Synthesis, structure, and properties of Li2In2MQ6 (M = Si, Ge; Q = S, Se): a new series of IR nonlinear optical materials

The four isostructural compounds Li(2)In(2)MQ(6) (M = Si, Ge; Q = S, Se) have been synthesized for the first time. They crystallize in the noncentrosymmetric monoclinic space group Cc with the three-dimensional framework composed of corner-sharing LiQ(4), InQ(4), and MQ(4) tetrahedra. The second-harmonic-generation signal intensities of the two sulfides and two selenides were close to those of AgGaS(2) and AgGaSe(2), respectively, when probed with a laser with 2090 nm as the fundamental wavelength. They possess large band gaps of 3.61(2) eV for Li(2)In(2)SiS(6), 3.45(2) eV for Li(2)In(2)GeS(6), 2.54(2) eV for Li(2)In(2)SiSe(6), and 2.30(2) eV for Li(2)In(2)GeSe(6), respectively. Moreover, these four compounds all melt congruently at relatively low temperatures, which makes it feasible to grow bulk crystals needed for practical application by the Bridgman-Stockbarger method.     

Na6MQ4 (M=Zn,Cd; Q=S,Se): Promising New Ternary Infrared Nonlinear Optical Materials

Four sodium-based ternary IR nonlinear optical (NLO) materials, Na₆MQ₄ (M=Zn, Cd; Q=S, Se), were prepared through a high-temperature flux method. The crystal structure of the compounds is built up of isolated [MQ₄] tetrahedra and a 3D framework formed by the NaQ_n (n=4, 5) units. The two selenides, Na₆MSe₄ (M=Zn, Cd), as promising IR NLO materials, show moderate second-harmonic generation (SHG) responses (0.9 and 0.5×AgGaS₂) with good phase-matching behavior, as well as high laser damage thresholds (2 and 1.9×AgGaS₂). The two sulfides, Na₆MS₄ (M=Zn, Cd), exhibit higher laser damage thresholds (13 and 4×AgGaS₂), but smaller SHG responses (0.3 and 0.2×AgGaS₂). Theoretical calculations and statistical analyses indicate that the SHG effect and band gap in the compounds originate mainly from the distorted NaQ₄ NLO-active units with a short Na−S bond length, which provides a new insight into the design of novel IR NLO materials.     

Syntheses, structures, physical properties, and electronic properties of some AMUQ3 compounds (A = alkali metal, M = Cu or Ag, Q = S or Se)

The seven new isostructural quaternary uranium chalcogenides KCuUS 3, RbCuUS 3, RbAgUS 3, CsCuUS 3, CsAgUS 3, RbAgUSe 3, and CsAgUSe 3 were prepared from solid-state reactions. These isostructural materials crystallize in the layered KZrCuS 3 structure type in the orthorhombic space group Cmcm. The structure is composed of UQ 6 octahedra and MQ 4 tetrahedra that share edges to form (2) infinity[UMQ 3 (-)] layers. These layers stack perpendicular to [010] and are separated by layers of face- and edge-sharing AQ 8 bicapped trigonal prisms. There are no Q-Q bonds in the structure, so the formal oxidation states of A/U/M/Q may be assigned as 1+/4+/1+/2-, respectively. CsCuUS 3 shows semiconducting behavior with thermal activation energy E a = 0.14 eV and sigma 298 = 0.3 S/cm. From single-crystal absorption measurements in the near IR range, the optical band gaps of these compounds are smaller than 0.73 eV. The more diffuse 5f electrons play a much more dominant role in the optical properties of the AMUQ 3 compounds than do the 4f electrons in the AMLnQ 3 compounds (Ln = rare earth). Periodic DFT spin band-structure calculations on CsCuUS 3 and CsAgUS 3 establish two energetically similar antiferromagnetic spin structures and show magnetic interactions within and between the layers of the structure. Density-of-states analysis shows M-Q orbital overlap in the valence band and U-Q orbital overlap in the conduction band.     

