Y. G. Shi

Pb2Ba3(BO3)3Cl: A Material with Large SHG Enhancement Activated by Pb-Chelated BO3 Groups

Pb(II) has long been associated with lone pair activity and is often substituted in alkali earth metal borates to create new nonlinear optical (NLO) materials with enhanced second harmonic generation (SHG) capabilities. However, large enhancement in isomorphic Pb-free analogues is rare. Here we report a new NLO material Pb2Ba3(BO3)3Cl with a phase-matching SHG response approximately 3.2× that of KDP and 6× higher than its isomorphic compound Ba5(BO3)3Cl. We show that the enhanced SHG response originates from a unique edge-sharing connection between lead-oxygen polyhedra and boron-oxygen groups, making the dielectric susceptibility more easily affected by the external electric field of an incident photon. This understanding provides a route to identify systems that would benefit from SHG-active cation substitution in isomorphic structures that exhibit weak or null SHG responses.

Na3Cd3B(PO4)4: a new noncentrosymmetric borophosphate with zero-dimensional anion units.

A new noncentrosymmetric borophosphate, Na(3)Cd(3)B(PO(4))(4), has been successfully synthesized by conventional solid state reaction for the first time. It crystallizes in the orthorhombic space group Pmc2(1) with unit cell parameters of a = 13.6854(3) Å, b = 5.3346(11) Å, c = 18.2169(4) Å, and Z = 4. Na(3)Cd(3)B(PO(4))(4) features zero-dimensional [B(PO(4))(4)](9-) anion units with Cd(2+) and Na(+)/Cd(2+) cations located around them, in which the BO(4) tetrahedron is surrounded by four PO(4) tetrahedra by sharing the vertexes of O atoms. Second harmonic generation (SHG) measurements show that Na(3)Cd(3)B(PO(4))(4) exhibits a SHG response 1.1 times larger than that of KH(2)PO(4) (KDP) and is phase matchable.

Further Examples of the P-O-P Connection in Borophosphates: Synthesis and Characterization of Li2Cs2B2P4O15, LiK2BP2O8, and Li3M2BP4O14 (M=K, Rb)

A new series of anhydrous mixed alkali-metal borophosphates--Li(2)Cs(2)B(2)P(4)O(15) (1), LiK(2)BP(2)O(8) (2), Li(3)K(2)BP(4)O(14) (3), and Li(3)Rb(2)BP(4)O(14) (4)--have been successfully synthesized by using the conventional solid-state reaction method. Compound 1 contains a novel fundamental building unit (FBU), [B(4)P(8)O(30)], with B/P = 1:2. Compound 2 contains an FBU of [B(2)P(4)O(16)] with B/P = 1:2. Compounds 3 and 4 are isotypic, and they have a [B(P(2)O(7))(2)] unit as their FBU. In all four compounds, their FBUs are connected through corner sharing to generate layered anionic partial structures, and then further linked with metallic polyhedra to form three-dimensional (3D) frameworks. Most interestingly, three of the four compounds contain direct P-O-P connections in their structures, which is extremely rare among borophosphates. Thermal analyses, IR spectroscopy, and UV/Vis/near-IR diffuse reflectance spectroscopy have also been performed on the four title compounds.

Magnetically Driven Metal-Insulator Transition in NaOsO3

The metal-insulator transition (MIT) is one of the most dramatic manifestations of electron correlations in materials. Various mechanisms producing MITs have been extensively considered, including the Mott (electron localization via Coulomb repulsion), Anderson (localization via disorder), and Peierls (localization via distortion of a periodic one-dimensional lattice) mechanisms. One additional route to a MIT proposed by Slater, in which long-range magnetic order in a three dimensional system drives the MIT, has received relatively little attention. Using neutron and x-ray scattering we show that the MIT in NaOsO(3) is coincident with the onset of long-range commensurate three dimensional magnetic order. While candidate materials have been suggested, our experimental methodology allows the first definitive demonstration of the long predicted Slater MIT.

Resistive switching phenomenon driven by antiferromagnetic phase separation in an antiperovskite nitride Mn3ZnN

A resistive-switching phenomenon driven by antiferromagnetic phase separation is observed for a manganese nitride Mn3ZnN, which crystallizes in the antiperovskite structure. Measurements of the lattice parameters, magnetic susceptibility, electrical resistivity, and specific heat from 2 K to 300 K reveal antiferromagnetic phase separation that appears below a temperature of approximately 190 K. The mechanism of the phase separation is highly complicated; nevertheless the accompanying resistive-switching phenomenon is useful for non-volatile memory applications.

Na11B21O36X2 (X=Cl, Br): Halogen Sodium Borates with a New Graphene‐Like Borate Double Layer

Borate not graphene: The [B6O12]∞(6-) single borate layer is a graphene-like layer (see figure). The weak Na(+)-Br(Cl)(-) ionic connection between the layers leads to the layer cleavage, and difficulty of the block crystal growth.

Raman spectroscopy study of α -, β -, γ − Na x Co O 2 and γ − ( Ca , Sr ) x Co O 2

Raman spectroscopy measurements have been performed on alpha-, beta-, and gamma-NaxCoO2 phases differing in their stacking of CoO6 octahedra along the c-axis direction. The results demonstrate that, in general, there are five Raman active phonons for gamma-Na0.75CoO2, two Raman active phonons for alpha-NaCoO2, and three Raman peaks for beta-Na0.6CoO2. We have also performed Raman-scattering measurements on several gamma-(Ca,Sr)(x)CoO2 (0.15 <= x <= 0.40) samples which show well-defined intercalated Ca/Sr ordering. The experimental data show that the intercalated cation ordering could result in visible alterations on Raman spectral structures. The observations of the spectral changes along with the variation of the CoO6 stacking, as well as the intercalated Sr/Ca ordering suggest that the interlayer interaction plays an important role for understanding the phonon properties in this layered system.

The effect of Ga on internal friction of pure Al before and after deformation

The grain boundary internal friction of pure Al and the same Al doped with different amounts of Ga (10, 50 and 410 ppm) was measured before and after high temperature deformation at two different modes (static tensile creep and cyclic reverse torsion). It was found that without deformation, the smaller amount of Ga (10 and 50 ppm) slightly increases, but the larger amount of Ga (410 ppm) obviously increases the activation energy. After tensile creep, the peak height for Al-10 ppm Ga and Al-50 ppm Ga decreases to a lower level, but keeps at a higher level after cyclic torsion, than that for pure Al and Al-410 ppm Ga. The results are interpreted in terms of perturbations in the grain boundaries due to slip and grain boundary roughening for stationary boundaries and an enhanced sliding by grain boundary migration. Migration and roughening are promoted by Ga contents up to 50 ppm while the effects are diminished by higher amounts of Ga. This is consistent with previous observations that smaller amounts of Ga increase the grain boundary mobility in pure Al.

Electron energy loss spectra of Na{sub 0.33}CoO{sub 2}{center_dot}yH{sub 2}O (y=0, 0.6, and 1.3)

Electron energy loss spectra have been obtained on materials with the nominal compositions of Na{sub 0.33}CoO{sub 2}{center_dot}yH{sub 2}O (y=0, 0.6, and 1.3). Spectral analysis revealed systematic changes in the low-loss energy region (<10 eV) and the core losses (O K, Co L{sub 3,2}) along with the water intercalation. The inter- (intra)band transitions and the relevant plasmon resonance were found to be sensitive to water content. Variations of the electronic structure and the Co valence states during hydration have been discussed based on our experimental results.

New phase transition in Na

We performed a Raman scattering study of Na