  A phase slip is a localized disturbance in the coherence of a superconductor
allowing an abrupt 2$\pi$ phase shift. Phase slips are a ubiquitous feature of
one-dimensional superconductors and also have an analogue in two-dimensions.
Here we present electrical transport measurements on boron-doped
nanocrystalline diamond (BNCD) microbridges where, despite their
three-dimensional macroscopic geometry, we find clear evidence of phase
slippage in both the resistance-temperature and voltage-current
characteristics. We attribute this behavior to the unusual microstructure of
BNCD. We argue that the columnar crystal structure of BNCD forms an intrinsic
Josephson junction array that supports a line of phase slippage across the
microbridge. The voltage-state in these bridges is metastable and we
demonstrate the ability to switch deterministically between different
superconducting states by applying electromagnetic noise pulses. This
metastability is remarkably similar to that observed in $\delta$-MoN nanowires,
but with a vastly greater response voltage.
