Untersuchung von Butter

Ohne Zusammenfassung     

Influence of internal strains on the phase diagram of the metamagnet DyPO4

The (H, T) and (M, T) diagrams of the three-dimensional Ising-like antiferro-magnet DyPO₄ have been studied by magnetooptical rotation and light-scattering techniques. It is shown that the shapes of these diagrams depend on the nature and treatment of samples. By increasing the temperature, the discontinuity in magnetization ΔM does not decrease linearly to zero at a tricritical point but, instead, ΔM shows a pronounced tail. In addition, at higher temperatures, the metamagnetic transition seems to remain of very weak first order. Internal strains and magnetoelastic coupling can explain these results.     

Radio of the nuclear electric quadrupole moments of 50V (I = 6) and 51V (I = 72)

In SmVO₄ the weak paramagnetism of the Sm³⁺ ions results in a very small paramagnetic shift of the vanadium nuclear resonance; the lines are narrow (?4 kHz) and there is no sign of saturation down to 1.7 K. The quadrupole splittings of the two nuclei have been measured at natural abundance in the same single crystal, giving the following value for the ratio of the nuclear electric quadrupole moments: ∥⁵⁰Q/⁵¹Q∥ = 4.07 (3). Values of ⁵¹Q = ?0.0515 (10) b and ⁵⁰Q = +0.209(6) b are suggested.     

Magnetic phase transition in CsVF4

Magnetization and specific heat measurements are reported on the quasi two-dimensional antiferromagnet CsVF₄. Diverging magnetic susceptibility and specific heat at the Néel temperature are observed in a weak field along the crystallographic c-direction, but with increasing field they are progressively smeared. A hysteresis is observed in dc magnetization below the temperature at which M/H reaches a maximum. We present a possible explanation for these phase transition phenomena from the point of view that this compound is composed of two crystallographically inequivalent magnetic sites.     

Electrochemical, spectral, and computational studies of metalloporphyrin dimers formed by cation complexation of crown ether cavities

The effect on the electrochemical oxidation and reduction potentials of 5,10,15,20-tetrakis(benzo-15-crown-5)porphyrin (TCP) and its metal derivatives (MTCP; M = Mg(II), VO(IV), Co(II), Ni(II), Cu(II), Zn(II), Pd(II), Ag(II)) upon potassium ion induced dimerization of the porphyrins was systematically performed in benzonitrile containing 0.1 M (TBA)ClO(4) by differential pulse voltammetry technique. The HOMO--LUMO energy level diagram constructed from the electrochemical data revealed destabilization of the HOMO level and stabilization of the LUMO level upon dimer formation while such a perturbation was larger for the HOMO level than the LUMO level. The geometry and electronic structure of a representative ZnTCP and its dimer, K(4)(ZnTCP)(2), were evaluated by the ab initio B3LYP method utilizing a mixed basis set of 3-21G(*) for Zn, K, O, and N and STO-3G for C and H. The inter-porphyrin ring distance of the dimer calculated from the optimized geometry agreed with the spectroscopically determined one, and the calculated HOMO and LUMO frontier orbitals revealed delocalization on both of the porphyrins rings. The metal-metal distances calculated from the triplet ESR spectra of the K(+) induced porphyrin dimers bearing paramagnetic metal ions in the cavity followed the trend Cu--Cu < VO--VO < Ag--Ag. However, the spectral shifts resulting from the exciton coupling of the interacting porphyrin pi-systems revealed no specific trend with respect to the metal ion in the porphyrin cavity. Additionally, linear trends in the electrochemically measured HOMO--LUMO gap and the energy corresponding to the most intense visible band of both MTCP and K(4)(MTCP)(2) were observed. A reduced HOMO--LUMO gap predicted for the dimer by B3LYP/(3-21G(), STO-3G) calculations was confirmed by the results of optical absorption and electrochemical studies.     

Nucleation and crystallization of WO3 from pure and Pb2+ doped NaF fluxes

DTA runs and flux growth experiments have shown that the crystallization temperatures of WO₃ from NaF flux are in the range of 1020–1090°C. Addition of Pb²⁺ influences the crystal growth and the crystallization temperatures are altered (within this range). A thermal effect giving rise to an exothermal DTA peak was observed above the crystallization temperature. This peak occurs at a higher temperature when lead ions are present. We propose an explanation based on pre-crystallization clustering and on the number of nucleation sites on the surface of the platinum crucible.     

Ueber Verseifung

Ohne Zusammenfassung