Structural, elastic and vibrational properties of celestite, SrSO₄, from synchrotron x-ray diffraction, thermal diffuse scattering and Raman scattering

Abstract

In order to resolve inconsistencies encountered in published data for SrSO4, the elasticity and the phase stability of celestite has been studied using thermal diffuse scattering, high pressure powder synchrotron X-ray diffraction, Raman scattering and DFT calculations. The structure of SrSO4 is found to be stable up to 62 GPa at ambient temperature. The preferred values for the components of the elastic stiffness tensor have been determined using X-ray thermal diffuse scattering and are (in GPa): c11 = 105, c22 = 92, c33 = 114, c44 = 16, c55 = 31, c66 = 26, c12 = 40, c13 = 52, c23 = 37. The preferred value for the bulk modulus is K=62(2) GPa. This work shows that thermal diffuse scattering collected at two temperatures allows the determination of the full elastic tensor of crystals with low space group symmetry.

Raman Study of Barite and Celestine at Various Temperatures

“…At temperatures above 450 • C, the peak becomes slightly asymmetric in shape and is more accurately fitted by a mixed Gaussian and Lorentzian curve (Figure 4). Although this splitting is not apparent at room temperature, Kloprogge et al [35] reported the splitting of the ν 1 band of celestine at 77 K and Girard et al [36] reported the appearance of a shoulder on the low wavenumber side of celestine with increasing pressure. The ν 3 bands of barite all show a systematic decrease in wavenumber with increasing temperature with the 1138 cm −1 band exhibiting a non-linear temperature dependence (Table 3).…”

Elastic stiffness coefficients of thiourea from thermal diffuse scattering

“…Ambient temperature is a good starting point, and 265 and 235 K can be easily reached by employing a nitrogen jet. The choice of a ÁT of 30 K was based on previous studies (Wehinger et al, 2017;Girard et al, 2019) where it was used successfully.…”

“…Further mathematical background is provided by e.g. Wehinger (2013), Wehinger et al (2017) or Girard et al (2019). We fitted the TDS data using the open-source package TDS2EL2 with the multitemperature approach (Wehinger et al, 2017).…”

“…6). We used 0.06 Å À1 as a lower limit on the basis of previous studies (Wehinger et al, 2017;Girard et al, 2019). We fitted several ROIs between 0.06 and 0.2 Å À1 to determine whether this change had noticeable consequences on the results of the fitting procedure.…”

“…The samples do not need to be transparent and small sample sizes (tens to hundreds of micrometres) are sufficient. Girard et al (2019) demonstrated that this approach can be used to obtain the tensor of an orthorhombic crystal. The purpose of the present study is to expand this approach to organic materials, where sometimes only small crystals unsuitable for many other methods, e.g.…”