Structural, magnetic, transport, and thermoelectric properties of the pseudobrookite AlTi 2 O 5 − Ti 3 O 5 system

We investigated the structural, magnetic, transport, and high-temperature thermoelectric properties of single crystals of the pseudobrookite Al1-xTi2+xO5 for 0 <= x <= 1 grown using a floating zone. We found a correlation of spin-singlet Ti3+-Ti3+ dimers coupled with the lattice even in the conductive alpha and lambda phases which develops with increasing x . This developing dimer correlation reduces the number of unpaired Ti3+ ions, which makes the compound more conductive owing to the suppression of disorder for x up to about 0.75. The dimer fluctuation causes a critical enhancement of the magnetic susceptibility at around 150 K in the lambda phase near the boundary (x similar to 0 . 9) between the lambda and the beta phases. Such a correlation of the spin-singlet Ti3+-Ti3+ dimers may produce a high Seebeck coefficient in the conductive alpha and lambda phases leading to a large thermoelectric power factor at high temperatures.