Negative compressibility of selenium chains confined in the channels of AlPO₄-5 single crystals

Abstract

Pressure induced structural and electronic transitions of Se helical chains confined inside nano-channels are studied. Raman scattering and optical absorption experiments show strong evidence of band gap reduction under high pressure. Ab initio calculations reveal that under hydrostatic compression, the Se chains should elongate and the change in morphology leads to a softening of phonons and narrowing of band gaps, and these signatures are observed in experiments. Our investigation demonstrates a negative compressibility in one dimension.Selenium is a group VI non-metallic element with a band gap of about 2 eV at ambient pressure. To realize metallization for bulk selenium with a concomitant structural phase transition, a large pressure up to tens of GPa is necessary 1-3 . Such phase transition phenomena of polycrystalline selenium have been observed at very high pressures by in situ Raman and X-ray diffraction. The metallization 4 and anomalous liner expansion coefficient under 20 GPa pressure 5 have been examined for crystalline selenium using density functional calculations. Here, we investigate the property of a single Se chain under pressure and we demonstrate that a much lower pressure is sufficient to induce detectable changes in the properties of a confined Se chains inside nano-channels. The pressure induced structural and electronic changes of Selenium chains confined in zeolite channels are studied using Raman spectroscopy and optical absorption spectra, and the results hint at a trend towards metallization as we increase the pressure. Such changes are interpreted using density functional theory (DFT) calculations. The calculations focus on understanding the hydrostatic pressures effect applied on the single trigonal helical

Silver Oxalate: Mechanical Properties and Extreme Negative Mechanical Phenomena

“…The crystal structure and mechanical properties of silver oxalate were determined using first principles solid‐state methods. The description of solid‐state crystalline compounds using computational modelling techniques is sufficiently advanced nowadays to predict their mechanical properties in good agreement with experimental measurements . The present computations were carried out separately with several different sets of calculation parameters associated to increasingly more demanding computations and the analysis of the convergence of the calculated crystal structures, associated energies, and properties showed that they were nearly converged with respect to the calculation parameters.…”

Negative linear compressibility from rotating rigid units

“…Negative linear compressibility (NLC) is the anomalous property of expanding in one direction when a compressive hydrostatic pressure is applied. A few materials have been reported in literature to exhibit NLC . It has also been predicted by means of DFT simulations or ab initio calculations in platinum sulfide , some zeolites and metal‐organic frameworks (MOFs) .…”

Thermodynamics of substances with negative thermal expansion and negative compressibility

“…Recently, substances with negative isothermal compressibility β were discovered [11][12][13][14][15][16][17]. For them, from Eqs.…”