An electrostatic interaction correction for improved crystal density prediction

Recent work by others has shown that the densities of C,H,N,O molecular crystals are, in many instances, given quite well by the formula M/V_m, in which M is the molecular mass and V_m is the volume of the isolated gas phase molecule that is enclosed by the 0.001 au contour of its electronic density. About 41% of the predictions were in error by less than 0.030 g/cm³, and 63% by less than 0.050 g/cm³. However, this leaves more than one-third of the compounds with errors greater than 0.050 g/cm³, or in some instances, 0.100 g/cm³. This may indicate that intermolecular interactions within the crystal are not being adequately taken into account in these cases. Accordingly, the effectiveness of including a second term that reflects the strengths, variabilities and degree of balance of the positive and negative electrostatic potentials computed on the surfaces of the isolated molecules, has been included. The database was selected such that half of the densities predicted by M/V_m had errors larger than 0.050 g/cm³. The introduction of the electrostatic interaction correction produced a marked improvement. Overall, 78% of the predictions are within 0.050 g/cm³ of experiment, with 50% within 0.030 g/cm³. Among those that originally all had errors larger than 0.050 g/cm³, 67% are now less. The reasons for the better performance of the dual-variable formula are analysed.     

一种测定某些离子导体的导电基本参数的新方法

利用低频交变电场在某些离子导体中能引起偏振态改变的光衍射特性,发展了一种测量这些离子导体的导电基本参数的新方法,并且用它测定了α-LiIO₃单晶的基本离子导电参数,测得其载流子的迁移率激活能E_μ=0.36eV;夫仑克耳缺陷的形成能为E_M=0.59eV;300K时正、负载流子的数密度均为1.6×10¹⁷cm^-3,相对浓度均为1.07×10^-5;当所加电场反平行于晶体的自发极化强 关键词：     

Neutron diffraction measurement of the Debye-Walker factor of solid hcp 4He

The Debye-Waller factor of hcp ⁴He at molar volumes V_m of 12.06 and 15.72 cm³ has been measured by neutron diffraction techniques. It has been found that for scattering vectors $\text{Q ? 7}\text{A}\text{?}{}^{\mathrm{?1}}$ the Debye-Waller factor can be well represented by a simple Gaussian. The Debye temperatures, appropriate to the Debye-Waller factor, were found to be 99.73 K (V_m = 12.06 cm³) and 55.86 K (V_m = 15.72 cm³). No evidence was found of any forbidden reflections.     

Predicting the viscosity and electrical conductivity of ionic liquids on the basis of theoretically calculated ionic volumes

Selected physical properties of the ionic liquids might be quantitatively predicted based on the volumes of the ions these systems are composed of. It is demonstrated that the ionic volumes calculated using relatively simple theoretical quantum chemistry methods can be utilised to estimate the viscosities and electrical conductivities of various commonly used ionic liquids. The fitting formulas of the exponential form are offered and their predictive usefulness is verified. The quality of such predictions is discussed on the basis of several ionic liquids involving [Tf₂N]^? and [BF₄]^? anions and 16 various cations. The dependence of the viscosity and electrical conductivity of the ionic liquids on the temperature is also investigated and the temperature-dependent equations are derived and compared to the experimentally measured values.     

Absorptionsspektren von Er3+ in InCl3 und in ScCl3

The optical absorption spectra of Er³⁺ in single crystals of InCl₃ and ScCl₃ have been obtained between 14,000 and 29,000 cm^?1. The observed crystal field splittings are interpreted in terms of crystal potential of symmetry 3m for ScCl₃ and of symmetry 2m for InCl₃. There is however found, that for both cases the splittings will be approximately explained by a crystal potential of cubic symmetry. The employed hostlattices are of special interest, because the ions of the iron series can occupy the same sites as the rare earth ions.     

The study of damage and optical properties in LiNbO3 implanted by MeV Er and He ions

Abstract

Two LiNbO₃ (X and Y cut) crystals from different companies were implanted by 3.0 MeV Er ions to a dose of 7.5 × 10¹⁴ ions/cm² and 3.5 × 10¹⁴ ions/cm² with different beam current densities, respectively. After annealing at 1060°C in air for 2 hours, one LiNbO₃ sample was implanted by 1.5 MeV He ions to a dose of 1.5 × 10¹⁶ ions/cm². The Rutherford backscattering/channeling and prism coupling method have been used to study the damage and optical properties in implanted LiNbO₃. The results show: (1) the damage in LiNbO₃ created by 3.0 MeV Er ions depends strongly on the beam current density; (2) after annealing at 1060°C in air for 2 hours, a good Er doped LiNbO₃ crystal was obtained; (3) there is waveguide formation possible in this Er-doped annealed LiNbO₃ after 1.5 MeV He ion implantation. It is suggested that annealing is needed to remove the damage created by MeV Er ions before the MeV He ion implantation takes place, to realize the waveguide laser for Er doped LiNbO₃.     

