Phase diagram of ammonia up to 200 GPa, search for ionic phase. Ionic and superionic conductivity of hot solid ammonia

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We will experimentally study transformations in ammonia at unexplored range of megabar pressures where a number of unusual phenomena are predicted. Dense ammonia NH3 is of fundamental interest as an archetype of hydrogen-bonded solids similar to water. But in contrast to water it might form at pressures P>90 GPa “ammonium amide” ionic solid consisting of alternate layers of NH+4 and NH-2 ions. We will search for the ionic phase by study X-ray, diffraction, Raman scattering and infrared absorption at 100-200 GPa. Another new state of NH3 ice was predicted under high pressures and temperatures: superionic solid phase with exceptionally fast hydrogen diffusion through a crystalline lattice of the remaining nitrogen ions. Superionic phase is a unique state of matter in which chemical bonds are breaking and reforming very rapidly. This phase is particularly relevant to planetary physics because the ice layer consisted of water, methane and ammonia is considered to be the source of the magnetic fields measured at Uranus and Neptune. In this project we will search for ionic conductivity of ammonia ice in the 60 – 120 GPa and 300-2500 K pressure-temperature domain by direct measuring protonic conductivity with impedance spectroscopy in the laser heated diamond anvil cell.