Crystal structures, electronic structures, and physical properties of Tl4MQ4 (M = Zr or Hf; Q = S or Se)

The ternary thallium chalcogenides of the general formula Tl(4)MQ(4) (M = Zr or Hf; Q = S or Se) were obtained from high-temperature reactions without air. These sulfides and selenides are isostructural, crystallizing in the triclinic system with space group P1 and Z = 5, in contrast to Tl(4)MTe(4) compounds that adopt space group R3. The unit cell parameters for Tl(4)ZrS(4) are as follows: a = 9.0370(5) ?, b = 9.0375(5) ?, c = 15.4946(9) ?, α = 103.871(1)°, β = 105.028(1)°, γ = 90.138(1)°, and V = 1183.7(1) ?(3). In contrast to the corresponding tellurides, the sulfides and selenides exhibit edge-shared MQ(6) octahedra, propagating along the c axis in a zigzag manner. All elements occur in the most common oxidation states, according to the formulation (Tl(+))(4)M(4+)(Q(2-))(4). Electronic structure calculations predict energy band gaps of 1.7 eV for Tl(4)ZrS(4) and 1.3 eV for Tl(4)ZrSe(4), which are in accordance with the large resistivity values observed experimentally.     

Syntheses, structure, and selected physical properties of CsLnMnSe3 (Ln = Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, Y) and AYbZnQ3 (A = Rb, Cs; Q = S, Se, Te)

CsLnMnSe(3) (Ln = Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, Y) and AYbZnQ(3) (A = Rb, Cs; Q = S, Se, Te) have been synthesized from solid-state reactions at temperatures in excess 1173 K. These isostructural materials crystallize in the layered KZrCuS(3) structure type in the orthorhombic space group Cmcm. The structure is composed of LnQ(6) octahedra and MQ(4) tetrahedra that share edges to form [LnMQ(3)] layers. These layers stack perpendicular to [010] and are separated by layers of face- and edge-sharing AQ(8) bicapped trigonal prisms. There are no Q-Q bonds in the structure of the ALnMQ(3) compounds so the formal oxidation states of A/Ln/M/Q are 1+/3+/2+/2-. The CsLnMnSe(3) materials, with the exception of CsYbMnSe(3), are Curie-Weiss paramagnets between 5 and 300 K. The magnetic susceptibility data for CsYbZnS(3), RbYbZnSe(3), and CsYbMSe(3) (M = Mn, Zn) show a weak cusp at approximately 10 K and pronounced differences between field-cooled and zero-field-cooled data. However, CsYbZnSe(3) is not an antiferromagnet because a neutron diffraction study indicates that CsYbZnSe(3) shows neither long-range magnetic ordering nor a phase change between 4 and 295 K. Nor is the compound a spin glass because the transition at 10 K does not depend on ac frequency. The optical band gaps of the (010) and (001) crystal faces for CsYbMnSe(3) are 1.60 and 1.59 eV, respectively; the optical band of the (010) crystal faces for CsYbZnS(3) and RbYbZnSe(3) are 2.61 and 2.07 eV, respectively.     

From single to multiple atomic layers: a unique approach to the systematic tuning of structures and properties of inorganic-organic hybrid nanostructured semiconductors

In order to systematically tailor the structures and properties of a unique family of inorganic-organic hybrid nanostructured materials based on II-VI semiconductors, we have designed and engineered a new group of two-dimensional crystalline [(M2Q2)(L)] nanostreuctures (where M = Zn, Cd; Q = S, Se; and L = ethylamine, n-propylamine, n-butylamine, n-amylamine, n-hexylamine). These compounds are composed of double atomic layers of M2Q2 separated by organic monoamines. The crystal structures of 2D-[(M2Q2)(L)] are characterized by powder X-ray diffraction (PXRD) analysis. The crystal structures of these compounds are similar to the 2D-[(MQ)(L)] series that we reported earlier, in that they also contain II-VI slabs sandwiched by organic monoamines. The main difference is in the thickness of the II-VI slabs, where they are single-layer (n = 1) in 2D-[(MQ)(L)] but double-layer (n = 2) in 2D-[(M2Q2)(L)]. Optical absorption experiments show that all double-layer compounds exhibit a blue shift in their absorption edge (0.6-1.2 eV), due to the quantum confinement effect (QCE). However, the extent of such a blue shift is significantly less than that of the single-layer 2D-[(MQ)(L)] systems (1.0-2.0 eV) as a result of the difference in their layer thickness. Thermogravimetric (TG) analysis has revealed nanosized II-VI (MQ) particles as the post-TG product of all double-layer hybrids.     

