Process for making isotropic negative thermal expansion ceramics

This invention pertains to isotropic, negative thermal expansion ceramics, and to a process for preparing isotropic, negative thermal expansion ceramics which may, for instance, be used in temperature compensating grating packages. Ceramic monoliths are described which exhibit tunable coefficients of thermal expansion from about −5 to −11×10° C.near ambient temperatures. These two-phase ceramics, which are fabricated, for example, by reactive sintering of WOand ZrO, consists of a matrix of ZrWOwith inclusions of ZrOhaving diameters less than 10 m. Additives may increase the density of the monoliths to greater than 98% of the calculated density. Green body densities, pre-sintered particle size distribution, sintering atmosphere, microstructure, and mechanical properties are discussed. These ceramics may be used as substrates for thermally compensating fiber Bragg gratings.