Wen-Dan Cheng

A Strong Second-Harmonic Generation Material Cd4BiO(BO3)3 Originating from 3-Chromophore Asymmetric Structures

In this communication, the novel nonlinear optical crystal material Cd(4)BiO(BO(3))(3) with 3-chromophore asymmetric structures of CdO(n), BiO(6), and BO(3) groups has been prepared by a flux method, and the single crystal structure has been determined with the space group Cm. It is the largest NLO coefficient for Cd(4)BiO(BO(3))(3) among borate systems, and the strong NLO response originates from cooperation effects of the 3-chromophore asymmetric structures composed of the polar displacement of d(10) Cd(2+) ion, stereochemically active lone pair of Bi(3+), and pi-delocalization of BO(3). These evidence are provided in view of evaluations of calculated density of states and electron-density difference maps. The experimental measurements show that the features of a large SHG effect, phase-match, and high thermal stability will be favorable in industrial production and applications for Cd(4)BiO(BO(3))(3).

Syntheses and characterization of new mid-infrared transparency compounds: centric Ba2BiGaS5 and acentric Ba2BiInS5.

Two new mid-infrared transparency compounds, centric Ba(2)BiGaS(5) (1) and acentric Ba(2)BiInS(5) (2), were synthesized from a high-temperature solid-state reaction in evacuated closed silica tubes. Their crystal structures were determined by a single crystal X-ray diffraction method at 293 K. The results of crystal structure solution indicate that compound 1 crystallizes in the centrosymmetric space group Pnma with trans- (1)(∞)[BiGaS(5)](4-) chain structure, while compound 2 crystallizes in the noncentrosymmetric polar space group Cmc2(1) with cis- (1)(∞)[BiInS(5)](4-) chain structure. Two types of lone-pair electrons alignment fashions within (1)(∞)[BiMS(5)](4-) chains result in destructive (for 1) or constructive (for 2) dipole moments, as illustrated in the crystal structures and the partial electron density maps based on the first-principles electronic structure computations. Powder second-harmonic generation (SHG) experiments with a 2.05 μm pumping laser show that the SHG efficiency of the polar compound 2 is approximately 0.8 times that of KTiOPO(4) (KTP) reference. Furthermore, SHG signal intensity measurements using different size particles of powder samples indicate that compound 2 can also achieve type I phase-matching, which makes the compound promising for practical applications.

Cov2O6 Single Crystals Grown in a Closed Crucible: Unusual Magnetic Behaviors with Large Anisotropy and 1/3 Magnetization Plateau

Single crystals of CoV(2)O(6) were obtained in a closed crucible using a flux method. Magnetic measurements showed that this material displays a large magnetic anisotropy and a 1/3 magnetization plateau under a magnetic field applied along the c axis.

Syntheses, Characterization, and Optical Properties of Ternary Ba–Sn–S System Compounds: Acentric Ba7Sn5S15, Centric BaSn2S5, and Centric Ba6Sn7S20

Three new ternary Ba-Sn-S system compounds, acentric Ba(7)Sn(5)S(15), centric BaSn(2)S(5), and centric Ba(6)Sn(7)S(20) have been designed and synthesized by a conventional high-temperature solid-state reaction method using the evacuated silica tubes. The crystal structure of Ba(7)Sn(5)S(15) shows the coexistence of a SnS(4) tetrahedral and a Sn(2)S(3) trigonal bipyramid. Importantly, the larger dipole moment of the [Sn(2)S(3)](2-) trigonal bipyramid group and the polarity enhancement of the bipyramidal arrangements result in a strong SHG effect at 2.05 μm, which is 10 times of the SHG intensity of the benchmark AgGaS(2) with the particle size of 30-46 μm and twice as much as that with the particle size of 150-212 μm. Evidently, the acentric Ba(7)Sn(5)S(15) is a novel IR NLO crystal material with a wide mid-IR window and a strong SHG effect, which is the first reported among the Ba-Sn-S ternary system. Moreover, Ba(7)Sn(5)S(15) can achieve type-I phase-matching that can be used for practical applications. In the centric BaSn(2)S(5,) all Sn atoms are coordinated by five S atoms to form novel SnS(5) trigonal bipyramid polyhedrons. In the other centric Ba(6)Sn(7)S(20), there is the coexistence of the two coordination patterns with a SnS(5) trigonal bipyramid and SnS(4) tetrahedral polyhedrons, featuring a special crystal structure in the Ba-Sn-S system.

