Nowadays, there is a strong demand for renewable energies. Currently the cost of photovoltaic systems is one of the main obstacles preventing production and application on a large scale. The family of this material is relevant in many fields including optoelectronics, solar cells and non-linear optics that have attracted considerable attention in the last thirty years. In particular, CdAl2S4 is a promising thioalluminate semiconductor applicable to photonic devices in the blue spectral region.
The study has been published in The Journal of Physical Chemistry and it has been carried out by researchers from Universitat Politècnica de València, Universitat de València, University College London, MSPD beamline of the ALBA Synchrotron, Universidad de la Laguna (Tenerife) and Institute of Electronic Engineering and Nanotechnologies from Chisinau (Moldova).
Using ALBA's X-rays at the Materials Science and Powder Diffraction (MSPD) beamline, researchers performed diffraction experiments toanalyze the structural changes of CdAl2S4 under high pressure. In ambient conditions CdAl2S4 crystallizes in defect chalcopyrite structure (DC) that suffers an order-disorder transition above 15GPa of pressure, reaching a disordered-rocksalt structure (DR). In a downstroke from 25GPa to ambient pressure, CdAl2S4 does not return to initial DC phase. Researchers have discovered that CdAl2S4 partially retains DR phase and partially transforms to spinel structure. The observation of the spinel phase could appear rather surprising since it was showed that many compounds of this family retain the DR phase metastable at ambient pressure or undergo a phase transition to the disordered zincblende (DZ) structure.
The recovered phase in spinel structure has been confirmed with both experimental and theoretical calculations, which suggests that spinel and DC structures are competitive under ambient conditions. It means that CdAl2S4 is on the borderline between spinel and DC structures.
"Note that in this study the spinel structure was obtained after a high pressure treatment at ambient temperature. Therefore, this work suggests that the growth of the spinel phase of CdAl2S4 at near ambient temperature is possible having implications on phase diagram of these materials", according to Juan Ángel Sans, the main author.
Fig: Representation of the crystalline structures in CdAl2S4: DC, DR and spinel.
