Configurational disorder can be compositionally engineered into mixed oxide by populating a single sublattice with many distinct cations. The formulations promote novel and entropy-stabilized forms of crystalline matter where metal cations are incorporated in new ways. Here, through rigorous experiments, a simple thermodynamic model, and a five-component oxide formulation, we demonstrate beyond reasonable doubt that entropy predominates the thermodynamic landscape, and drives a reversible solid-state transformation between a multiphase and single-phase state. In the latter, cation distributions are proven to be random and homogeneous. The findings validate the hypothesis that deliberate configurational disorder provides an orthogonal strategy to imagine and discover new phases of crystalline matter and untapped opportunities for property engineering.

Titanium oxide nanotubes were fabricated by anodic oxidation of a pure titanium sheet in an aqueous solution containing 0.5 to 3.5 wt% hydrofluoric acid. These tubes are well aligned and organized into high-density uniform arrays. While the tops of the tubes are open, the bottoms of the tubes are closed, forming a barrier layer structure similar to that of porous alumina. The average tube diameter, ranging in size from 25 to 65 nm, was found to increase with increasing anodizing voltage, while the length of the tube was found independent of anodization time. A possible growth mechanism is presented.

Multiwall carbon nanotubes have been dispersed homogeneously throughout polystyrene matrices by a simple solution-evaporation method without destroying the integrity of the nanotubes. Tensile tests on composite films show that 1 wt % nanotube additions result in 36%-42% and ϳ25% increases in elastic modulus and break stress, respectively, indicating significant load transfer across the nanotube-matrix interface. In situ transmission electron microscopy studies provided information regarding composite deformation mechanisms and interfacial bonding between the multiwall nanotubes and polymer matrix. © 2000 American Institute of Physics. ͓S0003-6951͑00͒04120-6͔Carbon nanotubes ͑NTs͒ have many remarkable physical characteristics such as novel electronic properties, 1 exceptionally high axial strengths and axial Young's moduli of the order of terra pascal. [2][3][4] The exact magnitude of these properties depends on the diameter and chirality of the NT and whether they are in single-wall or multiwall form. Because of their outstanding physical properties, carbon nanotubes have numerous potential applications.5 One class of nanotube materials is NT composites in which the nanotube architecture is established within a host matrix material. Foreseeable NT-polymer composite materials include those designed for structural applications or for functional applications that make use of their conductivity, electromagnetic interference shielding 6,7 and optoelectronic properties. Large-scale production of NT composites will, of course, depend upon a large and inexpensive supply of high quality nanotubes. Several continuous chemical vapor deposition methods may hopefully meet this requirement in the near future. 9,10The effective utilization of nanotubes in composite applications depends strongly on the ability to disperse the NTs homogeneously throughout the matrix without destroying the integrity of the NTs. Furthermore, good interfacial bonding is required to achieve load transfer across the NT-matrix interface, a necessary condition for improving the mechanical properties of polymer composites. Polymer-NT composites have been the topic of several recent studies which used epoxy resins 6,11-15 and thermoplastic polymers 16,17 as the matrix materials. In these studies the important issue of NT dispersion was not, however, studied in great detail. In this letter, we address both nanotube dispersion and deformation mechanisms in polymer composites by studying a model composite system in which multiwall NTs ͑MWNTs͒ are dispersed in a polystyrene ͑PS͒ matrix. The homogeneity of the composites and deformation mechanisms are studied by in situ transmission electron microscopy ͑TEM͒.In this work we employed a simple solutionevaporation 18 method assisted by high-energy sonication to prepare uniform MWNT-PS composite samples. First, the PS ͑48 000 or 280 000 molecular weight from Aldrich Chemical Company, Inc.͒ was dissolved in toluene with a mass ratio of 1:10. The MWNTs were dispersed separately in toluene by high-energy sonication ...

The stability of titanium oxide nanotube arrays at elevated temperatures was studied in dry oxygen as well as dry and humid argon environments. The tubes crystallized in the anatase phase at a temperature of about 280 °C irrespective of the ambient. Anatase crystallites formed inside the tube walls and transformed completely to rutile at about 620 °C in dry environments and 570 °C in humid argon. No discernible changes in the dimensions of the tubes were found when the heat treatment was performed in oxygen. However, variations of 10% and 20% in average inner diameter and wall thickness, respectively, were observed when annealing in a dry argon atmosphere at 580 °C for 3 h. Pore shrinkage was even more pronounced in humid argon environments. In all cases the nanotube architecture was found to be stable up to approximately 580 °C, above which oxidation and grain growth in the titanium support disrupted the overlying nanotube array.