Structure Tuning, Strong Second Harmonic Generation Response, and High Optical Stability of the Polar Semiconductors Na1-xKxAsQ2

• Published in: Journal of the American Chemical Society Vol. 143; no. 43; pp. 18204 - 18215
• Main Authors: Iyer, Abishek K, Cho, Jeong Bin, Byun, Hye Ryung, Waters, Michael J, Hao, Shiqiang, Oxley, Benjamin M, Gopalan, Venkat, Wolverton, Christopher, Rondinelli, James M, Jang, Joon I, Kanatzidis, Mercouri G
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society (ACS) 03.11.2021
• Subjects: chalcoarsenates; chalcogenide; dimensional reduction; INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; nonlinear optics
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/jacs.1c07993

We report the mixed cation compounds Na1-xKxAsSe2 (x = 0.8, 0.65, 0.5) and Na0.1K0.9AsS2 crystallize in the polar noncentrosymmetric space group Cc. The AAsQ(2) (A = alkali metals, Q = S, Se) family features one-dimensional (1D) 1/∞[AQ2-] chains comprising corner-sharing pyramidal AQ3 units in which the packing of these chains is dependent on the alkali metals. The parallel 1/∞[AQ(2)-] chains interact via short As ∙∙∙Se contacts, which increase in length when the fraction of K atoms is increased. The increase in the As ∙∙∙Se interchain distance increases the band gap from 1.75 eV in γ-NaAsSe2 to 2.01 eV in Na0.35K0.65AsSe2, 2.07 eV in Na0.2K0.8AsSe2, and 2.18 eV in Na0.1K0.9AsS2. The Na1-xKxAsSe2 (x = 0.8, 0.65) compounds melt congruently at approximately 316 °C. Wavelength-dependent second harmonic generation (SHG) measurements on powder samples of Na1-xKxAsSe2 (x = 0.8, 0.65, 0.5) and Na0.1K0.9AsS2 suggest that Na0.2K0.8AsSe2 and Na0.1K0.9AsS2 have the highest SHG response and exhibit significantly higher laser-induced damage thresholds (LIDTs). Theoretical SHG calculations on Na0.5K0.5AsSe2 confirm its SHG response with the highest value of d33 = 22.5 pm/V χ333(2) = 45.0 pm/V). The effective nonlinearity for a randomly oriented powder is calculated to be deff = 18.9 pm/V χeff(2) = 37.8 pm/V), which is consistent with the experimentally obtained value of deff = 16.5 pm/V χeff(2) = 33.0 pm/V). Three-photon absorption is the dominant mechanism for the optical breakdown of the compounds under intense excitation at 1580 nm, with Na0.2K0.8AsSe2 exhibiting the highest stability.