This material underwent a crystallographic phase transition, below 33K, which was induced by a cooperative Jahn-Teller effect. Twinning of the crystal occurred during the transition from the high-temperature tetragonal phase to the low-temperature orthorhombic phase, resulting in a domain structure. Single-crystal X-ray analyses of the tetragonal and twinned-orthorhombic phases confirmed a reduction in the site-symmetry of the Tb ion, from D2d (¯4m2-dodecahedral) for the high-temperature phase, to D2 (222-distorted dodecahedral) for the low-temperature phase. At the same time, the space-group symmetry decreased from D4h19 (I41/amd) to D2h24 (Fddd). The twinned orthorhombic phase was described as being composed of domains which were related to each other by a 180º rotation about the orthorhombic [110] axis.

Cooperative Jahn-Teller Induced Phase Transition of TbVO4: Single Crystal Structure Analyses of the Tetragonal High Temperature Phase and the Twinned Orthorhombic Phase Below 33K. K.Kirschbaum, A.Martin, D.A.Parrish, A.A.Pinkerton: Journal of Physics - Condensed Matter, 1999, 11[23], 4483-90