1 Crystallographic data

Structures of the stable xenon oxides, XeO, XeO $_2$ , and XeO $_3$ are given in table 9.1. For XeO, Pbcm phase becomes stable at 83 GPa, then it transforms to P2 $_1$ /m phase at 145 GPa. For XeO $_2$ , P2 $_1$ /c phase becomes stable at 102 GPa, and then a phase transition occurs at 198 GPa (P2 $_1$ /c to Cmcm). For XeO $_3$ , the stable phases are P4 $_2$ /mnm-XeO $_3$ (114 - 145 GPa), C2/c (145 - 198 GPa), and Pmmn ( $>$ 198 GPa). These crystal structures are shown in Figs. 9.1, 9.2, and 9.3.

Table 9.1: Structures of the stable xenon oxides, XeO, XeO $_2$ , and XeO $_3$ .

Phase	Pressure	Space group	Lattice parameters	Atomic coodinates
	(GPa)
XeO	100	Pbcm	a=2.944	Xe(4d) 0.468 0.121 0.250
			b=6.925	O (4d) 0.893 0.371 0.250
			c=4.781
XeO	200	P2 $_1$ /m	a=4.505	Xe1(2e) 0.313 0.250 0.709
			b=3.308	Xe2(2e) 0.168 0.250 0.194
			c=5.525	O1 (2e) 0.356 0.750 0.934
			$\beta$ =101.83 $^{\circ }$	O2 (2e) 0.232 0.750 0.509
XeO $_2$	150	P2 $_1$ /c	a=6.452	Xe1(4e) 0.874 0.588 0.723
			b=6.536	Xe2(4e) 0.626 0.370 0.302
			c=4.948	O1 (4e) 0.849 0.555 0.198
			$\beta$ =92.20 $^{\circ }$	O2 (4e) 0.394 0.546 0.164
				O3 (4e) 0.362 0.221 0.996
				O4 (4e) 0.898 0.234 0.436
XeO $_2$	200	Cmcm	a=5.943	Xe (4c) 0.000 0.213 0.250
			b=4.424	O (8g) 0.826 0.343 0.750
			c=3.642
XeO $_3$	130	P4 $_2$ /mnm	a=6.040	Xe (4g) 0.737 0.263 0.000
			c=3.465	O1 (8i) 0.625 0.881 0.000
				O2 (4e) 0.000 0.000 0.198
XeO $_3$	150	C2/c	a=9.167	Xe1(4a) 0.000 0.000 0.000
			b=5.835	Xe2(8f) 0.664 0.014 0.176
			c=6.824	O1 (8f) 0.681 0.747 0.935
			$\beta$ =98.34 $^{\circ }$	O2 (8f) 0.791 0.128 0.917
				O3 (8f) 0.876 0.872 0.748
				O4 (8f) 0.458 0.127 0.584
				O5 (4e) 0.500 0.257 0.250
XeO $_3$	200	Pmmn	a=3.443	Xe (2a) 0.750 0.750 0.807
			b=4.440	O1 (2b) 0.250 0.750 0.171
			b=3.613	O2 (4e) 0.750 0.000 0.316

$\includegraphics[scale=0.5]{pdf/xeo-s.png}$

Figure 9.1: Crystal structure of XeO-P2 $_1$ /m (stable at $P$ $>$ 145 GPa).

$\includegraphics[scale=0.5]{pdf/xeo2-s.png}$

Figure 9.2: Crystal structure of XeO $_2$ -Cmcm (stable at $P$ $>$ 198 GPa).

$\includegraphics[scale=0.5]{pdf/xeo3-s.png}$

Figure 9.3: Crystal structures of XeO $_3$ polymorphs. a), top view of two sublattices: XeO $_2$ chain + O $_2$ chain; b) front view of -O $_2$ -O $_2$ - chain in P4 $_2$ /mnm XeO $_3$ (stable from 114 GPa to 145 GPa); c) front view of -O $_2$ -O- chain in C2/c XeO $_3$ (stabel from 145 GPa to 198 GPa).