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The demand for efficient engineering components operating in harsh environments has necessitated the exploration of advanced protective measures. Thermal barrier coatings (TBCs) have emerged as a promising solution for improving the performance, durability, and lifespan of components exposed to high temperatures, corrosive conditions, and neutron irradiation. Advanced ceramic materials specially pyrochlore of zirconates significance are enhancing the performance and longevity of components exposed to extreme thermal conditions. Dual-phase innovative zirconate coatings and their hot corrosion mechanism, a complex phenomenon involving the simultaneous presence of multiple corrosive species, is extensively explored. The interplay between different corrosion mechanisms and their impact on TBCs are elucidated, providing valuable insights for the development of effective mitigation strategies. This article addresses the understanding the hot corrosion mechanism and corrosion types, new innovative dual phase composite systems with improved properties, their experience with molten salt and pure oxidation environments followed by the stresses experienced by TBCs, highlighting the importance of understanding and managing mechanical and thermal stresses during operation. Coatings design, material selection, and advanced manufacturing techniques are discussed as key factors in alleviating these stresses and enhancing TBC performance. To overcome the challenges associated with hot corrosion and stresses, innovative strategies are being investigated. These include the development of novel coatings compositions, the incorporation of protective layers, advanced characterization techniques, and the exploration of alternative materials. This piece of review article provides a thorough analysis of these techniques and how they might increase the robustness and dependability of TBCs. Finally, we highlight the contemporary applications of TBCs in gas turbines, aero engines, nuclear industries, and other high-temperature situations. • The current research conducts a thorough examination of degradation mechanisms in dual-phase thermal barrier coatings (TBCs) based on YSZ and zirconates of (gadolinium, samarium, neodymium and lanthanum). • Highlights the formation of new zirconate phases with varying gadolinium oxide, lanthanum oxide, samarium oxide, and neodymium oxide content. • Addresses the unique challenges and benefits associated with these advanced coatings. • Introduces new modes of degradation in dual-phase TBCs. [ABSTRACT FROM AUTHOR]

Single nano high-entropy pyrochlore-type compound (A2B2O7) with 7 different rareearth cations at site A and 3 different metal cations at site B with equiatomic amounts (7A1/7)2(3B1/3)2O7 is successfully obtained. The powder with nominal composition (La1/7Sm1/7Nd1/7Pr1/7Y1/7Gd1/7Yb1/7)2(Sn1/3Hf1/3Zr1/3)2O7 was fabricated by reacting metal nitrates (site A) and metal chlorides (site B) with glycine during the combustion reaction. The XRD analysis revealed that the powder attained during synthesis is in an amorphous state. To induce crystallization of the obtained pyrochlore structure, the post-calcination process at 600-1500 oC was conducted and studied. Results of this study showed that the monophase pyrochlore (A2B2O7) structure is obtained during the calcination at 900 °C. The high-density ceramic pellet with 97% of theoretical density and free of any additives was obtained through pressureless sintering at 1650 °C for 4 h in the air using the powder calcined at 900 °C. [ABSTRACT FROM AUTHOR]

The Chuktukon REE-Nb deposit occurs within the carbonatite laterite supergene zone Chadobets upland, South of the Siberian craton. A unique laterite profile up to 600 m thick was identified by deep drilling. The laterite developed upon ultramafic lamprophyres and Ti-Th-REE-rich carbonatites. Here we report new mineralogical and geochemical data on carbonatites and laterites that reveal the evolution of supergene processes in the Chuktukon deposit within vertical zonation: (from top to bottom): 1) laterite horizon or ferruginous cap rock (ferricrete); 2) loose ochreous weathering products (ochre zone or regolith zone); 3) secondary phosphate enrichment horizon (apatite-rich zone); 4) unevenly altered disintegrated carbonatites. The bulk contents of CaO and P 2 O 5 increases from primary carbonatite upwards due to the crystallization of carbonate-fluorapatite, and decrease in near-surface horizon due to the high leaching of rocks. The total REE 2 O 3 content is highest in the rocks of the regolith zone and the enriched zone due to the redistribution and concentration of these elements both in the form of impurities and as a result of the redeposition of their own mineral phases. The variations in compositions of apatite, pyrochlore and monazite from different horizons of laterite profile were chosen as a proxy for the REE distribution in the supergene zone. Fluorapatite is gradually being replaced by hydroxyl-fluorapatite and carbonate-hydroxyl-fluorapatite, as the degree of weathering of primary carbonatites increases. Pyrochlore-Ca-Na-F is being replaced by the (Ba Sr)-variety (with Ce and Pb) during the same processes. Monazite changes from (Ce)-dominated to (La)-dominated. This is influenced by the oxidation factor, the consequence of which is also the formation of cerianite in the upper horizon. The study of the mineral and geochemical features of such an object as Chuktukon provides an improved understanding of the patterns of redistribution of the main and ore components of carbonatites in the supergene zone and can be useful in the study of other supergene deposits and delineation of dispersion halos of ore components. [ABSTRACT FROM AUTHOR]

