Transport of Mg2+ cations and diffusion-induced spin-lattice relaxation of 51V NMR in orthovanadate Mg3V2O8

Magnesium orthovanadate Mg ₃V ₂O ₈ provides an excellent model for studying the transport of magnesium cations in a three-dimensional matrix with two types of Mg(1)O ₆ and Mg(2)O ₆ octahedra connected by edges and chains of VO ₄ tetrahedra isolated from each other. In the present paper, the magnesium cations have been found to be the ionic charge carriers in this system using the Tubandt method. The electrical conductivity ( σ) has been studied by the impedance spectroscopy in the range 770–1270 K. The activation energy of σ ( E_σ) has been demonstrated to be 1.25 eV in the range 923–1023 K. For the first time, the ⁵¹V NMR spectra have been obtained and analysed in the range 295‒900 K. The activation energy ( E _NMR) for the diffusive jumps of Mg ²⁺ cations has been identified to be 1.03 eV by analyzing the temperature dependence of the ⁵¹V spin-lattice relaxation. The smaller E _NMR value is due to the rapid movement of magnesium along the chains of Mg(2)O ₆ octahedra. Large E_σ value and low ionic conductivity indicate that the limiting step in Mg ₃V ₂O ₈ is the cation hopping between the chains of Mg(2)O ₆ octahedra through the intermediate Mg(1) positions.