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Complementary analytical approaches were employed to probe the effect of grain size on thermally induced oxidation of zirconium carbide (ZrC) utilizing thermogravimetric analysis, differential scanning calorimetry, and Raman spectroscopy, as well as synchrotron-based and laboratory-based X-ray diffraction (XRD) experiments. The oxidation mechanism and phase behavior of nanocrystalline ZrC (grain size ~ 20 nm) were compared with that of the more documented microcrystalline ZrC (grain size ~ 1 µm). Synchrotron XRD at the Advanced Photon Source with a hydrothermal diamond anvil cell (HDAC) used as a sample chamber revealed that the onset of oxidation is at ~ 380 °C for microcrystalline ZrC which is in agreement with previous work. In contrast, the critical oxidation temperature was ~ 330 °C for nanocrystalline ZrC. Additional high-temperature synchrotron XRD experiments at the National Synchrotron Light Source II using a lamp furnace in combination with Raman analysis showed that tetragonal ZrO2 forms as an initial oxidation product and transforms at higher temperatures to the monoclinic phase. Thermogravimetric analysis (TGA) coupled with differential scanning calorimetry (DSC) confirmed the X-ray results of a lower critical oxidation temperature for the nanocrystalline sample. Furthermore, the phase transformations in the oxide phase with associated critical temperatures were also evident in the thermodynamic data as exothermic heat events.

We fabricated a perovskite solar cell that uses a double layer of mesoporous TiO2 and ZrO2 as a scaffold infiltrated with perovskite and does not require a hole-conducting layer. The perovskite was produced by drop-casting a solution of PbI2, methylammonium (MA) iodide, and 5-ammoniumvaleric acid (5-AVA) iodide through a porous carbon film. The 5-AVA templating created mixed-cation perovskite (5-AVA)x(MA)1-xPbI3 crystals with lower defect concentration and better pore filling as well as more complete contact with the TiO2 scaffold, resulting in a longer exciton lifetime and a higher quantum yield for photoinduced charge separation as compared to MAPbI3. The cell achieved a certified power conversion efficiency of 12.8% and was stable for >1000 hours in ambient air under full sunlight.

The formation, properties, decomposition and reactions of ethoxy groups on ZrO2, CuO, and CuO/ZrO2 were followed by IR spectroscopy. The reaction of ethanol with terminal Zr-OH groups leads to the formation of monodendate ethoxy groups (type I), whereas the reaction of ethanol with tribridged Zr-OH grups results in the formation of bidendate ethoxyls (type II). In both cases, water is produced. Ethoxy groups of type II were also formed on CuO. The type of the surface species detected after interaction of ethanol with CuO/ZrO2 was the same as detected for both oxides (i.e., ZrO2 and CuO) separately. This suggests that no new phase was formed in the mixed oxide system. At higher temperatures, ethoxy groups were oxidized forming acetate ions. Gaseous ethanol present in the cell was oxidized to acetaldehyde without the intermediacy of ethoxy groups.

The properties of ferroelectric materials, which were discovered almost a century ago 1 , have led to a huge range of applications, such as digital information storage 2 , pyroelectric energy conversion 3 and neuromorphic computing 4 , 5 . Recently, it was shown that ferroelectrics can have negative capacitance 6 – 11 , which could improve the energy efficiency of conventional electronics beyond fundamental limits 12 – 14 . In Landau–Ginzburg–Devonshire theory 15 – 17 , this negative capacitance is directly related to the double-well shape of the ferroelectric polarization–energy landscape, which was thought for more than 70 years to be inaccessible to experiments 18 . Here we report electrical measurements of the intrinsic double-well energy landscape in a thin layer of ferroelectric Hf 0.5 Zr 0.5 O 2 . To achieve this, we integrated the ferroelectric into a heterostructure capacitor with a second dielectric layer to prevent immediate screening of polarization charges during switching. These results show that negative capacitance has its origin in the energy barrier in a double-well landscape. Furthermore, we demonstrate that ferroelectric negative capacitance can be fast and hysteresis-free, which is important for prospective applications 19 . In addition, the Hf 0.5 Zr 0.5 O 2 used in this work is currently the most industry-relevant ferroelectric material, because both HfO 2 and ZrO 2 thin films are already used in everyday electronics 20 . This could lead to fast adoption of negative capacitance effects in future products with markedly improved energy efficiency. A ferroelectric thin film that behaves as a single domain is found to exhibit both negative capacitance and the predicted double-well polarization–energy relationship.

