Reactivity of lithium and platinum at elevated densities

Through a series of x-ray diffraction experiments, combined with first-principles calculations, we show that the nobility of platinum can be overcome, reacting with lithium under compression at room temperature. Pressures as low as 2.3 GPa lead to the synthesis of ${\mathrm{Li}}_{11}{\mathrm{Pt}}_2$, exhibiting the highest lithium content of any known intermetallic compound. Above 16 GPa, ${\mathrm{Li}}_{11}{\mathrm{Pt}}_2$ expels Li and transforms to ${\mathrm{Li}}_2\mathrm{Pt}$. This change is accompanied by a transformation in bonding characterized by the formation of one-dimensional Pt-Pt bonds with increasingly covalent character at higher densities.

Figure 1

High-pressure x-ray diffraction data on ${\mathrm{Li}}_{11}{\mathrm{Pt}}_2$. (a) Rietveld profile refinement ($\lambda =0.4141$ Å) for ${\mathrm{Li}}_{11}{\mathrm{Pt}}_2$ ($w{R}_p=3.84\%, R_{\text{expt}}=3.66\%$): Experimental data shown with crosses, calculated profile shown in red, and the difference is shown as the lower black trace (raw x-ray diffraction image is shown in Fig. S1). (b) Diffraction patterns under increasing quasihydrostatic pressure. Peaks due to ${\mathrm{Li}}_{11}{\mathrm{Pt}}_2$ (bottom, black) broaden and rapidly lose intensity.

Figure 2

Crystal and electronic structure of ${\mathrm{Li}}_{11}{\mathrm{Pt}}_2$. (a) Change in unit-cell lengths with pressure for ${\mathrm{Li}}_{11}{\mathrm{Pt}}_2$: The inset shows the ${\mathrm{Li}}_{11}{\mathrm{Pt}}_2$ crystal structure, Li atoms are red, and Pt atoms beige. (b) Band structure of ${\mathrm{Li}}_{11}{\mathrm{Pt}}_2$ at 10 GPa.

Figure 3

High-pressure x-ray diffraction and crystal structure of ${\mathrm{Li}}_2\mathrm{Pt}$. (a) Rietveld profile refinement ($\lambda =0.4141$ Å, raw x-ray diffraction image is shown in Fig. S1) for ${\mathrm{Li}}_2\mathrm{Pt}$ ($w{R}_p=5.77\%, R_{\text{expt}}=3.35\%$). (b) $2\times 2$ supercell of ${\mathrm{Li}}_2\mathrm{Pt}$: Chains of Pt atoms lie along the $c$ axis, each coordinated by 12 Li atoms. Li atoms from graphenelike hexagonal sheets in the $ab$ plane.

Figure 4

Electronic structure of ${\mathrm{Li}}_2\mathrm{Pt}$ at (a) 0 and (b) 80 GPa. Pt $5s, 5p, 6s, 5d$ and Li $1s, 2s$ electrons are treated as valence. Spin-orbit coupling is included. (c) $\text{ELF}=0.34$ isosurface for ${\mathrm{Li}}_2\mathrm{Pt}$ at 0 GPa. Valence ELF maxima are represented by blue balls. The valence ELF maxima located at $6k$ and $1b$ sites are indicated by purple and black balls, respectively.