Nanostructured thin film of Nd2Sn2O7 pyrochlore obtained by solution processing of a single molecular precursor with Nd-Sn ratio of 1:1 was found to show unprecedently high selectivity towards hydrogen sensing in the temperature range 200 °C–450 °C. Formation of crystalline Nd2Sn2O7 upon annealing the xerogel in air at 800 °C was confirmed by powder X-ray diffraction analysis. The heat-treated pyrochlore films exhibited a porous structure with interconnected grains confirmed by scanning electron microscope images. The gas sensing behavior of the device towards various analyte gases (H2, CO, CH4, NO2, NH3) showed remarkably high selectivity towards H2, while no sensor response against other reducing and oxidizing gases was monitored. The highest sensitivity towards H2 was detected at 300 °C with a linear trend observed in the sensitivity values and H2 concentration (5%–30%). Intercorrelated analysis of sensor characteristics, surface spectroscopy before and after hydrogen treatment and implications of unique crystallographic features of the pyrochlore lattice demonstrated a novel defined subsequent detection mechanism, which strongly differs from conventional binary oxides like SnO2. The significant increase in operating temperature upon H2 exposure is apparently caused by the exothermic reaction between pyrochlore and molecular hydrogen to generate highly reactive hydride species during the detection mechanism. The high efficiency and reproducibility of the investigated sensor devices indicates the potential of Nd2Sn2O7 based sensors for hydrogen safety applications [ABSTRACT FROM AUTHOR]

Increasing the recovery of the niobium metal contained in the Nelsonite rocks presents a great challenge, considering the standards and the production targets of the China Molybdenum Company (CMOC) that produces phosphate and with tailings material, concentrate niobium minerals. At Chapadão mine, located in Goiás, a mid-west Brazil's state, the weathering profile reaches up to 100 meters and the ore is subdivided into three basic types, from top to bottom: Oxidized (OX), Top Micaceous (TM) and Base Micaceous (BM). In this study, samples from these three main bodies of Nelsonite were collected and tested in laboratory scale to identify which weathering level is more favourable to niobium concentrate production. In the niobium concentration process, there can be metal losses that can jeopardize the recovery of the niobium crystals. To evaluate these losses microscopy analysis was performed using samples from industrial plant survery. The results from flotation batch tests showed that BM presented the higher mass recovery and production capacity. According to the mineralogical results the main niobium losses were identified in the barite concentrate from apatite circuit and in the screening stage in the Niobium Plant feed. The batch test results showed that adjusting the cut size of the Niobium Plant there is a potential niobium recovery upgraded to 90% from Ba-pyrochlore, and, adding the barite concentrate product as an additional mass in the tailings feed, it will result together in more than 1 t/day of niobium concentrate final product, reducing the losses and utilizing better the ore blend recovery potential. [ABSTRACT FROM AUTHOR]

