From bone to dentin to nacre, biomaterials are structurally advanced composites with superior toughness and significant stiffness, based on simple building blocks. Here, using a series of molecular mechanics models with bioinspired topologies, we propose design mechanisms rooted in the simplest mechanical interactions—perfectly brittle linear elastic—which are shown to be sufficient to achieve superior toughness at high stiffness in biological composites. In a two-phase composite system, we show that by adapting the elastic constitutive laws of the matrix phase and by tuning the interactions of the constituents we can realize materials with a large range of combinations of toughness and stiffness. Notably, this can be achieved without changing the fracture energy of the individual composite components. Through a systematic analysis and the development of a simple model, we unveil basic design principles that lead to fundamental insights into the mechanics of natural composites for applications in a range of engineering disciplines.

Lead-free positive temperature coefficient of resistance (PTC) thermistors were synthesized from (1 − x/100)BaTiO3–(x/100)(Bi1/2K1/2)TiO3-based solid solutions, using a conventional mixed-oxide fabrication route, and sintered in N2 followed by air annealing. A maximum TC of 205 °C was achieved for x = 20. An increase in x from 0 to 20 decreased the grain size by more than 92% and increased room temperature resistivity (ρRT) by 7 orders of magnitude. For x ≤ 10, PTC ratio (ρmax/ρmin) ≈ 104.5 and temperature coefficient of resistivity (α) > 10.3%/°C were achieved using Mn and Al2O3:SiO2:TiO2 (AST) additions. For x > 10, ρmax/ρmin > 103 and α > 8%/°C were only obtained in samples sintered in N2 without subsequent air annealing. Complex impedance analysis revealed three relaxation processes, attributed to a semiconducting grain core, a PTC active grain boundary interface, and a grain boundary insulating layer. Local electrical activity was investigated by hot-stage conductive mode microscopy. The existence of symmetrical grain boundary electron beam-induced current and β-conductivity contrast at the grain boundaries, consistent with the presence of an electron trapping two-dimensional grain boundary plane, compensated by positive space charge layers and a low conductivity vacancy-rich layer, was revealed for the first time within this system.

This paper investigates the critical loading condition that causes the emission of dislocations in silicon subjected to nanoindentation. A theoretical model is established, which follows the deformation process that with increasing the indentation load, a phase transformation takes place, followed by partial dislocations emitting from the interface between the phase-transformed zone and the originally crystalline silicon when the indentation load reaches a critical value. In the model, the emission process represents the generation of a dipole of Shockley partial dislocations. One partial dislocation of the dipole, located at the interface, is considered immobile, whereas the other partial dislocation moves into the bulk of silicon. The effects of the indenter geometry and of the location of dislocation nucleation on the critical indentation load are discussed. The model predicts that a sharp indenter leads to a relatively smaller critical indentation load. The model prediction is verified by an indentation experiment.

Lattice volume expansion or amorphization renders EuTiO3 ferromagnetic, although the stable phase of crystalline EuTiO3 is an antiferromagnet. The lattice volume expansion is induced into the crystalline EuTiO3 thin film by utilizing the lattice mismatch between the thin film and a substrate. The magnetization at low temperatures monotonically increases with an increase in lattice volume for the crystalline EuTiO3 thin film, coincident with the results of calculations based on the hybrid Hartree–Fock density functional approach. The ferromagnetic interaction between Eu2+ ions is enhanced by the amorphization as well; the amorphous EuTiO3 thin film becomes a ferromagnet, and the Curie temperature is higher for amorphous Eu2TiO4 than for its crystalline counterpart. The phenomenon, that is, the volume expansion- and amophization-induced ferromagnetism, is explained in terms of the competition between ferromagnetic and antiferromagnetic interactions among Eu2+ ions.

The indentation method of nonlinear viscoelastic materials is investigated through combined numerical and experimental efforts to reveal the correlation between the viscoelastic kernel function and the indentation responses. It is shown that the viscoelastic kernel function of a nonlinear viscoelastic solid with viscous response characterized by a linear rate constitutive equation scales with the normalized relaxation load in an indentation relaxation test. This scaling relation does not depend on the geometry of the indented solid and the profile of the indenter. Therefore, it may serve as a fundamental relation for characterizing the viscoelastic properties of some biological soft tissues and artificial soft materials with regular/irregular surface morphology.

