  The high pressure(P)-high temperature(T) phase diagram of solid ammonia has
been investigated using diamond anvil cell and resistive heating techniques.
The III-IV transition line has been determined up to 20 GPa and 500 K both on
compression and decompression paths. No discontinuity is observed at the
expected location for the III-IV-V triple point. The melting line has been
determined by visual observations of the fluid-solid equilibrium up to 9 GPa
and 900 K. The experimental data is well fitted by a Simon-Glatzel equation in
the covered P-T range. These transition lines and their extrapolations are
compared with reported calculations.
