Full relativistic calculations of the quadrupole and electric field gradients for C2, N2, and O2

In the present work we calculate the energies,quadrupole moments,and electric field gradients(EFGs) of molecules C2,N2,and O2 based on the DIRRCI method with basis aug-cc-pVTZ-DK.We prove that the quadratic force constant k2 is the product of charge and EFG at its equilibrium nuclear distance.The dipole charge distributions for these symmetrical molecules are all in equilibrium,however,the quadrupole charge distributions are far from equilibrium;among these,there is the most remarkable deviation from equilibrium for N2,for its many charges concentrate on two sides of the molecule,which is in agreement with the well-known characteristic of the nitrogen molecule.The relativistic effect is remarkable even for the same period.     

Modal analysis of AC quadrupole magnet system for CSNS/RCS

The quadrupole magnet of the China Spallation Neutron Source (CSNS) Rapid-cycling Synchrotron (RCS) is operated at a 25 Hz sinusoidal alternating current which causes severe vibration. The vibration will influence the long-term safety and reliable operation of the quadrupole magnet. By taking the quadrupole magnet and girder as specific model system, a method for analyzing and studying the dynamic characteristic of the system is put forward by combining theoretical calculation with experimental testing. The theoretical modal analysis results coincide with the experimental testing results. It shows that the dynamic characteristic parameters of the structure can be obtained by modal analysis which will provide a theoretical basis for the further study and the magnet girder optimal design of CSNS/RCS.     

Structure of high spin state in proton-rich ~(74,76,78)Kr isotopes:A projected shell model description

The N≈Z nuclei in the mass A~80 region has been researched because of an abundance of nuclear structure phenomena.The projected shell model(PSM)was adopted to investigate the structure of high spin state in proton-rich 74,76,78Kr isotopes including yrast spectra,moment of inertia,electric quadrupole transitions and the behavior of single particle.The calculated results are in good agreement with available data and the shape coexistence in low-spin is also discussed.     

Structural properties of Bi1-xLaxFeO3 studied by micro-Raman scattering

This paper reports that La-doped BiFeO 3(Bi1-x La x FeO3,x = 0,0.1,0.2,0.3,0.6,0.8 and 1.0) were studied by using micro-Raman spectroscopy and x-ray diffraction(XRD).The XRD patterns indicate that the structure of Bi1-xLaxFeO 3 changes from rhombohedral BiFeO3 to orthorhombic LaFeO3.The results of Raman spectroscopy show good agreement with the XRD results.Strikingly,the phonon peak at around 610 cm-1 and the two-phonon peaks in the high frequency range exist in all compounds and enhance with increasing La substitution.The increasing intensity of the 610 cm-1 peak is attributed to the changes in the FeO 6 octahedron during the rhombohedral-orthorhombic phase transition.The enhancements of the two-phonon peaks are associated with the breakdown of the cycloid spin configuration with the appearance of the orthorhombic structure.These results indicate the existence of strong spin-phonon coupling in Bi1-xLax FeO3,which may provide useful information for understanding the effects of La content on the structural and magnetic properties of Bi1-xLaxFeO3.     

A b initio calculation of the growth of Te nanorods and Bi2Te3 nanoplatelets

In this paper the growth mechanism of a Te/Bi2Te3 novel structure is studied by ab-initio calculations. The results show that the growth of Te nanorods is determined by the adsorption energy of Te atoms on different crystalline Te surfaces. The adsorption energy of Te on the Te （001） surface is 3.29 eV, which is about 0.25 eV higher than that of Te on the Te （110）. This energy difference makes the preferential growth direction along the 〈 001 〉 direction. In addition, the higher surface energy of Bi2Te3 （110） and the lattice misfit between crystalline Bi2We3 and Te along 〈 001 〉 direction are considered to explain the growth of the Bi2Te3 nanoplatelets, in which Volmer-Weber model is used. The theoretical results are in agreement with experimental observation.     

A structure study of copper oxide for monolayer dispersion of anatase supported

The monolayer dispersion of copper oxide on the surface of anatase and its effect on the properties have been studied by X-ray photoelectron spectroscopy(XPS) and X-ray extended absorption fine structure(EXAFS).XPS results give an utmost dispersion capacity of 7.2mg/gTiO2.Strong interactions between copper oxide and anatase can be seen from EXAFS results.The structure of the supported CuO species is strongly dependent on the amount of CuO loading.When the content of CuO loading is below the utmost dispersion capacity,the surface of CuO/TiO2 is dominated by the highly dispersed CuO species having no-Cu-O-Cu-chains,The copper ion is located in an octahedral coordination environment,and the Cu－O-coordination distance is much longer than that in pure crystalline CuO,when CuO loading is exceeds the utmost dispersion capacity,crystalline CuO is formed on the surface of CuO/TiO2,From the result of the sturcture study,it is Cu-O octahedral Coordination and coordination distance change in comparation with pure crystalline Cuo on the surface CuO/TiO2 that have catalytic activity.     

