Flux Crystal Growth, Structure, and Optical Properties of the New Germanium Oxysulfide La₄(GeS₂O₂)₃

Abstract

Single crystals of a new germanium oxysulfide La4(GeS2O2)3 were grown out of a BaCl2-CaCl2 eutectic flux, and the crystal structure was determined via single-crystal X-ray diffraction. Ivory-white La4(GeS2O2)3 crystallizes in the centrosymmetric space group R-3 with lattice constants of a = b = 16.8283(3) Å, and c = 8.4140(2) Å. La4(GeS2O2)3 exhibits complex three-dimensional anion order in the framework composed of unusual GeS2O2 tetrahedra and three types of La-centered polyhedra. Moreover, the triangular arrangement of the GeS2O2 tetrahedra around a columnar structure of alternating facesharing LaO12 and LaS6O6 units resembles that of GeO4 tetrahedra in the apatite germanate La9.33(GeO4)6O2, which features face-sharing LaO9 columns. The combination of UV-Vis absorption measurements and first-principle calculations revealed the existence of an indirect optical band gap (Eg = 3.67 eV) between the valence band maximum composed of S 3p orbitals and the conduction band minimum composed of La 3d, La 4f, S 3p, and Ge 4s orbitals.

Two Mixed-Anion Units of [GeOSe3] and [GeO3S] Originating from Partial Isovalent Anion Substitution and Inducing Moderate Second Harmonic Generation Response and Large Birefringence

“…To be specific, when Ae/Ge ≤ 0.5, a 2D layer structure such as SrGe 2 O 3 S 2 will be adopted, when Ae/Ge = 1, a 1D chain structure such as AeGeOQ 2 will be formed, and when Ae/Ge ≥ 1.5, low-dimensional structures such as 0D Sr 3 Ge 2 O 4 Se 3 will be the preferred result. In view of the common ordering that highly electropositive cations are usually coordinated by highly electronegative oxygens to form ionic bonds, while the chalcogens are inclined to form covalent bonds because of their large sizes and polarizabilities, the crystal structures of oxychalcogenides are mainly zero-dimensional, one-dimensional, and two-dimensional. ,− In fact, few oxychalcogenides with 3D framework structure have been reported.…”

“…Highly electronegative halogen atoms (Cl ( χ p = 3.16), Br ( χ p = 2.96)) tend to form ionic bonds with metal atoms and have difficulty in replacing the chalcogen atoms (S, χ p = 2.58; Se, χ p = 2.55) in the [MQ 4 ] tetrahedra. In contrast, an O ( χ p = 3.44) atom seems like a better choice to introduce into chalcogenides, given some successful examples such as the [PO 3 S] unit in α-Na 3 PO 3 S, the [ZnS 3 O] unit in CaZnSO, SrZn 2 S 2 O, the [GaS 3 O] unit in Sr 5 Ga 8 O 3 S 14 , [GeO 2 Q 2 ] units in La 4 (GeS 2 O 2 ) 3 and Ae/Ge/O/Q (Ae = Ba, Sr; Q = S, Se,) − and the [SbOS 4 ] unit in Sr 6 Cd 2 Sb 6 O 7 S 10 . Unfortunately, oxysulfide mixed-anion SBUs are still relatively scarce and difficult to control with precision.…”

Cation Regulation to Investigate the Chalcogenide Borate RE6Nb2MgSB8O26 (RE = La–Nd) Family

“…It is clear from Figures and S4 that 1 and 2 have two optical transitions. For 1 , the smaller optical transition E g1 at 2.48 eV is probably due to defects from anion vacancies, while the larger optical transition E g2 at 4.19 eV should correspond to the intrinsic optical band gap . To verify this statement, we constructed structural models with the O 2– or S 2– anion lacking, respectively.…”

“…For 1, the smaller optical transition E g1 at 2.48 eV is probably due to defects from anion vacancies, while the larger optical transition E g2 at 4.19 eV should correspond to the intrinsic optical band gap. 28 To verify this statement, we constructed structural models with the O 2− or S 2− anion lacking, respectively. The calculated band structure of 1 shows that the absorption peak decreases by ∼2.5/2.9 eV, according to the impurity level.…”

Growth and Characterization of Lanthanum Germanide Thin Films by the Thermal Evaporation Technique

“…[ 32 ] These two examples provide an evidence about the origin of the bandgap of La 6 Ge films which are coated onto glass substrates. In fact the bond length of La–Ge being ≈3.146 Å [ 33 ] is longer than the bond length of La–O (2.66 Å) [ 34 ] and La–O is longer than that of Ge–O (1.69 Å). [ 35 ] This property makes the interaction between unbonded Ge atom and oxygen in glass substrates very strong resulting in the observed optical transitions.…”