ALBERT

All Library Books, journals and Electronic Records Telegrafenberg

X
feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    Electronic Resource
    Electronic Resource
    Annealing Metamict Zircon: A Powder X-ray Diffraction Study of a Highly Defective Phase (1999)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 82 (1999), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The transition from highly defective (metamict) to crystalline zircon is characterized by short-range structural order, which follows a different kinetic behavior than the corresponding long-range order. Experimental results from in situ powder X-ray diffraction experiments are analyzed using Rietveld refinement and direct Fourier analysis. The Rietveld refinement leads to a detailed assessment of the structural contraction of the crystalline portion of the same during thermal annealing. The Fourier analysis shows a highly heterogeneous distribution of interatomic bond distances. The main effect of structural annealing is a change of the distances between Si and O atoms and the average Si–Zr distance. The Zr–Zr distance seems to be less affected by this thermal treatment. Short-range order is recovered at lower temperatures than that of long-range order. Crystallinity is recovered anisotropically with slower annealing along the crystallographic c-direction than along the a-direction.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1999.tb02146.x
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 2
    Electronic Resource
    Electronic Resource
    Formation of needle shaped twin domains in cordierite: A computer simulation study (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 2414-2422 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The formation of needle shaped domains in cordierite is simulated using a simplified two-dimensional computer model with hexagonal symmetry and nonlocal (strain-induced) atomic interactions. Domain walls form along elastically soft directions as expected and sometimes needle domains appear during annealing. During annealing needles are then consumed by the coarsening process or retract into the domains to which they are attached. Needles have rounded, parabolic tips symptomatic of cordierite's comparatively low anisotropy energy. Needle splitting is not observed but a novel wetting mechanism by which auxiliary domains form at the needle tip is observed. These domains form such as to make a section of the needle tip a strain allowed domain wall and so reduce the bending energies of the domain walls in this region. At higher temperatures, needle domain walls become only poorly orientated along soft directions and needle domains become patchy with blunt tips and increased "wetting" at the needle tips. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.369559
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 3
    Electronic Resource
    Electronic Resource
    Temperature dependence of the domain wall width in LaAlO3 (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 722-727 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Twin wall related diffuse scattering intensities from a single crystal of LaAlO3 were determined using high-resolution x-ray diffraction methods. Rocking curves were measured for sample temperatures between 295 and 900 K. The wall thickness W was determined by comparing the observed diffraction profiles with structure factor calculations for a tanh(x/W) wall profile. It is shown that W(approximate)20 Å at low temperatures and increases slowly with temperature reaching values in excess of 200 Å near Tc(approximate)850 K with W∝|T−Tc|−1. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.369152
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 4
    Electronic Resource
    Electronic Resource
    Twinning in tetragonal leucite (1988)
    Springer
    Physics and chemistry of minerals 16 (1988), S. 298-303 
    Details
    ISSN: 1432-2021
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract The change from cubic to tetragonal symmetry in natural leucite, KAlSi2O6, involves two types of twinning, which appear sequentially with decreasing temperature: (1) lamellar, associated with the point group symmetry reduction m3m to 4/mmm; (2) merohedric, associated with the change 4/mmm to 4/m. Twin orientations have been deduced from X-ray precession photos and TEM diffraction patterns and images. These are confirmed by theory, using the concept of spontaneous strain and the symmetry relations between adjacent domains. Lamellar twins have boundaries parallel to {101} of the cubic phase, and are cross-cut by the merohedric twins, which have irregular boundaries with x and y in adjacent domains interchanged. On an electron microscopic scale, the distortion arising from twin intersections is revealed by a curvature of one twin wall adjacent to another, and by needle-shaped domains. The macroscopic orientation of the lamellar twins is related to the lattice parameters and hence the magnitude of the spontaneous strain. This in turn leads to the characterisation of the order parameter for the m3m to 4/mmm transformation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00220699
