The polymer‐based synthesis of ceramics such as SiCO (and SiCN) leads to the incorporation significant amounts carbon into their molecular structure. A key feature nanostructure these polymer‐derived is revelation persistent, 1–5 nm size domains by small‐angle X‐ray scattering. Here we present a model for nanodomains, which consistent with nuclear magnetic resonance (NMR) data and phenomenological properties (high resistance creep viscoelastic behavior). consists clusters silica tetrahedra...

Amorphous silicon–oxycarbide (SiCO) can retain large mole fractions of carbon when it is made from controlled pyrolysis silicon‐based polymers. The crystallization resistance these ceramics, which quite remarkable, varies with the content. In high‐carbon materials, usually accompanied by weight loss (resulting carbothermal reduction silica), whereas phase separation lead to without significant in low‐carbon materials. A simple graphical method developed estimate composition crystallized...

Carbon can be used to create unusual nanostructures of Si–C–O by controlled pyrolysis silsesquioxane organics. Unlike silica, these ceramics resist crystallization at ultrahigh temperatures. Their structure has been compared with that polymers, where crosslinked chains polymers in organics are replaced networks graphene the ceramics. The network sequesters nanoscale domains SiO 4 tetrahedra. resistance nanodomain attributed kinetic factors, namely obstruction long‐range diffusion silica. In...

A combination of methods, Bragg diffraction, small‐angle X‐ray scattering (SAXS), and transmission electron microscopy, is applied to the characterization nanodomains nanocrystals in polymer‐derived ceramics (PDCs). Detailed study two materials, silicon carbonitride (SiCN) a SiCN–zirconia nanocomposite, presented. The first contains domains which can be measured only by SAXS. However, nanocrystallites zirconia second material quantatively studied all three techniques. In both instances, we...

The authors provided detailed descriptions for setting up the re- quired system and performing experiments using individual scripts provided. While required considerable effort time, instructions facilitated evaluating results generating graphs that reproduced same patterns claimed by in paper Optimizing Distributed Protocols with Query Rewrites

Colossal magnetoresistance (CMR) composite materials have been synthesized to explore the possibility of improving magneto-transport and structural properties in CMR systems. In this work we describe (La1−xCaxMnO3)1−y (LCMO) (ZrO2)y (x≈0.3 0.0⩽y⩽0.40 mole %) composites that using a modified (non Pechini type) sol–gel technique. Magnetoresistivity was evaluated at 5 T field temperature range 5–300 K. The show higher magnitude MR compared pure LCMO. rises from base value 76%, for case y=0,...

The oxidation behavior of SiCN–ZrO 2 fibers and SiCN at 1350°C are compared. as‐measured parabolic rate constants for the two materials nearly same (15–20 × 10 −18 m /s). However, after implementing a correction difference in compositions, constant is 13.2 /s fiber, 29.4 SiCN. lower fiber ascribed to carbon content material.

SilconOxyCarboNitrides (SiCNO), made from thermal treatments of highly cross‐linked silicon, nitrogen, and oxygen containing polymers, exhibit intense luminescence that is broadly distributed over wavelengths 500–800 nm. The intensity sensitive to the composition, especially heat‐treatment temperature ( T HT ) these new materials. absorbance increases, thus brightness emission dims, as rises. phenomenology suggests presence two, spatially energetically separated, molecular complexes: one...

This communication reports new results on the enthalpy of formation pseudo‐amorphous ceramic compounds constituted from silicon, carbon, oxygen, and nitrogen (SiCNO), made polymer route. Again, like SiCO materials, although with one exception, crystalline components (SiO 2 cristobalite, β‐Si 3 N 4 , SiC, excess C) is negative. Some alloyed oxygen–nitrogen compositions yield enthalpies that are much more negative (∼100 kJ/g·atom) in comparison contain mainly oxygen or (∼20 kJ/g·atom). The...

We show that the rheology of a silazane‐based precursor for silicon carbonitride ceramic can be radically altered by reacting it with an alkoxide precursor. This modified drawn into fibers simple process. The fiber‐friendly is ascribed to creation linear polymer chains reaction between silazanes and alkoxides. made this process have excellent mechanical properties, reaching tensile strengths 2.8 GPa. Their structure amorphous.

The magnetic and electrical transport properties of La0.67Ca0.33MnO3 (LCMO): xSiCN (x=0–40 vol %) composites, synthesized by mechanical mixing citrate gel derived LCMO polymer ceramics SiCN, have been investigated as a function composition. ability SiCN to behave sintering additive leads interesting properties. Si+4, being strongly favored for tetrahedral coordination, cannot enter the perovskite lattice. Saturation moment, MS 68 emu/gm at 5 K kOe field pure shifts 79 in sample with x=0.05...

The established analysis for the study of oxidation using powder specimens is based on assumption monosized particles. experiments, however, are conducted powders with a distributed particle size. Here we present statistical approach calculation rate constant oxidation. results applied to new data studies dense silicon carbonitride amorphous ceramics. model requires wide range values fit short term and long‐term data, leading considerable ambiguity in estimate parabolic constant, k p , In...