Temperature-dependent electronic and magnetic properties are reported for nickel-deficient NiV 2 Se 4 . Single-crystal X-ray diffraction shows it to crystallize in the monoclinic Cr 3 S 4 structure type with space group I2∕m and vacancies on the Ni site, resulting in the composition Ni 0.85 V 2 Se 4 in agreement with our electron-probe microanalysis. Structural distortions are not observed down to 1.5 K. Nevertheless, the electrical resistivity shows metallic behavior with a broad anomaly around 150-200 K that is also observed in the heat capacity data. This anomaly indicates a change of state of the material below 150 K. It is believed that this anomaly could be due to spin fluctuations or charge-density-wave fluctuations, where the lack of long-range order is caused by vacancies at the Ni site of Ni 0.85 V 2 Se 4 . The non-linear temperature dependence of the resistivity as well as an enhanced value of the Sommerfeld coefficient 𝜸 = 104.0 (1) mJ mol −1 K −2 suggest strong electron-electron correlations in this material. First-principles calculations performed for NiV 2 Se 4 , which are also applicable to Ni 0.85 V 2 Se 4 , classify this material as a topological metal with Z 2 = (1; 110) and coexisting electron and hole pockets at the Fermi level. The phonon spectrum lacks any soft phonon mode, consistent with the absence of periodic lattice distortion in the present experiments.

The compound TiOCl is a quasi-1-dimensional (1D) quantum magnet (Seidel et al., 2003). Upon cooling, TiOCl undergoes a phase transition at Tc2 = 90 K towards a state with incommensurate magnetic order, followed by a second phase transition at Tc1 = 67 K towards a spin-Peierls state (Seidel et al., 2003; Shaz et al., 2005; van Smaalen et al., 2005). Both low-temperature phases involve structural distortions that have been characterized by x-ray diffraction. The absence of any phase transitions has been reported for scandium-doped TiOCl with doping levels 0.01 < x < 0.1 for ScxTi1-xOCl (Glancy et al., 2008(Glancy et al., , 2010 Zhang et al., 2010; Aczel et al., 2011). We have synthesized ScxTi1-xOCl for x = 0.005. Based on temperature-dependent x-ray diffraction experiments and specifichear measurements, we have found that the x = 0.005 compound transforms into incommensurate and spin-Peierls-like phases on cooling. Despite apparent large correlation lengths, these phases lack long-range order. A sluggish transformation is thus found between states of ScxTi1-xOCl that support different kinds of fluctuations.