Lattice Distortion Energy Research Articles

Novel Shape Evolution of BaMoO4 Microcrystals

Dendritic BaMoO(4) microcrystals with lengths of about 5-15 microm were synthesized simply under ambient conditions by a microemulsion-mediated method within an ultrashort time. The products were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), and field-emission scanning electron microscopy (FESEM), which showed that the products were in pure tetragonal BaMoO(4) structure and that an individual dendrite had a long central stem with four array shrunken branches. Detailed studies revealed that the formation of these 3-D structures was strongly dependent on the composition of the microemulsion. At prolonged aging time, the dendrites evolved into rods and further into particles, driven by the lattice distortion energy required to evolve the crystal from a metastable to a stable state. This novel crystal shape evolution provides insight into crystallization behavior given that the growth history and shape evolution process have traditionally been poorly understood.

Creep and recrystallization of large polycrystalline masses. III. Continuum theory of ice sheets

This work sets forth the first thermodynamically consistent constitutive theory for ice sheets undergoing strain-induced anisotropy, polygonization and recrystallization effects. It is based on the notion of a mixture with continuous diversity, by picturing the ice sheet as a ‘mixture of lattice orientations’. The fabric (texture) is described by an orientation-dependent field of mass density which is sensitive not only to lattice spin, but also to grain boundary migration. No constraint is imposed on stress or strain of individual crystallites, aside from the assumption that basal slip is the dominant deformation mechanism on the grain scale. In spite of the fact that individual ice crystallites are regarded as micropolar media, it is inferred that couples on distinct grains counteract each other, so that the ice sheet behaves on a large scale as an ordinary (non-polar) continuum. Several concepts from materials science are translated to the language of continuum theory, like, for example, lattice distortion energy , grain boundary mobility and Schmid tensor , as well as some fabric (texture) parameters like the so-called degree of orientation and spherical aperture. After choosing suitable expressions for the stored energy and entropy of dislocations, it is shown that the driving pressure for grain boundary migration can be associated to differences in the dislocation potentials ( viz . the Gibbs free energies due to dislocations) of crystallites with distinct c -axis orientations. Finally, the generic representation derived for the Cauchy stress is compared with former generalizations of Glen's flow law, namely the Svendsen–Gödert–Hutter stress law and the Azuma–Goto–Azuma flow law.

Supercluster of Electrons in Ultrathin TaSe2Nanocrystals

pffiffiffiffiffi p supercluster based on ffiffiffi 7 pffiffiffi 7 p clusters expected in triangle lattices. This new hierarchal structure and successive clustering cannot be explained by a conventional electron clustering mechanism assisted by background lattice distortions, i.e., charge-density-wave formation mechanism based on Fermi surface nesting. We propose an alternative possible formation mechanism based on saddle-point nesting, taking into account a trigonal symmetry as well as lattice distortion energy.

A study on crystalline residual stress of the iPP surface layer in Al/iPP/Al under the influence of microwave irradiation

AbstractThe residual stress of the iPP surface layer in Al/iPP/Al under the influence of microwave irradiation was investigated by thin film (TF)‐X‐ray diffraction (XRD). Depending on the irradiation time, we calculated the macro residual stress, micro stress, and lattice static distortion stress. The results show that the macroscopic residual tensile stress of irradiated iPP samples dropped from about 12 MPa to 4 MPa. D(300) (the β crystal phase) becomes larger from about 4 to 10 nm as the irradiation time increased, and the β‐form iPP becomes more perfect. However, for theα‐form phase, D(110) remains almost stable. Moreover, the microscopic distortion coefficient ε(300) that decreases from approximately 0.03 to 0.018, becomes smaller than ε(110) parallel to the irradiation time, so the microscopic stress of the β‐crystal is decreased. In addition, the lattice static distortion energy of the α‐form greatly increases from 2 to 6 MPa, but the lattice static distortion energy of the β‐crystals remains constant at about 1.5 MPa and is much smaller than that of the α‐crystals at the same irradiation time. These calculated results are in good agreement with that of the crystallinity and order parameter of the β‐crystals of the TF‐XRD. The lattice distortion energy is a major portion of the plastic deformation, therefore, it suggests that the lattice static distortion energy is the main cause of α → β crystalline transformation. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3759–3765, 2004

