We review our work on combinatorial search and investigation of morphotropic phase boundaries (MPBs) in chemically substituted BiFeO3 (BFO). Utilizing the thin-film composition spread technique, we discovered that rare-earth (RE = Sm, Gd, and Dy) substitution into the A-site of the BFO lattice results in a structural phase transition from the rhombohedral to the orthorhombic phase. At the structural boundary, both the piezoelectric coefficient and the dielectric constant are substantially enhanced. It is also found that the observed MPB behavior can be universally described by the average A-site ionic radius as a critical parameter, indicating that chemical pressure effect due to substitution is the primary cause for the MPB behavior in RE-substituted BFO. Our combinatorial investigations were further extended to the A- and B-site cosubstituted BFO in the pseudoternary composition spread of (Bi1−xSmx)(Fe1−yScy)O3. Clustering analysis of structural and ferroelectric property data of the fabricated pseudoternary composition spread reveals close correlations between the structural and ferroelectric properties. We show that the evolution in structural and ferroelectric properties is controlled solely by the A-site Sm substitution and not the B-site Sc substitution.

We have studied dynamic thermo-mechano-chemical responses of reactive metallic systems, both in clouds of small oxygen-free particles (∼1–10 μm in diameter) produced by fracturing Zr-rich bulk metallic glass and in pure Zr metal foils (∼25 μm thin), under thermal (laser ablation or pulse electrical heating) and mechanical loadings. The mechanical fracture/fragmentation and fragments reactions were time resolved using an integrated set of fast six-channel optical pyrometer, high-speed microphotographic camera, and time- and angle-resolved synchrotron x-ray diffraction. These small-scale tabletop real-time experiments performed on or near surfaces of reactive metals provide fundamental data, in atomistic scales or of particle clouds, regarding fragmentation mechanics, combustion mechanisms and kinetics, and dynamics of energy release under thermal and mechanical loadings. We present the results of pure Zr and Zr-rich amorphous metals, not only signifying diversified combustion mechanisms depending on microstructures, particle sizes, oxygen pressure, and ignition conditions but also providing fundamental data that can be used to develop and validate thermochemical and mechanochemical models for reactive materials.

In spite of its large lattice mismatch, Bi grows epitaxially in (111) orientation and almost free of defects on Si substrates. On Si(111), the Bi film is under compressive strain of less than 2% and shows a 6–7 registry to the Si(111)-(7 × 7) substrate. On Si(001), the compressive lattice strain of 2.3% results in the formation of an array of misfit dislocations with a periodicity of 20 nm. We studied the cooling process of ultrathin bismuth films deposited on Si(111) and Si(001) substrates upon excitation with short laser pulses. With ultrafast electron diffraction, we determined the thermal boundary conductance σK from the exponential decay of the transient film temperature. Within the error bars of 7%, the experimentally determined thermal boundary conductances are the same for both substrates and thus independent of the presence of a periodic array of misfit dislocations and the different substrate orientation.

Small-scale testing techniques such as nanoindentation and micro-/nanocompression are promising methods for addressing mechanical properties of ion-beam-irradiated materials. We performed different proton irradiations and critically evaluated the results obtained from nanoindentation and pillar compression, both performed parallel and perpendicular to the irradiation direction. Experiments parallel to beam direction suffer from variation of material properties with penetration depth. This is improved by cross-sectional experiments, thereby probing the effect of different doses along the beam penetration depth on mechanical properties. Finally, we demonstrate that, compared with nanoindentation, miniaturized uniaxial compression experiments offer a more reliable and straightforward interpretation of the mechanical data, as they impose a nominally uniaxial stress on a well-defined volume at a specific position. Moreover, the exposed pillar geometry is not influenced by surface contamination and enables in situ observation of the governing mechanical processes, which is typically not possible during indentation experiments in a half-space geometry.

