Near-Infrared Trapping by Surface Plasmons in Randomized Platinum-Ceramic Metamaterial for Thermal Barrier Coatings.

As the operation temperature of next generation gas turbine is targeted to be 1800 °C toward a higher efficiency and lower carbon emission, the near-infrared (NIR) thermal radiation becomes a major concern for the durability of the metallic turbine blades. Although thermal barrier coatings (TBCs) are applied to provide thermal insulations, they are translucent to the NIR radiation. It is a major challenge for TBCs to achieve optically thick with limited physical thickness (usually < 1 mm) for effectively shielding the NIR radiation damage. Here, an NIR metamaterial is reported, where a Gd2 Zr2 O7 ceramic matrix is randomly dispersed with microscale Pt (0.53 vol%) nanoparticles with a size of 100-500 nm. Attenuated by the Gd2 Zr2 O7 matrix, a broadband NIR extinction is achieved through the red-shifted plasmon resonance frequencies and higher-order multipole resonances of the Pt nanoparticles. A very high absorption coefficient of ≈3 × 104 m-1 , approaching the Rosseland diffusion limit for a typical coating thickness, minimizes the radiative thermal conductivity to ≈10-2  W m-1 K-1 and successfully shields the radiative heat transfer. This work suggests that constructing a conductor/ceramic metamaterial with tunable plasmonics could be a strategy to shield NIR thermal radiation for high temperature applications.

Theoretical insights into the Peierls plasticity in SrTiO3 ceramics via dislocation remodelling.

An in-depth understanding of the dislocations motion process in non-metallic materials becomes increasingly important, stimulated by the recent emergence of ceramics and semiconductors with unexpected room temperature dislocation-mediated plasticity. In this work, local misfit energy is put forward to accurately derive the Peierls stress and model the dislocation process in SrTiO3 ceramics instead of the generalized stacking fault (GSF) approach, which considers the in-plane freedom degrees of the atoms near the shear plane and describes the breaking and re-bonding processes of the complex chemical bonds. Particularly, we discover an abnormal shear-dependence of local misfit energy, which originates from the re-bonding process of the Ti-O bonds and the reversal of lattice dipoles. In addition, this approach predicts that oxygen vacancies in the SrTiO3 can facilitate the nucleation and activation of dislocations with improvement of fracture toughness, owing to the reduction of average misfit energy and Peierls stress due to the disappearance of lattice dipole reversal. This work provides undiscovered insights into the dislocation process in non-metallic materials, which may bring implications to tune the plasticity and explore unknown ductile compositions.

Ultra-dense dislocations stabilized in high entropy oxide ceramics.

Dislocations are commonly present and important in metals but their effects have not been fully recognized in oxide ceramics. The large strain energy raised by the rigid ionic/covalent bonding in oxide ceramics leads to dislocations with low density (∼106 mm-2), thermodynamic instability and spatial inhomogeneity. In this paper, we report ultrahigh density (∼109 mm-2) of edge dislocations that are uniformly distributed in oxide ceramics with large compositional complexity. We demonstrate the dislocations are progressively and thermodynamically stabilized with increasing complexity of the composition, in which the entropy gain can compensate the strain energy of dislocations. We also find cracks are deflected and bridged with ∼70% enhancement of fracture toughness in the pyrochlore ceramics with multiple valence cations, due to the interaction with enlarged strain field around the immobile dislocations. This research provides a controllable approach to establish ultra-dense dislocations in oxide ceramics, which may open up another dimension to tune their properties.

Diffused Lattice Vibration and Ultralow Thermal Conductivity in the Binary Ln-Nb-O Oxide System.

In the pursuit of low thermal conductivity materials for thermal management, one always tries to increase the material entropy by increasing the number of components in the materials to scatter heat-carrying phonons. However, it also drastically increases the technological complexity to synthesize materials with the target complex composition. Here, a material family is presented with simple composition Ln3 NbO7 , which only contains binary oxides of Ln2 O3 (Ln = Dy, Er, Y, Yb) and Nb2 O5 . The thermal conductivities approach the theoretical minimum limit, where the large chemical inhomogeneity due to the charge disorder and fluctuation of bonding length in Ln3 NbO7 plays a major role. Despite the simple composition, Ln3 NbO7 demonstrates an unprecedentedly high scattering rate of vibration states, as confirmed by the highest elastic constant/thermal conductivity ratio, as well as the diffused wavevector-frequency dispersion. In contrast to the conventional wisdom that low thermal conductivity materials should be explored in the pool of "complex" multiple-component materials, this work points out an avenue to look into materials with simple composition but large internal chemical inhomogeneity, which would be of both scientific and technological significance in the fields of thermal barrier coating, thermoelectric materials, etc.