alpha- and beta-A2Hg3M2S8 (A = K,Rb; M = Ge,Sn): polar quaternary chalcogenides with strong nonlinear optical response

The closely related phases alpha- and beta-A(2)Hg(3)M(2)S(8) (A = K, Rb; M = Ge, Sn) have been discovered using the alkali polychalcogenide flux method and are described in detail. They present new structure types with a polar noncentrosymmetric crystallographic motif and strong nonlinear second-harmonic generation (SHG) properties. The alpha-allotropic form crystallizes in the orthorhombic space group Aba2 with a = 19.082(2) A, b = 9.551(1) A, c = 8.2871(8) A for the K(2)Hg(3)Ge(2)S(8) analogue, and a = 19.563(2) A, b = 9.853(1) A, c = 8.467(1) A for the K(2)Hg(3)Sn(2)S(8) analogue. The beta-form crystallizes in the monoclinic space group C2 with a = 9.5948(7) A, b = 8.3608(6) A, c = 9.6638(7) A, beta = 94.637 degrees for the K(2)Hg(3)Ge(2)S(8) analogue. The thermal stability and optical and spectroscopic properties of these compounds are reported along with detailed solubility and crystal growth studies of the alpha-Kappa(2)Hg(3)Ge(2)S(8) in K(2)S(8) flux. These materials are wide gap semiconductors with band gaps at approximately 2.40 and approximately 2.64 eV for the Sn and Ge analogues, respectively. Below the band gap the materials exhibit a very wide transmission range to electromagnetic radiation up to approximately 14 microm. alpha-K(2)Hg(3)Ge(2)S(8) shows anisotropic thermal expansion coefficients. SHG measurements, performed with a direct phase-matched method, showed very high nonlinear coefficient d(eff) for beta-K(2)Hg(3)Ge(2)S(8) approaching 20 pm/V. Crystals of K(2)Hg(3)Ge(2)S(8) are robust to air exposure and have a high laser-damage threshold.     

LiGaGe2Se6: a new IR nonlinear optical material with low melting point

The new compound LiGaGe(2)Se(6) has been synthesized. It crystallizes in the orthorhombic space group Fdd2 with a = 12.501(3) ?, b = 23.683(5) ?, c = 7.1196(14) ?, and Z = 8. The structure is a three-dimensional framework composed of corner-sharing LiSe(4), GaSe(4), and GeSe(4) tetrahedra. The compound exhibits a powder second harmonic generation signal at 2 μm that is about half that of the benchmark material AgGaSe(2) and possesses a wide band gap of about 2.64(2) eV. LiGaGe(2)Se(6) melts congruently at a rather low temperature of 710 °C, which indicates that bulk crystals can be obtained by the Bridgman-Stockbarger technique. According to a first-principles calculation, there is strong hybridization of the 4s and 4p orbitals of Ga, Ge, and Se around the Fermi level. The calculated birefractive index is Δn = 0.04 for λ ≥ 1 μm, and the calculated major SHG tensor elements are d(15) = 18.6 pm/V and d(33) = 12.8 pm/V. This new material is promising for application in IR nonlinear optics.     

Straightforward route to the adamantane clusters [Sn4Q10]4- (Q = S, Se, Te) and use in the assembly of open-framework chalcogenides (Me4N)2M[Sn4Se10] (M = Mn(II), Fe(II), Co(II), Zn(II)) including the first telluride member (Me4N)2Mn[Ge4Te10

