Synthesis, structure and physical properties of spinel solid solutions Mg2TiO4–MgTi2O4

Abstract

We investigated the preparation condition for stoichiometric MgTi2O4 and the electromagnetic properties of the spinel solid solution Mg2−xTi1+xO4 (0≤x≤1). Only a highly reductive sintering atmosphere gives a possibility for the preparation of stoichiometric MgTi2O4, based on Ti3+. MgTi2O4 thus obtained shows a metal to spin singlet insulator transition accompanied by the structural change from cubic to tetragonal. Introduction of Ti3+ (d1, S=1/2) to the non-magnetic insulator Mg2Ti4+O4 acts partly as doping of carrier dopants and partly as a source of localized electrons. Increasing content of Ti3+ leads to their delocalization, resulting in the metallic MgTi2O4 at x=1.0. The Peierls-like transition observed in the stoichiometric MgTi2O4 rapidly smears out with the content of Ti3+ ion decrease, suggesting an important role of orbital degree of freedom as an effective mechanism for the transition, which seems to be significantly influenced by the randomness associated with the appearance of Ti4+ ions.