Nanocrystalline bulk materials (also called nanograined materials) are intrinsically unstable due to the excess grain boundary (GB) free energies. Dopants designed to segregate to boundaries have been proposed to lower excess GB energies, increasing stability against coarsening and enabling nanostructure features to survive high temperature processing and operational environments. It has been theoretically proposed that the GB energy of a material can eventually become zero as a function of dopant concentration, signifying negligible driving force for growth—an infinitely stable nanomaterial. In this work we use ultrasensitive microcalorimetry to experimentally measure the absolute GB energy of gadolinium-doped nanocrystalline zirconia as a function of grain size and show that the energy can indeed reach a quasi-zero energy state (∼0.05 J/m2) when a critical GB dopant enrichment is achieved. This thermodynamic condition leads to unprecedented coarsening resistance, but is a temperature dependent function; since increasing temperatures deplete the GB as the dopant dissolves back in the crystalline bulk.

MnOx –CeO2/t-ZrO2 catalyst was prepared by impregnation of nanotetragonal zirconia. The NO conversion of 5 wt% MnOx –CeO2/t-ZrO2 catalyst was 68.1% at 100 °C while that of 30 wt% MnOx –CeO2/t-ZrO2 catalyst was 97.4%. The x-ray diffraction, Brunner–Emmet–Teller measurements (BET), and H2-TPR showed surface properties of the prepared catalysts were good for selective catalytic reduction reactions. X-ray photoelectron spectroscopy analysis indicated that Mn4+ and Ce4+ oxidation states were predominant on the surface of the catalyst and so was lattice oxygen which was conducive to Lewis acid sites. NH3-TPD test results demonstrated that Lewis acid sites are predominant on the surface of catalyst. The presence of SO2 reduced the catalyst activity. The realized conversion dramatically decreased to 47% from nearly 100% after 8 h. Characterization of fresh and spent catalysts indicated the deterioration of active component and deposition of NH4HSO4 or (NH4)2SO4 contribute to SO2 poisoning.

This paper reviews progress in ultraviolet (UV) optoelectronic devices based on AlGaN films and their quantum wells (QWs), grown by plasma-assisted molecular beam epitaxy. A growth mode, leading to band-structure potential fluctuations and resulting in AlGaN multiple QWs with internal quantum efficiency as high as 68%, is discussed. Atomic ordering in these alloys, which is different from that observed in traditional III–V alloys, and its effect on device performance is also addressed. Finally, progress in UV-light-emitting diodes, UV lasers, UV detectors, electroabsorption modulators, and distributed Bragg reflectors is presented.

Mesocrystal—a new class of crystals compared with conventional single crystals and randomly distributed nanocrystal systems—has captured significant attention in recent decades. Current studies have been focused on the advanced synthesis as well as the intriguing properties of mesocrystal. In order to create new opportunities upon functional mesocrystals, they can be regarded as a new functional entirety when integrated with unique matrix environments. The elegant combination of mesocrystals and matrices has enabled researchers to realize enthralling tunabilities and to derive new functionalities that cannot be found in individual components. Therefore, mesocrystal-embedded system forms a new playground towards multifunctionalities. This review article delivers a general roadmap that portrays the enhancement of intrinsic properties and new functionalities driven by novel mesocrystal-embedded oxide systems. An in-depth understanding and breakthroughs achieved in mesocrystal-embedded oxide systems are highlighted. This article concludes with a brief discussion on potential directions and perspectives along this research field.

Epitaxial heterostructures composed of complex oxides have fascinated researchers for over a decade as they offer multiple degrees of freedom to unveil emergent many-body phenomena often unattainable in bulk. Recently, apart from stabilizing such artificial structures along the conventional [001]-direction, tuning the growth direction along unconventional crystallographic axes has been highlighted as a promising route to realize novel quantum many-body phases. Here we illustrate this rapidly developing field of geometrical lattice engineering with the emphasis on a few prototypical examples of the recent experimental efforts to design complex oxide heterostructures along the (111) orientation for quantum phase discovery and potential applications.

