The high-pressure lithium–palladium and lithium–palladium–hydrogen systems

Abstract

AbstractThe lithium–palladium and lithium–palladium–hydrogen systems are investigated at high pressures at and above room temperature. Two novel lithium–palladium compounds are found below $${18.7}\,{\mathrm{GPa}}$$ 18.7 GPa . An ambient temperature phase is tentatively assigned as $$F{\bar{4}}3m\,\hbox {Li}_{17}\hbox {Pd}_{4}$$ F 4 ¯ 3 m Li 17 Pd 4 , with $$a = 17.661(1)$$ a = 17.661 ( 1 ) Å at 8.64 GPa, isostructural with $$\hbox {Li}_{17}\hbox {Sn}_{4}$$ Li 17 Sn 4 . The other phase occurs at high-temperature and is $$I{\bar{4}}3m\, \hbox {Li}_{11}\hbox {Pd}_{2}$$ I 4 ¯ 3 m Li 11 Pd 2 , $$a = 9.218(1)$$ a = 9.218 ( 1 ) Å at 3.88 GPa and 200 $$^\circ {\mathrm{C}}$$ ∘ C , similar to $$\hbox {Li}_{11}\hbox {Pt}_{2}$$ Li 11 Pt 2 , which is also known at high pressure. The presence of hydrogen in the system results in an $$I{\bar{4}}3m$$ I 4 ¯ 3 m structure with $$a = 8.856(1)$$ a = 8.856 ( 1 ) Å at 9.74 GPa. This persists up to $${13.3}\,\mathrm{GPa}$$ 13.3 GPa , the highest pressure studied. Below $${2}\,{\mathrm{GPa}}$$ 2 GPa an fcc phase with a large unit cell, $$a = 19.324(1)$$ a = 19.324 ( 1 ) Å at 0.39 GPa, is also observed in the presence of hydrogen. On heating the hydrogen containing system at 4 GPa the $$I{\bar{4}}3m$$ I 4 ¯ 3 m phases persists to the melting point of lithium. In both systems melting the lithium results in the loss of crystalline diffraction from palladium containing phases. This is attributed to dissolution of the palladium in the molten lithium, and on cooling the palladium remains dispersed.