The material characterization toolbox has recently experienced a number of parallel revolutionary advances, foreshadowing a time in the near future when material scientists can quantify material structure evolution across spatial and temporal space simultaneously. This will provide insight to reaction dynamics in four-dimensions, spanning multiple orders of magnitude in both temporal and spatial space. This study presents the authors’ viewpoint on the material characterization field, reviewing its recent past, evaluating its present capabilities, and proposing directions for its future development. Electron microscopy; atom probe tomography; x-ray, neutron and electron tomography; serial sectioning tomography; and diffraction-based analysis methods are reviewed, and opportunities for their future development are highlighted. Advances in surface probe microscopy have been reviewed recently and, therefore, are not included [D.A. Bonnell et al.: Rev. Modern Phys. in Review]. In this study particular attention is paid to studies that have pioneered the synergetic use of multiple techniques to provide complementary views of a single structure or process; several of these studies represent the state-of-the-art in characterization and suggest a trajectory for the continued development of the field. Based on this review, a set of grand challenges for characterization science is identified, including suggestions for instrumentation advances, scientific problems in microstructure analysis, and complex structure evolution problems involving material damage. The future of microstructural characterization is proposed to be one not only where individual techniques are pushed to their limits, but where the community devises strategies of technique synergy to address complex multiscale problems in materials science and engineering.

We report on in situ stress relaxation behavior of vanadium dioxide thin films across the thermally driven metal–insulator transition (MIT) and size effects. Although the residual stress follows an inverse relationship with film thickness, the metal–insulator phase transition-induced stress varies nonmonotonically with increase in film thickness and grain size. Maximum transformation stress of −447 MPa is observed across the MIT for ∼170-nm-thick film with an average grain size of ∼70 nm. The interplay between constraint effects and nanostructure leads to nontrivial stress relaxation trends and provides insights into design of phase transition materials for switching devices.

Elastic modulus and internal friction of Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) and La0.58Sr0.4Co0.2Fe0.8O3-δ (LSCF) were determined from resonance frequencies and damping behavior, respectively, using an impulse excitation method. An elastic anomaly for BSCF around 476 K, with a corresponding peak in the internal friction, is attributed to the experimentally confirmed spin transition of Co3+. LSCF is in a ferromagnetic state below ∼220 K and in a paramagnetic state above ∼250 K. The elastic modulus of LSCF exhibits an anomaly between 473 and 1113 K, which is attributed to a transition from rhombohedral to cubic symmetry.

The exact solution of viscoelastic stresses in the bilayer system due to thermal and/or lattice mismatch is derived if both layers are Maxwell materials. When the thickness of one layer is much smaller than that of the other layer, the viscoelastic stresses in the bilayer system can be reduced to that of the thin film/substrate system. The relative film thickness and the position in the thin film/substrate systems are included in this solution. The average film stress decreases with increasing the normalized time and finally approaches zero in a long time. As the relative film thickness is equal to or less than 0.001, the average film stresses of the zeroth-order approximation, first-order approximation, and Hsueh and Lee model [J. Appl. Phys.91, 2760 (2002)] are close to that of exact solution. Nevertheless, as the relative film thickness is larger than 0.001, the accuracies of the zeroth-order approximation, first-order approximation, and Hsueh and Lee model are dependent on the normalized time and relative film thickness.

Experimental and simulation studies have shown that decreasing the grain size below a critical value results in softening rather than hardening in both the yield stress and flow stress of nanomaterials. In this work, a gradient plasticity framework is presented that can capture this softening behavior by treating grain boundaries as a separate phase with a finite thickness. The theoretical expression obtained for the yield stress as a function of the grain size can capture numerous experimental data that exhibit this “normal” to “abnormal” Hall–Petch transition, and an analytical equation is obtained that can predict the grain size at which this transition occurs. Furthermore, analytical expressions are obtained for the flow stress in nanomaterials, and they are in precise agreement with atomistic simulations on nanocrystalline Cu, which predict that below a critical grain size the flow stress decreases proportional to it.

The Maugis–Barquins (MB) solutions for the adhesive contact between an axisymmetric indenter and an elastic half-space are modified by incorporating the interfacial energy defined by the real area of contact. With the modified MB solutions, general relations for contact stiffness including adhesive effects in indentation analysis are derived. Numerical calculations showed that the difference in expected stiffness for the modified MB model compared to the standard MB results can be significant at low loads of interest in atomic force microscopy measurements and also for indentation tests at high load if the interfacial energy is large (∼0.1 J/m2) and the material is soft (Young’s modulus ≤100 MPa).