The reaction of K(2)Sn(2)Q(5) (Q = S, Se, Te) with stoichiometric amounts of alkyl-ammonium bromides R(4)NBr (R = methyl or ethyl) in ethylenediamine (en) afforded the corresponding salts (R(4)N)(4)[Sn(4)Q(10)] (Q = S, Se, Te) in high yield. Although the compound K(2)Sn(2)Te(5) is not known, this reaction is also applicable to solids with a nominal composition "K(2)Sn(2)Te(5)" which in the presence of R(4)NBr in en are quantitatively converted to the salts (R(4)N)(4)[Sn(4)Te(10)] on a multigram scale. These salts contain the molecular adamantane clusters [Sn(4)Q(10)](4-) and can serve as soluble precursors in simple metathesis reactions with transition metal salts to synthesize the large family of open-framework compounds (Me(4)N)(2)M[Sn(4)Se(10)] (M = Mn(2+), Fe(2+), Co(2+), Zn(2+)). Full structural characterization of these materials as well as their magnetic and optical properties is reported. Depending on the transition metal in (Me(4)N)(2)M[Sn(4)Se(10)], the energy band gaps of these compounds lie in the range of 1.27-2.23 eV. (Me(4)N)(2)Mn[Ge(4)Te(10)] is the first telluride analogue to be reported in this family. This material is a narrow band gap semiconductor with an optical absorption energy of 0.69 eV. Ab initio electronic band structure calculations validate the semiconductor nature of these chalcogenides and indicate a nearly direct band gap.     

Aluminosilicate relatives: Chalcogenoaluminogermanates Rb(3)(AlQ(2))(3)(GeQ(2))(7) (Q = S, Se)

The new compounds Rb(3)(AlQ(2))(3)(GeQ(2))(7) [Q = S (1), Se (2)] feature the 3D anionic open framework [(AlQ(2))(3)(GeQ(2))(7)](3-) in which aluminum and germanium share tetrahedral coordination sites. Rb ions are located in channels formed by the connection of 8, 10, and 16 (Ge/Al)S(4) tetrahedra. The isostructural sulfur and selenium derivatives crystallize in the space group P2(1)/c. 1: a = 6.7537(3) ?, b = 37.7825(19) ?, c = 6.7515(3) ?, and β = 90.655(4)°. 2: a = 7.0580(5) ?, b = 39.419(2) ?, c = 7.0412(4) ?, β = 90.360(5)°, and Z = 2 at 190(2) K. The band gaps of the congruently melting chalcogenogermanates are 3.1 eV (1) and 2.4 eV (2).     

Synthesis, structure, and optical properties of the quaternary seleno-gallates NaLnGa4Se8 (Ln = La, Ce, Nd) and their comparison with the isostructural thio-gallates

Three new quaternary seleno-gallates containing rare-earth metals and sodium cations, have been synthesized by a solid-state route in evacuated quartz ampoules: Na LnGa 4Se 8 ( Ln = La( I), Ce ( II) and Nd ( III)). The synthesis involved the stoichiometric combination of sodium polyselenides, rare-earth metal, Ga 2Se 3, and Se or elemental Ga in place of Ga 2Se 3. Single-crystal structure analysis indicated that the compounds are isostructural to the thio-analogue, NaNdGa 4S 8. The structures of I- III are described in terms of layers of GaSe 4 tetrahedra joined by corner- and edge-sharing; the alkali-metal cations and the trivalent rare-earth metal cations occupy square antiprismatic sites between the layers. The optical properties of the compounds have been investigated and compared with the isostructural thio-gallate. The band gap of I was located around 2.65 eV. The band gaps of II and III were 2.66 and 2.73 eV, respectively, considerably narrower than their thio-analogues ( approximately 3.4 eV). The contraction of the band gap was attributed to the shift of the valence band to higher energy due to the involvement of higher energy (4p) Se orbitals. The 4f --> 5d gap of II is found to be located around 2.32 eV, which is 0.26 eV narrower than the thio-analogue is due to a greater dispersion of the Ln-(5d) band caused by more covalent Ce-Se bonds as well as rising of the f level energy.     

