High pressure-high temperature phase diagram of ammonia

TL;DR

This study maps the high pressure-high temperature phase diagram of solid ammonia, identifying phase transitions and melting behavior up to 20 GPa and 900 K using diamond anvil cells.

Contribution

It provides experimental data on ammonia's phase transitions and melting line, extending the known phase diagram up to high pressures and temperatures.

Findings

Determined the III-IV transition line up to 20 GPa and 500 K.

Identified the melting line up to 9 GPa and 900 K.

No discontinuity at the expected triple point.

Abstract

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.