High-pressure phase transitions in diamondoid molecular crystals observed by in situ Raman spectroscopy
At a Glance
Section titled āAt a Glanceā| Metadata | Details |
|---|---|
| Publication Date | 2023-08-22 |
| Journal | Acta Crystallographica Section A Foundations and Advances |
| Authors | Hendrik Heimes, J. E. Bradby |
| Institutions | Australian National University |
Abstract
Section titled āAbstractāDue to their structural similarities with diamond (C), diamondoids are promising candidates for high-pressure, high-temperature synthesis of cubic and hexagonal nanodiamonds [1].Functionalised diamondoids can be used as a precursor material for the synthesis of nanodiamonds with desirable physical properties such as fluorescence [2].Four types of diamondoids, adamantane (C10H16), diamantane (C14H20), triamantane (C18H24), and tetramantane (C22H28) were studied with Raman spectroscopy using 533 nm unpolarized laser radiation.Experiments under high-pressure conditions up to 50 GPa were carried out in diamond anvil cells (DACs).Raman spectra at ambient conditions were compared with calculated spectra.The calculation was performed with density functional theory (DFT), using a DEF2-SVP basis set and the B3LYP hybrid functional.Although all investigated samples are crystalline, the simulation of Raman modes based on a single molecule yields accurate representations of Raman spectra (see Figure 1 a).The samples undergo phase transformations under elevated pressure, associated with changes in their Raman spectra as several new Raman modes emerge under compression as can be seen in Figure 1 b, associated with a symmetry reduction of the molecule.These phase transformations are fully reversible and the samples possess a sponge-like rebound after decompression.Future work will include in situ high-pressure neutron-diffraction methods to determine the precise crystal structures of the compounds.Furthermore, the samples will be studied with in situ Raman spectroscopy at high-pressures and hightemperatures using heated DACs to investigate the reaction to pure carbon phases such as cubic or hexagonal diamond.Figure 1.a) Phase transitions in adamantane and diamantane detected through emerging peaks upon increasing pressure.Calculated and experimental spectra of four different diamondoid molecule crystals.