Study of surface cell Madelung constant and surface free energy of nanosized crystal grain

Surface cell Madelung constant is firstly defined for calculating the surface free energy of nanosized crystal grains, which explains the physical performance of small crystals and may be greatly beneficial to the analysis of surface states and the study of the dynamics of crystal nucleation and growth. A new approximative expression of the surface energy and relevant thermodynamic data are used in this calculation. New formula and computing method for calculating the Madelung constant α of any complex crystals are proposed, and the surface free energies and surface electrostatic energies of nanosized crystal grains and the Madelung constant of some complex crystals are theoretically calculated in this paper. The surface free energy of nanosized-crystal-grain TiO₂ and the surface electrostatic energy(absolute value) of nanosized-crystal-grain α -Al₂O₃ are found to be the biggest among all the crystal grains including those of other species.     

Annealing Effect on Photovoltages of Quartz Single Crystals

We investigate the photovoltaic effects of quartz single crystals annealed at high temperatures in ambient atmosphere. The open-circuit photovoltages and surface morphologies strongly depend on the heating treatments. When the annealing temperature increases from room temperature to 900℃, the rms roughness of quartz single crystal wafers increases from 0.207 to 1.011 nm. In addition, the photovoltages decrease from 1.994μV at room temperature to 1.551 μV after treated at 500℃, and then increase up to 9.8μV after annealed at 900℃. The inner mechanism of the present photovoltaic response and surface morphologies is discussed.     

α-Al2O3单晶的热释光和光释光特性

研究了纯α-Al₂O₃单晶的热释光发光曲线和三维发光谱，以及光释光衰变曲线，对它们的发光机理和剂量学特性进行了分析和讨论.实验观察到α-Al₂O₃单晶β射线照射后立即测量的热释光发光曲线，有峰温为76℃和207℃两个发光峰.经γ射线照射数小时后测量的三维发光谱，只有峰温207℃波长为416 nm发光峰，它与α-Al₂O₃:C晶体的发光波长基本相同，是受热激发到导带的电子与F< 关键词： 2O₃')" href="#">α-Al₂O₃ 三维发光谱 TL/OSL剂量响应     

Effects of NaN3 Added in Fe-C System on Inclusion and Impurity of Diamond Synthesized at High Pressure and High Temperature

Effects of NaN3 added in Fe-C system to synthesize nitric diamond at high pressure and high temperature are investigated. Diamond crystals with high nitrogen concentration are synthesized by the system of Fe-C and NaN3 additive at pressure 5.8 GPa and at temperatures 1750-1780 K for 15 min. The synthetic diamond crystals have a cubo-octahedral or octahedral shape with yellowish green or green colour. Some disfigurements are observed on the surfaces of most diamond crystals. The composition and content of inclusions formed by iron in diamond are changed and iron nitride is detected in diamond crystals synthesized with Fe-C-NaN3 additive. As the amount of NaN3 additive increases, Fe3C decreases and iron nitride increases with α-Fe being nearly constant. Moreover, the nitrogen concentrations in diamond crystals synthesized with 1.5 wt% NaN3 additive is up to 2250ppm in substitutional form.     

A STUDY ON SYNTHESIS OF La1-x SrxCrO3 BY SOL-GEL AND THEIR ELECTRICAL PROPERTIES

La_1-x Sr_xCrO₃ nanoparticles were prepared by the sol-gel method. The sintering temperature of the samples could be decreased to about 400 K. The crystal structures of La_1-x Sr_xCrO₃ at room temperature are all of the othorhombic perovskite GdFeO₃-type (x≤0.4). And the electrical conductivity increases with x, but when x>0.3 it decreases. The higher the sintering temperature, the better the electrical conductivity, because the grain size of the examples increases with increasing sintering temperature.     

