenges in dry reprocessing and molten salt reactor waste management. In this study, a single-phase pyrochlore-based high-entropy ceramic is synthesized to incorporate NdF 3 and CeF 3 as simulated molten salt radwastes. Various synthesis components have been explored, and the ceramics were characterized using x-ray diffraction (XRD) and Raman spectroscopy. Comparative analysis revealed that the size disorder is the critical factor to synthesize single-phase pyrochlore-based high-entropy ceramics. The effects of elemental ratio and the presence of variable valence elements on the synthesis of single-phase pyrochlore-based high-entropy ceramics are elucidated through the concept of size disorder. Two single-phase pyrochlore compositions have been successfully synthesized: #HE4 (Nd 2 (Ti 0.25 Zr 0.25 Hf 0.25 Sn 0.25) 2 O 7) and #HECe0.1 (Nd 2 (Zr 0.3 Hf 0.2 Sn 0.2 Nb 0.2 Ce 0.1) 2 O 7). These samples were tested with a 7-day leaching experiment using the Product Consistency Test Method PCT-B. The normalized release rates of all elements in #HE4 ranged from 10−7 to 10−9 g m−2 d−1, indicating excellent chemical durability. These findings suggest that medium- and high-entropy pyrochlore-based ceramics are effective for immobilizing radioactive nuclides in molten salt radwastes. [ABSTRACT FROM AUTHOR]

A Gd 2 Hf 2 O 7 ceramic with pyrochlore structure has been prepared by the sol-gel and cold-pressing sintering, the corrosion behavior and mechanism of CFAS powder (33CaO:10FeO 1.5 :13AlO 1.5 :44SiO 2) on the Gd 2 Hf 2 O 7 ceramic at 1673 K was investigated. Results showed that the average grain size of Gd 2 Hf 2 O 7 ceramic was 3.37 μm. The CFAS melt rapidly flowed and diffused into the interior of Gd 2 Hf 2 O 7 ceramics and reacted with Gd 2 Hf 2 O 7 to generate high melting point rod-shaped Ca 2 Gd 8 (SiO 4) 6 O 2 apatite and Hf-Gd oxides, which can effectively hinder further flow and diffusion of CFAS melt, resulting in a slow increased in corrosion depth with corrosion time. The penetration depth of the Gd 2 Hf 2 O 7 ceramic wafer after 30 h of CFAS corrosion at 1673 K was only 337.7 μm, showing excellent resistance to CFAS corrosion at high temperatures. [ABSTRACT FROM AUTHOR]

The Pechini method was used for the first time to synthesize the phase-pure nickel-containing cubic pyrochlore Bi 2 NiNb 2 O 9 (space group Fd-3m, a = 10.5371(5) Å), while the solid-phase reaction method provided no possibility to obtain impurities-free pyrochlore. At a synthesis temperature of 950°С, low-porosity ceramics with indistinct grain boundaries were formed. The results of elemental mapping indicated a uniform distribution of metal atoms on the surface of the sample. The X-ray energy dispersive analysis showed that the chemical composition of the synthesized sample corresponded to the predetermined theoretical composition. The calcination of the sample synthesized by the Pechini method was studied by the thermal analysis up to 1100°С. The functional composition of intermediate synthesis products was analyzed by vibrational spectroscopy (FTIR). In the FTIR spectrum of pyrochlore (4000–400 cm−1), absorption bands were identified at 829, 540, 654, and 490 cm−1. The dielectric properties of the pyrochlore were studied using an impedance spectroscopy. Pyrochlore Bi 2 NiNb 2 O 9 has the high relative dielectric permittivity of 145 and low dielectric losses of 0.001 (at 24°С, 1 MHz), which make it a promising for dielectric in multilayer ceramic capacitors. [ABSTRACT FROM AUTHOR]

Niobium (Nb) and tantalum (Ta) are quoted as "strategic" or "critical" elements for contemporaneous society. The main sources of Nb and Ta are minerals of the pyrochlore supergroup (PSGM) and the columbite group (CGM) mined from different magmatic lithologies. Textures and chemical compositions of PSGM and CGM often provide key information about the origin of NbTa mineralization. Therefore, we decided to carry out a detailed study of the relations between the PSGM and CGM and their post-magmatic transformations, and the Madeira peralkaline pluton (Brazil) is an ideal object for such a study. Textures of the PSGM and CGM were studied using BSE imaging and SEM mapping, and their chemical compositions were determined using 325 electron microprobe analyses. Pyrochlore from the Madeira granite can be chemically characterized as Na, Ca-poor, U- and Pb-dominant, and Sn- and Zn-enriched; REE are enriched only during alteration. Two stages of alteration are present: (i) introduction of Fe + Mn, with the majority of them consumed by columbitization; (ii) introduction of Si and Fe, and in lesser amounts also Pb and U: Si, Pb, and U incorporated into pyrochlore, iron forming Fe-oxide halos around pyrochlore. During both stages, F and Na decreased. In the case of a (nearly) complete pyrochlore columbitization, U and Th were exsolved to form inclusions of a thorite/coffinite-like phase. In contrast to altered pyrochlores from other localities, pyrochlore from Madeira shows a relatively high occupancy of the A-site. Although Madeira melt was Na-, F-rich, contemporaneous crystallization of cryolite consumed both elements and pyrochlore was, from the beginning, relatively Na-, F-poor. [ABSTRACT FROM AUTHOR]

