The complex nanodomain structure and energetic features of polymer-derived SiCN and SiOC ceramics have been investigated by multinuclear 1D and 2D solid-state NMR, micro-Raman, SAXS, XRD, HRTEM and oxidative high temperature oxide melt solution calorimetry, respectively. Structural models consistent with all these lines of evidence put emphasis on interconnected fractal domains stabilized by the mixed-bond-structure and interface bonding between nanodomains. The structural and thermodynamic role of hydrogen in the stabilization of interfacial bonding between the nanodomains in polysilylcarbodiimide-derived SiCN is reported as well. IntroductionEnabled by the development of sophisticated structural analytical methods there has been increasing emphasis in recent years in detailed studies related to the inuence of the local order, mid-range structure, and nanoscale heterogeneity of complex materials on their microstructure and properties. [1][2][3][4][5][6][7] At the same time, it has been realized that materials, which appear X-ray amorphous, are oen comprised of nanodomains of different structures and compositions. [2][3][4]8 The morphology of these intergrown nanodomains may signicantly inuence the physical properties and microstructure of these materials on a larger scale, especially when the domains differ signicantly in their chemistry, electrical conductivity, and/or mechanical properties. Thus controlling the domain structure offers a path to tailoring material properties and understanding the nature of such nanodomains is a challenge of both fundamental and practical importance.

Three silicon oxycarbide glasses (SiCO) with increasing C content were obtained through pyrolysis in inert atmosphere at 1000 °C of sol-gel derived siloxane networks containing Si-CH 3 and Si-H bonds. The glasses were further annealed at 1200, 1400, and 1500 °C to follow their evolution at high temperature. Quantitative information concerning the structure of glasses before and after annealing at high temperature was collected with a wide range of techniques (some of them used for the first time in this field) with the aim of probing the following: (i) the short-range order and chemical composition ( 29 Si and 1 H MAS NMR, RDF derived from X-ray and neutron scattering, inelastic neutron scattering, FT-IR, and elemental analysis), and (ii) the long-range order (X-ray and neutron diffraction) and microstructural features (HR-TEM combined with electron diffraction, Raman, porosity, and surface area measurements). This extensive collection of data, carried out on the same set of specimens, provided detailed and sound structural information on nearly-stoichiometric SiCO glasses and their high-temperature behavior.

Ceramics based on group IV-V transition metal borides and carbides possess melting points above 3000 °C, are ablation resistant and are, therefore, candidates for the design of components of next generation space vehicles, rocket nozzle inserts, and nose cones or leading edges for hypersonic aerospace vehicles. As such, they will have to bear high thermo-mechanical loads, which makes strength at high temperature of great importance. While testing of these materials above 2000 °C is necessary to prove their capabilities at anticipated operating temperatures, literature reports are quite limited. Reported strength values for zirconium diboride (ZrB2) ceramics can exceed 1 GPa at room temperature, but these values rapidly decrease, with all previously reported strengths being less than 340 MPa at 1500 °C or above. Here, we show how the strength of ZrB2 ceramics can be increased to more than 800 MPa at temperatures in the range of 1500–2100 °C. These exceptional strengths are due to a core-shell microstructure, which leads to in-situ toughening and sub-grain refinement at elevated temperatures. Our findings promise to open a new avenue to designing materials that are super-strong at ultra-high temperatures.

The way is open for the physical and chemical characterization and single‐crystal growth of the orthorhombic o′‐In2O3 polymorph. Orthorhombic In2O3 is synthesized from rhombohedral corundum‐type rh‐In2O3 under moderately high‐pressure and high‐temperature conditions (8–9 GPa, 600–1100 °C) followed by recovery to ambient pressure and temperature. The crystal‐structure data at ambient conditions confirm unambiguously the Rh2O3(II)‐type structure.