Structural modulation in the orbitally induced Peierls state of MgTi₂O₄

The structural properties associated with the orbitally induced Peierls transition in MgTi₂O₄ are characterized by in situ cooling TEM observations. A distinctive structural modulation with the wavevector of q₁ = 1/4 (0, 0, 4) has been well demonstrated below a critical temperature of about 260 K for MgTi₂O₄. Systematic analysis demonstrates that this structural modulation can be well explained by an orbital order existing in the low-temperature insulating phase. It is also noted that the nonstoichiometric feature commonly appearing in the present system could yield visible changes in both physical and structural properties. A low-temperature study of the microstructure of Mg[Ti_1.9Mg_0.1]O₄ reveals that a little substitution of Mg²⁺ for Ti³⁺ ions on the octahedral sites can disrupt the long-range order of the t_2g orbitals, resulting in complex tweed structures in the superstructure phase.