In a thin film system involving dissimilar materials, the residual stresses and microstructural defects are inevitable due to the misfits of lattice structures and thermal properties of the materials. Unfortunately, the relationship between the stresses and interface defects is still unclear to date. This article aims to clarify such an important relationship by a finite element (FE) analysis incorporating the dislocation distribution from high-resolution transmission electron microscopy. Layer removal and Raman spectroscopy were also conducted to explore the film-thickness effect. It was found that that residual stress variation in a thin film system is caused by the coupled effect of lattice-thermal misfits and discrete interfacial dislocations, that the residual stresses are dependent on the film thickness, and that it is particularly important to identify the correct density of interface dislocations for an accurate residual stress calculation by a FE analysis.

This study focuses on nanoindentation creep in polycarbonate (PC) and syndiotactic polystyrene (sPS) throughout the transient and steady-state regions. The viscoelastic Burgers model is used to explain transient creep data, while the power-law creep model is used to interpret steady-state creep data. The Newtonian shear viscosity of the Maxwell element and Young’s modulus of the Kelvin element are greater for the creep period than for the preload period, and an opposite trend is noted in the Newtonian shear viscosity of the Kelvin element and Young’s modulus of the Maxwell element. The fact that the Young’s moduli of Maxwell and Kelvin elements in the creep period are different from those in the preload period implies that a stress-induced mesomorphic structure forms or that crystallization occurs in nanoindentation creep. While the strain rate increases with decreasing preload period, the stress exponent factor is almost the same for all preload periods.

Microcompression test was applied to determine the Young’s modulus for elastically anisotropic materials for two different orientations of single crystalline Si. Although there is a clear difference in the apparent Young’s moduli for the different orientations, a significant underestimation of Young’s modulus was observed resulting from the substrate deformation as observed in both finite element simulation and experiment. This effect decreases with increasing aspect ratio. To correct the deviation of the apparent Young’s modulus from the theoretical values, a systematic framework of microcompression test is suggested. The modified Sneddon correction using the indentation modulus instead of Young’s modulus successfully yields Young’s moduli of single crystalline silicon in the [100] and [111] directions to within 5.3% and 2.0% deviation, respectively.

Nature and mechanism of interfacial reactions between boron nitride nanotubes (BNNTs) and aluminum matrix at high temperature (650 °C) are studied using high-resolution transmission electron microscopy (HRTEM). This study analyzes the feasibility of the use of BNNTs as reinforcement in aluminum matrix composites for structural application, for which interface plays a critical role. Thermodynamic comparison of aluminum (Al)-BNNT with analogous Al-carbon nanotube (Al-CNT) system reveals lesser amount of reaction in the former. Experimental observation also reveals thin (∼7 nm) reaction-product formation at Al-BNNT interface even after 120 min of exposure at 650 °C. The spatial distribution of the reaction-product species at the interface is governed by the competitive diffusion of N, Al, and B. Morphology of the reaction products are influenced by their orientation relationship with BNNT walls. A theoretical prediction on Al-BNNT interface in macroscale composite suggests the formation of strong bond between the matrix and reinforcement phase.

A freestanding bulk nanoporous copper with ultralow density has been fabricated through dealloying of as-cast dual-phase Cu1Mn1Al8 alloy, and the dealloying behavior was investigated systematically. The experimental results show that due to different electrochemical activities, the Al11Cu5Mn3 phase of the dual-phase precursor alloy dissolved before AlCu2Mn, which corresponds to the dramatical evolutions of microstructure and composition. Additionally, a formation pattern based upon a mechanism combined “dissolution–redeposition” pattern, “phase-separation” pattern, and “coarsening” process has been built to describe the evolution process, which includes four stages, sequentially defined as “dissolution of Al11Cu5Mn3,” “redeposition of Cu atoms,” “dealloying of AlCu2Mn,” and “coarsening.”

