Alkali metal polyhydrides are unstable and decompose into a monohydride and hydrogen at atmosphere. However, DFT calculations show that the alkali metal polyhydrides are stable under high pressure due to the negative enthalpies of formation of alkali metal polyhydrides [1, 2]. A series of XRD data for potassium (K) under high hydrogen pressure were collected at HPCAT beamline of APS after loading a small piece of potassium in a DAC and were pressurized with hydrogen as a pressure medium. Change of the atomic structure of laser-heated at 80 GPa was also analyzed by employing GSAS.
Potassium sample formed a KH at the initial pressure of hydrogen loaded by using a gas-loading system (1.66 GPa) with a lattice constant of 5.54 กส (FCC structure). The structure of the KH sample transformed to BCC at 4.87 GPa. The values of lattice constants changed from 5.54 to 4.04 กส, as increasing the pressure from 1.66 to 24.93 GPa, revealed the increment of volumetric hydrogen density from 59.71 to 152.98 kgH2/m3. The structure of KH was reversible as decreasing pressure to 1 atm. The structure, electrical transport properties of hydrogenated potassium as a function of pressure and temperature will be presented.
Reference
[1] E. Zurek et al., Proc. Natl. Acad. Sci. USA, 106, 17640 (2009).
[2] P. Baettig et al., Phys. Rev. Lett., 106, 237002 (2011).