Resistive switching behavior and mechanism of HfO_(x) films with large on/off ratio by structure design

Different bilayer structures of HfO_(x)/Ti(TiO_(x)) are designed for hafnium-based memory to investigate the switching characteristics. The chemical states in the films and near the interface are characterized by x-ray photoelectron spectroscopy,and the oxygen vacancies are analyzed. Highly improved on/off ratio(~104) and much uniform switching parameters are observed for bilayer structures compared to single layer HfO_(x) sample, which can be attributed to the modulation of oxygen vacancies at the interface and better control of the growth of filaments. Furthermore, the reliability of the prepared samples is investigated. The carrier conduction behaviors of HfO_(x)-based samples can be attributed to the trapping and de-trapping process of oxygen vacancies and a filamentary model is proposed. In addition, the rupture of filaments during the reset process for the bilayer structures occur at the weak points near the interface by the recovery of oxygen vacancies accompanied by the variation of barrier height. The re-formation of fixed filaments due to the residual filaments as lightning rods results in the better switching performance of the bilayer structure.

Structure and superconducting properties of Ru_(1-x)Mo_(x)(x=0.1-0.9)alloys

We report the detailed crystal structures and physical properties of Ru_(1-x)Mo_(x)alloys in the solid solution range of x=0.1-0.9.Structure characterizations indicate that the crystal structure changes from the hcp-Mg-type,toβ-CrFe-type,and then bcc-W-type.The measurements of physical properties show that the Ru_(1-x)Mo_(x)samples with x≥0.2are superconductors and the superconducting transition temperature T_c as a function of Mo content exhibits a dome-like behavior.

Critical behaviour in nuclear structure from spherical to axially symmetric deformed shape in IBM

To compare with the predictions of the transitional dynamical symmetry X（5） proposed by Iachello （2001 Phys. Rev. Lett. 87 052502）, the critical behaviours of U（5） SU（3） are studied in the space of two control parameters in the interacting boson model （IBM）. A simple-shaped phased diagram has been presented. It is found that X（5） predictions cannot be exactly reproduced by our calculations and that the best agreement is close to the calculations with boson numbers N = 11 and 12. By comparing with experimental data on X（5）-like nuclei, we find that X（5） predictions and IBM calculations can reproduce the energy ratios and E2 transition ones.

Quantum and classical correlations for a two-qubit X structure density matrix

We derive explicit expressions for quantum discord and classical correlation for an X structure density matrix. Based on the characteristics of the expressions, the quantum discord and the classical correlation are easily obtained and compared under different initial conditions using a novel analytical method. We explain the relationships among quantum discord, classical correlation, and entanglement, and further find that the quantum discord is not always larger than the entanglement measured by concurrence in a general two-qubit X state. The new method, which is different from previous approaches, has certain guiding significance for analysing quantum discord and classical correlation of a two-qubit X state, such as a mixed state.

Effects of Yttrium on the Microstructures and Interfaces in a Low Expansion Superalloy

The forms and structures of the phases in Fe-Ni-Co-Nb-Ti-Si low expansion superal-loys have been studied using analytical electron microscopy, high resolution electron microscopy, chemical phase analysis, X-ray diffraction, etc. The effects of yttrium on the microstructures and properties in the superalloys have also been investigated. The results reveal that trace yttrium mainly located in the platelet precipitates makes the crystal structure changed. The platelet precipitates become smaller, denser and rather homogeneous with appropriate yttrium addition. Compared with the conventional low expansion superalloy, the misfit of the platelet phase with the matrix in the yttrium-containing low expansion superalloy decreases from 0.7% to 0.07%, which indicates very low stress at the interface.

