Synchrotron X-ray powder diffraction and convergent beam electron diffraction studies on the cubic phase of MgV₂O₄ spinel

The A V₂O₄ (A=Mg²⁺, Zn²⁺, Cd²⁺) spinels are three-dimensional spin-1 frustrated systems with orbital degree of freedom, which have been known to possess intriguing orbital states causing releases of spin frustration at low temperatures. We have performed synchrotron X-ray and convergent beam electron diffraction measurements for one of these vanadates, MgV₂O₄ in order to clarify its crystal structure in the high temperature cubic phase, which is regarded as an important starting point for understanding the details of the low temperature phase. We have successfully observed that the [001] zone axis convergent beam electron diffraction pattern exhibits 4mm symmetry, suggesting the space group of Fd3̄m in the cubic MgV₂O₄. It has also been demonstrated that the crystal structure of the cubic MgV ₂O₄ contains VO₆ octahedra elongated along the threefold rotation axis. Based on our results, we discuss the orbital states of MgV₂O₄ as well as the other spinel vanadates.