The electronic structures and optical properties of the monoclinic ZrO 2 (m-ZrO 2 ) are investigated by means of first-principles local density approximation (LDA) + U approach. Without on-site Coulomb interactions, the band gap of m-ZrO 2 is 3.60 eV, much lower than the experimental value (5.8 eV). By introducing the Coulomb interactions of 4d orbitals on Zr atom ( U d ) and of 2p orbitals on O atom ( U p ), we can reproduce the experimental value of the band gap. The calculated dielectric function of m-ZrO 2 exhibits a small shoulder at the edge of the band gap in its imaginary part, while in the tetragonal ZrO 2 and cubic ZrO 2 it is absent, which is consistent with the experimental observations. The origin of the shoulder is attributed to the difference of electronic structures near the edge of the valence and conduction bands.

The aim of this study was to perform a narrative review to identify the modifications applied to the chemical structure of third- and fourth-generation zirconia ceramics and to determine the influence of these changes on the mechanical and optical properties. A bibliographical search using relevant keywords was conducted in the PubMed® and EBSCO databases. The abstracts and full texts of the resulting articles were reviewed for final inclusion. Fifty-four articles were included in this review. The analyzed topics were: (1) the composition of first- and second-generation zirconia materials (Y-TZP), (2) the behavior of the studied generations in relation to mechanical and optical properties, and (3) the modifications that were carried out on third-generation (5Y-TZP) and fourth-generation (4Y-TZP) zirconia materials. However, studies focusing on these specific characteristics in third- and fourth-generation zirconia materials are scarce. The review shows that there is a lack of sufficient knowledge about the chemical modifications of zirconia in the new generations.

The effects of CeO2, ZrO2, Nb2O5, and ZnO catalysts supported on carbon nanotubes (CNT) relative to cellulose hydrothermal hydrogenolysis in the presence of Ni/CNT and pressured H2 was studied in this work. The catalysts were characterized by inductively coupled plasma – optical emission spectrometry, X-ray diffraction, X-ray photoelectron spectrometry, transmission electron microscopy, NH3 temperature programmed desorption (TPD), and CO2-TPD. Glucose and its isomers were detected by mass spectrometry. The results showed that redox active CeO2/CNT with strong Lewis acid and strong Lewis base sites was active in C-C bong cracking, isomerization, dehydrogenation, and hydrodeoxygenation reaction, yielding 36.3% ethylene glycol and 17.2% 1,2-propylene glycol. The ZnO/CNT with Bronsted base accelerated isomerization, retro-aldol condensation, and dehydrogenation, yielding 20.7% 1,2-propylene glycol, 17.8% ethylene glycol, and 12.7% tetrahydrofuran dimethanol. The Nb2O5/CNT and ZrO2/CNT were inert to C-C bond cracking, whereas H+ in hot compressed water and the Bronsted acid in Nb2O5/CNT accelerated dehydration, yielding more sorbitol and sorbitans. The results provide reference for catalyst selection and product regulation in cellulose hydrogenolysis.

Purpose This paper aims to provide a review on the process of additive manufacturing of ceramic materials, focusing on partial and full melting of ceramic powder by a high-energy laser beam without the use of binders. Design/methodology/approach Selective laser sintering or melting (SLS/SLM) techniques are first introduced, followed by analysis of results from silica (SiO2), zirconia (ZrO2) and ceramic-reinforced metal matrix composites processed by direct laser sintering and melting. Findings At the current state of technology, it is still a challenge to fabricate dense ceramic components directly using SLS/SLM. Critical challenges encountered during direct laser melting of ceramic will be discussed, including deposition of ceramic powder layer, interaction between laser and powder particles, dynamic melting and consolidation mechanism of the process and the presence of residual stresses in ceramics processed via SLS/SLM. Originality/value Despite the challenges, SLS/SLM still has the potential in fabrication of ceramics. Additional research is needed to understand and establish the optimal interaction between the laser beam and ceramic powder bed for full density part fabrication. Looking into the future, other melting-based techniques for ceramic and composites are presented, along with their potential applications.

In this investigation, well defined mesoporous zirconia nanoparticles (ZrO 2 NPs) with cubic, tetragonal or monoclinic pure phase were synthesized via thermal recovery (in air) from chitosan (CS)- or polyvinyl alcohol (PVA)-ZrO x hybrid films, prepared using sol–gel processing. This facile preparative method was found to lead to an almost quantitative recovery of the ZrOx content of the film in the form of ZrO 2 NPs. Impacts of the thermal recovery temperature (450, 800 and 1100 °C) and polymer type (natural bio-waste CS or synthetic PVA) used in fabricating the organic/inorganic hybrid films on bulk and surface characteristics of the recovered NPs were probed by means of X-ray diffractometry and photoelectron spectroscopy, FT-IR and Laser Raman spectroscopy, transmission electron and atomic force microscopy, and N 2 sorptiometry. Results obtained showed that the method applied facilates control over the size (6–30 nm) and shape (from loose cubes to agglomerates) of the recovered NPs and, hence, the bulk crystalline phase composition and the surface area (144–52 m 2 /g) and mesopore size (23–10 nm) and volume (0.31–0.11 cm 3 /g) of the resulting zirconias.