Construction of Ultrathin Layered MXene-TiN Heterostructure Enabling Favorable Catalytic Ability for High-Areal-Capacity Lithium-Sulfur Batteries

Catalysis has been regarded as an effective strategy to mitigate sluggish reaction kinetics and serious shuttle effect of Li-S batteries.Herein,a spherical structure consists of ultrathin layered Ti_(3)C_(2)T_(x)-TiN heterostructures(MX-TiN)through in-situ nitridation method is reported.Through controllable nitridation,highly conductive TiN layer grew on the surface and close coupled with interior MXene to form unique 2D heterostructures.The ultrathin heterostructure with only several nanometers in thickness enables outstanding ability to shorten electrons diffusion distance during electrochemical reactions and enlarge active surface with abundant adsorptive and catalytic sites.Moreover,the(001)surface of TiN is dominated by metallic Ti-3d states,which ensures fast transmitting electrons from high conductive MX-TiN matrix and thus guarantees efficient catalytic performance.Calculations and experiments demonstrate that polysulfides are strongly immobilized on MX-TiN,meanwhile the bidirectional reaction kinetics are catalytically enhanced by reducing the conversion barrier between liquid LiPSs and solid Li_(2)S_(2)/Li_(2)S.As a result,the S/MX-TiN cathode achieves excellent long-term cyclability with extremely low-capacity fading rate of 0.022%over 1000 cycles and remarkable areal capacity of 8.27 mAh cm^(−2) at high sulfur loading and lean electrolytes.

Extraction and Absolute Crystal Structure of Stachyose

The title compound stachyose （C24H42021）, a biologicaly active tetrasaccharide, was characterized by X-ray diffraction analysis. It crystallizes in the orthorhombic system, space group P21212 with C24H42021, a = 23.8760（3）, b = 12.71028（I2）, c = 10.81279（11） A, V = 3281.36（6） A3, Z = 4, Dc= 1.511 g/cm3, Mr = 746.58, F（000） = 1576, and μ = 1.230 mm^-1. The final R = 0.0666 and wR = 0.1797 for 6298 observed reflections （I 〉 2σ（I））. The molecular crystal structure of stachyose shows absolute stereochemistry of fl-D-fructofuranosyl a-D-galactopyranosyl- （1→6）-a-D-galactopyranosyl-（1→6）-a-D-glucopyranoside. The molecule is composed of two a-D-galactoses, one a-D-glucose, and one r-D-fructose and sequentially linked as a-Gal （1 →6） a-Gal （1→6） a-Glc （1→2） fl-Fru. The title compound is stacked into a 3D layer structure through hydrogen bonds. NMR spectra data are also assigned. In the crystal packing, X-ray analysis indicates that there are two intramolecular and eleven intermolecular hydrogen bonds in this compound.

Synthesis and X-ray Crystal Structure of a New Molecular Clip

The synthesis and X-ray crystal structure of a new molecular clip 2 was reported. It （C24H24N4O2, Mr = 400.47） crystallizes in the space group C2/c with a = 15.587（2）, b = 8.5805（12）, c = 15.259（2） A, β = 102.448（3）°, V= 1992.9 （5）A63, Z = 4, Dc = 1.335 g/cm63,μ = 0.087 mm^-1 and F（000） = 848. It remains monomeric in the crystal and a tape-like structure is formed in the crystal structure of molecular clip. The most unusual structural feature of 2 is the boat conformation of its cyclohexyl ring imposed by the ring fusion at C（9）-C（9a）.

Impact of Surface Passivation on the Electronic Structure and Optical Properties of the Si1-xGex Nanowires

The electronic structures and optical properties of the [llO]-oriented Sil-xGex nanowires （NWs） passivated with different functional groups （-H, -F and-OH） are investigated by using first-principles calculations. The results show that surface passivation influences the characteristics of electronic band structures significantly： the band gap widths and types （direct or indirect） of the Si1-xGe, NWs with different terminators show complex and robust variations, and the effective masses of the electrons in the NWs can be modulated dramatically by the terminators. The study of optical absorption shows that the main peaks of the parallel polarization component of Si1-x Gex NWs passivated with the functional groups exhibit prominent changes both in height and position, and are red-shifted with respect to those of corresponding pure Si NWs, indicating the importance of both the terminators and Ge concentrations. Our results demonstrate that the electronic and optical properties of Si1-xGex NWs can be tuned by utilizing selected functional groups as well as particular Ge concentrations for customizing purposes.

