Structures of the Low-Temperature CDW and long rang ordering in Uranium

Electron-deficiency multicenter bonding (EDMB) has been proposed as an incipient, novel chemical bond behind the outstanding properties of promising materials as phase change materials, thermoelectrics, photovoltaic materials and topological insulators. High pressure (HP) can easily induced such EDMB in systems with stereochemically active lone electron pairs (SCALEPs). As we have evidenced for the mixed-valence Sn2S3, XAS has been proved to be an essential technique to unveil these EDMBs, in addition to single-crystal XRD and Raman spectroscopy under HP. This project aims to demonstrate how XAS can be used the emergence of these bonds in other Sn-based chalcogenides. Then, we propose to collect Sn K-edge XAS measurements on SnTe (without SCALEPs), SnSe and Sn3O4 (both with SCALEPs) under HP, up to 50 GPa, to undoubtedly propose the XAS technique as alternative tool to follow the emergence of EDMBs

Transition metal molybdates, such as NiMoO₄ and CoMoO₄, exhibit diverse functionalities in energy storage, catalysis, and spintronics due to their tunable electronic and magnetic properties. Both molybdates undergo a transition to an antiferromagnetic state at low temperatures. Despite their importance as multifunctional materials, their high pressure-low temperature (HP-LT) structural phase diagram remains unknown. Recent high-pressure single-crystal X-ray diffraction (HP SCXRD) studies on α-NiMoO₄ at room temperature (RT) suggest a possible structural transition near 15 GPa. This proposal aims to extend these investigations using HP SCXRD at both RT and LT to explore structural changes linked to magnetic ordering. By comparing the effects of Ni and Co substitution, we seek to establish key structure-property correlations. The findings will offer insights into pressure-induced phase transitions, magneto-structural interactions, and material stability under extreme conditions.

HERCULES practicals: Crystallography in a diamond anvil cell

Elemental Ge is one of the archetypal single component substances extensively studied over the years for exploring the behavior of liquid-liquid transitions. Nevertheless, the low-density semiconducting liquid observed in computer simulations yet to be experimentally observed for non-ambiguous interpretations of the properties of the liquid and as well as the nature of amorphous-amorphous transition w(which is believed to be thermodynamically linked with the transition in the liquid). The stable liquid above the melting line, on the other hand, is expected to be more closely packed (with enhanced metallic bonding) under high pressure. We aim to study the local structure and bonding characteristics of liquid Ge under extended pressure and temperature ranges by means of XAS measurements under shock compression. Expected results will have strong implications for understanding the liquid phases of simple covalent substances (like Si and others) under extreme conditions.

In this project, we aim to probe the lattice dynamics of RbCuBr3 under high-pressure conditions at ID15B.

Perovskite structures can be easily adapted not only by inorganic compositions, but by organic groups as well. In this proposal we aim to explore the pressure behaviour of double perovskite Sr2FeMoO6 and metal-organic perovskite ACuX3, in which A = [C(NH2)3] is guanidinium and X is the formate [HCOO]. Our aim is twice: evaluate the spin crossover in Sr2FeMoO6 up 50 GPa via powder XRD, and the pressure tuning of [C(NH2)3] and [HCOO] groups within ACuX3 system via single-crystal XRD.

Niobium (Nb) exhibits a remarkable high thermal stability and electronic properties. Despite its multiple applications in our modern industry, large uncertainties remain on its phase diagram including its high-pressure melting temperature and solid-solid phase transitions. To better understand the structural and electronic changes in Nb at relevant P/T conditions, we propose in this project to use time-resolved pulsed laser heating nano-XAS/XRD studies at the new ID24-DCM and ID27 beamlines of the ESRF-EBS, which may allow overcoming previous reported experimental limitations. The yet poorly explored electronic properties of pure Nb at extreme conditions could be of critical importance for potential new applications and industrial uses.

This proposal focuses on the study of High Entropy Carbides (HECs), a class of advanced ceramics with expected unique properties under high-temperature (HT) conditions. Six HECs with five equimolar transition metals from IVB (Ti, Zr, Hf) and VB (V, Nb, Ta) groups will be investigated using High-Resolution Powder X-Ray Diffraction, up to 1600 ºC. The research aims to assess HECs stability, phase transformations, phase segregations, and crystalline structure distortions. It will leverage synchrotron radiation techniques to provide critical insights on the behaviour of HECs under harsh conditions, advancing their applicability in various industries. Specifically, these findings may have implications for nuclear fusion reactors as Plasma Facing Materials (PFMs) due to their HT stability and radiation resistance. In addition, the results give us information for the HECs potential significant applications as Thermal Barrier Coatings (TBCs) in the aerospace and solar power plant industries.

This research proposal is dedicated to exploring the structural properties of Eu–Zn–As Zintl Pnictides (ZPs) under high-pressure (HP) conditions. The impact of HP on the structure and properties of these perspective quantum materials is poorly studied, although HP is often used to prepare bulk thermoelectric and to improve transport properties of materials.We propose to investigate following unreported yet ZPs within Eu–Zn–As phase space with different dimensionalities of polyanionic frameworks: Eu17Zn5As18 (0D), Eu3Zn2As4 (1D), and β-Eu2ZnAs2 (1D) and α-Eu2ZnAs2 (0D) under pressures up to 50 GPa. Single-crystal X-ray diffraction (SCXRD) studies under hydrostatic pressure will help us to provide insight into tunability mechanism within Zintl polyanionic frameworks of different dimensionalities under hydrostatic pressures. Followed by the physical property measurements, we aim to establish structure-property relationships necessary for designing novel quantum materials.