Nitazoxanide (NAZ) is an antiparasitic drug that reduces inflammation caused by the SARS-CoV-2 virus. The presence of nitro group in this drug makes it an environmental pollutant. Here, an electrochemical sensor for the determination of NAZ was developed based on bismuth-doped pyrochlore lanthanum stannate nanoparticles modified screen-printed carbon electrodes (BLSO NPs/SPCE). The BLSO NPs were prepared by a combination of co-precipitation and thermal calcination processes. The fabricated BLSO NPs were analyzed by different spectroscopic methods. X-ray diffraction analysis (XRD), Fourier transform-infrared spectroscopy (FT-IR), and Raman spectroscopy showed that the lattice parameters of the lanthanum stannate nanoparticles (LSO NPs) were increased after bismuth doping due to cell expansion. The morphology and oxidation state of the elements in the BLSO NPs were analyzed by field emission-scanning electron Microscopy (FE-SEM), high-resolution transmission electron microscopy (HR-TEM), and X-ray photoelectron spectroscopy (XPS). FE-SEM and HR-TEM analysis revealed that LSO, and BLSO exhibits as a nanoparticle morphology with 20–50 nm in size. Cyclic voltammetry (CV) showed that the electrochemical reduction of NAZ was enhanced after bismuth doping due to the synergistic effect of BLSO NPs. Electrochemical determination of NAZ was performed by DPV with a low detection limit of 4 nM between the linear range of 0.01–172 µM and an electrode sensitivity of 0.16 µA µM−1 cm−2. The developed NAZ sensor showed favorable results in terms of selectivity, repeatability, and stability. [Display omitted] • Bismuth doped Lanthanum Stannate (BLSO) pyrochlore was prepared. • BLSO NPs exhibited good electrochemical performance towards NAZ reduction. • Bismuth doping enhanced the electrochemical activity of LSO NPs. • The constructed electrode has LOD (4 nM) and sensitivity (0.16 µA µM−1 cm−2). • A promising electrode for NAZ detection is developed by exploring the doping strategy. [ABSTRACT FROM AUTHOR]

The detection and monitoring of organophosphate pesticides in environmental samples are of paramount importance due to their potentially harmful effects on human health and ecosystems. In this study, we present the detection of paraoxon ethyl (POE), a widely used organophosphate pesticide, utilizing an electrochemical method. We synthesized graphene oxide-incorporated pyrochlore-type lanthanum stannate (La 2 Sn 2 O 7 @GO) as a sensing material for enhanced detection sensitivity and selectivity. The electrochemical detection of POE was performed using a glassy carbon electrode modified with the synthesized nanocomposite. The modified electrode La 2 Sn 2 O 7 @GO/GCE exhibited a remarkable electrochemical response towards POE, showing a significant reduction potential and an increase in the peak current compared to the bare and other modified electrodes. The proposed electrochemical method showed excellent detection sensitivity and selectivity for POE, with a linear response range of concentrations from 0.01 to 360 μM and a low detection limit (LDL) of 2.73 nM. The sensor also exhibited good stability and reproducibility, making it a promising tool for practical pesticide detection applications. The developed sensor offers a cost-effective, sensitive, and reliable platform for the rapid monitoring of organophosphate pesticides in environmental samples, contributing to the advancement of pesticide detection technologies and environmental protection efforts. • La 2 Sn 2 O 7 @GO nanocomposites with more active sites/edges were synthesized. • La 2 Sn 2 O 7 @GO possessed the rapid heterogeneous electron transfer towards POE. • The developed sensor detects the POE with a detection limit of 2.73 nM. • Practical analysis of prepared sensor shows good recoveries on food and environmental samples. [ABSTRACT FROM AUTHOR]

The hydride-fluoride pyrochlore NaCaMg2F7-xHx has been synthesized at high pressure (2 GPa) from binary fluorides and hydrides. Contrary to initial expectations, we did not find strong evidence of selective hydride substitution in special anionic sites. F-center formation under UV irradiation at room temperature was observed, demonstrating the potential lability of hydride and enabling further systematic studies. [ABSTRACT FROM AUTHOR]

