Coordination Site Disorder in Spinel-Type LiMnTiO₄

LiMnTiO4 was prepared through solid-state syntheses employing different heating
and cooling regimes. Synchrotron X-ray and neutron powder diffraction
data found quenched LiMnTiO4 to form as single phase disordered
spinel (space group Fd3̅m),
whereas slowly cooled LiMnTiO4 underwent partial phase
transition from Fd3̅m to P4332. The phase behavior of quenched and slowly
cooled LiMnTiO4 was confirmed through variable-temperature
synchrotron X-ray and neutron powder diffraction measurements. The
distribution of Li between tetrahedral and octahedral sites was determined
from diffraction data. Analysis of the Mn/Ti distribution in addition
required Mn and Ti K-edge X-ray absorption near-edge structure spectra.
These revealed the presence of Mn3+ in primarily octahedral
and Ti4+ in octahedral and tetrahedral environments, with
very slight variations depending on the synthesis conditions. Magnetic
measurements indicated the dominance of antiferromagnetic interactions
in both the slowly cooled and quenched samples below 4.5 K.