Structural modulation in the orbitally induced Peierls state of MgTi(2)O(4).

ABSTRACT

The structural properties associated with the orbitally induced Peierls transition in MgTi(2)O(4) are characterized by in situ cooling TEM observations. A distinctive structural modulation with the wavevector of q(1) = 1/4 (0, 0, 4) has been well demonstrated below a critical temperature of about 260 K for MgTi(2)O(4). 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(1.9)Mg(0.1)]O(4) reveals that a little substitution of Mg(2+) for Ti(3+) 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.