A spherical indentation-based method and its numerical verification, which is capable of identifying the plastic properties, have been respectively provided by our previous work [P. Jiang, et al., J. Mater. Res.24, 1045 (2009)] and [T. Zhang, et al., J. Mater. Res.24, 3653 (2009)]. To examine its effectiveness for practical application, 10 typical metals were selected to perform experimental verifications. Here, the above method was used in combination with the Oliver–Pharr model to avoid its dependence on the previously known elastic modulus. To obtain reliable results, a reasonable calibration has been performed for the used spherical tip with imperfect shape. Finally, the present verification has shown that the deviations of yield strength and elastic modulus obtained from the indentation tests are at most 40% but are generally within 25%. And the effect of the difference in constitutive relationships between the ideal model and the actual material on the accuracy of the indentation-based method has also been illustrated.

A nanoindentation strain-rate jump technique has been developed for determining the local strain-rate sensitivity (SRS) of nanocrystalline and ultrafine-grained (UFG) materials. The results of the new method are compared to conventional constant strain-rate nanoindentation experiments, macroscopic compression tests, and finite element modeling (FEM) simulations. The FEM simulations showed that nanoindentation tests should yield a similar SRS as uniaxial testing and generally a good agreement is found between nanoindentation strain-rate jump experiments and compression tests. However, a higher SRS is found in constant indentation strain-rate tests, which could be caused by the long indentation times required for tests at low indentation strain rates. The nanoindentation strain-rate jump technique thus offers the possibility to use single indentations for determining the SRS at low strain rates with strongly reduced testing times. For UFG-Al, extremely fine-grained regions around a bond layer exhibit a substantial higher SRS than bulk material.

Self-separated Pb(Zr0.52Ti0.48)O3 (PZT) films were processed by a hydrothermal deposition and a rapid thermal separation method, followed by a sol–gel filling and sintering process. The films possess excellent piezoelectric and electromechanical properties close to those of bulk material. The maximum remnant polarization is over 30 μC/cm2 and the electromechanical coupling factor (kt) reaches as high as 0.52. The unique microstructure characteristics of the PZT films, such as their highly dense structure, columnar grains, well-connected grain boundaries, and well-dispersed nanopores, could all contribute to the enhanced piezoelectric and electromechanical properties.

(Pb0.87−0.07xBa0.10+0.07x)La0.02(Zr0.7Sn0.15Ti0.15)O3 ceramics with 0 ≤ x ≤1 were prepared by conventional solid-state reaction process, and their dielectric and electric field–induced pyroelectric properties were systemically investigated. Compared with conventional pyroelectric materials, (Pb0.87−0.07xBa0.10+0.07x)La0.02(Zr0.7Sn0.15Ti0.15)O3 ceramics exhibited higher pyroelectric coefficient and figure of merit, which are beneficial for the development of pyroelectric devices. The specimens with x = 0.65 showed good pyroelectric properties for practical applications. When a 500 V/mm dc bias field was applied, they showed the maximum pyroelectric coefficient of 12,200 μC/m2K and the figure of merit of 106 × 10−5 Pa−0.5 at 45 °C, which are larger than those observed from conventional pyroelectric materials. Improvement of pyroelectric property is beneficial for the development of infrared detectors.

(Pb0.87La0.02Ba0.1)(Zr0.75Sn0.25–xTix)O3 (PLBZST, 0.07 ≤ x ≤ 0.09) ceramics were prepared by the conventional solid state reaction process, and their crystal structural, ferroelectric (FE), dielectric, and pyroelectric properties were systemically investigated. A transformation from antiferroelectric (AFE) phase to FE phase was observed when x was higher than 0.08. With the content of Ti increasing from 0.07 to 0.09, the dielectric peak was steeper and the pyroelectric coefficient was greater under direct current (DC) bias fields. As the DC bias field increased from 300 V/mm to 600 V/mm, the pyroelectric coefficient increased from 4500 to 10500 μC/m2·K for PLBZST specimens with 0.09. Thus, large pyroelectric response is beneficial for the development of infrared sensors.

BaZrO3–BaTiO3 ceramics exhibit a shift in transformation temperatures as revealed by dielectric and viscoelastic spectroscopy; a phase diagram has been established. Sigmoid anomalies in Poisson’s ratio and bulk modulus during the ferroelastic transitions were observed in doped materials, which are not predicted by standard theories for phase transformations. “Hashin–Shtrikman” composite model with negative stiffness heterogeneity can well explain this phenomenon. Negative stiffness heterogeneity is considered to be caused by the strained BaTiO3 unit cells in the vicinity of BaZrO3-rich zones under the perturbation of lattice reconstruction.