Comparative Analysis of the Crystal Structures and Physical Properties of the Complex Group 14 Selenides Sr8Ge4Se17 and Ba8Sn4Se17

During our group's continued exploration of group 14 chalcogenides, we discovered two new compounds, Sr8Ge4Se17 and Ba8Sn4Se17. Both compounds have an 8:4:17 stoichiometric ratio but adopt different centrosymmetric crystal structures. Sr8Ge4Se17 crystallizes in the triclinic P1̅ space group with a = 11.8429(18) Å, b = 12.172(3) Å, c = 13.624(3) Å, α = 114.472(5)0, β = 97.396(5)0, γ = 107.040(5)0, and Z = 2. Ba8Sn4Se17 crystallizes in the monoclinic C2/c space group with a = 47.286(3) Å, b = 12.6294(5) Å, c = 25.7303(15) Å, β = 104.585(5)0, and Z = 16. The unit cell of Ba8Sn4Se17 is approximately eight times larger than the unit cell of Sr8Ge4Se17, which is a consequence of the differently aligned tetrahedra, resulting in a quadrupled a axis, unchanged b axis, and doubled c axis. The lattice parameters and atomic coordinates were finalized via Rietveld refinements on data collected at a high-energy synchrotron beamline. Both compounds are semiconductors with band gaps in the visible region. Sr8Ge4Se17 and Ba8Sn4Se17 have optical band gaps of 1.88 and 1.93 eV, respectively. Both compounds have remarkably low thermal conductivities owing to their low symmetries and large unit cells. The minimum experimental thermal conductivity values of Sr8Ge4Se17 and Ba8Sn4Se17 are 0.45 W m-1 K-1 at 321 K and 0.31 W m-1 K-1 at 324 K, respectively.

SnPQ3 (Q = S, Se, S/Se): A Series of Lone-Pair Cationic Chalcogenophosphates Exhibiting Balanced NLO Activity Originating from SnQ8 Units

Two chalcogenophosphates, SnPS_2.86Se_0.14 (1) and SnPSe₃ (2), are isostructural and crystallize in the monoclinic noncentrosymmetric space group Pn. Their three-dimensional (3D) structures are constructed by [Sn(1)Q₈] hendecahedra and [Sn(2)Q₈] dodecahedra by sharing Q vertices and edges, leaving cavities for isolated [P₂Q₆] (Q = S/Se, Se) dimers. A second-harmonic-generation (SHG) measurement indicates that 1 is phase-matchable with a response of approximately 1.2 × AgGaS₂ (AGS), which is verified by the theoretical calculation result. The powder sample of 1 exhibits a high laser-induced damage threshold of 3.9 × AGS. For comparison, the known SnPS₃ (3) was also synthesized and evaluated using the same method. The chemical composition-NLO performance relationship of 1-3 is also discussed. Dipole moment calculation results suggest that [SnQ₈] polyhedra make the main contribution to their excellent nonlinear optical (NLO) performance.

Non-centrosymmetric sulfides A2Ba6MnSn4S16 (A = Li, Ag): syntheses, structures and properties

Li₂Ba₆MnSn₄S₁₆ and Ag₂Ba₆MnSn₄S₁₆ are synthesized for the first time. By modulating disordered sites with Mn²⁺, they not only show strong SHG responses and wide band gaps (5.1, 2.7 × AgGaS₂; 2.88, 2.76 eV), but also possess paramagnetism.

Four new quaternary chalcogenides A2Ba7Sn4Q16 (A = Li, Na; Q = S, Se): syntheses, crystal structures determination, nonlinear optical performances investigation

Four new quaternary chalcogenides with interesting structures and potential nonlinear optical performances were synthesized for the first time.

Centrosymmetric to noncentrosymmetric structural transformation of new quaternary selenides induced by isolated dimeric [Sn2Se4] units: from Ba8Ga2Sn7Se18to Ba10Ga2Sn9Se22

An interesting centrosymmetric to noncentrosymmetric structure transformation from Ba₈Ga₂Sn₇Se₁₈to Ba₁₀Ga₂Sn₉Se₂₂induced by isolated dimeric [Sn₂Se₄] units was reported.

Syntheses and characterization of three new sulfides with large band gaps: acentric Ba4Ga4SnS12, centric Ba12Sn4S23 and Ba7Sn3S13

Three new sulfides with large band gaps, NCS Ba₄Ga₄SnS₁₂, CS Ba₁₂Sn₄S₂₃ and Ba₇Sn₃S₁₃ were synthesized for the first time. Ba₄Ga₄SnS₁₂ exhibits a desired balance between the band gap (2.90 eV) and the SHG intensity (34 × KDP).

Alkali earth MOx (x = 6, 7, 9, 12) polyhedra tuned cadmium selenites with different dimensions and diverse SeO32− coordinations

Alkali earth cation-tuned framework of cadmium selenites resulting in evolvement of the structures from high dimension to low dimension.

Band gap tuning from an indirect EuGa2S4 to a direct EuZnGeS4 semiconductor: syntheses, crystal and electronic structures, and optical properties

Novel EuZnGeS₄, with a direct band gap, can be obtained via simple substitution from EuGa₂S₄, with an indirect band gap.

[CH3NH3]2Ag4SnIV2SnIIS8: An Open-Framework Mixed-Valent Chalcogenidostannate

An open-framework chalcogenidostannate, namely, [CH₃NH₃]₂Ag₄Sn^IV₂Sn^IIS₈ (1), has been solvothermally synthesized and structurally characterized, which represents the first organically templated three-dimensional (3D) Ag-Sn-S compound containing the mixed valence of Sn(IV)/Sn(II) and displays visible-light-driven photocatalytic activity for degradation of crystal violet (CV).

Syntheses, crystal structures and physical properties of three new chalcogenides: NaGaGe3Se8, K3Ga3Ge7S20, and K3Ga3Ge7Se20

NaGaGe₃Se₈ has a layered structure, while K₃Ga₃Ge₇Q₂₀ (Q = S, Se) are constructed by incompletely isolated quasi-2D layers, leading to large channels loosely occupied by K⁺ cations.

Synthesis, crystal structure and second-order nonlinear optical property of a novel pentanary selenide (K3I)[InB12(InSe4)3]

A novel pentanary selenide (K₃I)[InB₁₂(InSe₄)₃] (P6₃22) features InSe₄ tetrahedron consolidated B₁₂ icosahedron and 1-D chain constructed by InSe₆ octahedron and B₁₂Se₁₂ cluster. It is an indirect semiconductor with the energy gap of 1.15 eV and second harmonic generation-active.

Syntheses, structures, and optical properties of Ba4Ga4SnSe12 and Ba6Ga2SnSe11

Two new quaternary selenides Ba₄Ga₄SnSe₁₂ and Ba₆Ga₂SnSe₁₁, representing the first two members in the A/M/Sn/Q (A = alkaline-earth metal; M = Al, Ga, In; Q = S, Se, Te) system, have been synthesized.

SnGa2GeS6: synthesis, structure, linear and nonlinear optical properties

SnGa₂GeS₆ possesses a powder second harmonic generation response and a band gap of 2.04 eV.

Designing the syntheses and photophysical simulations of noncentrosymmetric compounds

The designs of NCS compounds based on the normal development of NCS chromophores are presented and NLO properties are investigated.