Synthesis and study the influence of yttrium doping on band structure,optical, non-linear optical and dielectric results for Ca12Al14O33 (C12A7) single crystals grown using traveling-solvent floating zone (TSFZ) method

Ca₁₂Al₁₄O₃₃(C12A7)and Y_0.02Ca_11.98Al₁₄O₃₃(Y-C12A7)single crystals were grown by using the traveling-solvent floating zone(TSFZ)method.The temperature was increased to avoid the bubbles and cracks which may be formed during the preparation of the ingot material.We have started with the flux higher than the normal to avoid the bubbles and make good treatment for the solid-liquid interface.The structures of both Ca₁₂Al₁₄O₃₃(C12A7)and Y_0.02Ca_11.98Al₁₄O₃₃(Y-C12A7)were studied by using x-ray diffraction(XRD).Optical properties for C12A7 and Y-C12A7 single crystals have been studied in order to determine the optical parameters such as optical energy gap(Eg),refractive index n,oscillating energy(Eo),dispersion energy(Ed),volume energy loss function(VELF),and surface energy loss function(SELF).Finally,a new result for these samples is that the third-order nonlinear optical susceptibility(χ(3))was determined.The results have been discussed with effect of Y-doping on the C12A7 single crystals for optical and industrial applications.     

α-Al2O3:C晶体的热释光和光释光特性

以高纯α-Al₂O₃和石墨为原料,采用温梯法生长了α-Al₂O₃：C晶体,使用Ris TL/OSL-DA-15型热释光和光释光仪研究了其热释光和光释光特性.α-Al₂O₃：C晶体在462K附近有单一热释光峰,发射波长位于410nm.随着辐照剂量的增加,热释光强度逐渐增强,462K的热释光特征峰位置保持不变.α-Al₂O₃：C晶体的 关键词： 2O₃：C')" href="#">α-Al₂O₃：C 热释光 光释光     

Single crystal growth and characterizations of iron arsenide superconductor BaFe2-xNixAs2（0.0≤x≤0.12）

A series of big single crystals of BaFeFe_2-xNi_xAs₂ have been prepared by the FeAs self-flux method, with nominal nickel doping x = 0--0.12. The dimensions of the cleaved crystals are over 10~mm along ab plane and ～ 2~mm in maximum along the c direction. The measurements of x-ray diffraction, electrical resistance and magnetic property are carried out on the crystals. For the undoped parent compound BaFe₂As₂, both resistance and magnetization data display an anomaly associated with spin density wave and/or structural phase transition, with the transition temperatures at ～ 138~K. For Ni-doped BaFe_2-xNi_xAs₂ crystals, the superconducting critical temperature T_c ranges from 4.3~K for x=0.06 sample to 20~K for the optimally doped x=0.10 crystal.     

RAMAN SCATTERING OF α-ET3(ReO4)2 CHARGE-TRANSFER SALT

We describe the results of Haman studies on C=C stretch modes in α-ET₃(ReO₄)₂ charge-transfer salt with the incident laser beam polarised perpendicular and parallel to the large flat face of plate-like crystal. We have assigned central C=C stretch mode at 1454 cm^-1 and ring C=C stretch mode at 1470cm^-1. The change in ring C=C stretch vibration was observed at the metal-insulator transition of α-ET₃(ReO₄)₂ on warming due to the distortion of the ET molecules.     

Microstructure,optical,and photoluminescence properties ofβ-Ga2O3films prepared by pulsed laser deposition under different oxygen partial pressures

