Ba₂MAsQ₅ (Q = S and Se) Family of Polar Structures with Large Second Harmonic Generation and Phase Matchability

Abstract

Noncentrosymmetric chalcogenides containing stereochemically active lone pair elements, such as As, Sb, and Bi, offer a useful way to tune the band gap and enhance the second harmonic generation (SHG) response. Ba2As2–x Sb x Q5, Ba2As2–x Bi x Q5 (Q = S and Se), and Ba2As2S4.8Se0.2 are new chalcoarsenates that crystallize in the noncentrosymmetric monoclinic space group P21. These five new compounds crystallized with a three-dimensional (3D) Ba2As2Se5-type structure, containing AsQ3 units and [As2Q4]2– dimeric units. The [As2Q4]2– dimeric unit can be tuned by replacing As with Sb or Bi and Se with S. In contrast, Ba2As2S5 crystallizes in the orthorhombic space group Pca21. Differential thermal analysis suggested that Ba2As2S5, Ba2As2Se5, Ba2AsSbSe5, and Ba2As1.25Bi0.75Se5 melt congruently. The [M2Q4]2– unit plays a significant role in tuning the band gap of these compounds, decreasing from 2.02 eV in Ba2As2S5 to 1.37 eV in Ba2As1.25Bi0.75Se5. Powder SHG measurements showed all the compounds are essentially phase-matchable at 3300 nm. Ba2AsSbSe5 exhibits the highest χ(2) of 36 pm/V and a laser-induced damage threshold of 0.10 GW/cm2, comparable to that of AgGaQ2. These materials show significantly improved SHG behavior response to BaGa4Q7 compounds, making them attractive for commercial applications.

Visualizing the alignment of lone pair electrons in La3AsS5Br2 and La5As2S9Cl3 to form an acentric or centrosymmetric structure

“…The La–Br interactions within La 3 AsS 5 Br 2 of 3.04 (3)–3.44(3) Å are longer than the La–Cl interactions within La 5 As 2 S 9 Cl 3 of 2.83(1)–2.97(1) Å, which is expected due to the larger ionic size of Br − than Cl − . The As–S interactions are 2.26(1)–2.27(1) Å and 2.25(5)–2.28(5) Å for La 5 As 2 S 9 Cl 3 and La 3 AsS 5 Br 2 , respectively, which are close to many arsenic sulfide compounds such as As 4 S 4 (2.21–2.27 Å), 58 Ba 2 (As 1.5 Bi 0.5 )S 5 (2.21–2.43 Å), 59 CsCu 2 AsS 3 (2.24–2.27 Å), 60 Cs 2 Ag 2 As 2 S 5 (2.24–2.31 Å), 61 KCu 2 AsS 3 (2.26–2.30 Å), 62 etc. In addition to comparable interatomic distances, each unit cell of La 5 As 2 S 9 Cl 3 and La 3 AsS 5 Br 2 is constructed with the same polyhedra: two [LaX8] bicapped trigonal prisms, one [LaX7] capped trigonal prism, and one [AsS 3 ] trigonal pyramid, where X represents various combinations of S atoms and Cl atoms or Br atoms (Fig.…”

Syntheses, Crystal Structures, and Electronic Structures of Quaternary Group IV-Selenide Semiconductors

“…Exploration of metal chalcogenides with new compositions and structure types continues to be intriguing for solid-state scientists because of their diverse structural chemistry and physical properties. These chemical systems have interesting properties such as thermoelectric properties (e.g., SnSe and AgCrSe 2 ), , nonlinear optical properties (e.g., Ba 2 AsSbSe 5 and KCd 4 Ga 5 Te 12 ), , magnetic properties (e.g., (BaF 2 ) 2 Fe 2– x Q 3 and BaLnSn 2 Q 6 ( Q = Chalcogenide; Ln = La, Ce, and Pr)), , superconductivity (e.g., Ta 2 Se and FeSe), , and magnetoresistance (e.g., CdCr 2 Se 4 and Ag 2 Se), , to name but a few. The rich chemistries for synthetic exploration have been facilitated by the wide and systematic modulation of the structures and compositions possible in metal chalcogenides.…”

Na6Sn3P4S16: Sn(ii)-chelated PS4 groups inspired an ultra-strong SHG response

“…However, SCALP cation-centered polyhedra usually exhibit large distortion and a uniform polarized arrangement, which indicates that they have huge potential for an enhancement of inherent NLO effects. [25][26][27][28][29][30] Notably, introducing two or more types of NLO-active functional units into one structure is an effective way to strengthen the SHG effect. [31][32][33] Moreover, strong covalent P-S bonds in the tetrahedral PS 4 also contribute to the improved NLO response, and a series of thiopho-sphates have become more established as IR NLO candidates.…”