CsXSi15P21 (X = Sn or Pb): Polar Noncentrosymmetric Si–P Frameworks Stabilized by Covalent X –P Bonding
(2026) Chemistry of Materials — Vol. 38, n° 7, p. 3247-3255 (2026)
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- Authors
Yox, Philip 
Kyveryga, Victoria Soto, Ernesto Kovnir, Kirill
- Abstract
- (en) Metal silicon phosphides composed of earth-abundant Si and P tend to exhibit semiconducting properties and adopt diverse crystal structures with relatively small additions of structure-directing elements. The potential of silicon phosphide materials in nonlinear optical applications has been hindered by the inability to systematically produce noncentrosymmetric structures with such a flexible framework. In this work, two isostructural compounds with a novel noncentrosymmetric structure were made possible by the inclusion of elements with stereochemically active lone pairs (Sn 2+ and Pb 2+). The structures were determined through single-crystal and synchrotron powder X-ray diffraction. Analysis of chemical bonding in real space through the electron localization function revealed stereochemically active Pb 2+ and Sn 2+ species in a trigonal pyramidal coordination with {Pb/Sn}−P bonds. Such covalent bonding between Pb and P is quite uncommon in extended solids and has been reported in a few rare instances. Band structure calculations and linear optical measurements confirm the semiconducting nature of CsXSi 15 P 21 (X = Sn or Pb). The synthesis was optimized to yield high-purity polycrystalline samples. The nonlinear optical properties show promising second-harmonic generation (SHG) coefficients from the Kurtz−Perry method. First-principles calculations of the nonlinear optical properties support the experimentally determined SHG values and provide moderate values of birefringence, suggesting CsXSi 15 P 21 could be phase-matchable and practical nonlinear optical materials in the mid-IR region.
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Yox, P., Kyveryga, V., Soto, E., Warner, J., Viswanathan, G., Gamage, E., Wu, K., Zhang, B., Trinquet, V., Hautier, G., Rignanese, G.-M., & Kovnir, K. (2026). CsXSi15P21 (X = Sn or Pb): Polar Noncentrosymmetric Si–P Frameworks Stabilized by Covalent X –P Bonding. Chemistry of Materials, 38(7), 3247-3255. https://doi.org/10.1021/acs.chemmater.5c02878 (Original work published 2026)