Gas-turbine engines used in transportation, energy, and defense sectors rely on high-temperature thermal-barrier coatings (TBCs) for improved efficiencies and power. The promise of still higher efficiencies and other benefits is driving TBCs research and development worldwide. An introduction to TBCs—complex, multi-layer evolving systems—is presented, where these fascinating systems touch on several known phenomena in materials science and engineering. Critical elements identified as being important to the development of future TBCs form the basis for the five articles in this issue of MRS Bulletin. These articles are introduced, together with a discussion of the major challenges to improved coating development and the rich opportunities for materials research they provide.

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.

This article shows how the scanning transmission electron microscope provides a Z-contrast image (where Z is atomic number) that is often directly interpretable and can show higher resolution than a phase-contrast image. It represents an incoherent mode of imaging, similar to that described by Lord Rayleigh for the optical microscope over a century ago. Today, resolution has reached a half Ångstrom, and spectroscopic analysis of individual atomic columns, even of individual atoms in two-dimensional materials, has become possible.

Photoanodes based on TiO2-polyheptazine (TiO2-PH) hybrids are, due to the energetics of photogenerated charges, very promising for solar water splitting in terms of possibly reduced need for external electric bias. Visible (λ > 420 nm) light-driven photooxidation of water at TiO2-PH electrodes loaded with two different metal oxide cocatalysts was investigated. As compared with TiO2-PH photoanodes loaded with colloidal [iridium (IV) oxide] IrO2 deposited by colloidal deposition, photoelectrodes modified with CoOx oxygen-evolving cocatalyst (Co-Pi) deposited by photoassisted deposition precipitation method showed both higher photocurrents and more efficient oxygen evolution under prolonged irradiation. The minimum external electric bias needed to observe complete photooxidation of water to dioxygen at TiO2-PH photoanodes modified with Co-Pi was estimated to be ∼0.6 V at pH 7. The key factor limiting the photoconversion efficiency at low bias potentials is the fast primary recombination of photogenerated charges.

The highly specific functions of DNA can be used for designing novel functional materials. However, aqueous solubility and biochemical instability of DNA impede its direct utilization as a functional component. Herein, preparation of a hybrid material encapsulating the DNA molecules (double-stranded salmon sperm, 50–5000 base pairs) in robust host—sol–gel-derived silica—has been described. The encapsulation was carried out in two steps: hydrolysis of an acidic tetraethylorthosilicate [Si(OC2H5)4] sol and was followed by condensation near physiological pH upon addition of alkaline DNA-containing solutions. The gelation behavior and structural properties of the DNA–silica hybrids were investigated by 29Si nuclear magnetic resonance and by nitrogen adsorption. The selective adsorption of a DNA-interactive reagent molecule (ethidium bromide) in their diluted aqueous solutions on DNA–silica hybrids confirmed that the DNA molecules remained entrapped within the silica host without any deterioration. A DNA encapsulation mechanism correlating the silica microstructure and DNA holding efficiency has been proposed.