  Dislocations, line defects in crystalline materials, play an essential role
in the mechanical[1,2], electrical[3], optical[4], thermal[5], and phase
transition[6] properties of these materials. Dislocation motion, an important
mechanism underlying crystal plasticity, is critical for the hardening,
processing, and application of a wide range of structural and functional
materials[1,7,8]. For decades, the movement of dislocations has been widely
observed in crystalline solids under mechanical loading[9-11]. However, the
goal of manipulating dislocation motion via a non-mechanical field alone
remains elusive. Here, we present real-time observations of dislocation motion
controlled solely by an external electric field in single-crystalline zinc
sulfide (ZnS). We find that 30{\deg} partial dislocations can move back and
forth depending on the direction of the electric field, while 90{\deg} partial
dislocations are motionless. We reveal the nonstoichiometric nature of
dislocation cores using atomistic imaging and determine their charge
characteristics by density functional theory calculations. The glide barriers
of charged 30{\deg} partial dislocations, which are lower than those of
90{\deg} partial dislocations, further decrease under an electric field,
explaining the experimental observations. This study provides direct evidence
of dislocation dynamics under a non-mechanical stimulus and opens up the
possibility of modulating dislocation-related properties.