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 5
    Electronic Resource
    Electronic Resource
    Phase transitions in leucite: Dielectric properties and transition mechanism (1990)
    Springer
    Physics and chemistry of minerals 17 (1990), S. 444-452 
    Details
    ISSN: 1432-2021
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract To investigate the mechanisms for the cubic-tetragonal phase transition in leucite (KAlSi2O6), the frequency dependence of the dielectric constant (ɛ′), and of the electric conductivity (σ), have been measured as a function of temperature. The dielectric loss function, tan δ, contains two main features: (i) a classical Debye peak, with activation energy of 0.77 eV, ascribed to hopping of K-atoms between their channel (W) sites, via the vacant side-channel (S) sites; (ii) a heavily-overdamped relaxational mode which softens when the crystal is cooled towards the phase transition temperature. The latter relaxational mode shows a critical behaviour, and is thus directly correlated with the transition mechanism. As it is only the potassium ions that could relax at frequencies well below the optical phonon branches, it appears that their movement is relaxational (i.e. heavily overdamped) rather than phonon-like. At temperatures above the transition point, the relaxation of K+ in an electric field is analysed in terms of collective motions within tetragonal domains. Direct evidence for the existence of such domains follows from the presence of diffuse intensity in single-crystal X-ray diffraction experiments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00212214
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 6
    Electronic Resource
    Electronic Resource
    Phase transitions in leucite: X-ray diffraction studies (1989)
    Springer
    Physics and chemistry of minerals 16 (1989), S. 714-719 
    Details
    ISSN: 1432-2021
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract Lattice parameters, and intensities of selected X-ray reflexions, have been measured as a function of temperature for natural leucite, to characterise the phase transformation behaviour. At low temperatures leucite has a large ferroelastic distortion, but the temperature evolution of lattice parameters cannot be explained in terms of a purely ferroelastic phase transition; in particular, the considerable change in volume with temperature implies an additional transition mechanism, which we correlate with off-centring of K-ions in the low-temperature phase, and a collapse of the 〈111〉 structural channels. The transition behavior can therefore be rationalised in terms of two competing mechanisms: (I) Ferroelastic (consistent with the change m3m→ 4/mmm); (II) Volume-changing (consistent with m3m → 4/m). Coupling of the two order parameters QI, and QII gives rise to the intermediate 4/mmm tetragonal phase. Our results confirm the existence of an I4 1/a→I4 1/acd transition, but the non-disappearance of the 200 reflexion at high temperatures implies that the expected transition from I41/acd to Ia3d (cubic) symmetry does not occur. We attribute this to a residual strain field conjugated to the order parameter, due to defects (with possible Al/Si order). Nevertheless, within our experimental resolution, the lattice becomes metrically cubic at 665° C.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00223322
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 7
    Electronic Resource
    Electronic Resource
    Localized defects in radiation-damaged zircon (2000)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 56 (2000), S. 947-952 
    Details
    ISSN: 1600-5740
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The crystal structure of a radiation-damaged natural zircon, ZrSiO_{4} (\alpha-decay radiation dose is ca 1.8 × 10^{18} α-decay events g−1), has been determined. The anisotropic unit-cell swelling observed in the early stages of the amorphization process (0.17% along the a axis and 0.62% along the c axis compared with the undamaged material) is a consequence of the anisotropy of the expansion of ZrO_{8} polyhedra. Larger anisotropic displacement parameters were found for Zr and O atoms, indicating that the distortion produced by \alpha particle-induced localized defects mainly affects the ZrO_{8} unit. The overall shape of SiO_{4} tetrahedra remains essentially undistorted, while Si—O bonds are found to lengthen by 0.43%.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0108768100008582
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 8
    Electronic Resource
    Electronic Resource
    Structural states of natural potassium feldspar: An infrared spectroscopic study (1989)
    Springer
    Physics and chemistry of minerals 16 (1989), S. 649-658 
    Details
    ISSN: 1432-2021