Multilayer thin films have been widely used for their enhanced mechanical and tribological properties relative to the monolayers of equivalent thickness. However, the mechanical properties of the each constituent layer are rarely investigated due to the difficulty in separating the effects of the constituent layers. An inverse analysis method to identify the elastic moduli of the constituent layers of multilayer films is developed by fitting the finite element calculations with indentation measurements within the framework of numerical optimization. The method is verified against typical monolayer, bilayer, and trilayer film structures both numerically and experimentally. Uniqueness and substrate-independence of the extracted moduli are ensured by the multiple loading–unloading cycles of the indentation tests. The method provides a feasible way to characterize the intrinsic mechanical properties of the constituent layers of multilayered thin films and further to explore the dominant mechanism for the enhancement of their mechanical properties.

We investigate the orientation transition and strain relaxation in oxygenated epitaxial strontium-doped lanthanum nickelate, La1.875Sr0.125NiO4+δ (LSNO) thin films grown on single crystal strontium titanate, SrTiO3 (STO) substrates. Structural evolution has been studied as a function of film thickness by x-ray diffraction, pole figure analysis, and transmission electron microscopy (TEM). The LSNO layer grows epitaxial (OR1) with respect to the STO substrate with an orientation (001)OR1//(001)STO and <001>OR1//<001>STO. This orientation is maintained up to approximately 15 nm as observed from TEM, at which point it undergoes reorientation and lattice mismatch strain relaxation. The growth continues with a new orientation (OR2) as (100)OR2//(001)OR1 and with <100>OR2//<001>OR1 and <001>OR2//<001>OR1 with respect to the epitaxial LSNO layer. We consider possible mechanisms in detail leading to these phenomena given that the potassium nickel fluoride (K2NiF4)-structured lattice is able to accommodate excess oxygen interstitials and corresponding changes in the Ni valence state. By investigating the phase space of deposition parameters, we experimentally identify key factors leading to the reorientation phenomena.

Within the last decade, inkjet printing technology has developed from only a text and graphic industry to a major topic of scientific research and development. Inkjet printing can be used as a highly reproducible noncontact patterning technique to print at high speeds either small or large areas with high quality features; it requires only small amounts of functional materials, which immediately lower production costs. Furthermore, inkjet printing reduces the amount of processing steps due to its additive technique of materials deposition, which further decreases productions costs. This contribution provides a literature survey covering the latest results in low temperature sintering inkjet-printed metal precursor materials in a fast and efficient manner, aiming for roll-to-roll processing. The prepared features can be used as interconnects and contacts for microelectronic applications, including organic light-emitting diodes, organic photovoltaics, and radio frequency identification tags.

We describe the synthesis and fabrication of a graphene oxide (GO) and single-walled carbon nanotube (SWCNT) composite ink (GO–SWCNT ink) for electrochemically stable supercapacitors. Atomic force microscopy and scanning electron microscopy studies demonstrate that the obtained GO flakes are single layer with size distribution from 100 nm to 20 μm. SWCNTs are dispersed using a GO aqueous solution (2 mg/mL) with sonication support to achieve a SWCNT concentration of 12 mg/mL, the highest reported value so far without surfactant assistance. Raman spectroscopy studies indicate that the full-width at half-maximum of the G band increases with the mixing of SWCNT and GO indicating that electronic structure changes via π–π interactions of GO sheets and SWCNTs. Paper-based electrodes of supercapacitor were conveniently fabricated with GO–SWCNT composite ink via a dip casting method. By using different concentrations of SWCNT in the ink, the paper electrodes provide different capacitance values. The highest value of specific capacitance reaches 295 F/g at a current density of 0.5 A/g with a GO/SWCNT weight ratio of 1:5. The cycling stability for the GO–SWCNT paper electrode supercapacitors indicates capacitance retention of 85% over 60,000 cycles.

Thermomechanical fatigue (TMF) tests have been carried out in a nickel-based single crystal TMS-82 superalloy, and the dynamic evolutions of dislocations and stacking faults have been studied in detail. It is found that the reversible formation of stacking faults is always associated with the loading orientation. Specifically, stacking faults expand under compression and shrink under tension due to the disappearance and appearance of dislocations during the TMF process. Stacking faults result from shear of γ′ precipitates by 1/3<112> dislocations, which arise from the decomposition of 1/2<110> matrix dislocations. The calculations of critically resolved shear stress to push dislocations that glide in the γ′ particles confirm the expansion of stacking faults under compression. However, under tension, dislocations in γ channel prevent 1/2<110> dislocations to enter γ′ cuboids and consequently, stacking faults shrink. Appearance and disappearance of dislocations during TMF cycling are associated with plastic deformation and annealing process, respectively.

