Publications by Richard Gaal | EPFL Graph Search

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Hydrogen hydrates (HH) are a unique class of materials composed of hydrogen molecules confined within crystalline water frameworks. Among their multiple phases, the filled ice structures, particularly the cubic C2 phase, exhibit exceptionally strong host–guest interactions due to ultra-short H 2 -H 2 O distances and a 1:1 stoichiometry leading to two interpenetrated identical diamond-like sublattices, one comprised of water molecules, the other of hydrogen molecules. At high pressures, nuclear-quantum effec

Methane, the principal component of natural gas, is an important energy source and raw material for chemical reactions. It also plays a significant role in planetary physics, being one of the major constituents of giant planets. Here, we report measurement ...

Ammonium fluoride (NH₄F) exhibits a variety of crystalline phases depending on temperature and pressure. By employing Raman spectroscopy and synchrotron X-ray diffraction beyond megabar pressures (up to 140 GPa), we have here observed a novel dense solid p ...

Nitrogen, Earth’s most abundant atmospheric component, in the presence of water, is known to form clathrate hydrates, that are relevant to model the evolution of water-rich planets and satellites. Here, we map the high-pressure phase diagram of nitrogen hydrate up to 16 GPa at room temperature by combining neutron diffraction, Raman spectroscopy, and crystal structure prediction. We reveal a rich sequence of structural transformations, from sI/sII clathrates to hexagonal (sH) and tetragonal (sT) phases, cul

Hydrogen hydrates, formed from hydrogen and water under high-pressure and low-temperature conditions, exhibit a rich phase behavior governed by intricate intermolecular interactions. Their structural evolution under extreme conditions provides a unique pla ...

Water is the third most abundant molecule in the universe and a key component in the interiors of icy moons, giant planets and Uranus- and Neptune-like exoplanets1, 2–3. Owing to its distinct molecular structure and flexible hydrogen bonds that readily ada ...

The structure of amorphous NaCl solutions produced by fast quenching is studied as a function of pressure, up to 4 GPa, by combined neutron diffraction experiments and classical molecular dynamics simulations. Similarly to LiCl solutions the system amorphizes at ambient pressure in a dense phase structurally similar to the e-HDA phase in pure water. The measurement of the static structure factor as a function of pressure allowed us to validate a new polarizable force field developed by Tazi et al., 2012, ne

We report pressure-induced metallization in BaMn 2 P 2 based on resistivity measurements in a diamond anvil cell. At ambient pressure, the temperature-dependent resistivity is well described by a two-gap Arrhenius model, yielding intrinsic and extrinsic activation energies of approximately 0.2 and 0.04 eV, respectively. Angle-resolved photoemission spectroscopy (ARPES) shows no detectable spectral weight at the Fermi level within the measured momentum window. The growth of spectral weight at higher binding

Optical tweezers are commonly used and powerful tools to perform force measurements on the piconewton scale and to detect nanometer-scaled displacements. However, the precision of these instruments relies to a great extent on the accuracy of the calibratio ...

The temperature dependent resistivity and thermo-electric power of Cr-N codoped TiO2 were compared with that of single element N and Cr doped and undoped TiO2 using epitaxial anatase thin films grown by pulsed laser deposition on (100) LaAlO3 substrates. T ...

Hydrogen hydrates are among the basic constituents of our solar system's outer planets, some of their moons, as well Neptune-like exo-planets. The details of their high-pressure phases and their thermodynamic conditions of formation and stability are funda ...

It is generally accepted that nuclear quantum effects (NQEs) trigger the transition to the nonmolecular form of ice under increasing pressure. This picture is challenged in salty ice, where Raman scattering measurements up to 130 GPa of molecular ice VII c ...

Millimeter-sized cobalt doped rutile crystals with a bi-pyramidal shape are obtained by chemical vapour transport using scroll-type H2Ti3O7 nanotubes as a precursor in which Co2+ ions are introduced by a simple ion exchange method prior to the growth. Desp ...

Time-resolved x-ray absorption experiments have been performed on shocked tantalum. Using a single 100 ps synchrotron x-ray pulse, nanosecond-lived equilibrium states of shocked solid Ta have been measured by L-3-edge absorption spectroscopy. The energy sh ...

Gas hydrates consist of hydrogen-bonded water frameworks enclosing guest gas molecules and have been the focus of intense research for almost 40 y, both for their fundamental role in the understanding of hydrophobic interactions and for gas storage and ene ...

Hydrogen clathrate hydrates are ice-like crystalline substances in which hydrogen molecules are trapped inside polyhedral cages formed by the water molecules. Small cages can host only a single H-2 molecule, while each large cage can be occupied by up to f ...

Hydrogen hydrates exhibit a rich phase diagram influenced by both pressure and temperature, with the so-called C2 phase emerging prominently above 2.5 GPa. In this phase, hydrogen molecules are densely packed within a cubic icelike lattice and the interact ...

We present a new method of Ba2MgWO6 single crystal synthesis that allows to grow larger crystals using a BaCl2 and MgCl2 flux. Difficulties to grow single crystals of a size suitable for macroscopic material property measurements caused the majority of cha ...

We present an extensive study of the quantum dynamics of molecular hydrogen trapped within the nanocavities of two hydrate structures at low temperatures, namely, clathrate structure II and filled ice structure Cl. By inelastic neutron scattering measureme ...

The infrared reflectance of the transition-metal chalcogenide 1T-TaS2 has been measured at temperatures from 30 K to 360 K over 30-45 000 cm(-1) (4 meV-5.5 eV). The optical conductivity was obtained by Kramers-Kronig analysis. At 360 K only modest traces of the phonon lines are noticeable. The phonon modes are followed by a pseudo-gap-like increase of the optical conductivity, with direct optical transitions observed at frequencies above 1 eV. As the temperature decreases, the low-frequency conductivity als

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Dual quantum locking: Dynamic coupling of H 2 and H 2 O sublattices in hydrogen-filled ice

Diffusion in dense supercritical methane from quasi-elastic neutron scattering measurements

Structural phase transition in NH₄F under extreme pressure conditions

Discovery of a low-density filled-ice phase in nitrogen hydrate at high pressure

Hydrogen Hydrates Under Extreme Conditions: Insights Into High-pressure Phases and Implications for Planetary Interiors

Observation of plastic ice VII by quasi-elastic neutron scattering

Structural characterization of eutectic aqueous NaCl solutions under variable temperature and pressure conditions

Pressure-driven metal-insulator transition in BaMn2⁢P2 : A correlated Mn-pnictide analog of Fe-based superconductors

Calibration of optical tweezers with non-spherical probes via high-resolution detection of Brownian motion

Electrical property measurements of Cr-N codoped TiO2 epitaxial thin films grown by pulsed laser deposition

Observation of the most H2-dense filled ice under high pressure

Quantum versus classical protons in pure and salty ice under pressure

From nanotubes to single crystals: Co doped TiO2

White-line evolution in shocked solid Ta evidenced by synchrotron x-ray absorption spectroscopy

Observation of methane filled hexagonal ice stable up to 150 GPa

Large-cage occupation and quantum dynamics of hydrogen molecules in sII clathrate hydrates

Giant Splitting of the Hydrogen Rotational Eigenenergies in the C2 Filled Ice

Structure, heat capacity and Raman spectra of Ba2MgWO6 single crystals grown in BaCl2-MgCl2 flux

Quantum Dynamics of H-2 and D-2 Confined in Hydrate Structures as a Function of Pressure and Temperature

Phonon anomaly at the charge ordering transition in 1T-TaS2