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract Natural samples of K-feldspar representing various states of Al, Si order were characterised using X-ray methods, transmission electron microscopy, and Fourier transform infrared spectroscopy. Line profiles of infrared absorption bands were observed to show strong correlation with the degree of Al, Si order present. In particular, the absorption frequencies of the 540 cm−1 and 640 cm−1 bands were seen to vary by ca. 10 cm−1 between sanidine and microcline, with modulated samples respresenting intermediate behaviour. Linewidths of these modes also decrease by ca. 50% in this series. The experimental results are discussed within the framework of Hard Mode Infrared Spectroscopy (HMIS), and it is shown that the absorption frequencies vary with the short range order parameter τ = (4t1-1)2 and the symmetry breaking order parameter describing Al, Si order, Q od=(t1 0−t1 m)/Q od=(t1 0+t1 m), where t1 is the average Al occupancy on the T1 sites and t1 o and t1 m are the individual site occupancies of the T1 o and T1 m sites, respectively. The structural state of orthoclase is characterised by strain-induced modulations with large spatial variations of the modulation wavelength. No such modulations were observed in the degree of local Al, Si order. Sanidine shows mode hardening in excess of the extrapolated effect of symmetry breaking Al, Si order, which is presumably related to nonsymmetry breaking ordering between T1 and T2 sites and/or as yet unobserved short range order of the symmetry breaking ordering scheme. The possibility of an additional phase transition in K-feldspar at temperatures above 1300 K is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00223313
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 9
    Electronic Resource
    Electronic Resource
    Phase transitions in leucite: Order parameter behaviour and the Landau potential deduced from Raman spectroscopy and birefringence studies (1990)
    Springer
    Physics and chemistry of minerals 17 (1990), S. 259-265 
    Details
    ISSN: 1432-2021
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract Hard mode Raman Spectroscopy and optical birefringence studies have been used to evaluate the temperature behaviour of order parameters for the cubictetragonal phase transition in leucite. There is a strong temperature-dependence of Raman line frequencies near 498 cm−1 and 529 cm−1, and the optical birefringence decreases towards zero on heating. Above the transition temperature leucite still shows slight birefringence, which correlates with the persistence of the 200 X-ray reflexion at these temperatures, and is not compatible with the ideal cubic symmetry. Quantitative observations of the temperature evolution of Raman line-frequencies and the birefringence are consistent with an order parameter showing T 1g symmetry, and a nearly-tricritical phase transition behaviour. The results of earlier X-ray and DSC studies imply the operation of an additional order parameter, with E g symmetry; this is observed, but its influence on the transition behaviour is significant only at temperatures close to T c. The two order parameters are related via linear-quadratic or biquadratic coupling. We develop the form of the Landau Potential for leucite — including both order parameters and their couplings — to discuss the present observations and previous structural data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00201458
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 10
    Electronic Resource
    Electronic Resource
    Kinetic rate laws derived from order parameter theory III: Al, Si ordering in sanidine (1991)
    Springer
    Physics and chemistry of minerals 17 (1991), S. 563-568 
    Details
    ISSN: 1432-2021
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract The time dependence of the ordering and disordering of Al and Si in sanidine is described within the framework of the kinetic rate laws developed in papers I and II of this series. It was found that the relevant order parameter Q t is homogeneous and non-conserved. The rate law is: $$\frac{{dQ_1 }}{{dt}} = - \frac{1}{\tau }exp(--\Delta G_a^* /k_B T)\frac{{\delta G_0 }}{{\delta Q_t }}.$$ The Gibbs free energy G 0 has no symmetry constraints and we find: $$G_0 (Q_t ) = --HQ_t + \tfrac{1}{2}a_t (T--T_c^t )Q_t^2 + \tfrac{1}{3}b_t Q_t^3 $$ with at/H = 0.0170 K−, T t c = 686 K for the approximation H ≫b t. The predicted temperature dependence of $$Q_t^{eq} = 1/0.017 (T--686 K)$$ for T ≫ 686 K agrees well with the experimental observations. The equivalent rate law is in the approximation b t = 0. $$Q_t^{eq} = 1/0.017 (T--686 K)$$ expressions for the time constant τ** are given. It is shown that the potential derived from the chemical rate law by Mueller (1967, 1969) closely corresponds to the quadratic approximation of the Gibbs free energy G0(Qt).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00202235
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...