This article serves to introduce the January 2004 issue of MRS Bulletin on progress toward applications of ceramic nanostructures. Conventional ceramic materials are widely used today in areas ranging from structural to biological applications, and in devices as diverse as lasers, semiconductors, sensors, and piezoelectric components. Such materials include oxides, carbides, nitrides, mixed oxides, and composites.Over the last decade, the use of ceramic nanostructures has already changed the approach to materials design in many of these applications, by seeking structural control at the atomic level and tailoring of the engineering properties. The articles in this issue review the advantages of nanoceramics, their application in various fields, and the challenges involved in their fabrication.

The promises of nanotechnology are mostly based upon the ability to produce nanostructured materials with novel properties. Nanocomposites are defined here as a class of materials that contain at least one phase with constituents in the nanometer domain. This article describes the present state of knowledge of the fabrication of nanocomposite materials, with special emphasis on plasma forming of bulk parts. Future challenges facing the development of methods for consolidating nanocomposites with retained nanostructures are also highlighted.

This article focuses on nanocrystalline-matrix ceramic composites specifically designed for applications requiring improved fracture toughness. While the models and theory of toughening mechanisms for microcrystalline composites are well developed, the same cannot be said for their nanocrystalline counterparts. The difficulty in producing fully consolidated ceramic composites that retain a nanocrystalline structure is the main hurdle to thorough investigations in this area. Thus, much of the research on so-called nanocomposites has been on materials with microcrystalline matrices and nanometric second phases. In this article, we present the general principles of toughness mechanisms in microcrystalline ceramic composites, and then extend these ideas to consider how they should apply to ceramics with nanocrystalline matrices. While work in this area is still quite limited, we review current research focused on the production and testing of composites with nanocrystalline matrices and second phases, and we recap the results of some promising fracture toughness reports.

An improved understanding of the interactions at the nanoscale level between the bioceramics in medical implants and the hard or soft tissues in the human body could contribute significantly to the design of new-generation prostheses and postoperative patient management strategies.Overall, the benefits of advanced ceramic materials in biomedical applications have been universally accepted, specifically in terms of their strength, biocompatibility, hydrophilicity, and wear resistance in articulating joints.The continuous development of new-generation implants utilizing nanocoatings with novel nanosensors and devices is leading to better compatibility with human tissue and improved well-being and longevity for patients. This article gives a short overview of bioceramics and reexamines key issues of concern for processing and applying nanoceramics as biomaterials.

Nanoscale ceramic particles, such as layered double hydroxides (LDHs), have been developed to deliver drugs or genes into biological cells. In this article, we describe the controlled-release properties of LDHs as drug delivery carriers, the formation of bio-LDH nanohybrids, their in vivo and in vitro cytotoxicity tests, and their potential as anticancer gene delivery carriers. Unstable biomolecules can be intercalated into LDHs, displacing the interlayer anions; the drug or gene's negative charge is thus shielded, enabling penetration into the cell. In the slightly acidic environment of the cell, ceramic nanoplatelets of ∼100 nm diameter dissolve, thus releasing the intercalates in a controlled manner.

Nanotubular structures in the B-C-N ceramic system represent an intriguing alternative to conventional carbon nanotubes.Because of the ability to widely vary the chemical composition of nanotubes within the B-C-N ternary phase diagram and to change the stacking of C-rich or BN-rich tubular shells in multiwalled structures, a wide horizon opens up for tuning nanostructure electrical properties.Pure carbon nanotubes are metals or narrow-bandgap semiconductors, depending on the helicity and diameter, whereas those of BN are insulators with a ∼5.0eV gap independent of these parameters.Thus, the relative B/C/N ratios and/or BN-rich and C-rich domain spatial arrangements, rather than tube helicity and diameter, are assumed to primarily determine the B-C-N nanotube electrical response.This characteristic is highly valuable for nanotechnology:while tube diameter and helicity are currently difficult to control, continuous doping of C with BN, or vice versa, proceeds relatively easily due to the isostructural nature of layered C and BN materials.In this article, recent progress in the synthesis, microscopic analysis, and electrical property measurements of a variety of compound nanotubes in the ceramic B-C-N system is documented and discussed.

By controlling the morphology of organic and inorganic semiconductors on a molecular scale, nanoscale p–n junctions can be generated in a bulk composite. Such a composite is typically called a bulk heterojunction composite, which can be considered as one virtual semiconductor combining the electrical and optical properties of the individual components. Solar cells are one attractive application for bulk heterojunction composites. Conjugated polymers or oligomers are the favorite p-type semiconducting class for these composites, while for the n-type semiconductor, inorganic nanoparticles as well as organic molecules have been investigated. Due to the solubility of the individual components, printing techniques are used to fabricate them.