High-pressure and temperature-induced structural, elastic, and thermodynamical properties of strontium chalcogenides

Abstract

Pressure-and temperature-dependent mechanical, elastic, and thermodynamical properties of rock salt to CsCl structures in semiconducting SrX (X = O, S, Se, and Te) chalcogenides are presented based on model interatomic interaction potential with emphasis on charge transfer interactions, covalency effect, and zero point energy effects apart from long-range Coulomb, short-range overlap repulsion extended and van der Waals interactions. The developed potential with non-central forces validates the Cauchy discrepancy among elastic constants. The volume collapse (V P /V 0 ) in terms of compressions in SrX at higher pressure indicates the mechanical stiffening of lattice. The expansion of SrX lattice is inferred from steep increase in V T /V 0 and is attributed to thermal softening of SrX lattice. We also present the results for the temperaturedependent behaviors of hardness, heat capacity, and thermal expansion coefficient. From the Pugh's ratio (/ = B T /G H ), the Poisson's ratio (m) and the Cauchy's pressure (C 12 -C 44 ), we classify SrO as ductile but SrS, SrSe, and SrTe are brittle material. To our knowledge these are the first quantitative theoretical prediction of the pressure and temperature dependence of mechanical stiffening, thermally softening, and brittle nature of SrX (X = O, S, Se, and Te) and still await experimental confirmations.

Anomalous Lattice Thermal Conductivity in Rocksalt IIA–VIA Compounds

“…Because all the studied MX (M = Mg, Ca, Sr, and Ba and X = O, S, Se, and Te) compounds crystallize in the cubic ( Fm 3̅ m ) structure, they have three independent elastic constants such as longitudinal ( C 11 ), transverse ( C 12 ), and shear ( C 44 ) due to symmetry constraints ( C 11 = C 22 = C 33 , C 12 = C 13 = C 23 , C 44 = C 55 = C 66 , and C ij = C ji ). The calculated second-order elastic constants are given in Table S4 and are consistent with the available ultrasonic pulse echo − and Brillouin scattering measurements as well as with previous first-principles calculations. ,,,− The obtained elastic constants satisfy the Born stability criteria indicating the mechanical stability of all these MX (M = Mg, Ca, Sr, and Ba and X = O, S, Se, and Te) compounds. We then computed bulk ( B ) and shear ( G ) moduli from the calculated elastic constants with Voigt–Reuss–Hill (VRH) approximation using eqs and , respectively. Later, the obtained B and G values are used to calculate Young’s modulus ( E ) using eq .…”

“…The MX (M = Mg, Ca, Sr, and Ba and X = O, S, Se, and Te) compounds are extensively studied from the theoretical perspective, which mainly focused on exploring the elastic, , lattice dynamics, − thermodynamic, , and thermoelectric properties − at ambient and/or high-pressure conditions. However, very limited studies have been dedicated toward understanding the phonon transport in MgSe, MgTe, CaX (X = O, S, Se, and Te) and MTe (M = Mg, Ca, Sr, Ba, and Pb) compounds.…”

Structural and physical properties of 99 complex bulk chalcogenides crystals using first-principles calculations

“…Another useful parameter is G/K or Pugh’s modulus ratio 67 , 68 . According to Pugh’s criterion, crystals with G/K larger than 0.57 are brittle, and those with less than 0.57 tend to be more ductile 68 – 71 . Figure 7 shows the scattered plot of G versus K for the 54 crystals in the first main group, while Fig.…”

A first-principles study of the electronic, mechanical, vibrational, and optical properties of the zirconium carbide under high pressure

“…The formulas to obtain these values can be found in many references [9,25]. The Pugh's and Poisson's ratios indicate the ductility and brittleness of a material [26]: Pugh's ratio values greater than 0.5 are linked to brittle materials, and lower values are linked to ductile materials [27][28][29]; the relevant values for the Poisson's ratio (ν) are those 0.33 for metals, while those from 0.16 to 0.30 are related to ionic-covalent compounds [27][28][29]. Vickers hardness (H V ) is a measure used to determine the hardness of a material [30], and the K, ν, and H V values can be obtained using:…”