Synthesis, Crystal Structure and Biological Activity of 1,5-Bis(4-methoxyphenyl)-3-(4-methyl-1,2,3-thiadiazol-5-yl)pentane-1,5-dione

The title compound 1,5-bis（4-methoxyphenyl）-3-（4-methyl-1,2,3-thiadiazol-5-yl）-pentane-1,5-dione （C22H22N2O4S, Mr=410.49） has been synthesized by the reaction of 4-methyl-1,2,3-thiadiazole-5-carbaldehyde with 4-methoxyacetophenone, and its structure was characterized by IR, 1H NMR, H RMS, elemental analysis and single-crystal X-ray diffraction. The crystal of the title compound belongs to monoclinic, space group P21/c with a=11.159（3）, b=9.002（3）, c=20.192（6）, β=93.393（5）°, Z=4, V=2024.6（10） 3 , Dc=1.347 g/cm3 , μ=0.191 mm-1 , F（000）=864, R=0.0333 and wR （I〉2σ （I））=0.0840. In this molecule, the 1,2,3-thiadiazol ring is nearly vertical with both phenyl rings, and intermolecular weak hydrogen bonds of C-H…O and C-H…N types together with π-π stacking interactions and interactions between S（1）…N（2） are observed. The above three kinds of interactions extend the molecules into a two-dimensional layer framework. The preliminary biological test showed that the title compound had fungicidal activity.

Extraction and Crystal Structure of β-Sitosterol

The title compound β-sitosterol（C29H50O）, an active phytosterol in many medicinal and edible plants, was characterized by X-ray diffraction analysis and extensive nuclear magnetic resonance（NMR） data. It crystallizes in monoclinic system, space group P21 with C29H50O·1/2H2O, a = 9.4226（7）, b = 7.4824（9）, c = 36.889（3） , V = 2597.0（4） 3, Z = 4, Dx = 1.084 g/cm3, Mr = 423.70, F（000） = 948, and μ = 0.064 mm-1. The final R = 0.0886 and wR = 0.2234 for 10157 observed reflections（I 〉 2σ（I））. The molecular crystal structure of β-sitosterol shows relative stereochemistry of 24R-ethylcholest-5-en-3β-ol. The molecule is composed of one steroid nucleus（3 six-membered rings and 1 five-membered ring） and one sidechain of 10 carbons. There are two C29H50O molecules and one H2O molecule in a symmetrical unit, and the title compound is stacked into a special laminated structure through hydrogen bonds and van der Waal forces. The special laminated structure was first reported.

Influence of supersaturation on structure of sodium aluminate solutions with medium concentration: a solution X-ray diffraction study

Influence of supersaturation on the structure of a series of freshly prepared supersaturated sodium aluminate solutions with medium concentration was investigated by solution X-ray diffraction. Experimental results show that the basic Al-containing species in all kinds of supersaturated solution is four-coordinated ions. Opposite to Al-O distance contracted in highly concentrated solution, a little expand of the Al-O distance from 1.75 *@ to 1.85 *@ occurs with increasing supersaturation, which is consistent with the occurrence of oligomeric aluminate species. Meanwhile, O-O distance in the first shell of H 2O-H 2O(OH) in supersaturated sodium aluminate solution is obviously longer than in hydroxide sodium solution and becomes longer and longer with increasing supersaturation. Na-O bond length is about 2.4 *@ and changes little with supersaturation. The reason for Al-O bond expanding with supersaturation and its influence on the stability of solution was discussed.

