Coexistence of two charge-density waves of different symmetry in4Hb−TaSe2

The physical properties of $4Hb-\mathrm{Ta}{\mathrm{Se}}_2$ suggest the development of two charge-density waves (CDWs) of different symmetry. Electron and neutron diffraction studies establish that layers with octahedral and trigonal prismatic (TP) coordination undergo independent transitions to CDW states similar to $1T-\mathrm{Ta}{\mathrm{Se}}_2$ and $2H-\mathrm{Ta}{\mathrm{Se}}_2$, respectively. Although the "octahedral-CDWs" exhibit three-dimensional ordering, the "TP-CDWs" are uncorrelated due to weak interlayer forces. The possibility of a two-dimensional phase transition and the role of impurities are discussed.