Syntheses, Crystal Structure, and Second Harmonic Generation Response of Four Novel Noncentrosymmetric Tellurites of Quaternary A/M/Te/O (A = Ba, Sr, Ca; M = V, Nb, Ta) System: BaTa4Te3O17, BaNb4Te3O17, SrTa4Te3O17, and CaV2TeO8.

Four new noncentrosymmetric tellurites of quaternary A/M/Te/O (A = Ba, Sr, Ca; M = V, Nb, Ta) system, namely, BaTa4Te3O17 (1), BaNb4Te3O17 (2), SrTa4Te3O17 (3), and CaV2TeO8 (4), were synthesized and characterized by single-crystal X-ray diffraction, thermal analysis, diffuse reflectance spectroscopy, and powder second harmonic generation (SHG) response measurements. The isostructural compounds 1-3 crystallize in the P212121 space group and have a three-dimensional (Ta4Te3O17)2-/(Nb4Te3O17)2- anionic framework, whereas the layered compound 4 crystallizes in the Ccc2 space group and has a [V2TeO8]2- anionic layer. The phase-matching compounds 1, 2, and 3 and the non-phase-matching compound 4 show powder SHG responses equivalent to ∼27, ∼13, ∼24, and ∼68% of that of LiNbO3, respectively.

Syntheses, Crystal Structure, and Second Harmonic Generation Response of Noncentrosymmetric Layered Selenites and Tellurites of Antimony(V), ASb3X2O12 (A = K, Rb, Cs, Tl; X = Se, Te).

Eight quaternary selenites and tellurites of antimony(V), ASb3X2O12 (A = K, Rb, Cs, Tl; X = Se, Te), have been synthesized by solid state reactions and structurally characterized by single crystal X-ray diffraction. They are isostructural compounds, which crystallize in the polar noncentrosymmetric P63mc space group with hexagonal unit cell parameter values in the ranges of a = 7.1538(1)-7.2429(1) Å and c = 11.8978(4)-12.0478(3) Å. Their noncentrosymmetric layered structure consists of hexagonal-tungsten-oxide-related (Sb3X2O12)- layers interleaved with A+ ions. They have optical band gap values of 2.90-4.46 eV and showed powder second harmonic generation response equivalent to 1.0-37.2 × KDP.

Structural characterization of quaternary selenites of tungsten(VI), A 2W3SeO12 (A = NH4, Cs, Rb, K or Tl).

The quaternary A 2W3SeO12 (A = NH4, Cs, Rb, K or Tl) selenites have been prepared in the form of single crystals by hydro-thermal and novel solid-state reactions. They were characterized by X-ray diffraction, thermal and spectroscopic studies. All of them have a hexa-gonal tungsten oxide (HTO) related [W3SeO12]2- anionic framework with pyramidally coordinated Se4+ ions. The known A 2W3SeO12 (A = NH4, Cs or Rb) compounds are isostructural with the Cs2W3TeO12 compound and have a non-centrosymmetric layered structure containing intra-layer Se-O bonds. The new compound K2W3SeO12(α) is isostructural with the K2W3TeO12 compound and has a centrosymmetric three-dimensional structure containing inter-layer Se-O bonds. It is inferred that the new Tl2W3SeO12 compound has the same three-dimensional structure as K2W3SeO12(α).

Syntheses and characterization of phosphonates and diphosphonates of molybdenum, A4[(MoO3)5(O3PR)2]·xH2O, A2[Mo2O5(O3PR)2] and A2[Mo2O5(O3P-R-PO3)] (A = K, Rb, Cs, Tl, NH4).

Twenty new molybdenum phosphonates and diphosphonates have been synthesized and structurally characterized by single crystal and powder X-ray diffraction, CHN analyses, spectroscopic and thermal studies. Four of them are molecular phenyl- and benzyl-phosphonates containing discrete [(MoO3)5(O3PR)2]4- (R = Ph or CH2Ph) cyclic anions. The sixteen non-molecular compounds are layered isostructural phenylphosphonates, A2[Mo2O5(O3PPh)2] (A = NH4, Tl, Rb, Cs) and K1.5(H3O)0.5[Mo2O5(O3PPh)2] and the corresponding diphosphonate compounds with pillared anionic layers, A2[Mo2O5(O3P(CH2)3PO3)], A2[Mo2O5(O3P(CH2)4PO3)] and A2[Mo2O5(O3P(C6H4)PO3)]. The A+ ions reside in the interlayer region as well as in the cavities within the anionic layers.

Syntheses and Characterization of AM2V2O11 (A = Ba, Sr, Pb; M = Nb, Ta) Vanadates with Centrosymmetric and Noncentrosymmetric Structures.

Five isomorphous AM2V2O11 vanadates of niobium and tantalum, namely, BaNb2V2O11, BaTa2V2O11, SrNb2V2O11, SrTa2V2O11, and PbTa2V2O11, were prepared by solid-state reactions and structurally characterized by single-crystal and powder X-ray diffraction techniques. Barium and strontium compounds, respectively, have centrosymmetric and noncentrosymmetric types of layered structure, wherein [M2V2O11]2- anionic layers are interleaved with A2+ cations. Both types of layered structure are found for lead compound. The strontium and lead compounds are type I phase-matching materials with second-harmonic-generating efficiencies of 33-50% of LiNbO3, and their dielectric properties were evaluated. A three-dimensional structural variant was also identified for strontium compounds, which crystallize in noncentrosymmetric orthorhombic space group C2221.

Synthesis and structural characterization of AMV2O8 (A = K, Rb, Tl, Cs; M = Nb, Ta) vanadates: a structural comparison of A(+)M(5+)V2O8 vanadates and A(+)M(5+)P2O8 phosphates.

Eight new quaternary vanadates of niobium and tantalum, AMV2O8 (A = K, Rb, Tl, Cs; M = Nb, Ta), have been prepared by solid state reactions and structurally characterized by single crystal and powder X-ray diffraction (XRD) techniques. The two cesium compounds, unlike the known CsSbV2O8 with a layered yavapaiite structure, have a new three-dimensional structure and the other six compounds possess the known KSbV2O8 structure type. The three types of [(MV2O8)(-)]∞ anionic frameworks of twelve A(+)M(5+)V2O8 (A = K, Rb, Tl, Cs; M = Nb, Ta, Sb) vanadates could be conceived to be built by different connectivity patterns of M2V4O18 ribbons, which contain MO6 octahedra and VO4 tetrahedra. A structural comparison of these twelve vanadates and the nineteen A(+)M(5+)P2O8 phosphates has been made. The spectroscopic studies of these eight new quaternary vanadates are presented.