Theβ-Ga₂O₃films are prepared on polished Al₂O₃(0001)substrates by pulsed laser deposition at different oxygen partial pressures.The influence of oxygen partial pressure on crystal structure,surface morphology,thickness,optical properties,and photoluminescence properties are studied by x-ray diffraction(XRD),atomic force microscope(AFM),scanning electron microscope(SEM),spectrophotometer,and spectrofluorometer.The results of x-ray diffraction and atomic force microscope indicate that with the decrease of oxygen pressure,the full width at half maximum(FWHM)and grain size increase.With the increase of oxygen pressure,the thickness of the films first increases and then decreases.The room-temperature UV-visible(UV-Vis)absorption spectra show that the bandgap of theβ-Ga₂O₃film increases from4.76 e V to 4.91 e V as oxygen pressure decreasing.Room temperature photoluminescence spectra reveal that the emission band can be divided into four Gaussian bands centered at about 310 nm(~4.0 e V),360 nm(~3.44 e V),445 nm(~2.79 e V),and 467 nm(~2.66 e V),respectively.In addition,the total photoluminescence intensity decreases with oxygen pressure increasing,and it is found that the two UV bands are related to self-trapped holes(STHs)at O1 sites and between two O2-s sites,respectively,and the two blue bands originate from V_Ga^2-at Ga1 tetrahedral sites.The photoluminescence mechanism of the films is also discussed.These results will lay a foundation for investigating the Ga₂O₃film-based electronic devices.     

Effect of the stoichiometry on the electronic structure of the Ni（111）/α-Al2O3（0001） interface： a first-principles investigation

In this paper first-principles calculations of Ni（111）/α-Al2O3（0001） interfaces have been performed, and are compared with the preceding results of the Cu （111）/α-Al2O3（0001） interface [2004 Phil. Mag. Left. 84 425]. The AI- terminated and O-terminated interfaces have quite different adhesion mechanisms, which are similar to the Cu（111）/α Al2O3（0001） interface. For the O-terminated interface, the adhesion is caused by the strong O-2p/Ni-3d orbital hybridization and ionic interactions. On the other hand, the adhesion nature of the Al-terminated interface is the image-like electrostatic and Ni-Al hybridization interactions, the latter is substantial and cannot be neglected. Charge transfer occurs from Al2O3 to Ni, which is opposite to that in the O=terminated interface. The charge transfer direction for the Al-terminated and O-terminated Ni（111）/α-A1203（0001） interfaces is similar to that in the corresponding Cu（111）/α- Al2O3（0001） interface, but there exist the larger charge transfer quantity and consequent stronger adhesion nature, respectively.     

Temperature-frequency dependence and mechanism of dielectric properties for γ-Y2Si2O7

This paper reports that single-phase γ-Y2Si2O7 is prepared via a sufficient blending and cold-pressed sintering technique from Y2O3 powder and SiO2 nanopowder. It studies the dielectric properties of γ-Y2Si2O7 as a function of the temperature and frequency. The γ-Y2Si2O7 exhibits low dielectric loss and non-Debye relaxation behaviour from 25 to 1400℃ in the range of 7.3-18 GHz. The mechanism for polarization relaxation of the as-prepared γ-Y2Si2O7 differing from that of SiO 2 is explained. Such particular dielectric properties could potentially make specific attraction for extensive practical applications.     

The effects of interstitial oxygen on superconducting electronic phases in strontium and oxygen co-doped La1.937Sr0.063CuO4＋δ

Strontium and oxygen co-doped La1.937Sr0.063CuO4＋δ superconductor with Tc≈ 40K, which is obtained by oxidizing strontium-doped starting ceramic sample La1.937Sr0.063CuO4 in NaC10 solution, is annealed under different conditions to allow interstitial oxygen to redistribute. The evolution of the intrinsic superconducting property with the oxygen redistribution is studied in detail by magnetic measurements in various fields. It is found that there occurs the electronic phase separation from the single superconducting phase with Tc ≈ 40 K into two coexisting superconducting states with values of Tc： 15 and 40K or of 15 and 35 K in this system, depending on annealing condition. Our results indicate that the 15, 35 and 40 K superconducting phases associated with the excess oxygen redistribution are all thermodynamically meta-stable intrinsic states in this Sr/O co-doped cuprate.     