This paper studies the structural parameters and electrophysical properties (dielectric and piezo electric, as well as currents of thermostimulated depolarization) of samples of composition 0.20BiScO3·0.45PbTiO3·0.35PbMg1/3Nb2/3O3 (or in short 0.20BS·0.45PT·0.35PMN) obtained by ceramic and melt-hardening methods of synthesis. In the ceramic method, the samples were obtained from the starting oxides by two-stage firing. In the melt method, amorphous precursors were first obtained from heat-treated and non-heat-treated starting oxide mixtures by melting and subsequent quenching under sharply gradient temperature conditions. Samples were obtained after grinding, pressing, and thermal annealing of the synthesized precursors, and four types of samples differing in size and shape of the intermediate precursor particles (crystallites) were obtained. The X-ray phase analysis showed that the predominant phase in the studied samples is the perovskite phase; in both types of samples, up to 5 wt.% of impurity phase with pyrochlore structure was also present. The samples of 0.20BS·0.45PT·0.35PMN exhibit dielectric properties characteristic of relaxor ferroelectrics, and the polarized samples exhibit a pronounced piezo effect with a piezo modulus value of d33~200 pC/N. A comparative analysis of the properties of the samples obtained by different methods has been carried out. The essential advantage of the melt method is that its use allows obtaining varieties of four kinds of ferroelectric relaxors and reduces the time of synthesis of samples by 2–3 times. [ABSTRACT FROM AUTHOR]

The temperature dependence of amorphization in a high-entropy pyrochlore, (Yb0.2Tm0.2Lu0.2Ho0.2Er0.2)2Ti2O7, under irradiation with 600 keV Xe ions has been studied using in situ transmission electron microscopy (TEM). The critical amorphization dose increases with temperature, and the critical temperature for amorphization is 800 K. At room temperature, the critical amorphization dose is larger than that previously determined for this pyrochlore under bulk-like 4 MeV Au ion irradiation but is similar to the critical doses determined in two other high-entropy titanate pyrochlores under 800 keV Kr ion irradiation using in situ TEM, which is consistent with reported behavior in simple rare-earth titanate pyrochlores. [ABSTRACT FROM AUTHOR]

This study investigated the potential of A 2 Zr 2 O 7 pyrochlore phase oxides (A = La, Ce, Nd, and Gd) as solid oxide fuel cell (SOFC) electrolyte materials. A 2 Zr 2 O 7 ceramics were synthesized using the sol-gel process, and their disordered pyrochlore structure was confirmed by X-ray Diffraction and Rietveld refinement. Field Emission Scanning Electron Microscopy (FE-SEM) was used to examine the morphology of the materials, while X-Ray Photoelectron Spectroscopy (XPS) confirmed a high oxygen ion concentration. UV–Vis Diffuse Reflectance Spectroscopy (DRS) and density of states calculations consistently showed similar bandgap patterns in all zirconate pyrochlore. Density Functional Theory (DFT) simulations provided insights into the electronic structure and migration pathways. A two-probe conductivity study confirmed the relation between the ionic conductivity and ordering degree of pyrochlore. At 750 °C, LZO, CZO, and GZO exhibited ionic conductivity values of 5.44 × 10−3 S/cm, 3.00 × 10−3 S/cm, and 2.01 × 10−3 S/cm respectively, while NZO demonstrated a conductivity of 1.27 × 10−2 S/cm at 700 °C, which is higher than that of the other samples. This study favours the use of the sol-gel route for processing zirconate pyrochlore materials, highlighting its ability to achieve high densities at lower temperatures and exhibit enhanced ionic conductivity. A 2 Zr 2 O 7 has emerged as a promising oxide-ion conducting solid electrolyte for intermediate temperature SOFC applications within the 600–750 °C temperature range. [Display omitted] [ABSTRACT FROM AUTHOR]

Classical spin liquids are paramagnetic phases that feature nontrivial patterns of spin correlations within their ground-state manifold whose degeneracy scales with system size. Often they harbor fractionalized excitations, and their low-energy fluctuations are described by emergent gauge theories. In this work, we discuss a model composed of chiral three-body spin interactions on the pyrochlore lattice that realizes a novel classical chiral spin liquid whose excitations are fractonalized while also displaying a fracton-like behavior. We demonstrate that the ground-state manifold of this spin liquid is given by a subset of the so-called color-ice states. We show that the low-energy states are captured by an effective gauge theory which possesses a divergence-free condition and an additional chiral term that constrains the total flux of the fields through a single tetrahedron. The divergence-free constraint on the gauge fields results in two-fold pinch points in the spin structure factor and the identification of bionic charges as excitations of the system. Chiral spin liquids are nontrivial states of matter characterized by fractionalized excitations, but they have been mostly found in quantum models. Here the authors present a simple model of a classical chiral spin liquid, which exhibits fractons as low-temperature excitations. [ABSTRACT FROM AUTHOR]

