Spin-Peierls transition in TiPO${}_4$

We investigated the magnetic and structural properties of the quasi-one dimensional 3$d^1$-quantum chain system TiPO${}_4$ ($J\sim$ 965 K) by magnetic susceptibility, heat capacity, ESR, x-ray diffraction, NMR measurements, and by density functional calculations. TiPO${}_4$ undergoes two magnetostructural phase transitions, one at 111 K and the other at 74 K. Below 74 K, NMR detects two different ${}^{31}$P signals and the magnetic susceptibility vanishes, while DFT calculations evidence a bond alternation of the Ti…Ti distances within each chain. Thus, the 74 K phase transition is a spin-Peierls transition which evolves from an incommensurate phase existing between 111 K and 74 K.