Experimental and theoretical crystal-chemistry dataset of bulk orpiment As2S3
Description
The present dataset contains the results of the analysis of crystalline As2S3, whose mineralogical name is orpiment. The data were obtained from experimental characterisation of a natural sample of very high purity, and corroborated by ab initio Density Functional Theory (DFT) simulations. The dataset is organised as follows: 1) the Experimental folder contains the results from: a. Environmental Scanning Electron Microscopy ('ESEM' folder) imaging of the exfoliated sample, with several pictures of the sample; b. Confocal Raman microspectrometry ('Raman' folder), whose data comprises images of the samples and the associated spectra in text format (each spectrum has a second file that describes the conditions of its acquisition); c. X-ray diffraction ('XRD' folder), which contains the diffractogram collected for the powdered sample; 2) the Theoretical folder contains: a. the CIF files (Crystallographic Interchange Format) of the orpiment model optimized within the HSE06-D3 and B3LYP-D3 approaches; b. the Raman and infrared spectra calculated at the B3LYP-D3 level of theory; c. the electronic band structure of the mineral obtained with the HSE06-D3 method, with a Python3 script that was used to create the image reported in the folder; d. the elastic moduli in Voigt's notation and the mineral density in kg/m^3 of orpiment calculated using the B3LYP-D3 approach. The experiments were carried out using: - a Thermo Fisher Quattro S ESEM with field-emission gun (FEG) source, equipped with low-vacuum secondary electrons detector, angular back-scattered electron detector and energy dispersive spectroscopy (EDS) X-ray microanalysis; - a WITec Alpha 300 confocal Raman micro-spectrometer equipped with 532 nm and 785 nm lasers; - a Philips PW 1710 X-ray diffractometer (XRD). Theoretical simulations were performed using the CRYSTAL23 code (https://www.crystal.unito.it).
Files
Steps to reproduce
Preparation of the orpiment samples: A portion of the As2S3 orpiment sample (polycrystalline specimen) was ground to a fine powder before the subsequent analyses. At the same time, orpiment flakes from several nanometres up to a few micrometres thick were carefully separated by mechanical means, and deposited on aluminium stubs. X-ray powder diffraction: X-ray powder diffraction (XRPD) patterns were collected using a Philips PW 1710 diffractometer equipped with a graphite monochromator on the diffracted beam. Cu Kα X-rays were generated with 40 kV and 30 mA of power supply. The patterns were collected between 3° and 70° 2θ, with an angular step of 0.02° and integration time of 2 seconds. The specimen was ground for 20 minutes in an agate mortar and the powders were collected in a lateral-loading holder to avoid or minimize any possible preferential orientation of the crystallites. The diffractograms were analysed with the computer program Profex (https://www.profex-xrd.org/) which interfaces the BGMN program and was used for the Rietveld refinement within the fundamental parameters approach. Environmental Scanning Electron Microscopy: A Thermo Scientific Quattro S Environmental Scanning Electron Microscopy (ESEM) with field-emission gun, equipped with backscattered electron (BS), cathodoluminescence (CL) detectors and X-ray microanalysis with silicon-drift detector (SDD-EDS) was employed to study the morphology and local chemistry of the orpiment sample. After careful calibration, the ESEM analyses were carried out in low vacuum conditions, with 100 Pa of water vapour pressure inside the instrument chamber, an acceleration voltage of 15 kV and a beam current of 0.43 nA. Within these instrumental settings, no conductive coating was needed, obtaining an adequate compromise between imaging resolution and EDS chemical sensitivity. Confocal Raman microspectrometry: The Raman spectroscopy analysis was performed with a WITec alpha300R confocal Raman microscopy system, made of an optical microscope and an ultra-high throughput UHTS 300 VIS spectrometer with CCD camera and gratings of 600 g/mm. Green (532 nm) and red (785 nm) laser beam sources were used for the Raman excitation, setting the power between 1 mW (green laser) and 30 mW (red laser) to prevent heating the sample and photobleaching. The laser beam was focused on the sample with 20×, 50× and 100× Zeiss microscope objectives with a low numerical aperture objective (NA = 0.40) to avoid optical artefacts. The backscattered Raman spectra were collected in confocal mode between 100 and 1700 cm–1, with a resolution of about 2.7 cm–1 and an acquisition time of 10 minutes. The Rayleigh scattering line was removed by an edge filter.
Institutions
- Universita degli Studi di Bologna Dipartimento di Scienze Biologiche Geologiche ed Ambientali