Among different pollutants, organic dyes, phenolic compounds, and antibiotics are three types of hazardous contaminants that have become serious environmental issues. This work deals with the synthesis of new visible-light responsive CsM 0.25 W 1.75 O 6 (M = Ni, Co, Mn, Cu) compounds with a solid-state reaction induced defect pyrochlore structure followed by crushing in a ball mill. The prepared materials were characterized using scanning electron microscopy, X-ray diffraction with Rietveld refinement, X-ray photo-electron spectroscopy, differential thermal analysis, and nitrogen adsorption-desorption measurements at low-temperature. The optimized CsNi 0.25 W 1.75 O 6 (CsNiWO-2) compound was tested for its photocatalytic abatement efficient for several contaminants including methylene blue, phenol, as well as levofloxacin and isoniazid antibiotics. The influence of the various key aspects, such as photocatalyst dosage and hydrogen peroxide concentration, on the degradation efficiency of CsNiWO-2 was examined. The degradation efficiency of CsNiWO-2 (0.6 g L−1) towards methylene blue, phenol, levofloxacin, and isoniazid in the presence of H 2 O 2 (0.06 mol L−1) was 81.4, 47.9, 84.6, and 37.4 %, respectively. Thus, the developed material demonstrates promising properties to degrade methylene blue and levofloxacin. Also, the mechanism and comprehensive schemes for the photooxidation of methylene blue and levofloxacin were elucidated over CsNiWO-2. The present research potentially contributes to designing efficient defect pyrochlores for wastewater treatment under visible light irradiation. [Display omitted] • CsM 0.25 W 1.75 O 6 (M = Ni, Co, Mn, Cu) materials were prepared by a solid-state method. • First report of CsM 0.25 W 1.75 O 6 (M = Ni, Co, Mn, Cu) photodegradation activity. • Grinded CsNi 0.25 W 1.75 O 6 displayed highest activity in the degradation of MB and LFX. • Potential of CsNi 0.25 W 1.75 O 6 photocatalyst for wastewater treatment under LED light. [ABSTRACT FROM AUTHOR]

We describe how the methods of group theory (symmetry) are used to optimize the problem of exact diagonalization of a quantum system on a 16-site pyrochlore lattice. By analytically constructing a complete set of symmetrized states, the Hamiltonian can be completely block-diagonalized. As an example, we consider a spin-1/2 system with nearest-neighbour exchange interactions. We present the energy spectrum of a small system for a range of model parameters in the vicinity of the spin ice phase. [ABSTRACT FROM AUTHOR]

Pyrochlore oxides, specifically G d 2 Z r 2 O 7 , have been a subject of interest due to their unique structural, physical, and magnetic properties. These properties make pyrochlore oxides potential candidates for various technological applications, including magnetocaloric refrigeration. Magnetocaloric refrigeration is a promising alternative to conventional refrigeration methods, as it is more energy-efficient and environmentally friendly. By studying the magnetocaloric effect of pyrochlore oxides like G d 2 Z r 2 O 7 , researchers can gain a deeper understanding of the underlying mechanisms and potential applications of these materials in magnetocaloric refrigeration systems. By employing advanced computational methods such as Monte Carlo simulations and first-principles calculations based on the full-potential linearized augmented plane wave (FP-LAPW) a technique is employed to examine the magnetic structure, researchers can investigate the magnetocaloric effect of pyrochlore oxides with high accuracy and precision. This information has the potential to aid in the advancement of more effective magnetocaloric systems materials and ultimately lead to the design and optimization of advanced magnetocaloric refrigeration systems. [ABSTRACT FROM AUTHOR]

Next‐generation electrical and electronic systems rely on the development of efficient energy‐storage dielectric ceramic capacitors. However, achieving a synergistic enhancement in the polarization and in the breakdown field strength (Eb) presents a considerable challenge. Herein, a heterogeneous combination strategy involving embedding a high Eb plate‐like pyrochlore phase in a high‐polarization perovskite phase is proposed. The embedded plate‐like pyrochlore increases the breakdown field strength and promotes the dynamic polarization response. Meanwhile, the strong spin–orbit coupling effect of the 5d electrons is conducive to the maintenance of the high polarization value of the perovskite. Consequently, the prepared multilayer ceramic capacitor (MLCC) exhibits an ultrahigh Eb and a high polarization. More specifically, an energy storage density (Wrec) of 14.9 J cm−3 with an efficiency of up to 93.4% is achieved for the optimized pyrochlore/perovskite phase. Furthermore, the MLCCs also exhibits an Wrec of ≈ 7.7 J cm−3 ± 4.5% in the temperature range of −50–180 °C. Therefore, this heterogeneous combination strategy therefore provides a simple and effective method for improving the energy‐storage performances of dielectric ceramic capacitors. [ABSTRACT FROM AUTHOR]

