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Compositional Design Guides Property Control in A2M2+xTi1–(x/4)Q4 Semiconductors
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DOI：10.1021/jacs.5c04520.png)
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Abstract
En 中文
We introduce 15 new members to the A2M2+xTi1–(x/4)Q4 family (A = K, Rb, Cs; M = Cu, Ag; Q = S, Se, Te; x = 0 – 113) of semiconductors, for which all compositions afford the ThCr2Si2 structure-type with two-dimensional (2D) [M2+xTi1–(x/4)Q4]2– layers. We unveil how A, M, Q, and the vacancies inherent to the [M2+xTi1–(x/4)Q4]2– layers serve as four tunable compositional variables that influence both the local atomic and electronic structures with systematic impacts on the optoelectronic and thermal properties in a predictable manner. Namely, increased distortion within the [M2+xTi1–(x/4)Q4]2– layers occurs when M = Ag, lowering the melting temperatures of all Ag compounds relative to their Cu counterparts for a given Q. The electronic structures are primarily influenced by Q, with a substitution of S → Se → Te narrowing the average band gaps from 2.30 → 1.49 → 0.74 eV. For a given Q, however, Ag lowers the energy of the valence band maximum (VBM) compared to Cu, and relative to vacuum. Increasing the Ag/Ti ratio inserts additional Ag into the inherent vacancies within the [Ag2+xTi1–(x/4)S4]2– layers of Cs2Ag3.3Ti0.675S4 compared to Cs2Ag2TiS4, raising the valence band maximum from −5.26 → −4.83 eV, which in turn narrows the band gap from 2.48 → 1.85 eV. Such broad ranges in thermal and optoelectronic properties within this family provide interest for diverse applications. Moreover, because this work establishes the independent influences of A, M, Q, and the inherent vacancies on properties for a constant structure-type, all composition-property relationships should apply to other structure-types containing any of these elements or inherent vacancies.
Keywords:
A2M2+xTi1–(x/4)Q4
semiconductors
ThCr2Si2 structure-type
optoelectronic properties
thermal properties
Journal
IF:
15.6
Papers:
20.0W
Citations:
60.2W