Magnetism and correlation effects in titanium phosphate at high pressure

Titanium phosphate exhibits interesting properties as pressure and
temperature is varied e.g., the spin-Peierls transition. We have investigated the influence of
magnetism and electron correlation on this behaviour upon compression.

At ambient pressure TiPO₄ forms the orthorhombic structure
called phase I, with TiO₆ octahedra forming chains along the c-axis. As pressure
is increased these chains begin to dimerise, leading to the
incommensurate phase II, further increases of pressure locks the
dimerisation in the chains, forming the commensurate and dimerised phase III.
Even higher pressures leads to two new phases, IV and V, that show
a noticeable increase in density.[1]

The chains in phase III exhibit a behaviour similar to what has been observed in
VO₂, as a function of temperature. This suggests that TiPO₄ may be
useful to investigate the correlation effects in VO₂ at room
temperature but at high pressure.

At high pressure phase III undergoes a transition from a Mott
insulating state into a metallic one. This Mott transition triggers another
phase transition revealing two new, Mott insulating, phases, one non-magnetic
and dynamically stabilised and another antiferromagnetic with strong local
magnetic moments.

[1] - M. Bykov, et. al., Angewandte Chemie International Edition 55, 15053.