  Binary hydrides formed by the pnictogens of phosphorus, arsenic and antimony
are studied at high pressures using first principles methods. Stable structures
are predicted and their electronic, vibrational and superconducting properties
are investigated. We predict that SbH$_{4}$ and AsH$_{8}$ will be
high-temperature superconductors at megabar pressures, with critical
temperatures in excess of 100 K. The highly symmetric hexagonal SbH$_{4}$ phase
is predicted to be stabilized above about 150 GPa, which is readily achievable
in diamond anvil cell experiments. We find that all phosphorus hydrides are
metastable with respect to decomposition into the elements within the pressure
range studied. Trends based on our results and literature data reveal a
connection between the high-pressure behaviors and ambient-pressure chemical
quantities which provides insight into understanding which elements may form
hydrogen-rich high-temperature superconducting phases at high pressures.
