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

Abstract

Quantum chemical bonding descriptors have recently been utilized to design materials with tailored properties. We will review their usage to facilitate a quantitative description of bonding in chalcogenides as well as the transition between different bonding mechanisms. More importantly, these descriptors will also be employed as property predictors for several important material characteristics, including optical and transport properties. Hence, these quantum chemical bonding descriptors can be utilized to tailor material properties of chalcogenides relevant for thermoelectrics, photovoltaics and phase change memories.Relating material properties to bonding mechanisms also shows that there is a class of materials, which are characterized by unconventional properties such as a pronounced anharmonicity, a large chemical bond polarizability, and strong optical absorption. This unusual property portfolio is attributed to a novel bonding mechanism, fundamentally different from ionic, metallic and covalent bonding, which has been called 'metavalent'. In the concluding chapter, a number of promising research directions are sketched, which explore the nature of the property changes upon changing bonding mechanism and extend the concept of quantum chemical property predictors to more complex compounds.

Doping by Design: Enhanced Thermoelectric Performance of GeSe Alloys Through Metavalent Bonding

“…[6,50] This unconventional combination of properties differentiates the corresponding chemical bonding mechanism from metallic, covalent, and ionic bonding and has thus coined metavalent bonding (MVB). [6,49,50,[57][58][59][60] Concerning thermoelectrics, this raises an important question: why can the TE performance of GeSe be effectively improved through alloying with MVB compounds but not by conventional elemental doping? Understanding this question could accelerate the discovery and design of high-performance TE materials.…”

Metavalent Bonding-Mediated Dual 6s2 Lone Pair Expression Leads to Intrinsic Lattice Shearing in n-Type TlBiSe2

“…A relatively novel type of bonding in solids coined as metavalent bonding promises to be effective for achieving intrinsically low κ latt and consequently excellent thermoelectric properties in heavy metal-based chalcogenides. − Materials with metavalent bonding have a unique descriptor profile comprising (a) a large effective coordination number violating the 8-N rule, (b) moderate electrical conductivities, (c) a large Grüneisen parameter for the transverse optical (TO) mode, (d) a high optical dielectric constant (electronic susceptibility), and (e) a large Born effective charge (chemical polarizability) . Consequently, metavalent bonding is a one-pot recipe for superior thermoelectric performance as it simultaneously tunes the electronic properties (by tailoring the band anisotropy and valley degeneracy) and the thermal transport (soft-bonding arising from p-electron deficiency, large anharmonicity, and propensity for atom off-centering) .…”

Strong charge carrier scattering at grain boundaries of PbTe caused by the collapse of metavalent bonding

“…S3. MVB is a fundamental chemical bonding mechanism in solids that distinctively differs from covalent, ionic, and metallic bonding [38][39][40][41] . Since the bond rupture observed by APT is characteristic of MVB, this technique enables a local determination of the prevalent bonding mechanism.…”