Laser Raman spectral studies under d.c. bias on fast proton transport in molybdic acid (MoO3· 2H2O)

Laser Raman spectroscopy on samples across which a d.c. field has been applied is suggested as a new technique for studying ionic solids. As an example, the laser Raman spectra of a solid state proton conductor MoO₃ · 2H₂Ois reported with the d.c. field “on”. Two new peaks at 795 and 414 cm⁻¹ appear in the laser Raman spectra and their intensities grow with increasing time and applied d.c. voltage. Their appearance has been explained by assuming that H₃O⁺ ions are created by the d.c. field as the mobile charged ionic species. By monitoring the peak intensities of the 795 and 414cm⁻¹ bands at different places in the sample between the cathode and the anode, the diffusion coefficient has been estimated.     

TDPAC studies on181Hf implanted into diamond

¹⁸¹Hf ions were implanted at (900±10)K into (100) cleaved single crystal diamonds. After subsequent annealing residence site parameters were determined for the implanted ions employing the (133 keV)–(482 keV) cascade in¹⁸¹Ta in TDPAC technique. Fractions of 5% each were determined that experience axially symmetric electric field gradients (EFG) V_zz(1)=5.5×10¹⁷ V cm^–2 and V_zz(2)=9.6×10¹⁷ V cm^–2, respectively. The bulk of the ions are strongly disturbed by still higher electric field gradients.     

Ion transport in proton conducting solid polymer electrolytes

In this communication the ion transport properties of polyvinyl alcohol complexed with orthophosphoric acid (H₃PO₄) have been investigated. The proton conduction is confirmed by hydrogen gas evolved at the cathode of the coulometer and the transference number of H⁺ ion has been determined. The transient ionic current (TIC) technique has been used to detect the mobile ionic species and their mobilities are evaluated. The ionic mobility was found to be of the order of 10⁻⁴ cm².V⁻¹.s⁻¹ for H⁺ ions. It is observed that the bulk electrical conductivity increases with the temperature following the Arrhenius type behaviour. Variation of charge carrier concentration with the molar ratio of H₃PO₄ in the sample reveals that the carrier concentration is largely affected by the amount of dopant in the complexes.     

Volumetric, acoustic and spectroscopic studies for binary mixtures of ionic liquid (1-butyl-3-methylimidazolium hexafluorophosphate) with alkoxyalkanols at T = (288.15 to 318.15) K

Densities and speeds of sound have been measured for the binary mixtures of ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate [bmim][PF₆] with ethylene glycol monoethyl ether (EGMEE), diethylene glycol monoethyl ether (Di-EGMEE), triethylene glycol monoethyl ether (Tri-EGMEE) over the whole composition range at atmospheric pressure. Experimental densities have been used to estimate excess molar volumes, V^E. Changes in isentropic compressibility, Δκ_s have been estimated by using experimental speed of sound and density values. Excess properties were fitted to the Redlich-Kister polynomial equation to obtain the binary coefficients and the standard errors. The molecular scale interactions between ionic liquid and alkoxyalkanols have been investigated through ¹H NMR spectroscopy. NMR chemical shifts for hydroxyl group of alkoxyalkanols and their deviations show hydrogen bonding interactions of varying strengths between ionic liquid and alkoxyalkanol in their binary mixtures.     

V centers produced in KI crystals under KrCl excimer laser irradiation

Abstract

Irradiation of KI near 150 K with KrCl excimer laser irradiation (hv=5. 58 eV) produces V centers causing V₂ and V₃ bands. The two bands exhibit 100-type dichroism. In KI containing V centers, the 111 cm^?1 Raman signal attributed to I_3- molecular ions is observed. Under KrCl excimer laser irradiation at low temperatures, resonance Raman scattering effects have been also studied for KI, NaI and LiI.     

