TABLE 5.

Activation energies for the X diffusion process in both the perfect fluorite phase ( $E_{\text{a}}^{\text{c}}$ ) and the superionic states ( $E_{\text{a}}^{\text{s}}$ ). The reference values are from experiments, except for those marked.

Compound	Potential	${\mathit{E}}_{\text{a}}^{\text{c}}$ /eV		${\mathit{E}}_{\text{a}}^{\text{s}}$ /eV
		This work	Exp	This work	Ref
BaF2	Catlow and Norgett (1973)	2.90	1.6( 1), 2.52( 2)	0.61	0.48(2)
	Cazorla et al. (2018)	1.32		0.95
	Sayle et al. (2003)	1.30		0.73
CaF2	Bingham et al. (1989)	1.52	1.92( 3), 2.02( 1), 3.34( 2)	0.86	0.74(2)
	Catlow and Norgett (1973)	2.89		0.65
	Evangelakis and Pontikis (1989)	2.19		0.61
	Sayle et al. (2003)	1.63		0.82
Li2O	Asahi et al. (2014)	2.02	1.6( 4), 2.52( 5)	0.63	0.98 a (6)
	Oda et al. (2007)	1.68		0.67
	Pedone et al. (2006)	1.50		0.48
β-PbF2	Catlow and Norgett (1973)	1.95	1.04( 7)	0.81	-
SrCl2	Bendall and Catlow (1980)	1.89	4.43( 2)	0.83	0.42(2)
	Gillan and Dixon (1980)	1.07		0.86
SrF2	Bingham et al. (1989)	1.80	1.81( 3)	0.79	0.55(2)
	Catlow and Norgett (1973)	2.76		0.63
	Cazorla et al. (2018)	2.04		0.95
UO2	Cooper et al. (2014b)	5.35	2.46–2.57( 8)	1.43
	Morelon et al. (2003)	2.74		1.40

^awhich come from DFT calculations. References are: (1) Ando et al. (1980); (2) Voronin and Volkov (2001); (3) Bollmann et al. (1970); (4) Lorger et al. (2019); (5) Oishi et al. (1979); (6) Gupta et al. (2019); (7) Samara (1979); (8) Ando and Oishi (1983).