Polyanionic hydrides from polar intermetallics AeE2 (Ae = Ca, Sr, Ba; E = Al, Ga, In)

The hydrogenation behavior of the polar intermetallic systems AeE2 (Ae = Ca, Sr, Ba; E = Al, Ga, In) has been investigated systematically and afforded the new hydrides SrGa2H2 and BaGa2H2. The structure of these hydrides was characterized by X-ray powder diffraction and neutron diffraction of the corresponding deuterides. Both compounds are isostructural to previously discovered SrAl2H2 (space group P3m1, Z = 1, SrGa2H2/D2: a = 4.4010(4)/4.3932(8) A, c = 4.7109(4)/4.699(1) A; BaGa2H2/D2: a = 4.5334(6)/4.5286(5) A, c = 4.9069(9)/4.8991(9) A). The three hydrides SrAl2H2, SrGa2H2, and BaGa2H2 decompose at around 300 degrees C at atmospheric pressure. First-principles electronic structure calculations reveal that H is unambiguously part of a two-dimensional polyanion [E2H2]2- in which each E atom is tetrahedrally coordinated by three additional E atoms and H. The compounds AeE2H2 are classified as polyanionic hydrides. The peculiar feature of polyanionic hydrides is the incorporation of H in a polymeric anion where it acts as a terminating ligand. Polyanionic hydrides provide unprecedented arrangements with both E-E and E-H bonds. The hydrogenation of AeE2 to AeE2H2 takes place at low reaction temperatures (around 200 degrees C), which suggests that the polyanion of the polar intermetallics ([E2]2-) is employed as precursor.     

Structures and properties of the ternary thallium chalcogenides Tl2MQ3 (M = Zr, Hf; Q = S, Se)

We have synthesized new compounds of the formula Tl(2)MQ(3), with M = Zr and Hf and Q = S and Se, and studied their crystallographic features, electronic structures and electrical conductivity. These isostructural compounds crystallize in the monoclinic space group P2(1)/m (Z = 2), with unit cell parameters for the representative Tl(2)ZrS(3) of a = 7.9159(10) ?, b = 3.7651(5) ?, c = 10.275(2) ?, and β = 97.476(2)°. The Zr atoms of Tl(2)ZrS(3) are (distorted) octahedrally coordinated by the S atoms, with two such octahedra sharing edges along the c axis and forming infinite double chains running parallel to the b axis. Tl atoms separate these chains from one another along the a and c axes. The Tl atoms are also surrounded by S atoms in a distorted octahedral coordination. The structure may be viewed as alternating layers of Zr/Tl atoms and S atoms, and is therefore a distorted, ordered variant of the α-NaFeO(2) structure type. All atoms are in their standard oxidation states: Tl(+), Zr(4+), S(2-). The sulphide Tl(2)ZrS(3) has a calculated band gap of 1.15 eV, and the selenide Tl(2)HfSe(3) a gap of 0.57 eV. The electrical conductivity values of Tl(2)ZrS(3) and Tl(2)HfSe(3) at room temperature are 7.1 × 10(-6)Ω(-1) cm(-1) and 3.9 × 10(-3)Ω(-1) cm(-1), respectively.     

Rare-earth metal(III) oxide selenides M4O4Se[Se2] (M=La, Ce, Pr, Nd, Sm) with discrete diselenide units: crystal structures, magnetic frustration, and other properties