Polyoxotungstosilicates with the general formulas Cat4[SiW12O40] · mH2O and Cat6[SiW11O39Ni(H2O)] · nH2O were synthesized, where Cat = Rb+, Cs+, (CH3)4N+. By means of IR spectroscopy and x-ray diffraction analysis, it was shown that the compounds have the Keggin anion structure. The thermolysis of the obtained compounds within the temperature range of 600 – 800°C resulted in the formation of previously unknown pyrochlore-structure phases Rb12/13Si2/13W22/13Ni2/13O6 and Cs12/13Si2/13W22/13Ni2/13O6 with the with the unit cell parameters a of 10.284 and 10.309 Å, as well as phases with tungsten bronze structure Rb12/20Si3/20W36/20O6 and Si3/38W36/38O3. The synthesis of tungsten silicates with pyrochlore and tungsten bronze structure through thermolysis of polyoxotungstosilicates reduces the temperature of their preparation to 600 – 650°C and heating time to 1 h, thus extending the ranges of chemical compositions and their morphological diversity. [ABSTRACT FROM AUTHOR]

The modified sol-gel method (Pechini method) is shown to synthesize multielement oxides on the basis of bismuth niobate that crystallize in the pyrochlore structure (space group Fd-3m). The temperature for the synthesis of a single-phase sample amounts to 950°C, which is 100°C lower than the calcination temperature used in the conventional ceramic method of synthesis. The average crystallite size determined radiographically varies from 39 nm (850°C) to 48 nm (1050°C) depending on the sintering temperature. According to x-ray diffraction analysis, the unit cell parameter is equal to 10.4872(6) Å. The conducted elemental mapping indicates a uniform distribution of metal atoms on the sample surface, while energy dispersive x-ray analysis shows that the chemical composition of the synthesized sample corresponds to the specified theoretical composition. [ABSTRACT FROM AUTHOR]

Zirconate pyrochlores have been extensively studied as candidate waste forms for the immobilization of actinide wastes due to their flexible crystal chemistry, excellent structural stability, and exceptional radiation tolerance. Herein, we report the synthesis of a series of compounds Eu2Zr2–xO7–2x (x = 0–1, step = 0.125) using a co‐precipitation route to form solid solutions between the two end members, Eu2Zr2O7 pyrochlore and Eu2ZrO5 defect fluorite. It is important to understand the pyrochlore to defect fluorite transformation as a function of Zr/Ln molar ratio. The structural investigation by x‐ray diffraction has shown the increasing cation disorder and corresponding structural transitions from the ordered pyrochlore to disordered pyrochlore, then to defect fluorite. While diffuse reflectance spectroscopy provides similar optical absorption features reflecting the presence of Eu(III) ion, Raman spectroscopy has revealed more details on the phase transition and short‐range structures. This work highlights the structural flexibility in zirconate materials as potential nuclear waste forms for the immobilization of actinide‐rich waste streams, especially suitable for the separated minor actinides. [ABSTRACT FROM AUTHOR]

Energy input is an important factor affecting flotation effect, and energy input is mainly determined by stirring speed and stirring time. In order to explore the influence of energy input on the flotation kinetics of fine pyrochlore, the classical first-order kinetic model was determined as the best fitting model for the flotation process of fine pyrochlore by flotation rate test. The kinetic parameters of fine pyrochlore under different energy input were investigated. The mechanism of the agglomeration state of fine chaste stone and the adsorption capacity of surface reagent on the flotation kinetics under different energy input conditions was studied by means of optical microscope and mineral surface adsorption. The results show that the kinetic parameters of flotation rate constant k and the theoretical maximum recovery increase first and then decrease with the increase of energy input, and the maximum values of 0.038 78 and 89.711 8% are obtained at the stirring speed of 1 602 r/min and the stirring time of 3 min. The average particle size of the aggregates and the adsorption capacity on the mineral surface with the increase of energy input were consistent with the change trend of flotation kinetic parameters, and the maximum values of 141. 01 7m and 1. 377 mg/g were obtained at the stirring speed of 1 602 r/min and the stirring time of 3 min. When the energy input is too high or too low, the kinetic parameters are at a low level. The energy input is too low, the agglomeration effect is not good, there are more dispersed minerals, and the adsorption capacity of chemicals on the surface of minerals is low, which is not conducive to the collusion and adhesion between bubbles and particles. High energy input will destroy the formed clusters and the adsorbent layer on the surface, reduce the particle size of clusters and desorption of agents, and reduce the adhesion efficiency between bubbles and particles. Appropriate energy input is conducive to the formation of fine chastocystic agglomeration, enhance the adsorption of chemicals on the mineral surface, improve the collision and adhesion efficiency between bubbles and parties, and thus improve the flotation efficiency. [ABSTRACT FROM AUTHOR]

