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End date: 2019 × DDC: 540 × WGL Institute: IKZ ×

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    Electronic materials with a wide band gap: Recent developments
    (Chester : International Union of Crystallography, 2014) Klimm, D.
    The development of semiconductor electronics is reviewed briefly, beginning with the development of germanium devices (band gap E g = 0.66 eV) after World War II. A tendency towards alternative materials with wider band gaps quickly became apparent, starting with silicon (E g = 1.12 eV). This improved the signal-to-noise ratio for classical electronic applications. Both semiconductors have a tetrahedral coordination, and by isoelectronic alternative replacement of Ge or Si with carbon or various anions and cations, other semiconductors with wider E g were obtained. These are transparent to visible light and belong to the group of wide band gap semiconductors. Nowadays, some nitrides, especially GaN and AlN, are the most important materials for optical emission in the ultraviolet and blue regions. Oxide crystals, such as ZnO and β-Ga2O3, offer similarly good electronic properties but still suffer from significant difficulties in obtaining stable and technologically adequate p-type conductivity.
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    Crystal structure of distrontium lanthanum gallium pentaoxide, Sr2LaGaO5
    (München : R. Oldenbourg Verlag GmbH, 2000) Gesing, T.M.; Uecker, R.; Buhl, J.-C.
    GaLaO5Sr2, tetragonal, I4/mcm (No. 140), a = 6.9339(4) Å, c = 11.2823(8) Å, V= 542.4 Å3, Z = 4, R(P) = 0.018, wR(P) = 0.027, R(I) = 0.031, T= 295 K.
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    Heteroepitaxial growth of T-Nb2O5 on SrTiO3
    (Basel : MDPI, 2018) Boschker, Jos E.; Markurt, Toni; Albrecht, Martin; Schwarzkopf, Jutta
    There is a growing interest in exploiting the functional properties of niobium oxides in general and of the T-Nb2O5 polymorph in particular. Fundamental investigations of the properties of niobium oxides are, however, hindered by the availability of materials with sufficient structural perfection. It is expected that high-quality T-Nb2O5 can be made using heteroepitaxial growth. Here, we investigated the epitaxial growth of T-Nb2O5 on a prototype perovskite oxide, SrTiO3. Even though there exists a reasonable lattice mismatch in one crystallographic direction, these materials have a significant difference in crystal structure: SrTiO3 is cubic, whereas T-Nb2O5 is orthorhombic. It is found that this difference in symmetry results in the formation of domains that have the T-Nb2O5 c-axis aligned with the SrTiO3 <001>s in-plane directions. Hence, the number of domain orientations is four and two for the growth on (100)s- and (110)s-oriented substrates, respectively. Interestingly, the out-of-plane growth direction remains the same for both substrate orientations, suggesting a weak interfacial coupling between the two materials. Despite challenges associated with the heteroepitaxial growth of T-Nb2O5, the T-Nb2O5 films presented in this paper are a significant improvement in terms of structural quality compared to their polycrystalline counterparts.
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    Scanning X-ray nanodiffraction from ferroelectric domains in strained K0.75Na0.25NbO3 epitaxial films grown on (110) TbScO3
    (Copenhagen : Munksgaard, 2017) Schmidbauer, Martin; Hanke, Michael; Kwasniewski, Albert; Braun, Dorothee; von Helden, Leonard; Feldt, Christoph; Leake, Steven John; Schwarzkopf, Jutta
    Scanning X-ray nanodiffraction on a highly periodic ferroelectric domain pattern of a strained K0.75Na0.25NbO3 epitaxial layer has been performed by using a focused X-ray beam of about 100 14;nm probe size. A 90°-rotated domain variant which is aligned along [1 2]TSO has been found in addition to the predominant domain variant where the domains are aligned along the [12]TSO direction of the underlying (110) TbScO3 (TSO) orthorhombic substrate. Owing to the larger elastic strain energy density, the 90°-rotated domains appear with significantly reduced probability. Furthermore, the 90°-rotated variant shows a larger vertical lattice spacing than the 0°-rotated domain variant. Calculations based on linear elasticity theory substantiate that this difference is caused by the elastic anisotropy of the K0.75Na0.25NbO3 epitaxial layer.
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    Crystal structure of aluminium cyclononaphosphate, Al3P9O27
    (München : R. Oldenbourg Verlag GmbH, 2000) Fratzky, D.; Schneider, M.; Meisel, M.
