Most materials expand on heating and contract on cooling. However, an increasing number of materials with negative thermal expansion (NTE) have been discovered in recent years. In this article, we review the patents related to the synthesis and applications of several important families of negative thermal expansion materials. Particular attention has been paid to the families of NTE materials with open framework structures consisting of corner-sharing polyhedra that are relatively rigid but flexible in rotation such as A(MO4)2 (A=Zr, Hf or combinations of them; M=W, Mo or combinations of them), A4+P2O7 (A is an element with valance of +4, A and P can also be partially replaced by other elements with charge balance), A2(MO4)3 (A=Sc, Y, Al, Lu etc. and may be partially substituted by other elements) and Zr2P2WO12, Ca1-xMxZr4P6O24 (M= Sr, Ba, Mg). Some patents with the family of NTE materials with a framework structure consisting of relatively soft polyhedra connected by stiff cyanide bridges such as Zn(CN)2 and Cd(CN)2, etc. and the family of the NTE materials of perovskite manganese nitrides whose NTE is driven by magnetovolume effect are also involved. The most important applications of the NTE materials are to compensate for undesired positive expansion of other materials, creating ceramics, composites or devices with controllable overall negative, zero or positive coefficient of thermal expansion. The patents related to these applications are reviewed. Some problems existing with particular materials or applications are commented.
Keywords: Negative thermal expansion materials, negative thermal expansion ceramics, composites, low thermal expansion materials, zirconium tungstate, zirconnium molybdate, pyrophosphates, pyrovanadates, rare earth tungstate, rare earth molybdate, zirconium phosphate tungstate, sodium zirconium phosphate, zinc dicyanide, cadmium dicyanide, alkaline earth zirconium phosphates, perovskite manganese nitride
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