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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A family of rare U(IV)-containing quaternary fluorides, Na4MU6F30 (M = Mn(2+), Co(2+), Ni(2+), Cu(2+), and Zn(2+)), was synthesized in single crystal form via a mild hydrothermal technique utilizing an in situ U(VI) to U(IV) reduction step. The modified hydrothermal route is described, and the conditions to obtain single crystals in high yield are detailed. The crystal structures were determined by single crystal X-ray diffraction. The isostructural fluorides crystallize in a new structure type in the trigonal space group P3̅c1. They exhibit a complex three-dimensional crystal structure consisting of corner- and edge-shared UF9 and MF6 polyhedra. The main building block, a U6F30(6-) group, is arranged to create two distinct hexagonal channels, inside which MF6 octahedra and Na(+) cations are located. The copper-containing member of the series, Na4CuU6F30, is unusual in that the Cu(2+) cation exhibits a rare symmetrical coordination environment consisting of six identical Cu-F bond distances, indicating the lack of the expected Jahn-Teller distortion. Magnetic susceptibility measurements of Na4ZnU6F30 yielded an effective magnetic moment of 3.42 μB for the U(4+) (f(2)) cation in the structure. Measurements of the other members containing magnetic transition-metal cations in addition to U(4+), Na4MU6F30 (M = Mn(2+), Co(2+), Ni(2+), and Cu(2+)) yielded total effective magnetic moments of 10.2, 9.84, 8.87, and 8.52 μB for the Mn-, Co-, Ni-, and Cu-containing materials, respectively. No evidence for long-range magnetic ordering was found down to 2 K. Measurements of the magnetization as a function of applied magnetic field at 2 K for Na4MnU6F30 confirmed that the U(4+) magnetic cation exhibits a nonmagnetic singlet ground state at low temperature. Thermal stability measurements and UV-vis diffuse reflectance spectroscopy are also reported.

We find evidence for long-range and short-range (ζ = 70Å at 4 K) incommensurate magnetic order on the quasi-face-centered-cubic (FCC) lattices of the monoclinic double perovskites La2NaRuO6 and La2NaOsO6 respectively. Incommensurate magnetic order on the FCC lattice has not been predicted by mean field theory, but may arise via a delicate balance of inequivalent nearest neighbour and next nearest neighbour exchange interactions. In the Ru system with long-range order, inelastic neutron scattering also reveals a spin gap ∆ ∼ 2.75 meV. Magnetic anisotropy is generally minimized in the more familiar octahedrally-coordinated 3d 3 systems, so the large gap observed for La2NaRuO6 may result from the significantly enhanced value of spin-orbit coupling in this 4d 3 material. In the context of the interplay between geometric frustration and SOC, there has been less interest in 4d and 5d DPs with the electronic configuration d 3 . One downside is that d 3 systems are generally assumed to possess spin-only S = 3/2 ground states with quenched orbital angular momentum according to the usual L − S coupling scheme, since the magnetic B ′ ions are in a local octahedral environment, and this configuration should minimize the effects of SOC. Another issue is d3 DP systems are expected to behave more classically due to the large spins, and for almost all known cases long-range magnetic order is found [12]. Although magnetic order cannot be stabilized on the FCC lattice solely by NN AFM exchange interactions J 1 > 0, finite next nearest neighour (NNN) exchange J 2 or magnetic anisotropy can alleviate the classical ground state degeneracy [13] and allow the systems to order. The phase diagram of the J 1 -J 2 model has been determined theoretically for the FCC lattice using mean field theory (MFT) [14,15]. Four different collinear magnetic phases are found depending on the sign and magnitude of J 1 and J 2 , including ferromagnetism and Type I, Type II, and Type III antiferromagnetism. All four phases have been realized in d Recently, we investigated the magnetism of the monoclinic d 3 DPs La 2 NaRuO 6 and La 2 NaOsO 6 by magnetic susceptibility, heat capacity and neutron powder diffraction (NPD) [25]. The magnetic susceptibility shows a deviation from the Curie-Weiss law (θ CW = -57 K) at a temperature of 15 K for the Ru system, accompanied by a λ anomaly in the specific heat at the same temperature. While the magnetic susceptibility of the Os system shows a similar deviation from Curie-Weiss law behaviour (θ CW = -74 K) around 12 K, only a broad feature is observed in the specific heat. Furthermore, in contrast to the expected collinear magnetic ground states for d 3 systems, we found incommensurate long-range order in La 2 NaRuO 6 with a moment size of 1.87 µ B and no magnetic Bragg peaks for La 2 NaOsO 6 down to 4 K [25]. This behaviour is difficult to understand in the general context of d 3 DPs.In this letter, we have investigated these d 3 systems with muon spin relaxation (µSR) and time-of-flight neutron scattering measuremen...

A series of monoclinic distorted double perovskites of the general formula Ln 2MIrO6 (Ln = La, Pr, Nd, Sm–Gd; M = Mg, Ni) were grown as highly faceted single crystals from a potassium hydroxide flux. The structural distortions and the magnetic interactions in A2BB′O6 double perovskites can be “designed” via a judicious choice of A, B, and B′ cation sizes and by selecting magnetic or nonmagnetic ions to occupy the A, B, and/or B′ sites. A study of the relationship between the number of magnetic ions, the degree of monoclinic distortion, and the resulting magnetic interactions was conducted. Magnetic susceptibility and field dependent magnetization measurements were performed for all synthesized compounds. It was determined that smaller A-site lanthanide cations cause more pronounced monoclinic distortions, resulting in smaller M–O–Ir (M = Mg, Ni) bond angles that correlate with higher magnetic ordering temperatures. The magnetic susceptibility and field dependent magnetization data were both consistent with canted antiferromagnetism for most titled compositions, indicating a possible trend of increased spin canting, and thus increased ferromagnetic-like interactions, as a function of smaller lanthanide A site cation size.