Rare-earth zirconate pyrochlores, which exhibit various interesting properties, especially low thermal conductivity, are of great interest. Nonstoichiometry is an effective strategy involving defect engineering to reduce the thermal conductivity of materials. In this work, a long series of solid solutions, εSmO1.5·(1−ε)ZrO2 (ε = 0.200, 0.250, 0.350, 0.400, 0.450, 0.500, 0.525, 0.550, 0.600, and 0.650), were designed and synthesized to investigate the effects of nonstoichiometry on the structural evolution, defect chemistry, and thermal conductivity of SmO1.5–ZrO2 system across the entire pyrochlore phase field and phase transition regions. The similarity of all the Raman spectra provides an incredible opportunity to confirm the structural details and evolution of pyrochlore and defective fluorite, as well as the emergence of the expected point defects. A new solution mechanism concerning nonstoichiometry was proposed and confirmed by analyzing the variations in the experimental density and Raman spectra. The thermal conductivities of all the samples were measured, and investigated in terms of the phonon-scattering theory. The results show that the nonstoichiometry with SmO1.5 excess is more effective in reducing the thermal conductivity to an extremely low value of approximately 1 W/(m·K), which can be attributed to the dramatic decrease in the average acoustic velocity in addition to the strong phonon scattering of Zr ion vacancies and oxygen vacancies. On the other hand, the nonstoichiometry with ZrO2 excess significantly reduces the thermal conductivity at room temperature, but conversely leads to a slight increase of it above 200 °C. The former variation can be attributed to the phonon scattering of the 8a interstitial oxygen ions, which has a similar effectiveness to the defects on the SmO1.5-rich side. The latter variation may be attributed to the Umklapp scattering of phonons.

Grain boundaries in polycrystalline materials significantly affect their properties, such as ionic transport, corrosion, and chemical durability. The pyrochlore compound (Gd2Ti2O7) is employed as a model for complex oxides and is known for its diverse applications, including nuclear waste immobilization. Density functional theory-based first-principles molecular dynamics simulations were performed at different temperatures on the hydrated grain boundary system. The results show extensive transformations within the grain boundaries among hydrous water species (OH−, H2O, and H3O+). The temperature dependence of self-diffusion coefficients follows Arrhenius behavior, with an activation energy of 35.9 kJ/mol for hydrogen and 46.3 kJ/mol for oxygen. The lifetime of OH− is about three to four times longer than that of H2O at temperatures from 800 to 2100 K, suggesting the greater stability of OH− over H2O, a unique characteristic of the grain boundaries. The estimated lifetime of the hydrous species decreases as the temperature increases, with an activation energy of 9.9 kJ/mol for OH− and 13.4 kJ/mol for H2O. While Gd3+ is more mobile than Ti4+, both the Gd3+ and Ti4+ cations are orders of magnitude less mobile than the water species. The results suggest that water species are much more mobile within grain boundaries than in the bulk crystal and have the potential to penetrate deep into polycrystalline materials through grain boundaries, leading to grain boundary degradation and dissolution. The different mobilities of cations in complex oxides can lead to leaching of certain cations and incongruent dissolution during the chemical weathering of Earth and industrial materials. [ABSTRACT FROM AUTHOR]

Grain boundaries in polycrystalline materials significantly affect their properties, such as ionic transport, corrosion, and chemical durability. The pyrochlore compound (Gd2Ti2O7) is employed as a model for complex oxides and is known for its diverse applications, including nuclear waste immobilization. Density functional theory-based first-principles molecular dynamics simulations were performed at different temperatures on the hydrated grain boundary system. The results show extensive transformations within the grain boundaries among hydrous water species (OH−, H2O, and H3O+). The temperature dependence of self-diffusion coefficients follows Arrhenius behavior, with an activation energy of 35.9 kJ/mol for hydrogen and 46.3 kJ/mol for oxygen. The lifetime of OH− is about three to four times longer than that of H2O at temperatures from 800 to 2100 K, suggesting the greater stability of OH− over H2O, a unique characteristic of the grain boundaries. The estimated lifetime of the hydrous species decreases as the temperature increases, with an activation energy of 9.9 kJ/mol for OH− and 13.4 kJ/mol for H2O. While Gd3+ is more mobile than Ti4+, both the Gd3+ and Ti4+ cations are orders of magnitude less mobile than the water species. The results suggest that water species are much more mobile within grain boundaries than in the bulk crystal and have the potential to penetrate deep into polycrystalline materials through grain boundaries, leading to grain boundary degradation and dissolution. The different mobilities of cations in complex oxides can lead to leaching of certain cations and incongruent dissolution during the chemical weathering of Earth and industrial materials. [ABSTRACT FROM AUTHOR]

Abstract In addition to complex spin-ice and spin-liquid states of rare-earth pyrochlore oxides, A2Ir2O7 iridates have been recently proposed to host a cooling-field-controllable antiferromagnetic domain structure of iridium moments. Reliable and profound studies of the magnetic domain structure, including domains’ interfaces, have been frequently limited by insufficient sample quality or lack of single crystals. We report the magnetic properties of the for-the-first-time synthesised Lu2Ir2O7 and Er2Ir2O7 single crystals; focussing on the robust ferromagnetic component of magnetisation present in the material with the antiferromagnetically ordered state of the all-in-all-out (AIAO) type. Anisotropy of the system, as well as the effects of magnetic (Er3+) or nonmagnetic (Lu3+) local environments on Ir4+ moments, is studied. The size of the domains is calculated based on a simplified domain wall model. Results are discussed in the framework of AIAO and AOAI domains and interfaces on the geometrically frustrated lattice.

