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Lattice Sites (lattice + site)
Selected AbstractsX-ray structure study of the light-induced metastable states of the spin-crossover compound [Fe(mtz)6](BF4)2JOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 3 2001Joachim Kusz Iron(II) complexes exhibiting thermal spin-crossover may be converted from the 1A1 low-spin (LS) state to the 5T2 high-spin (HS) state by irradiation with green light (light-induced excited spin-state trapping, LIESST) and from the LS to the HS state by irradiation with red light (reverse LIESST). The lifetime of the metastable LIESST states may be sufficiently long to enable an X-ray diffraction study. The lattice parameters of a single crystal of [Fe(mtz)6](BF4)2 (mtz = methyltetrazole) (space group P21/n) were measured between 300 and 10,K. While one Fe lattice site (A) of the crystal changes from the HS to the LS state near 78,K, the other site (B) remains in the LS state. Using the green light (514,nm) of an argon ion laser the crystal was quantitatively converted to the HS state at 10,K. Irradiation of the crystal at 10,K by red light of a laser diode (820,nm) with site A in the LS and site B in the HS state converts site B almost completely to the LS state. The lattice parameters of both metastable states were measured up to 50,K, where they start to decay on a minute timescale. At 10,K, a full data set for evaluation of the crystal structure was recorded. The volume change of the crystal per complex molecule accompanying the spin transition is 31.5,Å3 at site A and close to zero [,0.21,(14),Å3] at site B. [source] The oxygen vacancy in Ga2O3: a double resonance investigation,MAGNETIC RESONANCE IN CHEMISTRY, Issue S1 2005H. J. Kümmerer Abstract When produced under reducing conditions, ,-Ga2O3 is transformed into an n -type semiconductor with delocalized conduction electrons that exhibit a very strong electron spin resonance (ESR) and a strong hyperfine coupling to the gallium nuclei of the host lattice. We apply the Overhauser-shift technique to investigate single crystals of this compound. With extension to the high magnetic field of a W-band spectrometer, we were able to resolve all spectral lines that were recorded and to assign them to their corresponding electronic and nuclear states. This separate analysis was the basis to access additional sample characteristics: the hyperfine coupling that is actually averaged out in the ESR signal, as well as the nuclear relaxation rates could be analyzed. Systematic measurements by varying the microwave power revealed the Overhauser shift in thermal equilibrium. The signal could be tracked to very small microwave saturation parameters, at which the deviation from the usual linear relation between power and shift becomes evident and the shift clearly approaches a constant value. This value in equilibrium was determined directly from a fit to a sequence of measurements, whereas standard X-band experiments only provided indirect conclusions. The probability densities of the electrons at the nuclei in the two nonequivalent crystallographic positions,the lattice sites with octahedral and tetrahedral coordination,could also be determined directly. The enhanced resolution revealed an otherwise hidden substructure in the nuclear resonance signals. On the basis of a microscopic model, this structure could be used to probe the environment of the oxygen vacancy more precisely and to determine the extension of the electronic wave function of the donor electrons. Copyright © 2005 John Wiley & Sons, Ltd. [source] Optical and magnetic properties of c -oriented ZnCoO filmsPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 11 2006Huijuan Zhou Abstract We investigated ZnCoO thin films prepared via sol-gel methods and dip-coating techniques. The Co concentrations range from 0.5% to 5%. The films show the wurtzite crystal structure of ZnO and are highly c -axis oriented grown on the quartz substrates. They have a typical grain size of 20 to 50 nm and a thickness between 300 nm and 1 µm. The fine structures of the Co (3d7) internal absorptions are well resolved, all zero-phonon lines (ZPL) and phonon replica related to the 4T1(F) , 4A2 are observed, demonstrating the good crystalline quality of the layers and the incorporation of the Co2+ on Zn2+ lattice sites. The films show paramagnetic behaviour. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Analysis of the local structure of AlN:Mn using X-ray absorption fine structure measurementsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2006Takao Miyajima Abstract The local structure around the Mn atoms in MOCVD-grown AlN:Mn films which show Mn-related red-orange photoluminescence with a 600nm-peak at room temperature was investigated using the X-ray absorption fine structure (XAFS) measurements. We found that Mn atoms occupy Al lattice sites in the AlN film and that the Mn ions have a charge between +2 and +3. From these results, we think that the red-orange luminescence is caused by the transition of d-electrons in the Mn ions. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Analysis of the local structure of InN with a bandgap energy of 0.8 and 1.9 eV and annealed InN using X-ray absorption fine structure measurementsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2006Takao Miyajima Abstract We compared the local structure around In atoms in microwave-excited MOCVD- and MBE-grown InN film which indicates an absorption edge at 1.9 and 0.8 eV, respectively. The co-ordination numbers of the 1st-nearest neighbor N atoms and the 2nd-nearest neighbor In atoms for MBE-grown InN were n(N) = 3.9 ± 0.5 and n(In) = 12.4 ± 0.9, which are close to the ideal value of n(N) = 4 and n(In) = 12 for InN without defects, respectively. By thermal annealing, the structure of MBE-grown InN was changed from InN to In2O3, and the absorption edge was changed from 0.8 to 3.5 eV. However, the microwave-excited MOCVD-grown InN had no structure of In2O3, and had the reduced co-ordination numbers of the 2nd-nearest neighbor In atoms of n(In) = 10.6-11.7. From these results, we conclude that the origin of the 1.9-eV absorption edge of InN is the imperfections (defects) of the In lattice sites of InN, rather than the generation of In2O3, which has a bandgap energy of 3.5 eV. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | |||||||||||||