Probes of axial and nonaxial hexadecapole deformation effects in nuclei around 230U

The structure properties for even–even nuclei around ²³⁰U, located on the hexadecapoledeformation island, are investigated using the potential-energy-surface calculation within the framework of the macroscopic-microscopic model. The impact of different deformation degrees of freedom(including axial and nonaxial quadrupole and hexadecapole deformations) on total energy,shell, and pairing contributions is analyzed, based on the projected energy maps and curves. The single-particle struc...     

Transport properties and anomalous fatigue effect of Ag/Bi0.9La0.lFeO3/La0.7Sr0.3MnO3 heterostructures

The transport properties and fatigue effect of Ag/Bi0.9La0.lFeO3/La0.7Sr0.3MnO3 heterostructures are described. By examining the I-V curves, an anomalous fatigue effect was found and its influences on resistive states were studied. I-V curves combined with C-f spectra were used to directly analyze the transport properties and fatigue effect. Compared to the first I-V cycle state, this structure shows more than one order increase of resistance after 100 cycles of ＂I-V curve training＂. The redistribution of oxygen vacancies in the depletion layer of Ag/Bi0.9La0.lFeO3 is believed to be responsible for the different resistance mechanisms and tenfold magnitude drop in resistance. The resistive switching is understood to be caused by electric field-induced carrier trapping and detrapping, which changes the depletion layer thickness at the Ag/Bi0.9La0.lFeO3 interface.     

Ferroelectric and dielectric properties of La/Mn co-doped Bi4Ti3O12 ceramics

La/Mn co-doped Bi4Ti3O12 ceramics,Bi3.25La0.75Ti3-xMnxO12(x=0.02,0.04,0.06,0.08),were prepared by the solid-state reaction method.The influence of manganese substitution for the titanium part in Bi 3.25 La 0.75 Ti 3 O 12 on the sintering behaviour,microstructure,Raman spectra and electrical properties was investigated.The experimental results show that the phase composition of all samples with and without manganese doping,sintered at 1000 ℃,consists of a single phase with a bismuth-layered structure belonging to the crystalline phase Bi4Ti3O12.There is no evidence of any impurity phase,but a small change in crystallographic orientation is observed.The Curie temperature of Bi3.25La0.75Ti3-xMnxO12 ceramics is steadily shifted to lower temperature with increasing Mn-doping content.Moreover,the remnant polarisation(Pr) of Bi3.25La0.75Ti2.92Mn0.08O12 samples increases with Mn-doping content,and the Bi3.25La0.75Ti2.92Mn0.08O12 sample exhibits the largest P r of 16.6 μC/cm 2.     

Electrical Properties of La-Doped Al2O3 Films on Si （100） Substrates as a High-Dielectric-Constant Gate Material

Amorphous La-doped Al2O3 （La： Al2O3） thin films are deposited on n-type （100） Si substrates by rf magnetron co-sputterlng. The composition of the deposited films is measured by energy dispersive x-ray spectroscopy： Capacitance-voltage measurement shows that the dielectric constant k of La-doped Al2O3 films ranges from 8.5 to 11.6 with the increasing La content, and the highest k value of 11.6 is obtained for the 20.14% La content film. In the structure of the Al/La：Al2O3/Si metal oxide semiconductor, the dominant conduction stems from the space- charge-limited current at different temperatures. In addition, the wavelength dependence of the transmittance is studied by ultraviolet spectroscopy and the band gap of all the deposited films is above 5.5eV. The results demonstrate that La-doped Al2O3 can meet the requirement of next-generation gate materials.     

Temperature dependence of the electric field gradient in HfF4.HF.2H2O

The hyperfine quadrupole interaction in HfF₄.HF.2H₂O was studied using the time differential perturbed angular correlation (TDPAC) technique. The electric field gradient (EFG) and the corresponding asymmetry parameter were measured in the temperature range from 9 to 350 K. The EFG is characterized by a rather strong increase with temperature, whereas the asymmetry parameter reaches its maximum value (η≈1) at aboutT=160 K. At 420 K, the complex is dehydrated and looses HF: The quadrupole parameters determined from subsequent TDPAC measurements are charateristic for HfF₄.     

Study of highT c superconductivity in Y1Ba2Cu3O7−x by PAC

HighT _c superconductivity in the YBaCuO superconductor has been investigated through the quadrupole interaction of the probe nuclei⁹⁹Tc. The quadrupole interactions were measured by the TDPAC method from 77 to 296 K. The probe nuclei⁹⁹Tc were introduced into the YBaCuO superconducting specimen by diffusion. The derived electric quadrupole interaction parameters show that the probe nuclei are subject to a unique EFG interaction and occupy a substitutional lattice site in the YBaCuO superconductor. A strong EFG of 10¹⁹ V/cm² was observed. The temperature dependence of the EFG exhibits a linear decrease with temperature increase. Anomalies of both EFG and ν were found in the superconducting transition temperature region. The role of the oxygen vacancies in the Cu−O chains is discussed.     