On the role of grain growth, recrystallization and polygonization in a continuum theory for anisotropic ice sheets

AbstractWe outline how to incorporate microscale effects of polycrystalline ice into a continuum description. Actually, analyses of ice cores in Antarctica show that different microstructures generally produce different responses, i.e. a non-uniform distribution of c axes gives rise to anisotropic behaviour. It has been recognized that, to describe certain microstructural processes, like recrystallization or polygonization, we need a parameter able to switch them on (e.g. dislocation density or its associated lattice distortion energy). With this in mind, balance equations for a continuum theory of an anisotropic ice sheet undergoing recrystallization have been recently proposed. In this work, we examine relations for some constitutive quantities, in order to take into account the effects of grain-boundary migration, nucleation and polygonization. We check our assumptions by explicit comparison with the first 1200 m of the Byrd (Antarctica) ice core. Current literature usually gives a relation between normal grain growth and grain boundary migration rate. Here, an equation for normal grain growth which also incorporates the influence of polygonization is suggested. It is based on experimental data from the same core in Antarctica. Polygonization is a microscopic process, but here we present a continuum description of the bending stresses which promote the fragmentation of crystallites in terms of the theory of mixtures with continuous diversity.

Multiple cluster model (MCM) for surface reaction systems

Multiple cluster model (MCM) for investigating surface reactions is formulated. In this model the reaction center, where electron correlation effects often play a key role, is described by an accurate high-level approximation, and bulk effects such as the lattice distortion energy are evaluated using a simple low-level approximation. Therefore, the MCM can properly simulate the potential energy hypersurface of the surface reaction system with a feasible computational cost. Since there exists no fixed atom in the MCM, we can rigorously characterize the stationary point (the minimum energy point or the transition state) on the potential energy hypersurface by vibrational frequency analysis. The MCM can be applied not only to surface systems, but also to various large systems. A detailed comparison of the MCM with the integrated molecular orbital+molecular mechanics (IMOMM), the integrated molecular orbital+molecular orbital (IMOMO), and ONIOM developed by Morokuma and co-workers is also presented. ©1999 John Wiley & Sons, Inc. Int J Quant Chem 71: 403–413, 1999

The effect of grinding on the sintering of raw petroleum coke

Preparation of dense carbon materials without use of any binder was attempted, effect of grinding treatment on the characteristics of raw petroleum needle coke and on the properties of the sintered carbon compacts was investigated, and the sintering mechanizm of the coke after grinding was discussed. It was found that the coke particle size and crystalline size was decreased and the specific surface area of the coke was increased with grinding, and the influence was obvious up to 20 hours grinding treatment. The interlayer spacing of the coke after graphitization at 2773 K was gradually increased and the a-axis constant was marginally reduced with the grinding time. Results from the sintering experiment show that carbon materials can be sintered from the ground coke, and the density and flexural strength of the sintering compacts reached stable values of 1.8 gcm −3 and about 70 MPa, respectively, after 20 hours grinding of the coke. The sintering ability of the coke after grinding was considered to result from the increase of surface energy, lattice distortion energy and fraction of volatile matters of the coke, which were induced by grinding treatment.

Ferroelectric phase transitions: A first-principles approach

Fundamental aspects of the theoretical study of bulk ferroelectric phase transitions through the construction of model Hamiltonians from first-principles calculations are reviewed. It is demonstrated that density-functional-theory linear-response calculations and total-energy calculations with symmetry-constrained ionic relaxation are very useful in the determination of the local mode variable and of the parameters in an explicit expression for the model Hamiltonian. Results of first-principles pseudopotential calculations of the lattice constant, phonon frequencies, and distortion energies for the perovskite ferroelectric PbTiO3 are presented. From this information, the local mode variable is identified, a model Hamiltonian is constructed and its finite-temperature behavior is studied with mean-field theory and Monte Carlo simulation. Very rough agreement with the observed Tc is obtained and various improvements and refinements of the calculation proposed. A well-controlled method for investigation of the intrinsic limitations of the model Hamiltonian approach, based on application to a simple rigid ion model, is outlined and preliminary results described.

