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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. [ABSTRACT FROM AUTHOR]

Large negative thermal expansion (NTE) was achieved at room temperature using the structural phase transition in Zn2P2O7. Particularly, Zn1.6Mg0.4P2O7 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. [ABSTRACT FROM AUTHOR]

Because of growing demands for thermal expansion control in a local region, typically inner components of electronic devices, there is currently a great deal of interest in negative thermal expansion (NTE) fine particles. The spray-drying method without grinding produced micrometer-scale fine particles of pyrovanadate Cu1.8Zn0.2V2O7 showing a large negative coefficient of linear thermal expansion αL ~ –14 ppm/K equivalent to that of the bulk body. The solid-solution system Cu1.8Zn0.2V2–xPxO7 maintains the NTE functionality in a wide x compositional range. Phosphorus substitution contributes to cost reduction and to improvement of electrical insulation. Control of the structural phase transition in the phosphate analog Zn2P2O7 by substituting Mg for Zn realized a huge negative αL exceeding –60 ppm/K over a wide temperature range including room temperature. Because small particles are obtainable even with the conventional solid-phase reaction, the 1 μm level fine particles were obtained successfully using the pulverization method without degrading the function. It has high practicality because it is composed only of inexpensive and environmentally friendly elements such as Zn, Mg, and P. These NTE fine particles are expected to support great progress in thermal expansion control engineering. [ABSTRACT FROM AUTHOR]

Rapid advances in modern technology have led to increasing demands for control of thermal expansion. Recently, it has become necessary to control thermal expansion in a local region at the micrometer level, especially in the field of electronic devices. To meet this demand, attempts have been made to produce micrometer or submicrometer scale fine particles showing negative thermal expansion (NTE). Here, recent studies on spry-dry synthesis of β-Cu1.8Zn0.2V2O7 ceramic particles are reviewed. This class of vanadates shows large NTE linear to temperature over a wide temperature range. This NTE originates from the microstructures consisting of voids and anisotropic thermal deformation of crystal grains in a ceramic particle. By reducing the size of the microstructures that produce NTE, large NTE equivalent to bulk was realized even for ceramic particles of about 2 μm sizes. Comparison with the conventional method shows that this method provides the benefit of obtaining fine particles of narrow particle size distribution with a shape close to a sphere. This achievement is expected to pave the way for the use of NTE materials to control thermal expansion of a local region, for example, internal components of advanced electronic devices such as three-dimensional integrated circuit. [ABSTRACT FROM AUTHOR]