Polytypism in LaOBiS2-type compounds based on different three-dimensional stacking sequences of two-dimensional BiS2 layers

Abstract

LaOBiS2-type materials have drawn much attention recently because of various interesting physical properties, such as low-temperature superconductivity, hidden spin polarization, and electrically tunable Dirac cones. However, it was generally assumed that each LaOBiS2-type compound has a unique and specific crystallographic structure (with a space group P4/nmm) separated from other phases. Using first-principles total energy and stability calculations we confirm that the previous assignment of the centrosymetric P4/nmm structure to LaOBiS2 is incorrect as a phonon instability renders this structure impossible. Furthermore, we find that the unstable structure is replaced by a family of energetically closely spaced modifications (polytypes) differing by the layer sequences and orientations. We find that the local Bi-S distortion leads to three polytypes of LaOBiS2 with different stacking patterns of the distorted BiS2 layers. The energy difference between the polytypes of LaOBiS2 is merely ~1 meV/u.c., indicating the possible coexistence of all polytypes in the real sample and that the particular distribution of polytypes may be growth-induced. The in-plane distortion can be suppressed by pressure, leading to a phase transition from polytypes to the high-symmetry P4/nmm structure with a pressure larger than 2.5 GPa. In addition, different choices of the intermediate atoms (replacing La) or active atoms (BiS2) could also manifest different ground state structures. One can thus tune the distortion and the ground state by pressure or substituting covalence atoms in LaOBiS2-family.

17 pages, 4 figures

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Cited by in corpus (11)

• Material Development and Physical Properties of BiS2-Based Layered Compounds
• Predicted electronic markers for polytypes of LaOBiS2 examined via angular resolved photoemission spectroscopy
• Symmetry-assisted protection and compensation of hidden spin polarization in centrosymmetric systems
• Ferro-lattice-distortions and charge fluctuations in superconducting LaO${}_{1-x}$F${}_x$BiS${}_2$
• Two-dimensional Dirac semiconductor and its material realization
• First-principles study of defect formation energies in LaO$X$S${}_2$ ($X=$ Sb, Bi)
• Enhanced thermoelectricity by controlled local structure in bismuth-chalcogenides
• Direct Observation of an Incommensurate Charge Density Wave in the BiS2-based Superconductor NdO1-xFxBiS2
• Pressure-induced superconductivity in layered pnictogen diselenide NdO${}_{0.8}$F${}_{0.2}$Sb${}_{1-x}$Bi${}_x$Se${}_2$ (x = 0.3 and 0.7)
• Pressure-induced enhancement of two-dimensionality in LaO1-xFxBi(Se/S)2 superconductors
• Crystal Structure and Thermoelectric Transport Properties of As-Doped Layered Pnictogen Oxyselenides NdO0.8F0.2Sb1-xAsxSe2