Phase Behavior and Crystal Structure of Perovskite-Type Rare Earth Complex Oxides

Several compounds of rare earth complex oxides containing manganese and titanium were synthesized in Ar, and their crystal structures were analyzed by powder X-ray diffraction data and Rietveld method. Structures of A0.67Ln0.33 Mn0.33Ti0.6703（A = Ca or Sr and Ln = rare earth） were found to have orthorhombic symmetry with the space group Pnrna, and their interatomic distances and bond angles were obtained. This space group was also derived from electron microscopic study. Electrical conductivity of Cao.67Ln0.33Mn0.33Ti0.6703 for several rare earth elements showed a semiconducting property with the activation energy of 0.4 eV. Some of these compounds of the strontium system show the antiferromagnetic properties below 10 K.

Synthesis and Crystal Structure of(3S,4R,Z)-3,6-dimethyl-2-(3-methylbut-2-enylidene)-2,3,3a,4,7,7a-hexahydrobenzofuran-3,4-diol

The title compound of（3S,4R,Z）-3,6-dimethyl-2-（3-methylbut-2-enylidene）-2,3,3a,4,7,7a-hexahydrobenzofuran-3,4-diol,C15H22O3,as a potential gastric cytoprotective agent has been synthesized by the reduction of bisabolangelone in methanol with sodium borohydride.The title compound was characterized by IR and NMR spectra.Meanwhile,the crystal was obtained and determined by X-ray single-crystal diffraction.Crystal data：monoclinic system,space group P21 with a = 6.0692（12）,b = 8.9954（18）,c = 13.182（3） ,β = 92.59（3）°,V = 718.9（2） 3,Z = 2,F（000） = 272,Dc = 1.156 g/cm3,μ = 0.633 mm-1,R = 0.0362 and wR = 0.1051 for 9490 independent reflections（Rint = 0.0172） and 2461 observed reflections（I 2σ（I））.Intermolecular O-H…O interactions link the molecules into one-dimensional infinite chains running along the b axis,which contributes to the stability of the crystal structure.

Structure of MgSO_4 in Concentrated Aqueous Solutions by X-Ray Diffraction

Detailed time-and-space-averaged structure of MgSO4 in the concentrated aqueous solutions was investigated via X-ray diffraction with an X’pert Pro θ-θ diffractometer at 298 K, yielding structural function and radial distribution function（RDF）. The developed KURVLR program was employed for the theoretical investigation in consideration of the ionic hydration and ion association. Multi-peaks Gaussian fitting method was applied to deconvolving the overlapping bands of Differential radial distribution function（DRDF）. The calculation of the geometric model shows that octahedrally six-coordinated Mg（H2O）62＋, with an Mg2＋…OW bond length of 0.201 nm dominates in the solutions. There exists contact ion-pair（CIP） in the more concentrated solution（1：18, H2O/salt molar ratio） with a coordination number of 0.8 and a characteristic Mg…S distance of 0.340 nm. The result indicates the hydrated SO42– ion happens in the solution. The S…OW bond distance was determined to be 0.382 nm with a coordination number of 13. The fraction of CIP increases significantly with the increasing concentration. The symmetry of the hydration structure of sulfate ion is lowered by forming complex with magnesium ion.

Synthesis,Crystal Structure and Thermal Analysis of N-(2,3-Dimethyl-phenyl)-N'-(methoxyl formyl)thiourea

N-（2,3-Dimethyl-phenyl）-N＇-（methoxyl formyl）thiourea was synthesized by the reacting of 2,3-dimethylaniline,potassium thiocyanate（KSCN） and methyl chloroformate（ClCOOCH 3）.Single crystal was obtained by slowly evaporation solvent at room temperature.The structure was characterized by elemental analysis,IR and X-ray crystalography.The compound crystallized：a triclinic system with space group Pī,a=0.83440（12） nm,b=0.89113（13） nm,c=0.93015（13） nm,α=76.548（2） o,β=63.906（2） o,γ=82.538（2） o,V=0.60379（15） nm 3,Z=2,D c =1.311 mg/m 3,F（000）=252,μ=0.256 mm-1,R 1 =0.0379,wR 2 =0.0919.The specific heat capacity of the title compound was determined by a Micro-DSC method,and the specific heat capacity was 1.25 J·g-1 ·K-1 at 298.15 K.Thermodynamic functions,relative to those at the standard temperature of 298.15 K,were calculated via thermodynamic relationship.The thermal behavior of the title compound under a non-isothermal condition was studied by differential scanning calorimetry/thermogravimetric（DSC/TG） method.There was an obvious endothermic peak in the DSC curve,the peak temperature was 479.43 K.The compound mass loss was 89.94% observed from the TG curve.

