SUPPLEMENTAL MATERIAL Pressure-Induced Amorphization Of

SUPPLEMENTAL MATERIAL

Pressure-induced amorphization of noble gas clathrate hydrates

Paulo H. B. Brant Carvalho,1 Amber Mace,2 Ove Andersson,3 Chris A. Tulk,4 Jamie Molaison,4 Alexander P. Lyubartsev,1 Inna M. Nangoi,5 Alexandre A. Leitão5 and Ulrich Häussermann1,*

1Department of Materials and Environmental Chemistry, Stockholm University, SE-10691 Stockholm, Sweden 2Department of Chemistry – Ångström Laboratory, Uppsala University, SE-75236 Uppsala, Sweden 3Department of Physics, Umeå University, SE-90187 Umeå, Sweden 4Chemical and Engineering Materials Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA 5Department of Chemistry, Federal University of Juiz de Fora, Juiz de Fora-MG, 36036-900, Brazil

SUPPLEMENTAL MATERIAL

This manuscript comprises several experiments on Xe and Ar clathrate hydrates run at the Spallation

Neutron Source (SNS)/Oak Ridge National Laboratory (ORNL), USA. Some samples contained ice (Ih) from the synthesis. Also lead was added to selected samples as pressure marker. The following text lists all experiments, their pathways and keystones.

A. Xe hydrate experiments (XH)

XH1. IPTS-18819.1 (19% Xe hydrate, 69% Lead, 12% Ice Ih)*1 Compression at 95 K, 20 bar/h up to 4.52(5) GPa. Small amounts of ice IX’†2(3%) were observed between

0.53(2) GPa and ~1 GPa, also coexisting with amorphous ice. Ice Ih was last observed at 0.73(3) GPa and became amorphous above this pressure before recrystallizing as ice VIII’ above 2.34(2) GPa. Xe hydrate became amorphous above 3.63(4) GPa.

XH2. IPTS-18819.2 Loading 1 (Xe hydrate, 11% Ice Ih) Compression at 95 K, 200 bar/h up to complete amorphization of the Xe hydrate phase (Fig. 4(a), main text). From the equation of state for ice VIII,1 the final pressure was estimated as 4.8 GPa. Xe hydrate amorphization was observed above 3.8 GPa. The sample was further compressed to ~8 GPa, at which pressure solid Xe (ccp) was observed forming with ice VIII’.

XH3. IPTS-18819.2 Loading 2 (Xe hydrate, 9% Ice Ih) Compression at 95 K, 650 bar/h up to complete amorphization of the Xe hydrate phase. Pressure at the last step estimated as 5.11 GPa. Decompression to atmospheric pressure lead to the recovery of ice VII and recrystallization of Xe hydrate. Heating to 150 K caused ice VII to transform into ice Isd, with final composition of 87% Xe hydrate and 13% ice Isd.

XH4. IPTS-20563 (22% Xe hydrate, 67% Lead, 11% Ice Ih) Compression at 95 K, 150 bar/h to 4.87(6) GPa. Amorphization of ice observed above 1.04(3) GPa. Small fraction of ice IX’ detected at 1.21(3) GPa and ice XV’ at 1.85(3) GPa. Recrystallization of ice VIII’ observed above 2.76(3) GPa. Amorphization of Xe hydrate observed above 3.87(5) GPa. Heating to 170 K, then cooling back to 95 K. Decompression to 0.41(7) GPa at 95 K, leading to the recovery of ice VII and recrystallization of Xe hydrate. Heating of the recovered sample lead to the transition sequence: recovered ice VII to IX’ (120 K), II (140 K), Ic (170 K) and Ih (200 K). Table S1 presents the complete change in sample composition with temperature at 0.4 GPa. Ice content was virtually unchanged (initial 33%, final 35%).

XH5. IPTS-21975 (31.4% Xe hydrate, 58.7% Lead, 9.9% Ice Ih) Compression at 95 K, 400 bar/h until full amorphization of the Xe hydrate phase at ~4 GPa. Ice VIII’ was observed at 2.67(26) GPa. Slow decompression lead to the recrystallization of Xe hydrate. Highly strained crystalline peaks were already observed at 3.41(8) GPa. The sample was slowly decompressed to 2.49(6) GPa and then heated to 170 K (Figure S1) and cooled back to 95 K, with no change observed in the hydrate phase. Pressure was released to 0.48(9) GPa, recovering crystalline Xe hydrate and ice VII. Ice content was virtually unchanged.

* Compositions are shown in w/w percent. † The observed diffraction pattern fits the assigned phase. The prime symbol indicates that the degree of proton ordering may vary.