The engineering of well-defined micro- and nanoscaled surface topographies on biomedical metals and polymeric materials has been explored as a strategy to control biological responses. In this review, the ability of surface features engineered by a variety of methods to promote or reduce protein, blood, and bacterial adhesion is discussed independent of surface chemistry. The interaction of proteins with surface topography is fundamentally important and influences the conformation, the types of protein, as well as the overall amount of protein adhesion, which in many instances is increased over the associated increase in surface area. The use of superhydrophobic surface features is discussed as a manner to engineer antifouling surfaces with protein, blood, and bacterial resistance.

Microcalorimetry was used to study the adsorption of water molecules on the surface of ZnAl2O4 nanoparticles ranging from the anhydrous to the fully hydrated states. Water adsorption of ZnAl2O4 showed similar behavior to the isostructural γ-Al2O3 and revealed possible existence of hydrophobic sites on the surfaces. At the lowest measured coverage (0.49 H2O per nm2), the enthalpy of adsorption is −155.46 kJ/mol. This value decays with increasing coverage and at around 13 H2O per nm2, the heat of adsorption levels at −44 kJ/mol, suggesting further adsorbed water has liquid-like features. The anhydrous surface energy for ZnAl2O4 was calculated to be 1.36 ± 0.08 J/m2 using water adsorption microcalorimetry data. High-temperature oxide melt solution calorimetry was also used to assess the surface energy, which was 1.29 ± 0.33 J/m2. Surface energies at different hydration states are reported and showed decrease with increasing coverage, suggesting that low humidity conditions allow higher driving forces for coarsening.

A novel combination of low-field magnetic alignment (MA) and templated grain growth (TGG) was used to fabricate highly textured diamagnetic 0.72Pb(Mg1/3Nb2/3)O3–0.28PbTiO3 (0.72PMN–0.28PT) ceramics. Samples were produced by nonaqueous slip casting of PMN–PT slurries, in which diamagnetic plate-like 0.4(Na1/2Bi1/2)TiO3–0.6PbTiO3 (0.4NBT–0.6PT) template particles were aligned by dynamic MA in a 2.2-T permanent magnet array. Template alignment improved as slurry viscosity increased, with a 32-vol% solid loading (a viscosity of ∼0.1 Pa s at 0.1 s−1) giving optimal texture quality (7.85° FWHM, f = 92 vol%) after sintering and TGG. Alignment was stable for more than 3 h during slip casting, allowing fabrication of ∼1-cm thick textured ceramics with high piezoelectric response (d33 = 1222 pC/N). The success of dynamic MA at low magnetic field (2.2 T) is attributed to an increase in driving force for alignment of large (5–10 μm) template particles relative to the randomizing effect of Brownian motion (i.e., thermal energy kBT).

In this article, the effects of substrate temperature on the crystallographic structure and first-order magnetic phase transition in iron-rhodium (FeRh) thin films are investigated. It was found that for the as-deposited FeRh thin films, 350–400 °C is the optimal range of substrate temperature for obtaining B2 ordered FeRh thin films. After postannealing, it was shown that 400 °C is the optimized substrate deposition temperature for obtaining the best chemical/atomic ordering in postannealed FeRh thin films. Magnetization studies indicate that the as-deposited FeRh thin film with substrate temperature of 350 °C does not show a first-order antiferromagnetic (AFM)- to-ferromagnetic (FM) phase transition behavior during heating process and it gives a typical FM behavior whereas the as-deposited FeRh thin film deposited at 400 °C shows a broad first-order AFM-to-FM phase transition during heating and cooling processes. Both the postannealed FeRh thin films deposited at 350 and 400 °C give a clear first-order AFM-to-FM phase transition with a residual magnetization of about 50–100 emu/cc. The residual magnetization may possibly be caused by the disordered bcc (α) FM phase, B2 ordered (α′) FM phase or a near-surface/interfacial ferromagnetism in the ordered FeRh thin films.

