Effect of crystal-growth conditions on charge-density-wave pinning inNbSe3

I describe a systematic study of the effects of vapor-transport growth conditions on the properties of ${\mathrm{NbSe}}_3$. Pinning of charge-density waves (CDW’s) in ${\mathrm{NbSe}}_3$ that is not intentionally doped is primarily by impurities rather than by intrinsic defects. A substantial fraction of these impurities may be derived from sources other than the Nb and Se starting materials. Oxygen, which is present in the starting Nb and Se, getters impurities from all sources, including those which are intentionally added. Consequently, impurity types and concentrations in transported crystals may differ significantly from those in the starting materials. I describe growth procedures that provide reasonable control over doping, and that yield high-quality ${\mathrm{NbSe}}_3$ crystals with residual resistance ratios ${\mathit{r}}_{\mathit{R}}$∼400 and bulk threshold electric fields ${\mathit{E}}_{\mathit{T}}$(T=50 K)<1 mV/cm. These results help to explain large inconsistencies between previous studies of CDW pinning in ${\mathrm{NbSe}}_3$.