Electronic structure of PbSnS3 and PbGeS3 semiconductor compounds with the mixed cation coordination

Abstract

The self-consistent band structure calculation of PbSnS 3 and PbGeS 3 ternary compounds with the mixed cation coordination was performed using the ab initio density functional theory method. It has been found that both compounds are indirect-gap semiconductors. The calculated band-gap widths are E gi = 0.75 eV for PbSnS 3 and E gi = 1.96 eV for PbGeS 3. It was performed the analysis of partial contributions to the total density of electronic states, which allowed to identify the genetic nature of valence and conduction bands. The feature of the structure of occupied energy bands in these compounds is the presence of isolated quasi-core d-band of lead atoms and the contribution of Pb6s-states of lone-electron pair to the top of valence band as well as to the second occupied subband. The electron density maps in the different planes have been analyzed. They clearly demonstrate presence of covalent-ionic bond character within the infinite chains and ribbons with prevailing charge concentration on Ge-S, Sn-S, Pb-S bonds, and a weak van der Waals bond component with participation of lone-electron pair of lead between layers as well as ribbons.

Maldistribution of Chemical Bond Strength Inducing Exceptional Anisotropy of Thermal Conductivity in Non‐Layered Materials

“…The distance between Pb and S atom in the nearest neighbor dioctahedron chain unit is about 3.1 Å, which weakens the bonding force of PbÀ S among different units. The Pb atoms in dioctahedron chain units coordinates with S atoms to form a trigonal pyramidal, leaving a bunch of lone pair electrons locating at the void sites, [29] which can be viewed as isolated weak bonds with neighboring dioctahedron chain units. We analyzed the ELF projected onto the (101) plane at 1 = 4 and 3 = 4 b lattice constant where Pb locate (Figure S8).…”

“…Herein, we take non-layered PbSnS 3 , which crystalizes as orthorhombic structures and belongs to Pnma space group, [28,29] as an example to explore the large anisotropy induced by maldistribution of chemical bond strength. We discovered an anisotropy ratio of k up to 7.1 at 200 K (and 5.5 at 300 K) which is extremely large among non-layered materials and can even surpasses some classical layered materials with vdW gaps such as Bi 2 Te 3 and SnSe.…”