Explore the vast range of titles available.

Sm2−xCaxZr2O7−x/2 (x = 0, 0.05, 0.1) and Gd2−xCaxZr2O7−x/2 (x = 0.05, 0.1) mixed oxides in a pyrochlore–fluorite morphotropic phase region were prepared via the mechanical activation of oxide mixtures, followed by annealing at 1600 °C. The structure of the solid solutions was studied by X-ray diffraction and refined by the Rietveld method, water content was determined by thermogravimetry (TG), their bulk and grain-boundary conductivity was determined by impedance spectroscopy in dry and wet air (100–900 °C), and their total conductivity was measured as a function of oxygen partial pressure in the temperature range: 700–950 °C. The Sm2−xCaxZr2O7−x/2 (x = 0.05, 0.1) pyrochlore solid solutions, lying near the morphotropic phase boundary, have proton conductivity contribution both in the grain bulk and on grain boundaries below 600 °C, and pure oxygen–ion conductivity above 700 °C. The 500 °C proton conductivity contribution of Sm2−xCaxZr2O7−x/2 (x = 0.05, 0.1) is ~ 1 × 10−4 S/cm. The fluorite-like Gd2−xCaxZr2O7−x/2 (x = 0.1) solid solution has oxygen-ion bulk conductivity in entire temperature range studied, whereas proton transport contributes to its grain-boundary conductivity below 700 °C. As a result, of the morphotropic phase transition from pyrochlore Sm2−xCaxZr2O7−x/2 (x = 0.05, 0.1) to fluorite-like Gd2−xCaxZr2O7−x/2 (x = 0.05, 0.1), the bulk proton conductivity disappears and oxygen-ion conductivity decreases. The loss of bulk proton conductivity of Gd2−xCaxZr2O7−x/2 (x = 0.05, 0.1) can be associated with the fluorite structure formation. It is important to note that the degree of Ca substitution in such solid solutions (Ln2−xCax)Zr2O7−δ (Ln = Sm, Gd) is low, x < 0.1. In both series, grain-boundary conductivity usually exceeds bulk conductivity. The high grain-boundary proton conductivity of Ln2−xCaxZr2O7−x/2 (Ln = Sm, Gd; x = 0.1) is attributable to the formation of an intergranular CaZrO3-based cubic perovskite phase doped with Sm or Gd in Zr sublattice.

High-entropy pyrochlore-type structures based on rare-earth zirconates are successfully produced by conventional solid-state reaction method. Six rare-earth oxides (La 2 O 3 , Nd 2 O 3 , Sm 2 O 3 , Eu 2 O 3 , Gd 2 O 3 , and Y 2 O 3 ) and ZrO 2 are used as the raw powders. Five out of the six rare-earth oxides with equimolar ratio and ZrO 2 are mixed and sintered at different temperatures for investigating the reaction process. The results demonstrate that the high-entropy pyrochlores (5RE 1/5 ) 2 Zr 2 O 7 have been formed after heated at 1000°C. The (5RE 1/5 ) 2 Zr 2 O 7 are highly sintering resistant and possess excellent thermal stability. The thermal conductivities of the (5RE 1/5 ) 2 Zr 2 O 7 high-entropy ceramics are below 1 W·m –1 ·K –1 in the temperature range of 300–1200°C. The (5RE 1/5 ) 2 Zr 2 O 7 can be potential thermal barrier coating materials.

Atomic scale study has been carried out to probe the pyrochlore phase formation in local scale and compare it with the long range ordering. Lanthanum zirconate (La 2 Zr 2 O 7 ) pyrochlore was synthesized by wet chemistry and characterized by X-ray diffraction to study the long range ordering. Time Differential Perturbed γ-γ Angular Correlation (TDPAC) Spectroscopy was performed to identify the pyrochlore phase formation in local scale. Electron paramagnetic resonance and Photo-luminescence spectroscopic studies were used to identify the defects in local scale. Role of annealing and defects in nucleation of pyrochlore phase has been explored in the present study. An early identification of pyrochlore phase was successfully done by TDPAC spectroscopy.

