The densification behaviors of two silicon nitride nanopowder mixtures based respectively on α-Si3N4 and β-Si3N4 as the major phase constituent were studied by spark plasma sintering. Sintering conditions were established where a low viscous liquid not in equilibrium with the main crystalline constituent(s) stimulated the grain sliding yet did not activate the reprecipitation mechanism that unavoidably yields grain growth. By this way of dynamic grain sliding full densification of silicon nitride nanoceramics was achieved with no noticeable involvement of α- to β-Si3N4 phase transformation and grain growth. This processing principle opens the way toward flexible and precise tailoring of the microstructures and properties of Si3N4 ceramics. The obtained silicon nitride nanoceramics showed improved wear resistance, particularly under higher Hertzian stresses.

Nanoindentation methods are well suited for probing the mechanical properties of a heterogeneous surface, since the probe size and contact volumes are small and localized. However, the nanoindentation method may introduce errors in the computed mechanical properties when indenting near the interface between two materials having significantly different mechanical properties. Here we examine the case where a soft material is loaded in close proximity to an interface of higher modulus, such as the case when indenting bone near a metallic implant. The results are derived from both an approximate analytical quarter space solution and a finite element model, and used to estimate the error in indentation-determined elastic modulus as a function of the distance from the apex of contact to the dissimilar interface, for both Berkovich and spherical indenter geometries. Sample data reveal the potential errors in mechanical property determination that can occur when indenting near an interface having higher stiffness, or when characterizing strongly heterogeneous materials. The results suggest that caution should be used when interpreting results in the near-interfacial region.

Buildings are stealthy contributors to global climate change. The energy needed to heat, cool, and light buildings, as well as manufacture construction materials, contributes more than half of greenhouse gas emissions worldwide. But Kevin Surace, chair and CEO of Serious Materials, has made it his mission to tackle the built environment head-on. An electrical engineer by training, he has worked at IBM, Seiko-Epson, National Semiconductor, and General Magic. He later started the companies Air Communications and Perfect Commerce. In 2002, he began to develop sound-muffling polymers as a sideline, shifting his focus to materials chemistry. Sound-dampening materials now account for much of Serious Materials' business, but the company has received most of its accolades for its energy-efficient products. We caught up with Surace at Serious Materials' headquarters in Sunnyvale, Calif., to talk about how materials science can help make green buildings good business.

The effect of BaCu(B2O5) (BCB) on the sintering temperature and microwave dielectric properties of Ba(Nd0.8Bi0.2)2Ti4O12 (BNBT) ceramics was investigated. The sintering temperature of the BNBT ceramics was significantly reduced from 1300 to 900 °C. Due to adding BCB into Ba(Nd1–xBix)2Ti4O12, the temperature coefficient of resonant frequency can be adjusted to zero with BCB content increasing. Good microwave dielectric properties of quality factor (Q×f) = 2600 GHz, εr = 75, and τf = 5 ppm/°C were obtained for BNBT with 7 wt% BCB sintered at 925 °C for 2 h, which make it a potential candidate for low temperature cofired ceramics applications.

Designing structural materials for tailored response at extreme conditions is a grand challenge in materials research. Such materials can be made using either “top-down” or “bottom-up” processes to create nanostructured metals and composites that contain atomically designed interfaces that not only block dislocation slip but also attract, absorb, and annihilate point and line defects. Such multifunctional material systems are not just high in strength but also tolerant of damage at extremes of irradiation, temperature, and mechanical stresses, and hence have applications as structural materials in nuclear power and other energy, transportation, and defense technologies. The exploration of these exceptional properties at extremes requires novel and unconventional methodologies, such as in situ experiments with high spatial and temporal resolution, complemented by simulation across multiple length and time scales.

Polyimide (PI)-matrix composite films containing inorganic nanoparticles (nano-Al2O3 and nano-TiO2) have been fabricated. A proposed model is used to explain different structures of the (Al2O3–TiO2)/PI (ATP) films synthesized by employing in situ polymerization. Dependences of dielectric permittivities of the ATP films on frequency and temperature were studied. Results show the breakdown strength of the films decreases with prolonging the corona aging time. The incorporation of the nano-Al2O3 and nano-TiO2 particles significantly improves the corona resistance of the films. The corona aging also influences the infrared absorbance, the glass transition temperature (Tg), and loss factor (tanδ) of the ATP films.