[Display omitted] • DFT + U + SOC approaches were used to examine structural and optoelectronic properties of pyrochlores Ta 2 A 2 O 7. • Band gap values show Ta 2 A 2 O 7 compounds are semiconductors. • Optical properties report Ta 2 Cd 2 O 7 has a higher value of the refractive index, reflectivity, absorption compared to Ta 2 Ge 2 O 7. • These pyrochlore oxides can effectively absorb photons in the UV energy range. • These pyrochlore oxides have refractive indices that range from 1.0 to 2.0. • These compounds are excellent for photovoltaic device applications if their band gap can be narrowed with the right doping. Due to their stable crystal structure and controllable lattice parameters, rare earth zirconates with pyrochlore type structures have demonstrated a promise for usage in practical applications. We have investigated the electronic and optical properties of pyrochlore oxide compound named Ta 2 A 2 O 7 (A = Cd and Ge) using density functional theory based on spin–orbit coupling and Hubbard (SOC + U) corrections to consider the existence electronic d orbitals of (A) and f elements (Ta). This study focuses on the characterization and investigation of pyrochlore oxides with the A 2 B 2 O 7 composition, which have significant technological applications including quantum spin ices, solid oxide fuel cells, and nuclear waste forms. No evidence regarding magnetic moment is obtained from the first run with spin-polarization setup. Also, from the spectra of TDOS was showing a similar overall profile for both spin channels. The electronic properties (total and partial) densities of states as well as the optical properties such as the complex dielectric function, refractive index, absorption coefficient and reflectivity for wavelengths in the visible spectrum have been reported to explore the potential use of these compounds in technological applications. Consequently, the investigated compounds can be used in optoelectronic device fabrication. [ABSTRACT FROM AUTHOR]

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Objective: To identify respiratory symptoms and evaluate lung function in mine workers. Methods: This was a cross-sectional observational study involving production sector workers of a pyrochlore mining company. The subjects completed the British Medical Research Council questionnaire, which is designed to evaluate respiratory symptoms, occupational exposure factors, and smoking status. In addition, they underwent pulmonary function tests with a portable spirometer. Results: The study involved 147 workers (all male). The mean age was 41.37 ± 8.71 years, and the mean duration of occupational exposure was 12.26 ± 7.09 years. We found that 33 (22.44%) of the workers had respiratory symptoms and that 26 (17.69%) showed abnormalities in the spirometry results. However, we found that the spirometry results did not correlate significantly with the presence of respiratory symptoms or with the duration of occupational exposure. Conclusions: The frequencies of respiratory symptoms and spirometric changes were low when compared with those reported in other studies involving occupational exposure to dust. No significant associations were observed between respiratory symptoms and spirometry results. [ABSTRACT FROM AUTHOR]

Bond valence sum analysis is a powerful tool used in evaluating and validating crystal structures; especially when those structures are complex in nature. The pyrochlore structure type is versatile in not only the unique bonding that it exhibits, but also in the properties that results from the structure. This paper aims to center the discussion of evaluating the pyrochlore structure using the bond valence sum method. In this study, novel quaternary pyrochlores with a general stoichiometry of A Bi M TeO 7 (A = Cd, Ca; M = Cr, Ga, Sc, In, Fe) were synthesized and characterized for their structural, magnetic, and dielectric properties. Two representative compounds within this series of pyrochlores, BiCaFeTeO 7 and BiCdFeTeO 7 , were structurally characterized utilizing a combination of high-resolution synchrotron X-ray diffraction and neutron diffraction revealing oxygen deficient pyrochlore systems which were off from the expected stoichiometry with respect to the M site. The A site of both pyrochlores were found to be moved off-center from the expected 16 d site to the 96 h displaced position at a magnitude of 0.25 Å and 0.22 Å for the Bi/Ca and Bi/Cd systems, respectively. These structures were evaluated using the bond valence sum method and compared with trends in the literature. The properties are also reported for the Bi/Ca system for the first time, showing relatively high dielectric constants with a low dielectric loss which are primarily independent of frequency and temperature. The magnetic measurements for the Bi/Ca system for the magnetic substitutions reveal a paramagnet and antiferromagnetic properties for the Fe and Cr analogs, respectively. The novel BiCa M TeO 7 quaternary pyrochlore system shows great promise as an emerging dielectric material. (a) A Bond Valence Sum (BVS) cross-sectional map for a (b) segmented portion of the BiCdFeTeO 7 structure. [Display omitted] [ABSTRACT FROM AUTHOR]