Syntheses and Characterizations of Cs2Cr3(BP4O14)(P4O13) and CsFe(BP3O11) Compounds with Novel Borophosphate Anionic Partial Structures

Explorations of the A(I)-M(III)-B(III)-P(V)-O quinary system under solid-state reactions led to an anhydrous cesium-chromium borophosphate-phosphate and an anhydrous cesium-iron borophosphate, namely, Cs(2)Cr(3)(BP(4)O(14))(P(4)O(13)) (1) and CsFe(BP(3)O(11)) (2). They both feature complicated three-dimensional (3D) frameworks and represent the first examples of borophosphate frameworks with a P-O-P connection. Compound 1 contains a novel anionic borophosphate partial structure [B(P(2)O(7))(2)](5-) with B:P = 1:4 besides an isolated [P(4)O(13)](6-) anion. Its 3D structure is composed of a layer of [CrB(P(2)O(7))(2)](n)(2n-) and a neutral layer of [Cr(2)(P(4)O(13))](n) interconnected with the linking of P-O-Cr, and the Cs ions are located at the space. Compound 2 contains another novel borophosphate anionic unit of [B(PO(4))(P(2)O(7))](4-) with B:P = 1:3, which further bridges the Fe cations to constitute the whole structure. Both compounds are of high thermal stable and transparent in the range of 0.75-7.1 microm. Magnetic measurements indicate that there exist antiferromagnetic interactions in both compounds.

Syntheses and magnetic properties study of isostructural BiM2BP2O10 (M = Co, Ni) containing a quasi-1D linear chain structure.

We present here the structures and magnetism of two quasi-1D linear chain compounds of BiM(2)BP(2)O(10) (M = Co, Ni), which were synthesized by traditional solid-state reactions for the first time. Two title compounds crystallize in the monoclinic system with space group P2(1)/c and feature novel 3D structures with a linear chain structure of {MO(6)}(n) further connected by [BP(2)O(10)](7-) anionic groups. The results of magnetic property measurements evidence the antiferromagnetic properties of both compounds in low magnetic field and a field-dependent metamagnetic transition from the antiferromagnetic to ferromagnetic ground state of the BiCo(2)BP(2)O(10) complex.

Syntheses, Crystal and Electronic Structures, and Characterizations of Quaternary Antiferromagnetic Sulfides: Ba2MFeS5 (M = Sb, Bi)

Two new quaternary sulfides, Ba(2)SbFeS(5) and Ba(2)BiFeS(5), were synthesized by using a conventional high-temperature solid-state reaction method in closed silica tubes at 1123 K. The two compounds both crystallize in the orthorhombic space group Pnma with a = 12.128(6) Å, b = 8.852(4) Å, c = 8.917(4) Å, and Z = 4 for Ba(2)SbFeS(5) and a = 12.121(5) Å, b = 8.913(4) Å, c = 8.837(4) Å, and Z = 4 for Ba(2)BiFeS(5). The crystal structure unit can be viewed as an infinite one-dimensional edge-shared MS(5) (M = Sb, Bi) tetragonal-pyramid chain with FeS(4) tetrahedra alternately arranged on two sides of the MS(5) polyhedral chain via edge-sharing (so the chain can also be written as (1)(∞)[MFeS(5)](4-)). Interestingly, the compounds have the structural type of a Ba(3)FeS(5) high-pressure phase considering one Ba(2+) is replaced by one Sb(3+)/Bi(3+), with Fe(4+) reduced to Fe(3+) for in order to maintain the electroneutrality of the system. As a result, the isolated iron ions in Ba(3)FeS(5) are bridged by intermediate MS polyhedra in Ba(2)MFeS(5) (M = Sb, Bi) compounds and form the (1)(∞)[MFeS(5)](4-) chain structure. This atom substitution of Ba(2+) by one Sb(3+)/Bi(3+) leads to a magnetic transition from paramagnetic Ba(3)FeS(5) to antiferromagnetic Ba(2)MFeS(5), resulting from an electron-exchange interaction of the iron ions between inter- or intrachains. Magnetic property measurements indicate that the two compounds are both antiferromagnetic materials with Néel temperatures of 13 and 35 K for Ba(2)SbFeS(5) and Ba(2)BiFeS(5), respectively. First-principles electronic structure calculations based on density functional theory show that the two compounds are both indirect-band semiconductors with band gaps of 0.93 and 1.22 eV for Ba(2)SbFeS(5) and Ba(2)BiFeS(5), respectively.

