Negative thermal expansion in Co3BO5 induced by ceramic microstructural effects

We discovered that sintered bodies of Co3BO5 exhibit negative thermal expansion (NTE), despite positive expansion of the crystal lattice. Dilatometry results show that, at temperatures of 400–550 K, sintered bodies of Co3BO5 exhibit NTE. Synchrotron x-ray diffraction experiments show that the crystal structure is maintained and that the lattice thermal expansion is positive. However, in this temperature range, the crystal lattice exhibits a great degree of anisotropic thermal deformation. The material microstructural effects found to exist for some NTE materials, such as Ca2RuO4 and Ti2O3, probably induced the NTE. Findings obtained from these experiments also demonstrate that Cu doping onto the Co sites alters the operating temperatures of NTE. Materials for which the unit cells exhibit anisotropic thermal deformation represent a vast reservoir of NTE materials.