The Tomtor massif of Paleozoic ultramafic alkaline rocks and carbonatites is located in the northern part of the Sakha Republic (Yakutia). The massif (its total area is ~ 250 km 2 ) is ~ 20 km in diameter, with a rounded shape and a concentrically zoned structure. The core of the massif consists of carbonatites surrounded by a discontinuous ring of ultramafic rocks and foidolites. The outer part is composed of alkali and nepheline syenites. All rocks are weathered and covered with eluvium, which is the thickest after carbonatites enriched in phosphates and REE. The weathering profile consists of four layers, from the top: kaolinite-crandallite, siderite, goethite, and francolite. The highest-grade ores are observed in the bedded deposit which fills depressions in “sagging” eluvium. The ores are laminated and cryptogranular, with high Nb, Y, Sc, and REE contents (on average, 4.5% Nb 2 O 5 , 7-10% REE 2 O 3 , 0.75% Y 2 O 3 , and 0.06% Sc 2 O 3 ). The highest-grade ores are natural Nb and REE concentrates. The total REE content in some layers is > 10%. The morphologic features of the highest-grade phosphate ores from the northern part of the Burannyi site were studied. The ore-forming minerals belong to the pyrochlore group, crandallite group (goyazite), and monazite-Ce. The pyrochlore group minerals occur mainly as crystals that were completely replaced by barium-strontium pyrochlore and/or plumbopyrochlore but retained the original faces; also, they occur as numerous conchoidal fragments. The grains of the pyrochlore group minerals sometimes have a zonal structure, with an unaltered pyrochlore core and a reaction rim. Goyazite occurs predominantly as colloform grains. According to SEM and TEM data, monazite occurs in the ores as ~ 50 nm particles, which cover the outer part of halloysite tubes (800–3000 nm long and 300 nm in diameter) as a dense layer and make up peculiar biomorphic aggregates. The mineralogical data, the occurrence of biomorphic aggregates, and the close association of organic remains with ore minerals suggest that the high-grade ores of the Tomtor deposit, including the Burannyi site, resulted from a hydrothermal-sedimentary process with a presumably important role of bioaccumulation of REE phosphates. [ABSTRACT FROM AUTHOR]

Based on a typical ZnO varistor composition (97·0 mol.-% ZnO, 1·0 mol.-% Bi2O3, 1·0 mol.-% Sb2O3, 0·5 mol.-% MnO and 0·5 mol.-% Co3O4), phase development of the ZnO varistor during sintering has been investigated using in situ high temperature X-ray diffraction up to 900°C, and conventional ambient X-ray diffraction for samples sintered at 900°C to 1250°C. The results indicate that α-Bi2O3 can be detected until 700°C; the pyrochlore phase can be detected in the samples heat treated at 700°C and up to 1250°C; the spinel phase is present at and .900°C. However, the main phases in the varistor are established by 950°C. By this temperature, the essential microstructure features are formed, and the varistors exhibit non-linear electrical properties, with a non-linear coefficient α of 35 and breakdown field of 8000 V cm-1. With increasing sintering temperature, both the α value and breakdown field decrease. [ABSTRACT FROM AUTHOR]

A series of pyrochlore-type lead-ruthenium oxide (Pb2Ru2O7-8) containing various amounts of oxygen vacancies was prepared by varying the heat-treatment temperature, and the oxygen reduction reaction (ORR) activity as well as the electrochemical redox property in acid and alkaline solution was evaluated using rotating disk electrode. The specific ORR activity was increased with increasing the amount of oxygen vacancies, and linearly correlated to the charge amount of electrochemical redox of Pb2Ru2O7-8 both in acid and alkaline solution. We concluded that the surface oxygen vacancy participates in the electrochemical redox of Pb2Ru2O7-8, and at the same time, behaves as the active site for ORR. The ORR activity in alkaline solution was much higher than that in acid solution, possibly because of the difference of the facility of electrochemical desorption of adsorbed oxygen species in the ORR process. Additionally, the effect of humidity on the ORR activity was investigated by single cell test. It was revealed that Pb2Ru2O7-8 shows absolutely high ORR activity in dry condition. [ABSTRACT FROM AUTHOR]