Influences of thermal annealing, the electrolyte pH, and current density on the interface state density distribution of anodic MOS structures

2 /p-Si MOS structures were prepared in 0.1 M K₂SO₄ electrolyte with a pH of 7 (the 0.1 M KOH solution was buffered with H₂SO₄) at current densities of 3, 5, and 7 mA/cm² and with four different pH values of the electrolyte at 3 mA/cm². It is found that thermal annealing at a relatively low temperature can be used to improve the anodic MOS characteristics. Moreover, of the pH and current density it followed that the pH has a dominant role in the interface electrical properties. The lowest interface state densities at the maximum and the midgap positions are 7.1×10¹¹ and 2.7×10¹⁰ eV^-1cm^-2 for a sample made with pH=7, J=3 mA/cm². The characteristics of this sample seem satisfactory for device applications of anodized p-Si. Received: 8 July 1996/Accepted: 22 January 1997     

50 MeV Li3+ ion irradiation effect on structural, electrical, and dielectric properties of PVA-based nanocomposite polymer electrolytes

Nanocomposite polymer electrolyte thin films of polyvinyl alcohol (PVA)-orthophosphoric acid (H₃PO₄)-Al₂O₃ have been prepared by solution cast technique. Films are irradiated with 50 MeV Li³⁺ ions having four different fluences viz. 5?×?10¹⁰, 1?×?10¹¹, 5?×?10¹¹, and 1?×?10¹² ions/cm². The effect of irradiation on polymeric samples has been studied and characterized. X-ray diffraction spectra reveal that percent degree of crystallinity of samples decrease with ion fluences. Glass transition and melting temperatures have been also decreased as observed in differential scanning calorimetry. A possible complexation/interaction has been shown by Fourier transform infrared spectroscopy. Temperature-dependent ionic conductivity shows an Arrhenius behavior before and after glass transition temperature. It is observed that ionic conductivity increases with ion fluences and after a critical fluence, it starts to decrease. Maximum ionic conductivity of ～2.3?×?10^?5 S/cm owing to minimum activation energy of ～0.012 eV has been observed for irradiated electrolyte sample at fluence of 5?×?10¹¹ ions/cm². The dielectric constant and dielectric loss also increase with ion fluences while they decrease with frequency. Transference number of ions shows that the samples are of purely ionic in nature before and after ion irradiation.     

Processing and characterization of ultra-thin yttria-stabilized zirconia (YSZ) electrolytic films for SOFC

Sub-micron yttria-stabilized zirconia (YSZ) electrolyte layer was prepared by a liquid state deposition method and with an average thickness of 0.5 μm to improve the performance of the anode-supported solid oxide fuel cell (SOFC). The YSZ precursors, containing yttrium and zirconium species and an additive, poly-vinyl-pyrrolidone (PVP), were spin-coated on a Ni/YSZ anode substrate. Several properties, including crystalline phases, microstructures, and current–voltage (I–V) characteristics, were investigated. The thin film of 4 mol% Y₂O₃-doped ZrO₂ (4YSZ) consisted of cubic, tetragonal, and a trace of monoclinic phases, and showed a crack-free layer after sintering at 1300 °C. The anode supported SOFC, which consists of the Ni–YSZ anode, 4YSZ electrolyte, and Pt/Pd cathode, showed power densities of 477 mW/cm² at 600 °C, and 684 mW/cm² at 800 °C. Otherwise, the surface cracks of the other YSZ-coated samples (e.g. 8YSZ) can be repaired by a multi-coating method.     

Quantitative comparison of different preionization schemes of KrF laser discharges

* fluorescence radiation from the ion–ion recombination process in the gas volume during the preionization phase, therefore allowing spatial resolution by partial imaging of the volume. Volume-integrated and temporally resolved measurements are carried out to determine the average of absolute preionization densities by comparison with a theoretical model of the temporal behaviour of the recombination process. Spatially resolved measurements reveal the distribution of the preionization density. The preionization densities determined from spark and sliding/corona discharges schemes are considerably higher (n_e ⁰?10¹² cm^-3) than those obtained from pulsed X-ray preionization (n_e ⁰?10⁷ cm^-3). Received: 3 October 1997/Revised version: 6 January 1998     

Effect of accumulation on the formation of multiply charged ions in solids under grazing incidence of multiple laser radiation

The effect of accumulation on the formation of multiply charged ions in optically opaque solids as a function of the number and the angle of incidence of laser pulses is investigated by mass spectrometry. It is revealed that the accumulation effect manifests itself at prethreshold power densities q = 10⁸–10⁹ W/cm² irrespective of the angle of incidence of laser radiation α = 18°–85° and at subthreshold power densities q > 10¹⁰ W/cm² in the case of grazing incidence of laser radiation at an angle α = 85°. The accumulation effect brings about an increase in the maximum charge multiplicity Z _max of tungsten ions and a decrease in the number of impurity ions and in their intensity. No accumulation effect is observed at subthreshold power densities when laser radiation is incident at an angle α = 18°.     

