Single crystals of the m = 8 member of the low-dimensional monophosphate tungsten bronzes (PO2)4(WO3)2m
family were grown by chemical vapour transport technique and the high crystalline quality obtained allowed a reinvestigation of the physical and structural properties. Resistivity measurements revealed three anomalies at T
C1 = 258 K, T
C2 = 245 K and T
C3 = 140 K, never observed until now. Parallel X-ray diffraction investigations showed a specific signature associated with three structural transitions, i.e. the appearance of different sets of satellite reflections below T
C1, T
C2 and T
C3. Several harmonics of intense satellite reflections were observed, reflecting the non-sinusoidal nature of the structural modulations and a strong electron–phonon coupling in the material. These transitions could be associated with the formation of three successive unconventional charge density wave states.
Seebeck coefficient in low-dimensional fluctuating charge density wave systems
