Neutron and X-ray diffraction experiments revealed that ferromagnetic NaV6O11 (Tc = 64.2 K) undergoes two-step second-order structural phase transitions upon cooling: hexagonal (P63/mmc) → hexagonal (P63mc) → orthorhombic (Cmc21). Its structure at 200 K was determined by single-crystal X-ray analysis: hexagonal, P63mc, a = 5.7049(2) Å, c = 13.0796(8) Å, and Z = 2. The P 63/mmc → P63mc transition is believed to accompany a magnetic transition at 245 K. V(1) octahedra, which construct an edge-sharing kagomé-type network, form a trimer on the P63/mmc → P 63mc transition. V(2) octahedra, which form face-sharing dimers, separate into two nonequivalent types on the hexagonal-hexagonal transition. The P63mc → Cmc 21 transition occurs at a temperature between 35 and 40 K, which is lower than Tc. V(1) octahedra split into two nonequivalent types on the P63mc → Cmc 21 transition. The transitions are compared with those in V2O3, V2O4, and LixVO2. The crystal structure of NaV6O11 lacks the center of symmetry below Tc, which allows a canted-spin arrangement for the ferromagnetic state if the Dzyaloshinski-Moriya interaction exists. No structural phase transition was observed for SrV6O11 (Tc = 70 K) between 22 and 373 K.
All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Ceramics and Composites
- Condensed Matter Physics
- Physical and Theoretical Chemistry
- Inorganic Chemistry
- Materials Chemistry