Recent Advances in Low-Positive, Zero, and Negative Thermal Expansion Materials: Fundamentals and Applications

Low-positive, near-zero, and negative thermal expansion materials are relatively rare. Although these unusual thermal expansion properties have been reported in the past for a few phases, systematic studies of the physical mechanisms and crystallography underlying these properties are more recent. This increased interest in this exotic class of materials arose from newly discovered materials showing these properties near room temperature or over a large temperature range.
The existence of such material properties in useful temperature ranges is fundamental for application purposes.
The effort to optimize the use of these materials in bulk form and as fillers in different matrices, for a variety of properties, ranging from high thermal shock resistance to controlled thermal expansion of polymeric, metallic, or ceramic matrices, is a more recent endeavor.

Since research in the area of low-positive, near-zero, and negative thermal expansion materials is still very recent, there are severe gaps of knowledge, principally related to the effective application of these materials. For example, more systematic studies of the important application properties such as hygroscopicity and first-order phase transition are still lacking.

Production of anhydrous phases with tailored coefficients of thermal expansion and synthesis of dispersed powders through soft-chemical routes are some of the most basic questions. In addition, consolidation of such powders by sintering to translucent or transparent highly dense bulk materials, with high mechanical resistance, is still far from systematic.
Although some studies show the potential of these materials for controlling the thermal expansion of polymeric, metallic, or ceramic matrices, we are still far from the full development of technologies that take advantage of these composites.
The proposal of new potential applications also requires exploration of all related properties of these materials.
Yet some more, fundamentals aspects, such as defect chemistry, are completely unknown, as are important crystallographic aspects, such as water molecules locations inside framework structures.
Also, there is still a need for new and superior materials with low, zero, and negative thermal expansion. Therefore, the exploration of new systems continues to be an important topic.

Besides regular papers and short communications on the most recent and exciting results, the area needs more targeted review papers on specific issues, since the vast majority of the current reviews, although useful, approach almost exclusively the issue of negative thermal expansion, and in a general way.
We encourage contribution on all topics related to low-positive, near-zero, and negative thermal expansion materials, but especially on:

• Systematic studies of important application properties, such as thermal and electrical conductivity, and mechanical properties
• Evaluation of the potential for new applications
• New or optimized soft-chemical routes for the synthesis of dispersed nanometric or submicron powders
• Consolidation of powders through advance sintering approaches
• Preparation and characterization of polymer-matrix, metal-matrix, and ceramic-matrix composites reinforced with low-positive, near-zero, and negative thermal expansion fillers
• Crystallographic aspects of low-positive, near-zero, and negative thermal expansion materials
• New low-positive, near-zero, and negative thermal expansion systems
• New methods for the control of the thermal expansion
• Defect chemistry of low-positive, near-zero, and negative thermal expansion materials
• New mechanisms of low-positive, near-zero and negative thermal expansion materials