  Recent theoretical and experimental studies of hydrogen-rich materials at
megabar pressures (i.e., >100 GPa) have led to the discovery of very
high-temperature superconductivity in these materials. Lanthanum superhydride
LaH$_{10}$ has been of particular focus as the first material to exhibit a
superconducting critical temperature (T$_c$) near room temperature. Experiments
indicate that the use of ammonia borane as the hydrogen source can increase the
conductivity onset temperatures of lanthanum superhydride to as high as 290 K.
Here we examine the doping effects of B and N atoms on the superconductivity of
LaH$_{10}$ in its fcc (Fm-3m) clathrate structure at megabar pressures. Doping
at H atomic positions strengthens the H$_{32}$ cages of the structure to give
higher phonon frequencies that enhance the Debye frequency and thus the
calculated T$_c$. The predicted T$_c$ can reach 288 K in
LaH$_{9.985}$N$_{0.015}$ within the average high-symmetry structure at 240 GPa.
