Thermal Expansion of Nb ₂ O ₅

The high‐temperature thermal expansion of monoclinic Nb 2 O 5 was studied with X‐ray and dilatometric techniques. The X‐ray axial thermal expansion was anisotropic; the mean coefficients in the a, b , and c directions, respectively, were 5.3, 0, and 5.9×10 −6 °C ‐1 from room temperature to 1000°C. It is proposed that this anisotropy causes microcrack formation in sintered polycrystalline samples. The bulk linear thermal expansion of both sintered and hot‐pressed samples was determined with a dilatometer from room temperature to 1200°C. A hysteresis effect between heating and cooling data observed for sintered samples was attributed to the occurrence and recombination of internal microcracks.