A cubic pyrochlore with the composition Bi1.865Co1/2Fe1/2Ta2O9+Δ (space group Fd-3m, a = 10.5013(8) Å) was synthesized from oxide precursors using solid-phase reactions. These ceramics are characterized by a porous microstructure formed by randomly oriented grains of an elongated shape with a longitudinal size of 0.5–1 µm. The electronic state of cobalt and iron ions in oxide ceramics was studied by NEXAFS and XPS spectroscopy. The parameters of the XPS spectra of Bi4f, Bi5d, Ta4f, Co2p, and Fe2p ionization thresholds for a complex pyrochlore were compared with the parameters of the corresponding oxides of the transition elements. The energy position of the XPS-Ta4f and -Ta5p spectra is shifted towards lower energies compared to the binding energy in tantalum(V) oxide by 0.75 eV. According to XPS spectroscopy, bismuth and tantalum cations have the corresponding effective charge of +3 and +(5-δ). The NEXAFS-Fe2p spectrum of ceramics coincides with the spectrum of Fe2O3 in its main spectrum characteristics and indicates the content of iron ions in the oxide ceramics in the form of octahedral Fe(III) ions, and according to the character of the Co2p spectrum, cobalt ions are predominantly in the Co(II) state.

Although the smaller size of nanophosphors renders processability and flexibility for next-generation devices, concurrent surface prolificity stifles the phosphor efficiency, and in turn, their superiority. To circumvent the surface side effect in the Y2Sn2O7:Eu nanophosphor, the present work articulates a co-substituent (Zr4+)-assisted revival of stifled luminescence. Steady-state and time-resolved photoluminescence studies revealed that with respect to nanophosphors without a Zr substituent, the Zr-substituted Y2Sn2−xZrxO7:Eu (x = 0.25, 0.5) pyrochlore nanophosphor exhibited multi-fold augmentation in lifetime and quantum efficiency values, which are key parameters for ascertaining the photoluminescence performance. The experimental and theoretical outcomes indicate that Eu3+ prefers to be in close proximity to Zr4+ ions in the Y2Sn2−xZrxO7:Eu (x = 0.25, 0.5) pyrochlore lattice to counterbalance the individual substitution consequences and generate appropriate electronic distributions and polar interactions. This proximity preference of Zr–Eu facilitates the occupation of Eu3+ in the interior region of nanoparticles and avoids the surface sensitivity. Furthermore, the lifetime values for the Y2Sn2−xZrxO7:Eu (x = 0.25, 0.5) pyrochlore nanophosphor are 5–6 ms, and the internal quantum efficiency is approximately 80%, which is the highest of any pyrochlore nanosized phosphor reported thus far, to the best of our knowledge. Thus, this work deciphered an innovative pathway for evasion of the surface-quenching effect without compromising homogeneity in the structural ordering and vicinal symmetry of the dopant/substituent across the dimensions of nanophosphors. [ABSTRACT FROM AUTHOR]

In this study, La 2 (TiZrSnHfGe) 2 O 7 high entropy oxides were firstly prepared by solid state reaction method. The effects of different sintering temperatures on the structure, morphology and dielectric properties were studied. When the pre-calcination temperature is 1300 °C, the powder exhibits a single pyrochlore phase instead of defective fluorite phase. The existence of high entropy affects the changes in the crystal structure of A 2 B 2 O 7 type oxides, resulting in lattice distortion. The dielectric results showed that the ceramics have certain frequency dispersion, and the dielectric properties are affected by temperature and frequency. Due to the high entropy effect, the La 2 (TiZrSnHfGe) 2 O 7 ceramic exhibits good dielectric stability at both high and low frequencies. The formation of defect dipole clusters in the system results in the increase of dielectric constant. It is feasible to change the dielectric properties of ceramics by designing high entropy oxides, which showed the potential value in microelectronics field. [ABSTRACT FROM AUTHOR]

Dry reforming with CO 2 is one potential method for tar removal and further production of syngas in biomass gasification, but the crucial catalysts with good reaction characteristics are still being developed. In the work, Ni/pyrochlore was proposed to be utilized as catalysts in the dry reforming of tar, and thermodynamic calculation, reaction progress test, and materials characterization were conducted to reveal dry reforming characteristics over Ni/pyrochlore catalysts and the reaction mechanism behind. Results show that YS 0.2 C catalyst exhibits the best activity (toluene and CO 2 conversion of 70.1% and 79.5%) and stability among all catalysts under the optimized conditions of 700 °C with a CO 2 /toluene molar ratio of 7. Analysis on physicochemical properties of the catalysts indicate Sr doping can effectively promote catalytic reforming by enhanced interaction between Ni and support, CO 2 adsorption and oxygen mobility. The work offers a promising catalyst type in improving tar removal by dry reforming. • Systematic study on pyrochlore supported Ni catalysts in the dry reforming of tar. • Ni/Y 1.8 Sr 0.2 Ce 2 O 7 exhibits superior activity and stability during dry reforming. • Reaction conditions were optimized to be at 700 °C with CO 2 /toluene = 7. • Sr doping contributes to the interaction, CO 2 adsorption and oxygen mobility. [ABSTRACT FROM AUTHOR]