1 B. Ar hydrate experiments (AH)

AH1. IPTS-18412.2 (Ar hydrate, 11.8% Ice Ih) Compression at 95 K, 10 bar/h until amorphization above 1.3 GPa (pressure estimated from Ar hydrate’s equation of state, see main text). Ice Ih observed completely amorphous at 1.1 GPa.

AH2. IPTS-18819 (44.9% Ar hydrate, 34% Lead, 21.1% Ice Ih) Compression at 95 K, 30 bar/h to 2.60(14) GPa. The Ar hydrate phase became fully amorphous above

1.41(23) GPa. Starting at 1.06(26) GPa, ice Ih fully converted to ice IX’ and to ice VIII’ above 2.00(15) GPa, without forming HDA ice. AH3. Title: IPTS-20563 Loading 1 (Ar hydrate, 50.7% Lead) Compression at 95 K, 300 bar/h to 3.15(16) GPa. Ar hydrate became amorphous above 1.34(10) GPa. Heating to 170 K at 1.3 GPa, cooled back to 95 K and recovered both amorphous ice and amorphous Ar hydrate to atmospheric pressure. On heating to 200 K at atmospheric pressure, Ar hydrate recrystallized at

120 K and decomposed into ice Ih and Ar (gas) at 150 K. AH4. IPTS-20563 Loading 2 (36Ar hydrate, 75% Lead) Compression at 95 K, 300 bar/h to 2.02(7) GPa. Ar hydrate became amorphous above 1.45(17) GPa. Heating to 170 K, cooled back to 95 K and recovered both amorphous ice and amorphous Ar hydrate to atmospheric pressure. AH5. IPTS-20563 Loading 3 (Ar hydrate, 64.7% Lead) Compression at 95 K, 300 bar/h to 1.88(4) GPa (Fig. 4(b), main text). Ar hydrate became amorphous above 1.47(4) GPa. Heating to 170 K, cooled back to 95 K and recovered both amorphous ice and amorphous Ar hydrate to atmospheric pressure.

References

1. Klotz, S. et al. Bulk moduli and equations of state of ice VII and ice VIII. Phys. Rev. B 95, 174111 (2017).

2 Table I. Changing composition of crystalline fraction upon heating the recovered sample XH5 at ~0.4 GPa a b T (K) steel Xe hydrate lead ice Ih ice Ic ice II ice IX’ Ice VIII’ 95 3.4% 14.1% 70.3% - - - - 12.2% 110 3.6% 14.7% 69.8% - - - - 11.9% 120 3.2% 14.0% 71.7% - - - 1.2% 9.9% 130 1.6% 16.1% 71.7% 0.0% 0.0% 0.9% 6.7% 3.0% 140 - 16.7% 72.0% 0.3% 0.5% 3.4% 7.1% - 150 - 16.7% 71.9% 0.3% 0.6% 7.6% 2.9% - 160 - 17.9% 70.7% 0.6% 0.7% 10.1% - - 170 - 17.9% 71.0% 0.5% 0.7% 9.9% - - 180 - 18.2% 70.8% 0.8% 0.9% 9.3% - - 190 - 18.2% 71.0% 1.4% 0.9% 8.5% - - 200 - 17.7% 72.5% 1.6% 1.0% 7.2% - - 210 - 18.0% 72.1% 5.6% 0.6% 3.7% - - 220 - 16.9% 74.0% 9.1% 0.0% 0.0% - - aSteel from the anvil material. b Stacking disorder ice, ice Isd, observed in diffraction as a mixture of hexagonal ice and cubic ice.

Table II. Changing composition of crystalline fraction upon heating the recovered sample AH5 at atmospheric pressure

T (K) Ar hydrate lead ice Ih ice Ic 95 0.0%a 100% - - 120 6.9% 93.1% - - 130 14.5% 85.5% - - 140 20.8% 78.4% - 0.8% 150 22.7% 74.4% 0.0% 2.9% 160 22.3% 68.6% 4.3% 4.8% 170 27.0% 63.6% 4.6% 4.8% 180 27.7% 62.4% 5.9% 4.1% 190 27.7% 61.5% 7.7% 3.0% 200 29.7% 56.4% 13.4% 0.6% aThe recovered Ar hydrate is in an amorphous state at 95 K, and the Bragg diffraction peaks observed are 100% from lead, whereas amorphous Ar hydrate contributes only with diffuse scattering.

Figure S1. NPD patterns measured on decompression and resurging of crystalline features back from an amorphous state. Asterisk marks lead peaks; lead was added to the sample for pressure marking. Cross marks peak from ice (111 reflection of ice VII or 112 reflection of ice VIII).

Figure S2. Structure section from MD snaphots comparing (a) Xe hydrate and (b) Ar hydrate at different pressures.