Nanostructured materials: basic concepts and microstructure☆

Deformation of nanocrystalline materials by molecular-dynamics simulation: relationship to experiments?

Melting and superheating of crystalline solids: From bulk to nanocrystals

Nanocrystalline materials, with a grain size of typically < 100 nm, are a new class of materials with properties vastly different from and often superior to those of the conventional coarse-grained materials. These materials can be synthesized by a number of different techniques and the grain size, morphology, and composition can be controlled by controlling the process parameters. In comparison to the coarse-grained materials, nanocrystalline materials show higher strength and hardness, enhanced diffusivity, and superior soft and hard magnetic properties. Limited quantities of these materials are presently produced and marketed in the US, Canada, and elsewhere. Applications for these materials are being actively explored. The present article discusses the synthesis, structure, thermal stability, properties, and potential applications of nanocrystalline materials.

Nanocrystalline materials – Current research and future directions

Stabilizing nanocrystalline materials with dopants

Nanostructured Cu-Bi alloys prepared by co-evaporation in a continuous gas flow

We report on a combined study, by in situ x-ray diffraction at temperatures between 293 and 80 K, differential scanning calorimetry, and coherent quasielastic neutron scattering (QENS), of thin Ga films confined at grain boundaries in ${\mathrm{Al}}_{2}{\mathrm{O}}_{3}\ensuremath{-}\mathrm{G}\mathrm{a}$ nanocomposites that are produced by high-energy ball milling. We find that a molar fraction of Ga of up to 0.18 does not undergo phase change in the temperature interval investigated, which contains the bulk melting temperature ${T}_{M}^{\mathrm{bulk}},$ and conclude that this Ga is located in confined layers at grain boundaries, with an estimated thickness of six atomic monolayers. In samples with a higher overall molar fraction, the Ga in excess of molar fraction 0.18 melts and crystallizes reversibly when cycled between 100 and 320 K. For such samples, QENS at 320 K, that is, 17 K above ${T}_{M}^{\mathrm{bulk}},$ indicates three distinct diffusion coefficients $D$ for Ga: one below the resolution limit, ${D}_{1}l1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}{\mathrm{cm}}^{2}/\mathrm{s},$ one agreeing with the bulk liquid value, ${D}_{2}=3.4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}{\mathrm{cm}}^{2}/\mathrm{s},$ and a faster coefficient ${D}_{3}=2.4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}{\mathrm{cm}}^{2}/\mathrm{s}.$ We argue that the smaller and medium diffusion coefficients, ${D}_{1}$ and ${D}_{2},$ represent, respectively, solidlike layers near the ${\mathrm{Al}}_{2}{\mathrm{O}}_{3}\ensuremath{-}\mathrm{G}\mathrm{a}$ interface and liquid Ga in the core of interfacial layers and in liquid droplets. The fast diffusion coefficient ${(D}_{3})$ may be due to diffusion on free surfaces.

Kinetics of gallium films confined at grain boundaries

Local structure and size effects in nanophase palladium: An X-ray absorption study

The melting behavior of thin Ga films confined at the grain boundaries of nanostructured alumina was investigated by DSC. At temperatures near T m part of the Ga film is molten whereas about six monolayers remain solid even 20 K above T m . The diffusion of the Ga was investigated by means of QENS. The molten Ga film exhibits a lower diffusivity than bulk liquid Ga. This is rationalised in terms of the confined geometry.

H. Konrad

Papers

Nanostructured Cu-Bi alloys prepared by co-evaporation in a continuous gas flow

Kinetics of gallium films confined at grain boundaries

Local structure and size effects in nanophase palladium: An X-ray absorption study

Mobility of Ga confined in nanostructured alumina

X-Ray Absorption Study of Local Structure in Nanophase Palladium