X-ray diffraction measurement of the Jahn-Teller distortion in TmVO₄

Single crystal X-ray diffraction has been used to determine the magnitude and temperature dependence of the tetragonal-to-orthorhombic distortion below the cooperative Jahn-Teller phase transition occuring in TmVO₄ at 2.15 K. The results are in good agreement with mean field theory and with the results of a previous investigation of the soft acoustic mode above the transition. It can be concluded that the interaction of long wavelength acoustic phonons with the ground doublet of the Tm³⁺ ion is the dominant mechanism for the transition.