The rare-earth metal(III) oxide selenides of the formula La4O4Se[Se2], Ce4O4Se[Se2], Pr4O4Se[Se2], Nd4O4Se[Se2], and Sm4O4Se[Se2] were synthesized from a mixture of the elements with selenium dioxide as the oxygen source at 750 degrees C. Single crystal X-ray diffraction was used to determine their crystal structures. The isostructural compounds M4O4Se[Se2] (M=La, Ce, Pr, Nd, Sm) crystallize in the orthorhombic space group Amm2 with cell dimensions a=857.94(7), b=409.44(4), c=1316.49(8) pm for M=La; a=851.37(6), b=404.82(3), c=1296.83(9) pm for M=Ce; a=849.92(6), b=402.78(3), c=1292.57(9) pm for M=Pr; a=845.68(4), b=398.83(2), c=1282.45(7) pm for M=Nd; and a=840.08(5), b=394.04(3), c=1263.83(6) pm for M=Sm (Z=2). In their crystal structures, Se2- anions as well as [Se-Se]2- dumbbells interconnect {[M4O4]4+} infinity 2 layers. These layers are composed of three crystallographically different, distorted [OM4]10+ tetrahedra, which are linked via four common edges. The compounds exhibit strong Raman active modes at around 215 cm(-1), which can be assigned to the Se-Se stretching vibration. Optical band gaps for La4O4Se[Se2], Ce4O4Se[Se2], Pr4O4Se[Se2], Nd4O4Se[Se2], and Sm4O4Se[Se2] were derived from diffuse reflectance spectra. The energy values at which absorption takes place are typical for semiconducting materials. For the compounds M4O4Se[Se2] (M=La, Pr, Nd, Sm) the fundamental band gaps, caused by transitions from the valence band to the conduction band (VB-CB), lie around 1.9 eV, while for M=Ce an absorption edge occurs at around 1.7 eV, which can be assigned to f-d transitions of Ce3+. Magnetic susceptibility measurements of Ce4O4Se[Se2] and Nd4O4Se[Se2] show Curie-Weiss behavior above 150 K with derived experimental magnetic moments of 2.5 micro B/Ce and 3.7 micro B/Nd and Weiss constants of theta p=-64.9 K and theta p=-27.8 K for the cerium and neodymium compounds, respectively. Down to 1.8 K no long-range magnetic ordering could be detected. Thus, the large negative values for theta p indicate the presence of strong magnetic frustration within the compounds, which is due to the geometric arrangement of the magnetic sublattice in form of [OM4]10+ tetrahedra.     

Syntheses and characterization of six quaternary uranium chalcogenides a(2)m(4)u(6)q(17) (a = rb or cs; m = pd or pt; q = s or se)

The A(2)M(4)U(6)Q(17) compounds Rb(2)Pd(4)U(6)S(17), Rb(2)Pd(4)U(6)Se(17), Rb(2)Pt(4)U(6)Se(17), Cs(2)Pd(4)U(6)S(17), Cs(2)Pd(4)U(6)Se(17), and Cs(2)Pt(4)U(6)Se(17) were synthesized by the high-temperature solid-state reactions of U, M, and Q in a flux of ACl or Rb(2)S(3). These isostructural compounds crystallize in a new structure type, with two formula units in the tetragonal space group P4/mnc. This structure consists of a network of square-planar MQ(4), monocapped trigonal-prismatic UQ(7), and square-antiprismatic UQ(8) polyhedra with A atoms in the voids. Rb(2)Pd(4)U(6)S(17) is a typical semiconductor, as deduced from electrical resistivity measurements. Magnetic susceptibility and specific heat measurements on single crystals of Rb(2)Pd(4)U(6)S(17) show a phase transition at 13 K, the result either of antiferromagnetic ordering or of a structural phase transition. Periodic spin-polarized band structure calculations were performed on Rb(2)Pd(4)U(6)S(17) with the use of the first principles DFT program VASP. Magnetic calculations included spin-orbit coupling. With U f-f correlations taken into account within the GGA+U formalism in calculating partial densities of states, the compound is predicted to be a narrow-band semiconductor with the smallest indirect and direct band gaps being 0.79 and 0.91 eV, respectively.     

In-phase alignments of asymmetric building units in Ln4GaSbS9 (Ln = Pr, Nd, Sm, Gd-Ho) and their strong nonlinear optical responses in middle IR

New noncentrosymmetric rare-earth metal gallium thioantimonates, Ln(4)GaSbS(9) were synthesized from stoichiometric element mixtures at 950 °C by high-temperature solid-state reactions. These compounds crystallize in orthorhombic space group Aba2 (no.41) with a = 13.799(3)-13.427(5) ?, b = 14.187(3)-13.756(5) ?, c = 14.323(3)-13.954(5) ?, V = 2804(2)-2577 (2) ?(3), and Z = 8 on going from Ln = Pr to Ho. The asymmetric building units, bimetallic polar (Sb(2)S(5)) units, and dimeric (GaS(4))(2) tetrahedra are in-phase aligned as an infinite single anionic chain of {[(Ga(2)S(6))(Sb(2)S(5))](10-)}(∞) that is further packed in a noncentrosymmetric pseudolayer motif perpendicular to the c axis. Three of the title compounds show large powder second harmonic generation (SHG) effects at 2.05 μm, and two of them also exhibit large transparency ranges (1.75 or 0.75 to 25 μm) in the middle-IR region. Significantly, the Sm-member exhibits the strongest SHG response among sulfides to date with intensity approximately 3.8 times that of the benchmark AgGaS(2). The band structures, indirect band gap nature, bonding strengths, and lone pair effects around Sb have also been studied by Vienna ab initio simulation package calculations.     