The aim of this study was the synthesis of hard and low-abrasive novel implant materials with built-in time-dependent antibacterial properties, which can be tailored by a well-defined time-dependent and finite release of metal ions. We were able to synthesize such smart implant surfaces employing ECR (electron cyclotron resonance)-plasma on typical titanium implant material by transforming a polymer film into diamond-like carbon (DLC) which contains metal nanoparticles as reservoirs for controlled metal ion release. We found that the amount of released antibacterial metal ions is a biexponential function of time with a high release rate during the first few hours followed by a decreased ion release rate within the following days. To describe our experimental findings, we developed a kinetic model assuming that both nanoparticles near the surface and nanoparticles in the DLC bulk contribute to the total amount of ions released with different time constants.

Boron cluster chemistry roared to life in the 20th century with seminal discoveries outlining the incredibly versatile chemistry of boron, producing a range of neutral and ionic boron compounds that paved the way for a robust suite of hybrid materials that incorporate these electronically delocalized inorganic clusters with the additional organic flexibility. Looking toward further materials research in the 21st century, these stable, inorganic polyhedral borane clusters discovered during previous century will provide a particularly fertile ground for exploration. These stable clusters have already seen significant exploration, but their utility has been obscured by classical synthetic routes using highly toxic neutral borane compounds. This incongruity is quite ironic given the current variety of medical explorations conducted with the essentially nontoxic dodecahedral borane dianion. This article will lay out some essential context and outline key synthetic studies that may dramatically simplify access to these unique compounds to a broader community of materials scientists and engineers.

A systematic study of SiC layer preparation in CH3SiCl3–Ar–H2 system by fluidized bed chemical vapor deposition was given. The phase, morphology, grain size, and crystal structure of the products were investigated based on series characterizations methods. Free silicon was formed at lower temperatures while free carbon was formed at higher temperatures. By introducing argon in the deposition system, silicon formation was suppressed and cauliflower structure with subordinate small particles was observed. The formation mechanisms of different microstructures were discussed. The experimental phase diagram of CVD SiC composed of three regions of SiC + Si, SiC and SiC + C was established and boundaries of the three regions were given. The phase diagram obtained can be used to guide the new applications of SiC series materials. The low-temperature dense SiC, porous SiC with tunable densities, small grained SiC, and composite SiC materials were prepared successfully, also it was indicated that SiC jointing technology can be developed based on the phase diagram accordingly in the future.

A continuous process was developed to synthesize submicron boron carbide particles from boric acid and sucrose-based precursor solutions using a home-made spray pyrolysis system. A control set of samples was also prepared for comparison purposes of the microstructure and morphology of the ones synthesized via the spray pyrolysis method. Moreover, nickel nitrate was used in a precursor solution to investigate its catalyst effects on the reaction kinetics of boron carbide formation. The boron carbide phase was observed in the particles synthesized with spray pyrolysis at a reactor temperature of 1550 °C. The average particle size was approximately 0.46 μm. No effect of nickel additions was observed as a catalyst in boron carbide formation. Computational fluid dynamics software was used to model and simulate the experimental system. Simulation results provided information about the residence time and the temperature distribution along the tube reactor.

Rapid increases in global energy use and growing environmental concerns have prompted the development of clean and sustainable alternative energy technologies. Electrical energy storage (EES) is critical for efficiently utilizing electricity produced from intermittent, renewable sources such as solar and wind, as well as for electrifying the transportation sector. Rechargeable batteries are prime candidates for EES, but widespread adoption requires optimization of cost, cycle life, safety, energy density, power density, and environmental impact, all of which are directly linked to severe materials challenges. This article presents a brief overview of the electrode materials currently used in lithium-ion batteries, followed by the challenges and prospects of next-generation insertion-reaction electrodes and conversion-reaction electrodes with a Li+ working ion. Finally, we discuss future directions involving solid electrolytes, multi-electron transfer hosts, and other working ions.