The interplay of spin-orbit coupling with other relevant parameters gives rise to the rich phase competition in complex ruthenates featuring octahedrally coordinated Ru4+. While locally, spin-orbit coupling stabilizes a nonmagnetic Jeff = 0 state, intersite interactions resolve one of two distinct phases at low temperatures: an excitonic magnet stabilized by the magnetic exchange of upper-lying Jeff = 1 states or Ru2 molecular orbital dimers driven by direct orbital overlap. Pyrochlore ruthenates A2Ru2O7 (A = rare earth, Y) are candidate excitonic magnets with geometrical frustration. We synthesized In2Ru2O7 with covalent In-O bonds. This pyrochlore ruthenate hosts a local Jeff = 0 state at high temperatures; however, at low temperatures, it forms a unique nonmagnetic ground state with nearly linear Ru-O-Ru molecules, in stark contrast to other A2Ru2O7 compounds. The disproportionation of covalent In-O bonds drives Ru2O molecule formation, quenching not only the local spin-orbit singlet but also geometrical frustration. [ABSTRACT FROM AUTHOR]

Boosting the reaction stability without sacrificing the activity and cost is extremely important but full of challenges for the RuO2‐based oxygen evolution catalysts. Herein, porous and B‐site substituted Y2[Mn0.2Ru0.8]2O7 (p‐Y2[Mn0.2Ru0.8]2O7) pyrochlore toward oxygen evolution reaction is innovatively synthesized. The formed meso‐/macroporous structure can increase the specific surface area and corresponding active sites, meanwhile, Mn‐substitution can modulate the electronic structure, stabilize the morphology, and reduce the dosage of Ru species. Interestingly, the p‐Y2[Mn0.2Ru0.8]2O7 performs 50 h stable operation, significantly outperforming the commercial RuO2(CM) counterpart with less than 2 h life. Furthermore, the required overpotential to achieve 10 mA cm−2 is only 266 mV, accompanied with favorable reaction kinetics and catalyst utilization. [ABSTRACT FROM AUTHOR]

A new series of 20-component fluorite-based compositionally complex oxides (20CCFBO x Nb/Ta) with the general chemical formula (15RE 1/15) 2 x +1 (Ce 1/3 Zr 1/3 Hf 1/3) 3–3 x (Nb 1/2 Ta 1/2) x O 8- δ (0 ≤ x ≤ 1, where 15RE 1/15 = La 1/15 Pr 1/15 Nd 1/15 Sm 1/15 Eu 1/15 Gd 1/15 Tb 1/15 Dy 1/15 Y 1/15 Ho 1/15 Er 1/15 Tm 1/15 Yb 1/15 Lu 1/15 Sc 1/15) are synthesized. Despite that the Gibbs phase rule allows for the existence of up to 20 phases at the thermodynamic equilibrium, 17 of the 20CCFBO x Nb/Ta compositions synthesized in this study all possess single ultrahigh-entropy phases in fluorite, pyrochlore, or weberite structure, as shown by X-ray diffraction (XRD). Only < 1 vol% of secondary phases are observed in two compositions near the phase-transition points. With changing compositional variable x , this series of 20CCFBO x Nb/Ta undergoes an abrupt fluorite-pyrochlore transition at x = ∼0.27 and an abrupt pyrochlore-weberite transition at x = ∼0.87. Careful characterization reveals abrupt changes of order parameters at both phase transitions. In addition, weberite short-range ordering can persist into the long-range pyrochlore phase, which leads to the lowest thermal conductivities. [ABSTRACT FROM AUTHOR]

A comprehensive study of the structural properties of the heavily investigated rare-earth A 2 Ir 2 O 7 iridate series under extreme conditions is presented. From Pr 2 Ir 2 O 7 to Lu 2 Ir 2 O 7 , the series is sufficiently covered by iridates with A = Pr, Sm, Dy, Ho, Er, Tm, Yb, and Lu; general trends and systematics within the series, including the understudied heavy-rare-earth members, are dependably followed. Temperature- and pressure-dependent synchrotron X-ray powder diffraction experiments reveal robustness of the pyrochlore structure throughout the series, down to 4 K and up to 20 GPa. The thermal expansivity of the pyrochlore lattice is determined, all falling in the Debye temperature range of θ D = 360–420 K. The pressure compressibility shows a systematic increase of the bulk modulus with the rare-earth atomic number from K = 180–210 GPa. Combining the results of thermal measurements (Debye temperature) and pressure measurements (bulk modulus) enables us to determine the Grüneisen parameter of selected members and compare it to previous studies. Temperature and pressure evolution of the fractional coordinate of oxygen at 48 f Wyckoff position, the sole free fractional coordinate in the crystal structure, is investigated and discussed regarding the antiferromagnetic ordering of the Ir magnetic moments. In addition to results on A 2 Ir 2 O 7 iridates, the temperature and pressure evolution of the crystal structure of an IrO 2 minority phase is followed. The tetragonal rutile-type structure is stable down to the lowest temperature. However, an application of pressure of approximately 15 GPa induces a structural transition: The tetragonal structure is orthorhombically distorted. The orthorhombic structure is still not fully stabilised at 20 GPa, and further distortion of the lattice (or subsequent structural transformations) is expected with increasing external pressure. [ABSTRACT FROM AUTHOR]