BaBi(SeO3)2Cl: a new polar material showing high second-harmonic generation efficiency enhanced by constructive alignment of chloride ions

The novel oxychloride BaBi(SeO3)2Cl with polar crystal structure was first synthesized by using hydrothermal method at a mild temperature of 200 °C. It crystallizes in the orthorhombic Cmc21 (36) space group with cell parameters of a = 5.2804(2) A, b = 20.0535(9) A, c = 6.9070(3) A, V = 731.39(5) A3, and Z = 4. The compound features a two-dimensional [Bi(SeO3)2Cl]2− anionic layer structure stacking along the crystallographic b-axis direction. Within the [Bi(SeO3)2Cl]2− layer, BiO4 quadrangular pyramids bridge two types of Se(1)O3 and Se(2)O3 triangular pyramid through corner-sharing manner into a [Bi(SeO3)2]− chain. The [Bi(SeO3)2]− chains are aligned along c-axis direction with chloride ions adjacent to bismuth cations, and the 2D [Bi(SeO3)2Cl]2− forms. As a consequence, local dipole moments of the building block layers are arranged in a constructive fashion, which is favourable to enhance the second-order nonlinear properties of materials. Powder Kurtz–Perry method was utilized to evaluate the second-harmonic generation (SHG) efficiency, indicating a strong SHG effect (about 16 times that of KH2PO4 (KDP) reference). More excitingly, BaBi(SeO3)2Cl can achieve type I phase-matching, which make the compound feasible for practical applications. In addition, first-principles density functional theory (DFT) calculations were also performed to illustrate the relationships between crystal structure and optical properties.

Planar tetra-coordinate carbon resulting in enhanced third-order nonlinear optical response of metal-terminated graphene nanoribbons

Metal-terminated graphene nanoribbons (M-GNRs) with planar tetra-coordinate carbons (PtC) are investigated theoretically for a third-order nonlinear optical (NLO) response by using the sum-over-states (SOS) method. The third order NLO polarizability, two-photon absorption (TPA) and nonlinear reflectivity are investigated within the third-harmonic generation (THG) or degenerate four-wave mixing (DFWM) processes. The origins of third order NLO polarizability and TPA are analyzed in terms of the charge transfer process, which indicates that tetra-coordinate carbons in M-GNRs have an important role in the third-order NLO response. The dynamic nonlinear reflectivity of the M-GNR presents a resonant characteristic due to the large third order NLO polarizability. Moreover, the third order NLO polarizability and TPA cross section values increase as the ribbon size increases in the low frequency region of incident light, which indicates that their NLO properties can be tailored by controlling the ribbon size. This paper aims to shed light on the design of NLO properties and understanding of the NLO response mechanisms of graphene related materials.

Unusually Large Magnetic Anisotropy in a CuO-Based Semiconductor Cu5V2O10

A CuO-based material Cu(5)V(2)O(10) was successfully grown in a closed crucible using Sr(OH)(2)·8H(2)O as flux. The structure of Cu(5)V(2)O(10) can be viewed as being composed of two types of zigzag Cu-O chains running along the b- and c-axes, which shows a two-dimensional crosslike framework with 12-column square tunnels along the a-axis. Magnetic measurements show that Cu(5)V(2)O(10) exhibits unexpected large magnetic anisotropy, which is the first time magnetic anisotropy energy of ∼10(7) erg/cm(3) in the CuO-based materials has been observed. The origins of large anisotropy are suggested to arise from strong anisotropic exchanges due to the particular bonding geometry and the Jahn-Teller distortion of Cu(2+) ions. Further, the band structure investigated by the GGA+U method suggests that Cu(5)V(2)O(10) is a semiconductor.