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Published on: April 14, 2020
Topology-Preserving Ionic-Unit Substitution Enables Sphalerite-Like Phosphides Achieving Superior Infrared Optical
Qichao Zhao1, Bingxuan Li2, Guang Peng1
1State Key Laboratory of Crystal Materials, Tianjin Key Laboratory of Functional Crystal Materials, Institute of Functional Crystal, College of Materials Science and Engineering, Tianjin University of Technology, Tianjin, China.
Abstract:
Non-centrosymmetric (NCS) inorganic phosphides have emerged as promising candidates for infrared (IR) nonlinear optical (NLO) applications; however, their rational design remains challenging because general structure-generation principles are largely absent. Here, we identify a topological relationship between sphalerite lattice and NCS A-X-M-P (A: alkaline earth metals; X: halogens; M: ds, and p block element) phosphides. This relationship holds that specific covalent clusters within the sphalerite lattice can be replaced by A4X ionic motifs while preserving the sphalerite-like topology of tetrahedral framework, and leads to a phase-evolution rule described by the general formula [A4X][MnPn+6]. Building upon this framework, we predict that alkaline-earth cations can be substituted by stereochemically active lone-pair (SCALP) cations to modulate NLO properties. Guided by these principles, eight new desired phosphides, [Ca4X][Zn1.5Si12.5P20], [Ca3.8Ge0.2X][Si11P17], [Ca3.6Sn0.4X][Si11P17], and [Ca3.6Pb0.4X][Si11P17] (X = Cl and Br) were successfully designed and synthesized via a lithium-mediated solid-state reaction. These materials exhibit strong SHG responses (1.2-2.3 × ZGP @ 2900 nm), tunable optical band gaps (1.42-2.02 eV), broad IR transparency range (up to ∼9.5 µm) and moderate birefringence (0.03-0.05 @ 2900 nm). This work establishes a predictive topological substitution principle for generating NCS phosphides and expands the chemical space of lone-pair-containing phosphides with promising infrared optical functionalities.
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