Highlights: [•] Ru and Pt in the pyrochlore are the active sites for dry reforming of methane. [•] Ru pyrochlore is more active toward DRM than Pt pyrochlore. [•] This is the first ever study of the structure and activity of these materials for DRM. [ABSTRACT FROM AUTHOR]

Abstract: Volatile Organic Compounds (VOCs) from industrial coating operations could be valuable energy resources if collected and used effectively. A promising approach is to generate syngas stream for Solid Oxide Fuel Cells (SOFCs) application by autothermal reforming of them. However, conventional nickel-based catalysts with whatever promoters/supports or formulations are not very successful for this process for lacking of activities or deactivating quickly due to sintering or carbon deposition at the presence of high percentage of aromatic compounds or sulfur chemicals. By contrast, there also exist many big challenges for precious metal-based catalysts in terms of longevity and cost effectiveness. In this paper, Ruthenium noble metal dispersed in a formulation of pyrochlore structure was explored, and various VOCs with wide range of monoaromatics additives of various species and fairly amount of naphthalene was used as fuels to simulate actual VOCs. It was found that this catalyst not only had quite good initial activity but also showed very good stability during the longevity tests, which was considered as important as, if not more important than, the former for commercialization. Eventually, actual VOC collected from a painting-booth was tested for this autothermal reforming process. The longevity test verified the high activities and good stabilities of this catalyst. Most likely the precious metal atomically dispersed in a stable structure of pyrochlore contributed to the super performance, although fundamental studies to understand the reaction mechanism was much needed. [Copyright &y& Elsevier]

Abstract: Technetium-99 is one of the most abundant, long-lived radiotoxic isotopes in used nuclear fuel (UNF). As such, it is targeted in UNF separation strategies such as UREX+, for isolation and encapsulation in solid waste forms for storage in a nuclear repository. We report here results regarding the incorporation of Tc-99 into ternary oxides of different structure types: pyrochlore (Nd2Tc2O7), perovskite (SrTcO3), and layered perovskite (Sr2TcO4). The goal was to determine synthesis conditions of these potential waste forms to immobilize Tc-99 and to harvest crystallographic, thermophysical and hydrodynamic data. Within these studies, Rietveld structure refinement was applied to allow for crystallographic characterization, while a physical property measurement system (PPMS) was used to determine thermophysical properties. The ternary oxides exhibited good crystallinity and their lattice parameters and atomic coordinates could be refined to high accuracy. Low refinement residuals (RBragg) of 2.0, 2.4, and 3.9% were achieved for Nd2Tc2O7, SrTcO3, and Sr2TcO4, respectively. The strontium technetates, SrTcO3 and Sr2TcO4, show superconductivity at rather high critical temperatures of Tc = 7.8K and 7K, respectively. Nd2Tc2O7 did not show any changes in magnetic properties above 3K. [Copyright &y& Elsevier]

Abstract: In order to solve the soot emission problems from diesel engines, a series of La2Sn1.8M0.2O7 (M= Sn, Mn, Fe, Co, Cu) oxides with pyrochlore structure were synthesized by co-precipitation, and investigated for soot oxidation with a O2/NO mixture by Temperature-programmed Oxidation. The incorporation of transition metals strongly influences the crystallite size, surface area and redox properties of the catalysts. All the pyrochlore oxides display catalytic soot oxidation activity with nearly 100% selectivity towards CO2. The doped pyrochlores exhibit higher activities than the undoped, which may be related to the enhancement of reducibility. Among them, La2Sn1.8Mn0.2O7 possessed the best activity with Ti = 341°C. The pyrochlore oxides seem to be a novel active alternative for catalytic soot oxidation. [Copyright &y& Elsevier]

