A new noncentrosymmetric (NCS) and polar material containing two lone-pair cations, Bi(3+) and I(5+), and exhibiting an Aurivillius-type (Bi(2)O(2))(2+) layer has been synthesized and structurally characterized. The material, BiO(IO(3)), exhibits strong second-harmonic generation (SHG), ∼12.5 × KDP (or ∼500 × α-SiO(2)), using 1064 nm radiation, and is found in the NCS polar orthorhombic space group Pca2(1) (No. 29). The structure consists of (Bi(2)O(2))(2+) cationic layers that are connected to (IO(3))(-) anions. The macroscopic polarity, observed along the c-axis direction, may be attributed to the alignment of the IO(3) polyhedra. In addition to the crystal structure and SHG measurements, polarization and piezoelectric measurements were performed, as well as electronic structure analysis.

The semiconductors Li(2)CdGeS(4) and Li(2)CdSnS(4), which are of interest for their nonlinear optical properties, were synthesized using high-temperature solid-state and polychalcogenide flux syntheses. Both compounds were found to crystallize in Pmn2(1), with R1 (for all data) = 1.93% and 1.86% for Li(2)CdGeS(4) and Li(2)CdSnS(4), respectively. The structures of both compounds are diamond-like with the tetrahedra pointing in the same direction along the c axis. The alignment of the tetrahedra results in the structure lacking an inversion center, a prerequisite for second-harmonic generation (SHG). A modified Kurtz nonlinear optical powder technique was used to determine the SHG responses of both compounds. Li(2)CdGeS(4) displayed a type I phase-matchable response of approximately 70x alpha-quartz, while Li(2)CdSnS(4) displayed a type I non-phase-matchable response of approximately 100x alpha-quartz. Diffuse-reflectance spectroscopy was used to determine band gaps of 3.10 and 3.26 eV for Li(2)CdGeS(4) and Li(2)CdSnS(4), respectively.

A methodology for the design of polar, inorganic structures is demonstrated here with the packing of lambda (Λ)-shaped basic building units (BBUs). Noncentrosymmetric (NCS) solids with interesting physical properties can be created with BBUs that lack an inversion center and are likely to pack into a polar configuration; previous methods to construct these solids have used NCS octahedra as BBUs. Using this methodology to synthesize NCS solids, one must increase the coordination of the NCS octahedra with maintenance of the noncentrosymmetry of the bulk. The first step in this progression from an NCS octahedron to an inorganic NCS solid is the formation of a bimetallic BBU. This step is exemplified with the compound CuVOF(4)(H(2)O)(7): this compound, presented here, crystallizes in an NCS structure with ordered, isolated [Cu(H(2)O)(5)](2+) cations and [VOF(4)(H(2)O)](2-) anions into Λ-shaped, bimetallic BBUs to form CuVOF(4)(H(2)O)(6)·H(2)O, owing to the Jahn-Teller distortion of Cu(2+). Conversely, the centrosymmetric heterotypes with the same formula MVOF(4)(H(2)O)(7) (M(II) = Co, Ni, and Zn) exhibit ordered, isolated [VOF(4)(H(2)O)](2-) and [M(H(2)O)(6)](2+) ionic species in a hydrogen bond network. CuVOF(4)(H(2)O)(7) exhibits a net polar moment while the heterotypes do not; this demonstrates that Λ-shaped BBUs give a greater probability for and, in this case, lead to NCS structures.

A noncentrosymmetric (NCS) polar compound, Pb 3 SeO 5 , has been hydrothermally synthesized and structurally characterized by single crystal X-ray diffraction. Pb 3 SeO 5 exhibits a two-dimensional crystal structure consisting of layers of R-PbO-like "slabs" that are linked through SeO 3 polyhedra. Structurally, it is the bridging SeO 3 polyhedra between the R-PbO-like slabs that results in the NCS and polar nature of Pb 3 SeO 5 . Powder second-harmonic generation (SHG) measurements using 1064 nm radiation indicates that Pb 3 SeO 5 exhibits a strong SHG efficiency of ∼300 Â R-SiO 2 . Additional SHG measurements indicate the material is type-I phase-matchable. Converse piezoelectric measurements revealed a d 33 value of ∼81 pm/V, and a pyroelectric coefficient of -42 μC/(m 2 K) at 65 °C was also determined. Using first principle density functional theory (DFT) calculations, we demonstrated that polarization reversal in Pb 3 SeO 5 is not energetically favorable;the material is polar but not ferroelectric. Our calculations also indicate that both Pb 2þ and Se 4þ cations exhibit a stereoactive lone-pair. In addition, differential scanning calorimetry measurements revealed an irreversible phase transition at ∼440 °C. Finally, infrared, UV-vis and thermogravimetric measurements were also performed. Crystal data:

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