Study of the structure and electric quadrupole interaction in the intermetallic compound Hf2Fe

The electric quadrupole interactions at¹⁸¹Ta probe nuclei in a cubic Hf₂Fe lattice were studied by the TDPAC method. In addition, the crystalline structure study of the Hf₂Fe compound was performed. The results of the EQI measurement show the presence of two independent interactions, one at low frequency, characterized by ω _Q ⁽¹⁾ =33 Mrad/s and δ=30%, and the other at high frequency described by ω _Q ⁽²⁾ =207 ± 2 Mrad/s and δ=4%. Both interactions are found to be compatible with the crystalline structure established in this investigation. The large temperature dependence of the electric field gradient of the second interaction in the range from 78K to 1183K was determined. The change in the EFG follows the empiricalT ^3/2 -relation.     

Electric field gradients at Ta in Zr and Hf inter-metallic compounds

Here we calculate the electric field gradient (EFG) at the nucleus of the substitutional Ta impurity site in Zr₂T and Hf₂T (T=Cu, Ag, Au, and Pd) C11_b inter-metallic compounds. We use the ab initio FP-LAPW method as embodied in the Wien97 code in a super-cell approach and include lattice relaxations around the impurity. Our results are compared with EFG values inferred from measurements of the quadrupole coupling constants at the ¹¹¹Ta probe in these compounds performed with the time differential perturbed angular correlation (TDPAC) technique. We also performed EFG calculations for the pure inter-metallic compounds. Through the comparison of theoretical and experimental EFGs in these cases, we elucidate the role played by the Ta probe in the TDPAC measurements of Hf and Zr compounds. Our results show that, although the EFGs at the Hf site are very similar to the EFGs at the Ta impurity, there is no direct correlation between the Zr and Ta EFGs.     

PAC measurements of In-Pt intermetallic compounds

The quadrupole interaction parameters for¹¹¹Cd in In₇Pt₃ and In₃Pt₂ compounds were measured by TDPAC in the temperature range 80–1000 K. The EFG temperature behavior follows theT ^3/2 relation.     

Electric quadrupole interactions in the CdTiO3 perovskite2

The TDPAC technique has been used to measure the EFG at the Cd site in the perovskite CdTiO₃. The experimental results obtained at 293 K are compared with ionic lattice sum calculations of the EFG. In addition measurements at 16 and 77 K show that no considerable modification of the EFG is observed at the Cd site at temperatures below and above the previously described phase transition at 50 K.     

Quadrupole interaction at111Cd in RRh3B2 compounds (R=Ce to Gd) and absence of transferred hyperfine field at111Cd in GdRh3B2

The quadrupole interaction at¹¹¹Cd in RRh₃B₂ compounds studied by the TDPAC technique supports the prediction that Ce in CeRh₃B₂ is not trivalent. The highly anisotropic EFG indicates that¹¹¹Cd in GdRh₃B₂ cannot occupy the rare earth site. The transferred magnetic hyperfine field at¹¹¹Cd is nearly zero which supports the conjecture that the impurity probe nuclei are at the 3g(Rh) site.     

Investigation of muonium quadrupole interaction in α-quartz in the temperature region 75–120 K

The parameters of the muonium quadrupole interaction in α-quartz as well as the orientation of the EFG tensor principal axes are determined. It is shown that there is no temperature dependence of these characteristics in the temperature region 75–120 K. The assumption of the reversal of the sign of the q?uadrupole constant with temperature increase from 120 K to room temperature is confirmed. It is shown that the change of the quadrupole interaction strength and symmetry is caused by the diffusion of muonium.     

TDPAC studies of111mCd in calciproteins: Calmodulin and parvalbumin

TDPAC measurements of the 150–247 keV gamma-ray cascade in¹¹¹Cd have been performed at room temperature on Calmodulin (CaM) and Parvalbumin (Pa) labelled with radioactive^111mCd. The anisotropy of the coincidence counting rate shows a time-dependent behaviour, typical of two different nuclear quadrupole interactions (NQI) in CaM. The NQI parameters indicate the presence of two distinct metal-binding sites, presenting non-equivalent local electric charge structure. In Pa samples, only one NQI is observed and the measured electric field gradient (EFG) value agrees well with the large one obtained in CaM.     

Electric field gradient studies in SnSe

The EFG in IV–VI compound semiconductor SnSe was studied using two hyperfine interaction techniques, namely, TDPAC and Mössbauer spectroscopy. The EFG in this material increases sharply up to 300 K and thereafter at higher temperatures it gets saturated. However, the conductivity increases steadily at all the temperatures. The conductivity curve has two slopes. The first portion is due to the population of shallow Cd acceptor levels. Thus, in SnSe also the variation of the EFG with temperature is complex, as in other medium-gap semiconductors.