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Instruments / Technical Area	Publication Details	Published
I15-Extreme Conditions	Gold(I) sulfide: unusual bonding and an unexpected computational challenge in a simple solid D. Santamaria-Perez , D. Daisenberger , J. Ruiz-Fuertes , T. Marqueno , R. Chulia-Jordan , C. Muehle , M. Jansen , P. Rodriguez-Hernandez , A. Muñoz , Erin R. Johnson , A. Otero-De-La-Roza Chemical Science DOI: 10.1039/C9SC00371A Diamond Proposal Number(s): [16212] Open Access Show Abstract ▼ Abstract: We report the experimental high-pressure crystal structure and equation of state of gold(I) sulfide (Au2S) determined using diamond-anvil cell synchrotron X-ray diffraction. Our data shows that Au2S has a simple cubic structure with six atoms in the unit cell (four Au in linear, and two S in tetrahedral, coordination), no internal degrees of freedom, and relatively low bulk modulus. Despite its structural simplicity, Au2S displays very unusual chemical bonding. The very similar and relatively high electronegativities of Au and S rule out any significant metallic or ionic character. Using a simple valence bond (Lewis) model, we argue that the Au2S crystal possesses two different types of covalent bonds: dative and shared. These bonds are distributed in such a way that each Au atom engages in one bond of each kind. The multiple arrangements in space of dative and shared bonds are degenerate, and the multiplicity of configurations imparts the system with multireference character, which is highly unusual for an extended solid. The other striking feature of this system is that common computational (DFT) methods fail quite spectacularly to describe it, with 20% and 400% errors in the equilibrium volume and bulk modulus, respectively. We explain this by the poor treatment of static correlation in common density-functional approximations. The fact that the solid is structurally very simple, yet presents unique chemical bonding and is unmodelable using current DFT methods, makes it an interesting case study and a computational challenge.	May 2019
I15-Extreme Conditions	Dense post-barite-type polymorph of PbSo4 anglesite at high pressures David Santamaria Perez , Raquel Chulia-Jordan , Dominik Daisenberger , Placida Rodriguez-Hernandez , Alfonso Muñoz Inorganic Chemistry DOI: 10.1021/acs.inorgchem.8b03254 Diamond Proposal Number(s): [21356] Show Abstract ▼ Abstract: Synchrotron X-ray diffraction measurements on lead sulfate have been performed up to 67 GPa using He as pressure transmitting medium. Experiments reveal the existence of a reversible pressure-induced phase transition from the initial Pnma barite-type to the P212121 post-barite-type structure at pressures above 27 GPa. This phase transition involves a volume collapse of 2.4% and requires a considerable pressure overshoot (large pressure range with coexistence of phases) to overcome the large kinetic barrier of the transition. DFT calculations confirm the experimental observations and support the hypothesis that post-barite-type phase is the thermodynamically stable high-pressure structure for ABO4 ternary oxides with large A and small B atoms. The mechanism of the phase transition is described, and the compressibility and anisotropy of both polymorphs are estimated.	Feb 2019
	Structural evolution of CO2-filled pure silica LTA zeolite under high-pressure high-temperature conditions David Santamaria Perez , Tomas Marqueño , Simon Macleod , Javier Ruiz-Fuertes , Dominik Daisenberger , Raquel Chulia-Jordan , Daniel Errandonea , Jose Luis Jorda , Fernando Rey , Chris Mcguire , Adam Makhluf , Abby Kavner , Catalin Popescu Chemistry Of Materials DOI: 10.1021/acs.chemmater.7b01158 Show Abstract ▼ Abstract: The crystal structure of CO2-filled pure-SiO2 LTA zeolite has been studied at high pressures and temperatures using synchrotron-based x-ray powder diffraction. Its structure consists of 13 CO2 guest molecules, 12 of them accommodated in the large α-cages and 1 in the β-cages, giving a SiO2:CO2 stoichiometric ratio smaller than 2. The structure remains stable under pressure up to 20 GPa with a slight pressure-dependent rhombohedral distortion, indicating that pressure-induced amorphization is prevented by the insertion of guest species in this open framework. The ambient-temperature lattice compressibility has been determined. In situ high-pressure resistive-heating experiments up to 750 K allow us to estimate the thermal expansivity at P~5 GPa. Our data confirm that the insertion of CO2 reverses the negative thermal expansion of the empty zeolite structure. No evidence of any chemical reaction was observed. The possibility of synthesizing a silicon carbonate at high temperatures and higher pressures is discussed in terms of the evolution of C – O and Si – O distances between molecular and framework atoms.	May 2017

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