Second-harmonic generating properties of polar noncentrosymmetric aluminoborate solid solutions, Al(5-x)Ga(x)BO9 (0.0 ≤ x ≤ 0.5)

A series of solid solutions of polar aluminoborate materials, Al(5-x)Ga(x)BO(9) (0.0 ≤x≤ 0.5) have been synthesized by standard solid-state reactions using Al(2)O(3), Ga(2)O(5), and B(OH)(3) as reagents. The phase purities, crystal structures, and solid solution behavior of the reported materials have been investigated by powder X-ray diffraction. Solid solutions of Al(5-x)Ga(x)BO(9) crystallize in the polar noncentrosymmetric space group, Cmc2(1), with a three-dimensional structure consisting of distorted MO(4), MO(5), MO(6), and BO(3) polyhedra (M = Al or Ga). Powder second-harmonic generating (SHG) measurements on the Al(5)BO(9) using 1064 nm radiation, indicate the material has a SHG efficiency of approximately 2 times that of α-SiO(2) and is not phase-matchable (type 1). Further nonlinear optical (NLO) measurements on the Al(5-x)Ga(x)BO(9) solid solutions indicate a sharp increase in SHG efficiency up to 10 times that of α-SiO(2) for x≥ 0.4. Close structural examination suggests that the alignment of the asymmetric π-delocalization of BO(3) groups is responsible for the abrupt increase of SHG efficiency.     

Noncentrosymmetric inorganic open-framework chalcohalides with strong middle IR SHG and red emission: Ba3AGa5Se10Cl2 (A = Cs, Rb, K)

Novel SHG effective inorganic open-framework chalcohalides, Ba(3)AGa(5)Se(10)Cl(2) (A = Cs, Rb and K), have been synthesized by high temperature solid state reactions. These compounds crystallize in the tetragonal space group I ?4 (No.82) with a = b = 8.7348(6) - 8.6341(7) ?, c = 15.697(3) - 15.644(2) ?, V = 1197.6(3) - 1166.2(2) ?(3) on going from Cs to K. The polar framework of (3)(∞)[Ga(5)Se(10)](5-) is constructed by nonpolar GaSe(4)(5- )tetrahedron (T1) and polar supertetrahedral cluster Ga(4)Se(10)(8-) (T2) in a zinc-blende topological structure with Ba/A cations and Cl anions residing in the tunnels. Remarkably, Ba(3)CsGa(5)Se(10)Cl(2) exhibits the strongest intensity at 2.05 μm (about 100 times that of the benchmark AgGaS(2) in the particle size of 30-46 μm) among chalcogenides, halides, and chalcohalides. Furthermore, these compounds are also the first open-framework compounds with red photoluminescent emissions. The Vienna ab initio theoretical studies analyze electronic structures and linear and nonlinear optical properties.     

Synthese und Strukturen von Bis(amino)germa- und -stanna-Chalkogeniden

Synthesis and Structures of Bis(amino)germa and -stanna Chalcogenides The cyclic bis(amino)germylene 1 and the -stannylene 2 react with elemental S, Se and Te to yield oxydation products of the general formula Me₂Si(NtBu)₂MEl₂M(NtBu)₂SiMe₂ (M = Ge, El = S ( 4 ), El = Se ( 5 ), El = Te ( 6 ); M = Sn, El = Se ( 9 ), El = Te ( 10 )). As may be deduced from X-ray structures ( 4, 5, 6, 9, 10 ) all compounds show similar central skeletons: the three spirocyclicly connected four-membered rings SiN₂M (2x) and MEl₂M are oriented in an orthogonal way to oneanother. The germanium and the tin atoms thus are in a distorted tetrahedral coordination while the chalcogen atoms only have two neighbours in acute angles. If 1 is allowed to react with trimethylamine-N-oxide, the oxygen is transferred to germanium and [Me₂Si(NtBu)₂GeO]₃ ( 3 ) is formed. Contrarily to the other compounds 3 can be described as a trimer. There is a central almost planar Ge₃O₃ six-membered ring, the germanium atoms serving as spiro-cyclic centres to three GeN₂Si four-membered rings (X-ray structure of 3 ). In the central four-membered rings of 4, 5, 6, 9 and 10 no transanular bonding between the chalcogen atoms have to be considered although these atoms have small distances to oneanother. The mean M-El distances have been found to be: Ge? O 1.762(5), Ge? S 2.226(3), Ge? Se 2.363(3), Ge? Te 2.592(5), Sn? Se 2.536(3), Sn? Te 2.741(3) Å.     