Numerical study of IP3-induced Ca2+ spiral pattern evolution

The effect of change in concentration of messenger molecule inositol 1,4,5-trisphosphate (IPspiral wave, Ca$^{2 + }$, IPspiral wave, Ca$^{2 + }$, IP$_{3}$Project supported by the National Natural Science Foundation of China (Grant Nos 10575041 and 10747005)0545The effect of change in concentration of messenger molecule inositol 1,4,5-trisphosphate (IP$_{3})$ on intracellular Ca$^{2 + }$spiral pattern evolution is studied numerically. The results indicate that when the IP$_{3}$ concentration decreases from 0.27\,$\mu $M, a physiologically reasonable value, to different values, the spiral centre drifts to the edge of the medium and disappears for a small enough IP$_{3}$ concentration. The instability of spiral pattern can be understood in terms of excitability-change controlled by the IP$_{3}$ concentration. On the other hand, when the IP$_{3}$ concentration increases from 0.27\,$\mu $M, a homogeneous area with a high Ca$^{2 + }$ concentration emerges and competes with the spiral pattern. A high enough IP$_{3}$ concentration can lead the homogeneous area to occupy the whole medium. The instability of spiral pattern is ascribed to the change in stability of a stationary state with a high Ca$^{2 + }$ concentration.     

Stability of small Ni-Ti bimetallic clusters studied by density functional theory

The low-energy structures and the electronic and the magnetic properties of small NiNiNi$_{m}$Ti$_{n}$ clusters, lowest-energy structure, electronic and magnetic propertiesProject supported by the National Natural Science Foundation of China (Grant No.~10874039), and the Natural Science Foundation of Hebei Province of China (Grant Nos.~A2009000246 and 2009000243).3120A, 3640B, 2110K7/3/2009 12:00:00 AMThe low-energy structures and the electronic and the magnetic properties of small NiNiNi$_{m}$Ti$_{n}$ clusters, lowest-energy structure, electronic and magnetic propertiesProject supported by the National Natural Science Foundation of China (Grant No.~10874039), and the Natural Science Foundation of Hebei Province of China (Grant Nos.~A2009000246 and 2009000243).3120A, 3640B, 2110K7/3/2009 12:00:00 AMThe low-energy structures and the electronic and the magnetic properties of small Ni$_{n}$Ti$_{n}$ ($n=1$--$6$) and Ni$_{m}$Ti$_{n}$ ($1 \le n \le 4$, $1 \le m \le 4$, $n \ne m$) clusters are investigated by performing all-electron calculations based on density functional theory. Ground states and several isomers near the ground states are determined for these clusters. The results indicate that the growth of small Ni$_{m}$Ti$_{n}$ clusters prefers to form rich Ti--Ni and Ti--Ti bonds. When the percentage of titanium atoms is significantly greater than that of nickel atoms, the nickel atoms are most frequently found above the surface; in contrast, the titanium atoms prefer the bridging sites. A M\"{u}lliken spin population analysis indicates that the total spin of titanium-nickel clusters is not always zero.http://cpb.iphy.ac.cn/CN/10.1088/1674-1056/19/4/043102https://cpb.iphy.ac.cn/CN/article/downloadArticleFile.do?attachType=PDF&id=111644NimTin;clusters;lowest-energy;structure;electronic;and;magnetic;propertiesThe low-energy structures and the electronic and the magnetic properties of small Nin Tin(n = 1-6) and Ni m Ti n(1 ≤ n ≤ 4,1 ≤ m ≤ 4,n ≠ m) clusters are investigated by performing all-electron calculations based on density functional theory.Ground states and several isomers near the ground states are determined for these clusters.The results indicate that the growth of small Ni m Ti n clusters prefers to form rich Ti-Ni and Ti-Ti bonds.When the percentage of titanium atoms is significantly greater than that of nickel atoms,the nickel atoms are most frequently found above the surface;in contrast,the titanium atoms prefer the bridging sites.A Mu¨lliken spin population analysis indicates that the total spin of titanium-nickel clusters is not always zero.     