    Al3O27P9, trigonal, P3̄c1 (No. 165), a = 10.935(2) Å, c = 9.191(2) Å, V = 951.8 Å3, Z = 8, Rgt(F) = 0.037, wRref(F2) = 0.094, T = 293 K.
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    Redetermination of EuScO3
    (Chester : International Union of Crystallography, 2009) Kahlenberg, V.; Maier, D.; Veličkov, B.
    Single crystals of europium(III) scandate(III), with ideal formula EuScO3, were grown from the melt using the micro-pulling-down method. The title compound crystallizes in an ortho-rhom-bic distorted perovskite-type structure, where Eu occupies the eightfold coordinated A sites (site symmetry m) and Sc resides on the centres of corner-sharing [ScO6] octa-hedra (B sites with site symmetry ). The structure of EuScO3 has been reported previously based on powder diffraction data [Liferovich & Mitchell (2004). J. Solid State Chem. 177, 2188-2197]. The results of the current redetermination based on single-crystal diffraction data shows an improvement in the precision of the structral and geometric parameters and reveals a defect-type structure. Site-occupancy refinements indicate an Eu deficiency on the A site coupled with O defects on one of the two O-atom positions. The crystallochemical formula of the investigated sample may thus be written as A(0.032Eu0.968)BScO2.952.
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    Crystal structure of distrontium praseodym gallium pentaoxide, Sr2PrGaO5
    (München : R. Oldenbourg Verlag GmbH, 1999) Gesing, T.M.; Uecker, R.; Buhl, J.-C.
    GaO5PrSr2, tetragonal, I4/mcm (No. 140), a = 6.8441(2) Å, c = 11.2534(4) Å, V = 527.1 Å3, Z = 4, R(P) = 0.035, wR(P) = 0.052, R(I) = 0.038, T = 295 K. © by Oldenbourg Wissenschaftsverlag.
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    Crystal structure of praseodym gallate, Pr4Ga2O9
    (München : R. Oldenbourg Verlag GmbH, 1999) Gesing, T.M.; Uecker, R.; Buhl, J.-C.
    Ga2O9Pr4, monoclinic, P121/c1 (No. 14), a = 7.8256(4) Å, b = 11.0322(5) Å, c = 11.4959(7) Å, β = 109.187(3)°, V = 937.4 Å3, Z = 4, R(P) = 0.026, wR(P) = 0.034, R(I)= 0.033, T = 295 K.
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    Quasi-Transient Calculation of Czochralski Growth of Ge Crystals Using the Software Elmer
    (Basel : MDPI, 2019) Miller, Wolfram; Abrosimov, Nikolay; Fischer, Jörg; Gybin, Alexander; Juda, Uta; Kayser, Stefan; Janicskó-Csáthy, Jószef
    A numerical scheme was developed to compute the thermal and stress fields of the Czochralski process in a quasi-time dependent mode. The growth velocity was computed from the geometrical changes in melt and crystal due to pulling for every stage, for which the thermal and stress fields were computed by using the open source software Elmer. The method was applied to the Czochralski growth of Ge crystals by inductive heating. From a series of growth experiments, we chose one as a reference to check the validity of the scheme with respect to this Czochralski process. A good agreement both for the shapes of the melt/crystal interface at various time steps and the change in power consumption with process time was observed. © 2019 by the authors. Licensee MDPI, Basel, Switzerland.
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    Numerical modelling of the czochralski growth of β-Ga2O3
    (Basel : MDPI, 2017) Miller, Wolfram; Böttcher, Klaus; Galazka, Zbigniew; Schreuer, Jürgen
    Our numerical modelling of the Czochralski growth of single crystalline β-Ga2O3 crystals (monoclinic symmetry) starts at the 2D heat transport analysis within the crystal growth furnace, proceeds with the 3D heat transport and fluid flow analysis in the crystal-melt-crucible arrangement and targets the 3D thermal stress analysis within the β-Ga2O3 crystal. In order to perform the stress analysis, we measured the thermal expansion coefficients and the elastic stiffness coefficients in two samples of a β-Ga2O3 crystal grown at IKZ. Additionally, we analyse published data of β-Ga2O3 material properties and use data from literature for comparative calculations. The computations were performed by the software packages CrysMAS, CGsim, Ansys-cfx and comsol Multiphysics. By the hand of two different thermal expansion data sets and two different crystal orientations, we analyse the elastic stresses in terms of the von-Mises stress.