  The Exozodi survey aims to determine the occurrence rate of bright
exozodiacal discs around nearby main sequence stars using infrared
interferometry. Although the Exozodi survey targets have been carefully
selected to avoid the presence of binary stars, the results of this survey can
still be biased by the presence of unidentified stellar companions. Using the
PIONIER data set collected within the Exozodi survey, we aim to search for the
signature of point-like companions around the Exozodi target stars. We use both
the closure phases and squared visibilities collected by PIONIER to search for
companions within the ~100 mas interferometric field of view. The presence of a
companion is assessed by computing the goodness of fit to the data for a series
of binary models with various separations and contrasts. Five stellar
companions are resolved for the first time around five A-type stars: HD 4150,
HD 16555, HD 29388, HD 202730, and HD 224392 (although the companion to HD
16555 was independently resolved by speckle interferometry while we were
carrying out the survey). In the most likely case of main sequence companions,
their spectral types range from A5V to K4V. Three of these stars were already
suspected to be binaries from Hipparcos astrometric measurements, although no
information was available on the companions themselves so far. In addition to
debiasing the statistics of the Exozodi survey, these results can also be used
to revise the fraction of visual binaries among A-type stars, suggesting that
an extra ~13% A-type stars are visual binaries in addition to the ones detected
in previous direct imaging surveys. We estimate that about half the population
of nearby A-type stars could be resolved as visual binaries using a combination
of state-of-the-art interferometry and single-aperture imaging, and we suggest
that a significant fraction of these binaries remains undetected to date.
