Combined Experimental and Theoretical Studies: Lattice-Dynamical Studies at High Pressures with the Help of Ab Initio Calculations

Abstract

Lattice dynamics studies are important for the proper characterization of materials, since these studies provide information on the structure and chemistry of materials via their vibrational properties. These studies are complementary to structural characterization, usually by means of electron, neutron, or X-ray diffraction measurements. In particular, Raman scattering and infrared absorption measurements are very powerful, and are the most common and easy techniques to obtain information on the vibrational modes at the Brillouin zone center. Unfortunately, many materials, like most minerals, cannot be obtained in a single crystal form, and one cannot play with the different scattering geometries in order to make a complete characterization of the Raman scattering tensor of the material. For this reason, the vibrational properties of many materials, some of them known for millennia, are poorly known even under room conditions. In this paper, we show that, although it seems contradictory, the combination of experimental and theoretical studies, like Raman scattering experiments conducted at high pressure and ab initio calculations, is of great help to obtain information on the vibrational properties of materials at different pressures, including at room pressure. The present paper does not include new experimental or computational results. Its focus is on stressing the importance of combined experimental and computational approaches to understand materials properties. For this purpose, we show examples of materials already studied in different fields, including some hot topic areas such as phase change materials, thermoelectric materials, topological insulators, and new subjects as metavalent bonding.

Revisiting the Nature of Chemical Bonding in Chalcogenides to Explain and Design their Properties

“…Furthermore, metavalent bonding has been employed to explain the broadening of Raman lines with increasing temperature in GeTe [130] and in amorphous Sb 2 Se 3 , where the emergence of a superconducting phase has been attributed to it. The role of metavalent bonding in high pressure dynamical studies is reviewed in reference [131] using theoretical and experimental data.…”

High-Pressure Synthesis of β- and α-In2Se3-Like Structures in Ga2S3

“…At this point, we want to mention that a nice way to distinguish between centrosymmetric and noncentrosymmetric structures is by means of RS measurements, especially when analyzed together with lattice dynamics calculations . Usually, noncentrosymmetric structures lead to a larger number of Raman-active modes than centrosymmetric structures, as has been shown for the R 3 m and R -3 m phases of Ga 2 S 3 in the previous section and in In 2 Se 3 .…”

Crystal Structure Prediction and Lattice Dynamical Calculations for the Rare Platinum-Group Mineral Zaccariniite (RhNiAs)

“…The latter can then be used to confirm the correctness of the predicted structure by means of conventional Raman scattering experiments, which are typically less involved than other analytical tools. In addition, following the recent Gedankenexperimente of Manjón et al [27], high-pressure Raman measurements might be used to properly assign the phonon modes of the mineral, just by comparing the experimental results with theoretical phonon frequencies as a function of pressure. This method, applied by Manjón and collaborators over the last few years to many different material systems [27], might provide further confirmation regarding the correctness of the crystal structure predictions of USPEX.…”

“…An alternative means of identifying the nature of zone-center phonon modes in materials has been recently outlined by Manjón et al [27]. These authors have stressed that, as in the cases of many rare minerals, such as zaccariniite, a large number of materials cannot be obtained in a single-crystal form, and, therefore, it is not possible to correctly identify their Raman spectra by polarization-dependent Raman measurements.…”

“…In the case of rare minerals, such as zaccariniite, once the crystal structure has been inferred from the USPEX computations, it is clear that the joint theoretical and experimental method proposed by Manjón et al [27] would allow one to further support the results of the crystal structure predictions. With regards to this, it should be mentioned that high-pressure Raman measurements involve microsamples similar to those found in PGMs, which should be loaded into a diamond anvil cell (DAC) and measured using a micro-Raman setup.…”