Pyrochlore-group minerals are common in the Neoproterozoic Sevattur carbonatite complex. This complex is composed of dolomite-, calcite-, banded- and blue carbonatite together with pyroxenite, albitite and diverse syenites. This work reports the paragenetic-textural types and compositional variation of pyrochlore hosted by dolomite carbonatite, banded carbonatite and albitite together with that of alteration assemblages containing belkovite and baotite. On the basis of composition, five different types of pyrochlore are recognised and termed Pcl-I through to Pcl-V. The Pb-rich Pcl-I are present exclusively as inclusions in U-rich Pcl-IIa in dolomite carbonatite. The alteration assemblages of Pb-poor Pcl-IIb + Ba-rich or Ba–Si- rich Pcl-IV + belkovite (dolomite carbonatite) and Si-rich Pcl-V + baotite (banded carbonatite) formed after Pcl-IIa differ in these carbonatites. The albitite hosts extremely U-Ti-rich Pcl-III, mantled by Ba-rich potassium feldspar. In common with the banded carbonatite, Pcl-V is formed by alteration of Pcl-III where this mantle is partially, or completely broken. The Ba-Si-enrichment of Pcl-IV and Pcl-V together with the ubiquitous presence of baryte in all Sevattur lithologies suggests late-stage interaction with a Ba-Si-rich acidic hydrothermal fluid. This fluid was responsible for leaching silica from the associated silicates and produced Pcl-V in the silicate-rich lithologies of the banded carbonatite and albitite. The absence of Pcl-V in dolomite carbonatite is a consequence of the low modal abundance of silicates. The complex compositional diversity and lithology specific pyrochlore alteration assemblages suggest that all pyrochlore (Pcl-I to Pcl-IV) were formed initially in an unknown source and transported subsequently in their respective hosts as altered antecrysts.

High-performance dielectrics are widely used in high-power systems, electric vehicles, and aerospace, as key materials for capacitor devices. Such application scenarios under these extreme conditions require ultra-high stability and reliability of the dielectrics. Herein, a novel pyrochlore component with high-entropy design of Bi 1.5 Zn 0.75 Mg 0.25 Nb 0.75 Ta 0.75 O 7 (BZMNT) bulk endows an excellent energy storage performance of W rec ≈ 2.72 J/cm 3 together with an ultra-high energy efficiency of 91% at a significant enhanced electric field E b of 650 kV/cm. Meanwhile, the temperature coefficient (TCC) of BZMNT (∼ −220 ppm/°C) is also found to be greatly improved compared with that of the pure Bi 1.5 ZnNb 1.5 O 7 (BZN) (∼ −300 ppm/°C), demonstrating its potential application in temperature-reliable conditions. The high-entropy design results in lattice distortion that contributes to the polarization, while the retardation effect results in a reduction of grain size to submicron scale which enhances the E b . The high-entropy design provides a new strategy for improving the high energy storage performance of ceramic materials.

SignificanceQuantum materials have properties that defy conventional theories of solids. Explaining these unusual properties is a frontier in physics, which promises both technological applications and fundamentally new states of matter. Yb2Ti2O7 is a center of attention in this work. While it becomes ferromagnetic at very low temperature, its excitation spectrum resembles that of a quantum spin liquid. We show using neutron scattering on high-quality crystals that the unusual spectra may arise as a superposition of ferromagnetic and antiferromagnetic spin waves. This indicates that these disparate forms of magnetism actually coexist in Yb2Ti2O7, which is consistent with near-perfect degeneracy. The unconventional properties of Yb2Ti2O7 thus appear to arise from the atomic-scale interplay between two conventional types of order. We use neutron scattering to show that ferromagnetism and antiferromagnetism coexist in the low T state of the pyrochlore quantum magnet Yb2Ti2O7. While magnetic Bragg peaks evidence long-range static ferromagnetic order, inelastic scattering shows that short-range correlated antiferromagnetism is also present. Small-angle neutron scattering provides direct evidence for mesoscale magnetic structure that we associate with metastable antiferromagnetism. Classical Monte Carlo simulations based on exchange interactions inferred from ⟨111⟩-oriented high-field spin wave measurements confirm that antiferromagnetism is metastable within the otherwise ferromagnetic ground state. The apparent lack of coherent spin wave excitations and strong sensitivity to quenched disorder characterizing Yb2Ti2O7 is a consequence of this multiphase magnetism.