多晶Li3+xV1-xTxO4(T=Ge,Si)离子导电性能的改善

本文用阻抗谱方法研究了Li_3+xV_1-xT_xO₄(T=Si,Ge)多晶的离子导电性,发现一些工艺条件如成型压强、烧结时间和烧结程序对电导率有很大影响。注意分析了这些影响的物理起因。最佳工艺条件是:在大约8t/cm²压强下成型样品。在1000℃连续烧结5至6天,烧结过程中,应尽量避免温度波动。在此条件下制备的Li_3.5V_0.5Ge_0.5关键词：     

Ionic compressibilities and ionic radii - systematic trends

Ionic radii and compressibilities have been calculated for a number of monovalent and divalent ions and radicals on the basis of the compressible ion theory. In this theory, the compression energy of an ion is given as a two-parameter function of its radius,A exp (−r/p), the radius and compressibility of the ion being monotonically decreasing functions of the compressing force acting on it. Choosing a standard force reflecting the average environment in the alkali halides, univalent radii and compressibilities have been calculated. This is the first theory to estimate ionic compressibilities. The values show systematic trends among groups of related ions. Anions are found to be significantly more compressible than cations (e.g., the compressibilities of Ca⁺⁺, K⁺, Cl⁻ and S^{− −} are respectively 0.8530, 1.342, 2.952 and 5.150 × 10⁻¹² cm²/ dyne). Multivalent or ‘crystal’ radii and compressibilities have also been calculated by scaling the standard force by the square of the ionic charge. The calculated ionic radii are closer to experimental values than the classical empirical radii.     

Dipole formation and electrical properties of high-k/SiO2 interface according to the density of SiO2 interfacial layer

The effect of SiO₂ buffer layers with various atomic densities on the interface dipole of high-k/SiO₂ is confirmed. An ultrathin SiO₂ layer is formed on Si using the plasma-enhanced chemical vapor deposition (PECVD), H₂O₂ oxidation and nitric acid oxidation (NAOS). The atomic density ratio between the SiO₂ layer with various methods and the high-k is calculated respectively. As the oxygen density of the SiO₂ increased, the amount of the dipole and the flatband voltage (V_FB) shift decreased. Furthermore, leakage current density of the H₂O₂ (0.9 × 10⁻² A/cm²) due to the formation of low-density SiO₂, decreases by approximately six orders of magnitude when SiO₂ buffer layer is inserted using the NAOS (5.13 × 10^-8 A/cm²). Consequently, it is demonstrated that the dipoles that affects the V_FB shift is formed by the diffusion of oxygen ions between the high-k and SiO₂ interface, which has a significant effect of the MOS capacitor.     

Lithium ion conduction in A-site deficient perovskites R1/4Li1/4TaO3 (R=La,Nd, Sm and Y)

New lithium ion conductors of perovskite-type compounds R_1/4Li_1/4TaO₃ (R=La, Nd, Sm and Y) were synthesized, and their crystal structure and lithium ion conductivity were characterized. Symmetry of the perovskite lattice changed from cubic for La_1/4Li_1/4TaO₃ to tetragonal for Nd_1/4Li_1/4TaO₃ and Sm_1/4Li_1/4TaO₃, and to orthorhombic for Y_1/4Li_1/4TaO₃. The alternate ordering of R and Li ions and vacancies at the A-sites was observed for Nd_1/4Li_1/4TaO₃, Sm_1/4Li_1/4TaO₃ and Y_1/4Li_1/4TaO₃. The cube root (V^1/3) of the subcell volume decreased with decreasing the ionic radius of R cations which act as spacers for the perovskite lattice. With decrease in V^1/3 from La_1/4Li_1/4TaO₃ to Y_1/4Li_1/4TaO₃, the bulk conductivity at 400 K decreased from 1.4×10⁻¹ S m⁻¹ to 5.0×10⁻⁷ S m⁻¹ and its activation energy increased from 0.35 eV to 0.85 eV. The subcell volume and the ordering at the A-sites are major factors in influencing lithium ion conduction in these perovskite-type conductors.