EFFECT OF CRYSTAL-GROWTH CONDITIONS ON CHARGE-DENSITY-WAVE PINNING IN NBSE3

I describe a systematic study of the effects of vapor-transport growth conditions on the properties of NbSe3. Pinning of charge-density waves (CDW's) in NbSe3 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 NbSe3 crystals with residual resistance ratios r(R) approximately 400 and bulk threshold electric fields E(T)(T = 50 K) < 1 mV/cm. These results help to explain large inconsistencies between previous studies of CDW pinning in NbSe3.