To determine whether plastic-hardening behavior occurs in metal nanowires, an atomistic simulation was performed to investigate the tension process in a bicrystal Cu nanowire. The results indicate that bicrystal Cu nanowires exhibit strain-hardening behavior, unlike their single-crystal counterparts. The strain-hardening behavior is related to the orientation of two crystal grains, and the number of atoms determines whether strain-hardening behavior occurs in the asymmetrically tilted bicrystal Cu nanowires. Strain hardening occurs in almost bicrystal Cu nanowires with different orientation angles. The initial yield stress is determined by the grain whose orientation angle is closer to 45° among the two crystal grains, resulting in a high value of the tilting tendency factor, and thus making it easier to generate slip.

The p-type doping of high purity semi-insulating 4H polytype silicon carbide (HPSI 4H-SiC) by aluminum ion (Al+) implantation has been studied in the range of 1 × 1019 to 8 × 1020 /cm3 (0.39 μm implanted thickness) and a conventional thermal annealing of 1950 °C/5 min. Implanted 4H-SiC layers of p-type conductivity and sheet resistance in the range of 1.6 × 104 to 8.9 ×102 Ω□, corresponding to a resistivity in the range of 4.7 × 10−1 to 2.7 × 10−2 Ω cm have been obtained. Hall carrier density and mobility data in the temperature range of 140–720 K feature the transition from a valence band to an intraband conduction for increasing implanted Al ion concentration from 1 × 1019 /cm3 to 4 × 1020 /cm3. A 73% electrical activation, 31% compensation and 146 meV ionization level have been obtained using a best-fit solution of the neutrality equation to Hall carrier data for the lowest concentration.

Absorption losses in tellurite glasses due to OH− ions were reduced by melting the glasses under a reactive atmosphere of Cl2 + O2 gas. Incorporation of dry Cl2 + O2 gas has a major influence on the reduction of OH− species, which is found to be consistent with thermochemical data. Absorption loss due to OH− ions in bulk glasses prepared from the as-received raw materials and processed under a reactive atmosphere was 1000 and 60 dB/m, respectively. Gaussian fits have been used to identify the different species of OH− attached to the structural units present in the glass. All of the OH− species (free and bonded to Te), units can be reduced by melting the starting raw materials in a reactive atmosphere of Cl2 + O2. The net reduction in OH− absorbance at 3.2 µm was 1.1 cm−1, which is equivalent to 500 ppm. OH− reduction in tellurite glasses using O2 gas bubbling shows a reduction in the fundamental absorption band from 1.8 to 0.57 cm−1 after 75 min.

The influence of different TiO2precursors (laboratory-prepared sol–gel powders, dried and thermally treated at 400 °C, and commercial powders such as anatase by Aldrich and P25 Aeroxide by Evonik) on the structure and morphology of the titanate nanotubes obtained by hydrothermal method was investigated by x-ray diffraction (XRD) and transmission electron microscopy (TEM) measurements. In all cases, titanate-based nanotubes were obtained, having similar structure and morphology. The effect of the thermal treatment on the structural stability was also studied by differential thermal analysis and thermogravimetry analysis (TG/DTA) and differetial scanning calorimetry (DSC) measurements up to 600 °C, to determine the transformation of titanate nanotubes into other phases. Complementarily, by XRD investigation, the phases that develop after the thermal treatment of the titanate nanotubes in 110–400 °C temperature range were identified. The TEM micrographs come to confirm the deterioration of morphology and transformation from nanotubes to particles. The thermal stability of the investigated nanotubes led to the conclusion that this property depends not only on the sodium content but also on the type of precursor. The highest thermal stability was noticed for the nanotubes synthesized starting with anatase (Aldrich) commercial powder.

Multiwalled carbon nanotubes (MWNTs), due to their unique electrical conductivity and mechanical properties, have led to our interest in their application of water splitting process. This carbon nanotube-based electrode, synthesized by plasma ehanced chemical vapor deposition (PECVD), provides a ∼6 times enhancement of hydrogen production via water electrolysis compared to a graphite electrode in acidic electrolyte. Our PECVD-grown vertically aligned carbon nanotubes show good adhesion to the graphite substrate and long-term sustainability in a strong acid solution without the need for any complicated and expensive pretreatment. Furthermore, the neutral potassium phosphate solution electrolyte (KPi electrolyte) using cobalt salt as the catalyst, as was reported recently, has been used to demonstrate the long-term compatibility of the MWNTs electrode under different electrolyte. MWNTs from thermal chemical vapor deposition growth technique were also fabricated and compared with the PECVD-grown samples.