The fabrication and properties of fiber metallic glass laminates (FMGL) composite composed of Al-based metallic glasses ribbons and fiber/epoxy layers were reported. The metallic glass composite possesses structural features of low density and high specific strength compared to Al-based metallic glass and crystalline Al alloys. The material shows pronounced tensile ductility compared to monolithic bulk metallic glasses.

The effects of variable conversion parameters on the microstructure and critical currents of TFA-derived YBa2Cu3O7 (YBCO) films annealed under low-pressure conditions were investigated, accompanied by the analysis of their relationship with the nucleation process and the growth rate. It is found that non-c-axis oriented YBCO grains are formed under high supersaturation conditions, i.e., by increasing oxygen pressure, water pressure, or temperature. The optimal PH2O–PO2 window for preparation of completely c-axis oriented YBCO films expands as the total pressure rises from 50 to 100 mbar due to the decrease of supersaturation at enhanced total pressure; the corresponding maximum growth rate is only slightly increased up to 0.6 nm/s. Additionally, it is shown that the gas flow needs to be high enough to avoid random nucleation of YBCO grains. A single gas-flow–water-pressure diagram, showing simultaneously the film-growth rate, allows visualizing the cross-linked influence of processing parameters to achieve c-axis oriented YBCO films with Jc above 1 MA/cm2 in one single growth step.

Materials scientists involved in synthesis are exceptionally skilled at designing and constructing individual molecules with the goal of introducing rationally tailored chemical and physical properties. However, the task of assembling such special molecules into organized, supramolecular structures with precise, nanometer-level organizational control to execute specific functions presents a daunting challenge. Soft and hard matter suitable for unconventional types of electronic circuitry represents a case in point and, in principal, offer capabilities not readily achievable with conventional silicon electronics. In this context, “unconventional” means circuitry that can span large areas, can be mechanically flexible and/or optically transparent, can be created by large-scale, high-throughput fabrication techniques, and has atomic-level tunability of properties. In the process of preparing, characterizing, and fabricating prototype devices with such materials, we learn many new things about the electronic and electrical properties of the materials and the interfaces between them. This account briefly overviews recent progress in three interconnected areas: (1) organic semiconductors for complementary π-electron circuits, (2) soft matter high-κ gate dielectrics for organic and inorganic electronics, and (3) metal-oxide semiconductors as components in such devices. Space limitations allow only touching upon selected highlights in this burgeoning field.

We present a detailed study of the morphology and composition of tungsten oxide (WO3) thin films, grown by radio frequency magnetron reactive sputtering at substrate temperatures varied from room temperature (RT) to 500 °C, using infrared (IR) absorption, Raman spectroscopy, and x-ray photoelectron spectroscopy (XPS). This work includes valuable new far-IR results about structural changes in microcrystalline WO3. Both IR absorption and Raman techniques reveal an amorphous sample grown at RT and initial crystallization into monoclinic structures for samples grown at temperatures between 100 and 300 °C. The Raman spectra of the samples grown at high temperatures indicate, apart from the monoclinic structure, a strain effect, with a distribution revealed by confocal Raman mapping. XPS indicates that the film surface maintains the stoichiometry WOx, with a value of x slightly greater than 3 at RT due to oxygen contamination, which decreases with increasing temperature.

Sub-10 nm monodispersed NaYF4:Eu/Ba nanocrystals were synthesized by a hydrothermal method. Under 396-nm excitation, in addition to the characteristic emissions of Eu3+ ions, an intense emission band originating from the d–f transition of the Eu2+ ions is also observed, indicating that Eu3+ and Eu2+ coexist in Eu/Ba-codoped NaYF4 nanocrystals. The dependence of the luminescence on the Ba2+ concentration was studied. Tunable photoluminescence of NaYF4:Eu nanocrystals was successfully achieved by codoping with Ba2+ ions. In addition, when the Ba/Ln ratio is 3:7 and 4:1, pure cubic Ba0.92Y2.15F8.29:Eu and tetragonal BaYF5:Eu nanocrystals were obtained, respectively.