Synthesis,Crystal Structure,and Biological Activity of Naphthalen-2-yl4-methyl-1,2,3-thiadiazole-5-carboxylate

The title compound naphthalen-2-yl-4-methyl-1,2,3-thiadiazole-5-carboxylate （C 14 H 10 N 2 O 2 S,M r=270.31） was synthesized by the reaction of 4-methyl-1,2,3-thiadiazole-5-carbonyl chloride with 2-naphthol,and its structure was characterized by IR,1 H NMR,high-resolution mass spectrometry and single-crystal X-ray diffraction.The crystal belongs to orthorhombic,space group Pbcn with a=23.475（5）,b=9.6640（19）,c=10.814（2）,β=90.00°,Z=8,V=2453.2（9） 3,M r=270.30,D c=1.464 g/cm 3,μ=0.262 mm-1,F（000）=1120,R=0.0444 and wR=0.1099.X-ray analysis revealed that the thiadiazole and naphthalene rings were non-planar,while the thiadiazole ring and the ester group were essentially planar,and two intermolecular hydrogen bonds C（6） H（6）···O（1） and C（14） H（14）···O（1） were observed.The preliminary biological test showed that the title compound had antifungal and antivirus activities against tobacco mosaic virus.

Crystal structure and thermal expansion of perovskites containing uranium(VI) and rare-earth elements

By the method of high-temperature reactions in solid phase, compounds with the general formula MⅡ（AⅢ2/3U1/3）O3（MⅡ=Sr, AⅢ=Sc, In;MⅡ=Ba, AⅢ=Sc, In, Y, Nd-Lu） were synthesized.Their structures（space groups Fm 3 m and Pnma） were refined by the Rietveld method and morphotropic transition in Ba（Ln2/3U1/3）O3 on the border of Gd-Tb was discovered.By means of high-temperature X-ray diffraction, phase transitions were studied and thermal expansion coefficients were determined.

Synthesis and Crystal Structure of N-[4-(4-Methyl-phenylsulfamoyl)-phenyl]- 4-methyl-1,2,3-thiadiazole-5-carboxamide

The crystal structure of the title compound （C17H16N4O3S2, Mr = 388.46） has been determined by single-crystal X-ray diffraction. The crystal belongs to monoclinic, space group P21/c with a = 13.688（2）, b = 16.704（3）, c = 8.3308（12）A, β = 99.474（6）°, V = 1878.8（5） A^3, Mr = 388.46, Z = 4, Dc = 1.373 g/cm3, μ = 0.308 mm^–1, F（000） = 808, R = 0.0389 and wR = 0.0917. X-ray analysis reveals that the crystal structure involves intermolecular N–H…O and N–H…N hydrogen bonds, which link the molecules into a layer parallel to the ac plane.

Synthesis and Crystal Structure of Cupric Complex with Propylenebis(oxamic acid)

The violet red sheet like single crystals of dimeric complex K 2Cu(pba)·3H 2O) 2, where pba=propylenebis (oxamic acid), were prepared. Crystals are triclinic, molecular formula Cu 2K 4O 18 N 4C 14 H 24 , M r =819.84, space group P1, a=10.450(2), b=10.675(3), c=13.054(9) , α=107.04(5), β=100.21(6), γ=88.54(2)°, V=1370(1) 3, D x =1.99 g/cm 3 and Z=2. The structure was solved by direct methods with final R =0.050 and R w =0.066 for 3827 observed reflections with I】3σ(I) . Two nitrogen atoms and two oxygen atoms from the oxamide coordinate to the Cu Ⅱ atom forming a distorted square planar geometry.