Growth of Mn5Ge3 ultrathin film on Ge（111）

The growth of Mn5Ge3 ultrathin films with different thicknesses, prepared by solid phase epitaxy, is studied. The results of scanning tunnelling microscopy and low energy electron diffraction studies show that the film can be formed and it is terminated with a （√3 × √3） R30° surface reconstruction when the thickness of Mn exceeds 3 monolayers. The magnetic properties show that the Curie temperature is about 300 K and the T^2-dependent behaviour is observed to remain up to 220 K.     

Effects of exchange interaction and spin-fluctuation on the magnetic and magneto-optic properties of NdF3

The exchange interaction between the electrons in the different magnetic ions and the spin-fluctuation of the magnetic ions exist in the paramagnetic media NdF3. The exchange interaction between the electrons in the different magnetic ions may be equivalent to an effective field Hin that is in direct proportion to the magnetization M. The spin-fluctuation of the magnetic ions leads the coefficient of the effective field to vary with temperature. The effective field is given as Hin = -（0.75 ＋ 0.22T） × 10^-5M in NdF3. When the secondary crystal field effect is taken into account, the magnetic susceptibility and Verdet constant are calculated for NdF3 by means of the effective field Hin and the applied field He. The calculated results are in agreement with the measured ones.     

First-principles study of structures and electronic properties of cadmium sulfide clusters

The lowest-energy structures and the electronic properties of CdnSn （n = 1 - 8） clusters have been studied by using denslty-functional theory simulating package DMol^3 in the generalized gradient approximation （GGA）. The ring-like structures are the lowest-energy configurations for n = 2, 3 and the three-dimensional spheroid configurations for n = 4 - 8. The three-dimensional structures may be considered as being built from the Cd2S2 and Cd3S3 rings. Compared to the previous reports, we have found the more stable structures for CdnSn（n = 7, 8）. Calculations show that the magic numbers of CdnSn （n = 1-8） clusters are n = 3 and 6. As cluster size increases, the properties of CdnSn clusters tend to bulk-like ones in binding energy per CdS unit and Mulliken atomic charge, obtained by comparing with the calculated results of the wurtzite and zinc blende CdS for the same simulating parameters.     

Enhanced optical nonlinear absorption of graded Au--TiO2 composite films

This paper reports that single-layer and graded Au-TiO2 granular composite films with Au atom content 15%- 66% were prepared by using reactive co-sputtering technique. The third-order optical nonlinearity of single-layer and graded composite films was investigated by using s- and p-polarized Z-scans in femtosecond time scale. The nonlinear absorption coefficient βeff of single-layer Au-TiO2 films is measured to be -2.3×10^3-0.76×10^3 cm/GW with Au atom content 15%-66%. The βeff value of the 10-layer Au-TiO2 graded film is enhanced to be -2.1×10^4cm/GW calculated from p-polarized Z-scans, which is about ten times the maximum βeff of single-layer films. Broadened response in the wavelength region 730-860 nm of the enhanced optical nonlinearity of graded Au-TiO2 composite films was also investigated.     

Spontaneous magnetization and resistivity jumps in bilayered manganite （La0.8Eu0.2）4/3Sr5/3Mn2O7 single crystals

Owing to the inhomogeneous state resulting from the doping of a small number of Eu ions into Laa/3Sr5/3Mn2O7, from the resulting single crystal （La0.8Eu0.2）a/3Sr5/3Mn2O7 we have observed the magnetization jump, the resistivity jump, as well as the relaxation phenomena. For （Lao.sEuo.2）a/3Sr5/3Mn2O7, it has a very delicate ground state due to the interplays among spin, charge, orbital, lattice degrees of freedom. Consequently, the magnetization state is sensitive to temperature, magnetic field, as well as time. Meanwhile, the evolution of the magnetization with time shows a spontaneous jump when both the temperature and the magnetic field are constant. Similar step-like behaviours are also observed in resistivity. All these results suggest that Eu doping can greatly modulate the physical properties of Laa/3Sr5/3Mn2O7 and cause such interesting behaviours.