The electrochemical selectivity of a Ca2Ru2O7-y pyrochiore catalyst towards carbonate formation was investigated and compared to platinum. During constant current operation, an increase in CO2 content was observed at the anode effluent when Ca2Ru2O7-y was used as the cathode catalyst, compared to Pt/C. Carbonate selectivity for Pt/C was 1.78, while for Ca2Ru2O7-y it was 7.33, a 4.1X increase, which confirmed the preferential formation of carbonate on the pyrochlore. This elevated selectivity was attributed to the high surface basicity of the pyrochlore catalyst, which led to preferential CO2 adsorption. During constant voltage operation, a 134% CO2 concentration increase was measured at the anode effluent when 10% CO2 was supplied to the cathode inlet. Optimal fuel cell performance on the carbonate cycle was obtained with a 90% O2/10% CO2 cathode concentration, where maximum currents where 4X compared to operation with no CO2. Higher CO2 concentrations were matched with a gradual decrease in performance. This was attributed to a relatively low electrochemical activity, which combined with high surface basicity, led to O2 Site blocking. Thin-film electrode experiments showed excellent electrochemical stability on the oxygen reduction region. An increase in the current and a positive shift in the half-wave potential were observed when CO2 was added to the electrolyte in ex-situ three electrode experiments. [ABSTRACT FROM AUTHOR]

Synthesis of a carbonate selective Ca2Ru2O7-y catalyst was investigated using solid-state and hydrothermal routes. The resulting materials were physically characterized by x-ray diffraction, BET gas adsorption, scanning electron microscopy and temperature programmed desorption. The solid-state reaction of precursor oxides, CaO and RuO2, led to the formation of a perovskite phase. A hydrothermal route using O2 as an oxidizing agent yielded a mostly amorphous phase primarily comprised of unreacted precursor. The use of low concentration KMnO2 (10 mM) as a replacement for O2 in the hydrothermal synthesis, in combination with high pH (∼14) and moderate temperature (200°C), yielded a highly crystalline, thermally stable Ca2Ru2O7-y pyrochlore. The increase in crystallinity was attributed to the ability of permanganate to maintain ruthenium in the +5 oxidation state required for formation of the pyrochlore phase. Micron-sized primary particles with a high density of ∼50 nm surface nanocrystallites were obtained. The presence of the nanocrystallites gave the pyrochlore a high surface area, 174 m2/g. The pyrochlore showed preferential surface adsorption of CO2 compared to H2O, making it a feasible candidate for a carbonate selective catalyst. This preferential adsorption was attributed to the use of calcium, an alkaline earth metal, which gave the pyrochlore a high surface basicity. [ABSTRACT FROM AUTHOR]

Abstract: In this communication a new ceramic pigment based on codoping pyrochlore Y 2Sn2O7 with V 5+ and Ca2+ has been obtained. The limit of solid solution of CaxY 2−xV xSn2−xO7 is around . Pigment becomes stable in double firing glazes (CIEL∗a∗b∗=78/5/35 5% w. enamelled) but unstable in single firing glazes such as based on CaO–ZnO–SiO2 chemical system. Using unconventional methods of synthesis the reactivity of the system and final pigmenting power of the powder is enhanced in the case of ammonia coprecipitation of a mixture of nitrates and tin chloride. [Copyright &y& Elsevier]

Wakefieldite-(Ce,La) and vanadinite in coarse-grained calciocarbonatites (sövites) are for the first time reported from the northeastern part of the worldwide largest fluorite deposit at the Amba Dongar carbonatite ring dike, India. Sövite in this part of the carbonatite ring dike is rich in pyrochlore, calcite and magnetite. Pyrochlore makes up almost 50% of some sövite samples and shows core-to-rim compositional changes. The core of pyrochlore consists of primary fluorcalciopyrochlore with high F and Na contents while the margins gained elevated amounts of Pb, La and Ce with the associated loss of F and Na due to circulation of hydrothermal solutions. The presence of wakefieldite-(Ce,La) and vanadinite points to an exceptionally high V abundance in hydrothermal solutions formed towards the end of the carbonatite magma activity. This investigation thus opens new promising areas for Nb and REE prospection in the eastern part of the Amba Dongar carbonatite body. [ABSTRACT FROM AUTHOR]

The article focuses on research into the fabrication of advanced piezoelectric thin films on silicon wafers. It states that some materials have a significantly greater piezoelectric response over traditional piezoelectric materials, such as lead magnesium niobate-lead titanate (PMN-PT), which can be used in nanoelectromechanical systems and microelectromechanical systems. It comments on the presence of pyrochlore in PMN-PT which has poor piezoelectric properties, and methods of preventing it.