The development of sensitive, selective, and reliable glucose biosensors remains a persistent challenge in clinical diagnostics. In this study, we exploited the advantageous (electro)catalytic properties of bismuth ruthenate (Bi2Ru2O7) pyrochlore clusters, known for their high surface activity and metallic-like conductivity, and the favorable physicochemical properties of multi-walled carbon nanotubes (MWCNTs) by combining them with glucose oxidase (GOD) in a sensitive and selective disposable glucose biosensor. The integration of Bi2Ru2O7 enabled an enhanced and more reproducible response of the biosensor along with fast and improved communication between the supporting electrode and the upper biosensing layer. The architecture of the biosensor involves the deposition of an MWCNT layer on a ferrocyanide-modified screen-printed carbon electrode (FCN-SPCE), followed by the application of a biorecognition layer including GOD and Bi2Ru2O7 clusters. The voltammetric biosensor showed excellent electroanalytical performance, capable of detecting low glucose concentrations with a detection limit of 40 µM along with a linear response across the examined concentration range of 1.0–20.0 mM. The biosensor exhibited good reproducibility with a relative standard deviation (RSD) of 1.2% and interference-free operation against several of the most common interfering compounds. The practical applicability of the biosensor was demonstrated by the determination of glucose in a real serum sample spiked with different concentrations of glucose.

Pyrochlores offer an ideal playground to investigate the magnetic ground state of frustrated magnetic systems. In this class of materials, competition between various magnetic interactions remains frustrated and prevents an ordered magnetic state at low temperatures. Tb2Sn2O7 has recently attracted significant attention due to its ordered spin-ice state. Additionally, in such systems, application of external magnetic field might result in exotic magnetic states. Our current investigation on Tb2Sn2O7 reveal the presence of a new phase associated with fifth order susceptibility at low temperatures and high magnetic fields. In this compound, at zero fields, for a stabilized spin-ice state, the singlet–singlet state separated by δ play an imperative role. Under magnetic fields, δ increases and the Zeeman energy associated with the magnetic anisotropy is believed to get enhanced; which can be the key ingredient for evolution of higher-order moments, above 10 kOe, in this compound.

A novel class of high-entropy pyrochlore ceramics (HEPCs) with multiple heavy and light rare-earth elements at the A site were successfully synthesized via solid-state reaction. Both the XRD patterns and Raman spectroscopy demonstrated the single pyrochlore structure feature of seven kinds of HEPCs. Electron microscopic images revealed the typical morphology and the homogeneous distribution of all rare-earth elements. It can be concluded that the significance of configuration entropy in the HEPC system has promoted the tervalent lanthanide nuclides to form a single pyrochlore structure. This work is expected to provide guidance for the further design of high-entropy pyrochlore/fluorite ceramics.

High-entropy ceramics (HECs) have quickly gained attention since 2015. To date, nearly all work has focused on five-component, equimolar compositions. This perspective article briefly reviews different families of HECs and selected properties. Following a couple of our most recent studies, we propose a step forward to expand HECs to compositionally complex ceramics (CCCs) to include medium-entropy and non-equimolar compositions. Using defective fluorite and ordered pyrochlore oxides as two primary examples, we further consider the complexities of aliovalent cations and anion vacancies as well as ordered structures with two cation sublattices. Better thermally insulating yet stiff CCCs have been found in non-equimolar compositions with optimal amounts of oxygen vacancies and in ordered pyrochlores with substantial size disorder. It is demonstrated that medium-entropy ceramics can prevail over their high-entropy counterparts. The diversifying classes of CCCs provide even more possibilities than HECs to tailor the composition, defects, disorder/order, and, consequently, various properties.