Impressive structural diversity and polymorphism in the modular compounds ABi3Q5 (A = Rb, Cs; Q = S, Se, Te)

An outstanding example of structural diversity and complexity is found in the compounds with the general formula ABi(3)Q(5) (A = alkali metal; Q = chalcogen). gamma-RbBi(3)S(5) (I), alpha-RbBi(3)Se(5) (II), beta-RbBi(3)Se(5) (III), gamma-RbBi(3)Se(5) (IV), CsBi(3)Se(5) (V), RbBi(3)Se(4)Te (VI), and RbBi(3)Se(3)Te(2) (VII) were synthesized from A(2)Q (A = Rb, Cs; Q = S, Se) and Bi(2)Q(3) (Q = S, Se or Te) at temperatures above 650 degrees C using appropriate reaction protocols. gamma-RbBi(3)S(5) and alpha-RbBi(3)Se(5) have three-dimensional tunnel structures while the rest of the compounds have lamellar structures. gamma-RbBi(3)S(5), gamma-RbBi(3)Se(5), and its isostructural analogues RbBi(3)Se(4)Te and RbBi(3)Se(3)Te(2) crystallize in the orthorhombic space group Pnma with a = 11.744(2) A, b = 4.0519(5) A, c = 21.081(3) A, R1 = 2.9%, wR2 = 6.3% for (I), a = 21.956(7) A, b = 4.136(2) A, c = 12.357(4) A, R1 = 6.2%, wR2 = 13.5% for (IV), and a = 22.018(3) A, b = 4.2217(6) A, c = 12.614(2) A, R1 = 6.2%, wR2 = 10.3% for (VI). gamma-RbBi(3)S(5) has a three-dimensional tunnel structure that differs from the Se analogues. alpha-RbBi(3)Se(5) crystallizes in the monoclinic space group C2/m with a = 36.779(4) A, b = 4.1480(5) A, c = 25.363(3) A, beta = 120.403(2) degrees, R1 = 4.9%, wR2 = 9.9%. beta-RbBi(3)Se(5) and isostructural CsBi(3)Se(5) adopt the space group P2(1)/m with a = 13.537(2) A, b = 4.1431(6) A, c = 21.545(3) A, beta = 91.297(3) degrees, R1 = 4.9%, wR2 = 11.0% for (III) and a = 13.603(3) A, b = 4.1502(8) A, c = 21.639(4) A, beta = 91.435(3) degrees, R1 = 6.1%, wR2 = 13.4% for (V). alpha-RbBi(3)Se(5) is also three-dimensional, whereas beta-RbBi(3)Se(5) and CsBi(3)Se(5) have stepped layers with alkali metal ions found disordered in several trigonal prismatic sites between the layers. In gamma-RbBi(3)Se(5) and RbBi(3)Se(4)Te, the layers consist of Bi(2)Te(3)-type fragments, which are connected in a stepwise manner. In the mixed Se/Te analogue, the Te occupies the chalcogen sites that are on the "surface" of the layers. All compounds are narrow band-gap semiconductors with optical band gaps ranging 0.4-1.0 eV. The thermal stability of all phases was studied, and it was determined that gamma-RbBi(3)Se(5) is more stable than the and alpha- and beta-forms. Electronic band calculations at the density functional theory (DFT) level performed on alpha-, beta-, and gamma-RbBi(3)Se(5) support the presence of indirect band gaps and were used to assess their relative thermodynamic stability.