Vast Structural and Polymorphic Varieties of Semiconductors AMM′Q₄ (A = K, Rb, Cs, Tl; M = Ga, In; M′ = Ge, Sn; Q = S, Se)

Abstract

2− ) have been prepared by solid-state syntheses and structurally characterized by single-crystal X-ray diffraction techniques. These new phases fill in the missing links in these quaternary systems and crystallize in various two-dimensional layered polymorphs, while combinations containing large M 3+ and M′ 4+ cations also adopt an extended three-dimensional (3D) network structure. The AMM′Q 4 materials exhibit a wide range of band gaps with colored selenides (1.8 eV < E g < 2.3 eV) and mostly white sulfides (2.5 eV < E g < 3.6 eV). These phases have direct band gaps except for the thallium analogues and the cubic AGaSnSe 4 -cP84. First-principles theoretical calculations of the electronic band structures reveal critical insight into the structure/property relationships of these materials. The distinct polymorphism of these quaternary phases is studied by discussing kinetic and thermodynamic factors responsible for the crystallization, structural considerations, and complementary density functional theory (DFT) calculations.

Structure, Second-, and Third-Harmonic Generation of Li4P2S6: A Wide Gap Material with a High Laser-Induced Damage Threshold

“…(3) = 1.60 × 10 5 pm 2 /V 2 for AgGaSe 2 , 16 indicating a case for a near-static limit with an insignificant λ dependence. Between 2400 and 2600 nm, Li 4 P 2 S 6 has an effective χ (3) of ∼0.34 × 10 5 pm 2 /V 2 .…”

“…This condition must be established for the estimation of the THG coefficient (third-order nonlinear susceptibility) without any complication arising from bandgap absorption of THG. Since the THG coherence length cannot be experimentally determined, the third-order nonlinear susceptibility, χ (3) , was calculated using the Kurtz powder method for the non-phase-matching case 16 i k j j j j j y…”

“…In particular, we found that the onedimensional (1-D) family AAsQ 2 (A = Li, Na, K; and Q = S, Se) has some of the highest SHG outputs in the IR to date (648 pm/V for γ-NaAs 0.95 Sb 0.05 Se 2 ) 9−15 and that the twodimensional (2-D) family AGaM′Q 4 (A = K, Rb, Cs, Tl; M′ = Ge, Sn; and Q = S, Se) outperforms the THG of industrystandard material AgGaS 2 by up to four times. 16 Theoretical studies on the chalcoarsenates show that the reduced dimensionality leads to a high degree of separation between adjacent chain orbitals, flattening the electronic bands and increasing the overall nonlinear response. 13 This begets our hypothesis that 0-D materials should have even higher nonlinear responses because each polarizable unit is fully isolated from its neighbor.…”

“…Higher harmonic generation via chalcogenides is largely done by designing devices, such as by using phase-change materials or metasurfaces, 29−31 while absolute THG measurements are compared against SHG reference materials such as AgGaS 2 and AgGaSe 2 . 16,32 Other material classes measure against transition metal dichalcogenides such as WS 2 , 33 or αquartz, 34,35 but there is a lack of appropriate reference materials for THG because the field has focused on materials optimization and engineering rather than materials discovery. This is particularly lamentable because all materials, regardless of their internal symmetry, have a THG response.…”

Investigation into Structural Variation from 3D to 1D and Strong Second Harmonic Generation of the AHgPS4 (A+ = Na+, K+, Rb+, Cs+) Family

“…The downside is that strongly electropositive alkali or alkaline-earth metals serving as template cations may drive the unsymmetrical units to stack in an antiparallel manner, leading to crystallization in a centrosymmetric (CS) space group. A recent example of this phenomenon is the quaternary chalcogenides AGaM′Q 4 (A = alkali metals; M′= Ge, Sn; Q = chalcogen), 36,37 which are all CS solids. In addition, it is rough to project and control the framework structures under the absence of a firm theory.…”