Abstract
The complete elastic stiffness tensor of thiourea has been determined from thermal diffuse scattering (TDS) using high-energy photons (100 keV). Comparison with earlier data confirms a very good agreement of the tensor coefficients. In contrast with established methods to obtain elastic stiffness coefficients (e.g. Brillouin spectroscopy, inelastic X-ray or neutron scattering, ultrasound spectroscopy), their determination from TDS is faster, does not require large samples or intricate sample preparation, and is applicable to opaque crystals. Using high-energy photons extends the applicability of the TDS-based approach to organic compounds which would suffer from radiation damage at lower photon energies.
Highlights
The elastic stiffness tensor c describes how stress relates to strain
In our preliminary thermal diffuse scattering (TDS) experiments with 14 keV photons, we found that our organic samples suffered radiation damage after being exposed to the beam for just a few minutes
As expected from the RADDOSE calculations described above, our samples remained intact without any noticeable degradation of the scattering signal after being exposed to the Phonon dispersion relations of thiourea, calculated using density functional theory (DFT)
Summary
The elastic stiffness tensor c describes how stress relates to strain. It comprises at most 21 independent coefficients for a triclinic crystal, the cij coefficients (in Voigt notation), which are determined by the bonding system and the properties of the atoms (Fedorov, 1968). For INS, large samples (several cubic millimetres in size) are necessary, and for IXS, only a very few beamlines at synchrotron radiation facilities exist that allow the required high-resolution energy- and momentum-resolved measurements to be carried out. This method is both time consuming and experimentally challenging (Waeselmann et al, 2016)
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