Microstructure and physical properties of two charge density wave states in NbSe₃ nanowires

The whisker-like niobium triselenide (NbSe₃) nanowires were synthesized using the traditional solid state reaction. X-ray diffraction experiment suggested the monoclinic structure (P 2₁/m), and crystal morphology analysis indicated that the band-like shape is the stable morphology. Two charge density wave (CDW) states were observed at around 140 K and 50 K, respectively, and the nonlinear effect was detected in the CDW states from the R-T and I-V measurements. The doped Fe atoms, as pinning centers, play an important role in the nonlinear properties of the CDW state. Electron diffraction and HRTEM experiments were carried out at different temperatures in order to investigate the structural features and their evolution. The sets of incommensurate modulation spots with modulation vector q₁ ∼ (h,k ±0.243 l) appeared below 145 K, and other sets of complex superstructure spots with modulation vector q₂ ∼ (h,k +0.3, l +1.3424), q ₃ ∼ (h,k -0.3137,1.5685), q₄ = (1/3,k,1) and q ₅ =(0.5,0.25,0.5) were observed at [1 0 0] and [3 0 1] zone axis at about 20 K, respectively, suggesting the complex incommensurately modulated structures in this material.