Thermal expansion, by which a material’s volume increases when heated, is a universal phenomenon deriving from the thermal vibration of the atoms that constitute solids. Since the discovery of low thermal expansion in Invar alloys at the end of the 19th century, the “abnormality” of thermal expansion has given birth to new sciences and technologies. This article describes studies of thermal expansion anomalies from low thermal expansion of Invar alloys to the giant negative thermal expansion (giant NTE) materials recently discovered. Moreover, prospects for future research are presented. One turning point is the large isotropic NTE of ZrW₂O₈ discovered in 1996. Starting with manganese nitride in 2005, various materials have been found to have negative linear expansion coefficients that are many times larger than those of conventional NTE materials, although some operating-temperature constraints exist. These achievements have overturned the conventional wisdom which holds that negative coefficients of linear expansion do not engender large values. Additionally, the achievements established the concept of “giant” or “colossal” NTE. This article emphasizes recent important findings of enhanced NTE caused by material microstructural effects that are peculiar to ceramic bodies, and “hybrid” NTE by which multiple mechanisms work simultaneously. Additionally, this article introduces an attempt to produce fine particles of NTE material and use them as a thermal expansion compensator, especially for thermal-expansion control of resin.

Large negative thermal expansion (NTE) was achieved at room temperature using the structural phase transition in Zn₂P₂O₇. Particularly, Zn_1.6Mg_0.4P₂O₇ has a negative coefficient of linear thermal expansion αL of about –60 ppm/K at temperatures of 289–374 K. Co-doping of Mg and another element at the Zn site was found to be effective for control of NTE properties and for improvement of thermal expansion compensating ability. The present phosphates are expected to have widely various practical applications as thermal expansion compensators because they contain no toxic or expensive elements. Moreover, they can be prepared using a simple solid-state reaction method in air.

Layered ceramics with composite surface layers were prepared using Ce₂Zr₃(MoO₄)₉ (CZM), a low-temperature sintering ceramics, as the matrix and ZrW₂O₈, a negative expansion material, as the dispersoid. Their thermal shock resistance properties were compared with those of the monolithic matrix and similarly prepared layered ceramics with alumina or zirconia dispersed composites layers. Bending strength before thermal shock was measured, and no significant increase in strength was observed with the addition of ZrW₂O₈, and no systematic relationship was observed between the thermal expansion coefficient difference of the matrix and dispersoids in the composites prepared in this study. On the other hand, thermal shock fracture tests showed that the addition of ZrW₂O₈ increased the critical temperature difference (∆Tc) from 100°C to 150°C compared to monolithic CZM, indicating an improved thermal shock resistance. The critical temperature difference tended to increase with decreasing the coefficient of thermal expansion of the added dispersoids.