The thermal dilation experiment and the martensite transformation features of modified high Cr ferritic heat-resistant steel upon continuous cooling were explored at various cooling rates. The “spread” martensite transformation model was introduced to investigate the influence of the cooling rate applied on the martensite transformation behaviors. The martensite fraction, martensite formation rate, and the density of martensite laths were obtained as a function of cooling rate. Both the onset and offset temperatures of the martensite transformation decrease with the increase of cooling rate, and the martensite formation rate bursts at the beginning of transformation and then reaches a peak rapidly. The fitted data based on the proposed kinetic model indicated that the aspect ratio of martensite lath decreases, instead the density of martensite laths increases, with the increase of cooling rate.

The addition of Al to a Mg–10Gd alloy was found to lead to substantial grain size reduction during casting at concentrations between 0.8% and 1.3%. At these concentrations, Al2Gd particles were found at the center of grains, and the orientation relationship $[112]_{{\rm{Al}}_{\rm{2}} {\rm{Gd}}} \,{\rm{‖}}\,[2\bar 1\bar 10]_{{\rm{\alpha - Mg}}} ,\,(1\bar 10)_{{\rm{Al}}_{\rm{2}} {\rm{Gd}}} \,{\rm{‖}}\,(0\bar 110)_{{\rm{\alpha - Mg}}} $ was found reproducibly between Al2Gd and α-Mg, indicating that these are the heterogeneous nucleant particles that form in situ at these Al contents. Most of these nuclei were between 2 and 7 μm in size. Furthermore, little grain coarsening was observed during solution treatment, particularly compared with an alloy grain refined by Zr particles where substantial coarsening occurred. This appears to be because Al2Gd particles restrict grain boundary motion during solution treatment.

The structural and magnetic properties of the Al cosubstituted cubic spinel ferrite series MgAlxFe2−xO4 (x = 0.0, 0.4, 0.8, and 1.0) synthesized through a coprecipitation method were characterized by means of x-ray powder diffraction, infrared (IR) spectroscopy, transmission electron microscopy (TEM), differential thermal analyses, and vibrating sample magnetometer. Lattice constants determined from x-ray diffraction (XRD) measurements exhibit a decrease with increasing Al3+ ions in the ferrites system. The particle size using TEM was ∼33 nm for magnesium ferrite, which is in good agreement with values obtained by XRD method. The crystallization spinel formation for the parent ferrite MgFe2O4 using differential thermal analysis (DTA) technique was 454 °C. The two main bands observed in the IR spectra (tetrahedral and octahedral) were in the range (568–628 cm−1) and (431–460 cm−1), respectively. Magnetization curve shows the highest value for the sample with concentration x = 0.4.

Single-walled carbon nanotube (SWNT) radical anions will react with tetrahydrofuran and generate ethylene, enolates, and a partially hydrogenated nanotube backbone. The experimental evidence suggests that there are sp3 C–H binding interactions. The total gravimetric content of hydrogen on a sample averages from 3.5% to 3.9% w/w, about four times the total amount observed for nanotubes hydrogenated via traditional Birch reduction reactions. Furthermore, the hydrogen desorbs at temperatures up to 400 °C less than those observed for the hydrogenated SWNTs formed after the Birch reduction. Finally, the first room temperature electron spin resonance spectrum of a nanotube radical ion is also reported.

Nanohybrid shish kebab (NHSK) structure, in which fibrous carbon nanotubes (CNTs) act as shish, while polymer lamellae as kebab, is of particular interest both scientifically and technologically. In this work, two types of CNTs with the same diameter range and different topography structure, namely multiwalled carbon nanotubes (MWNTs) with a relatively smooth surface and double-walled carbon nanotubes (DWNTs) bundles with a groove structure, were used to induce polyethylene (PE) crystallization for the formation of NHSK. For PE/MWNTs system, NHSK was formed only at a relatively low crystallization temperature (Tc), and PE lamellae are not completely perpendicular to the long axis of MWNTs. However, for PE/DWNTs bundles system, NHSK could be obtained even at a much higher Tc, and almost all the PE lamellae are perpendicular to CNTs long axis, due to the unique “groove structure” formed by DWNTs bundles. The enhanced nucleation ability and the facilitated lamellae orientation by using DWNTs bundles are not only of great crystallography interest but also are very important for functional design in nanodevice applications.