Low-Temperature X-Ray Diffraction Studies on Vanadium Sesquioxide

X-ray diffraction patterns and microphotographs were obtained from single crystals and powder samples of ${\mathrm{V}}_2{\mathrm{O}}_3$ , cooled to liquid nitrogen temperatures. The c axis, in the hexagonal unit cell, expanded ${\text{5.8×10}}^{\text{−6}}\mathrm{/°}\mathrm{C}$ while the a axis contracted ${\text{22.9×10}}^{\text{−6}}\mathrm{/°}\mathrm{C}$ , over the range from room temperature to the transformation temperature of about minus 145°C. Below this temperature a microphotograph showed a typical martensitic structure. The low-temperature x-ray diffraction reflections split for all reflections except those of the (000l) type. The (000l) type reflections indicated a lattice contraction below the transformation. Those x-ray reflections that split showed expansions in the interplanar spacings. The low-temperature powder pattern could be indexed on the basis of a monoclinic unit cell; $\text{a\hspace{0.17em}=\hspace{0.17em}8.57}$ , $\text{b\hspace{0.17em}=\hspace{0.17em}4.98}$ and $\text{c\hspace{0.17em}=\hspace{0.17em}13.88\hspace{0.17em}A}$ with $\text{β\hspace{0.17em}=\hspace{0.17em}91.6°}$ .