In this present work, photocatalysts based on a new pyrochlore-type solid solution were prepared using the ceramic method at 1000°C. X-ray diffraction (XRD) analysis shows the existence of a solid solution with pyrochlore structure Bi1.5Sb1.5Zn1–xCuxO7 (0 ≤ x ≤ 1). Scanning Electron Microscope (SEM) images exhibited a slight difference in the external morphology of the samples. The UV-diffuse measurement revealed a change in the absorbance from the UV part for the zinc-rich compound to the visible part for the copper-rich compound. The Energy band gap values were between 3.15 and 1.84 eV. The photocatalytic activity of these prepared mixed oxides was studied for the photo-degradation of the dye Orange II (ORII) as an organic pollutant, in the presence of hydrogen peroxide (H2O2) as an oxidising agent, under sunlight irradiation, by varying different parameters such as the catalysts mass, the oxidant volume, the concentration of the pollutant and the pH. The experimental results obtained by UV-visible spectroscopy revealed that the removal efficiency of ORII increased with increasing the irradiation time for all tested photocatalysts. The pseudo-first-order kinetic model gave the best fit, with the highest correlation coefficients (R2 = 0.99). The results of this study revealed the potential and various advantages of these new efficient photocatalysts. [ABSTRACT FROM AUTHOR]

A cubic pyrochlore with the composition Bi1.865Co1/2Fe1/2Ta2O9+Δ (space group Fd-3m, a = 10.5013(8) Å) was synthesized from oxide precursors using solid-phase reactions. These ceramics are characterized by a porous microstructure formed by randomly oriented grains of an elongated shape with a longitudinal size of 0.5–1 µm. The electronic state of cobalt and iron ions in oxide ceramics was studied by NEXAFS and XPS spectroscopy. The parameters of the XPS spectra of Bi4f, Bi5d, Ta4f, Co2p, and Fe2p ionization thresholds for a complex pyrochlore were compared with the parameters of the corresponding oxides of the transition elements. The energy position of the XPS-Ta4f and -Ta5p spectra is shifted towards lower energies compared to the binding energy in tantalum(V) oxide by 0.75 eV. According to XPS spectroscopy, bismuth and tantalum cations have the corresponding effective charge of +3 and +(5-δ). The NEXAFS-Fe2p spectrum of ceramics coincides with the spectrum of Fe2O3 in its main spectrum characteristics and indicates the content of iron ions in the oxide ceramics in the form of octahedral Fe(III) ions, and according to the character of the Co2p spectrum, cobalt ions are predominantly in the Co(II) state. [ABSTRACT FROM AUTHOR]

Flat bands are intriguing platforms for correlated and topological physics. Various methods have been developed to create flat bands utilizing lattice geometry, but the investigation of orbital symmetry in multiorbital materials is a new area of focus. Here, we introduce a site symmetry-based approach to emerging multiorbital 2D and 3D flat bands on the kagome and pyrochlore lattices. As a conceptual advance, the one-orbital flat bands are shown to originate as mutual eigenstates of isolated molecular motifs. Further developing the mutual eigenstate method for multiple orbitals transforming differently under the site symmetries, we derive interorbital hopping generated flat bands from the antisymmetric interorbital Hamiltonian and introduce group-theoretic descriptions of the flat band wavefunctions. Realizations of multiorbital flat bands in realistic materials are shown to be possible in the Slater-Koster formalism. Our findings provide new directions for exploring flat-band electronic structures for novel correlated and topological quantum states. [ABSTRACT FROM AUTHOR]

In addition to complex spin-ice and spin-liquid states of rare-earth pyrochlore oxides, A2Ir2O7 iridates have been recently proposed to host a cooling-field-controllable antiferromagnetic domain structure of iridium moments. Reliable and profound studies of the magnetic domain structure, including domains’ interfaces, have been frequently limited by insufficient sample quality or lack of single crystals. We report the magnetic properties of the for-the-first-time synthesised Lu2Ir2O7 and Er2Ir2O7 single crystals; focussing on the robust ferromagnetic component of magnetisation present in the material with the antiferromagnetically ordered state of the all-in-all-out (AIAO) type. Anisotropy of the system, as well as the effects of magnetic (Er3+) or nonmagnetic (Lu3+) local environments on Ir4+ moments, is studied. The size of the domains is calculated based on a simplified domain wall model. Results are discussed in the framework of AIAO and AOAI domains and interfaces on the geometrically frustrated lattice. [ABSTRACT FROM AUTHOR]