First-principles model hamiltonians for ferroelectric phase transitions

Abstract Formal aspects of the construction of model Hamiltonians for the study of ferroelectric phase transitions are reviewed. It is demonstrated that first-principles linear-response calculations and total-energy calculations with symmetry-constrained ionic relaxation are very useful in the determination of the local mode variable and of an explicit expression for the model Hamiltonian. Results of first-principles pseudopotential calculations of the lattice constant, distortion energies and Born effective charges Z* for the perovskite ferroelectric PbTiO3 are discussed. A test of the model Hamiltonian approach through application to a minimal rigid ion model and comparison with Monte Carlo simulation is outlined, and preliminary results described.

First-principles model hamiltonians for ferroelectric phase transitions

Abstract Formal aspects of the construction of model Hamiltonians for the study of ferroelectric phase transitions are reviewed. It is demonstrated that first-principles linear-response calculations and total-energy calculations with symmetry-constrained ionic relaxation are very useful in the determination of the local mode variable and of an explicit expression for the model Hamiltonian. Results of first-principles pseudopotential calculations of the lattice constant, distortion energies and Born effective charges Z* for the perovskite ferroelectric PbTiO3 are discussed. A test of the model Hamiltonian approach through application to a minimal rigid ion model and comparison with Monte Carlo simulation is outlined, and preliminary results described.

Elastic and coulombic contributions to real-space hole pairing in doped La2CuO4

The energetics of three types of possible polaron pair in doped La2CuO4 have been investigated by computer-simulation techniques based on lattice-energy minimisation. The most energetically favourable pairing configurations have been obtained. O–—O– pairing is calculated to be bound by 0.119 eV. For Cu3+—Cu3+ and Cu3+—O– pairing, interlayer configurations are found to be more favourable than intralayer pairing and the nearest-neighbour pairing is unfavourable. The binding energy of the pairs is found to be related to the pair distance and geometry of the pair. The Coulomb repulsive energy between hole pairs is estimated and the interlayer pairing is found to be more effective at screening Coulomb interactions between holes. The lattice distortion energy caused by polaron pairing is estimated and is taken into account in the calculation.

Lattice Distortion Energy Spectra of Vacuum‐deposited Copper Films

Crystal Research and TechnologyVolume 26, Issue 7 p. K163-K168 Short Note Lattice Distortion Energy Spectra of Vacuum-deposited Copper Films N. C. Chourasia, N. C. Chourasia Metallurgical Engineering Department, Faculty of Technology and Engineering, M.S. University of Baroda, P.O. Box No 51, Kalabhavan, Vadodara – 390001, IndiaSearch for more papers by this authorV. L. Gadgeel, V. L. Gadgeel Metallurgical Engineering Department, Faculty of Technology and Engineering, M.S. University of Baroda, P.O. Box No 51, Kalabhavan, Vadodara – 390001, IndiaSearch for more papers by this authorG. K. Shivakumar, G. K. Shivakumar Metallurgical Engineering Department, Faculty of Technology and Engineering, M.S. University of Baroda, P.O. Box No 51, Kalabhavan, Vadodara – 390001, IndiaSearch for more papers by this author N. C. Chourasia, N. C. Chourasia Metallurgical Engineering Department, Faculty of Technology and Engineering, M.S. University of Baroda, P.O. Box No 51, Kalabhavan, Vadodara – 390001, IndiaSearch for more papers by this authorV. L. Gadgeel, V. L. Gadgeel Metallurgical Engineering Department, Faculty of Technology and Engineering, M.S. University of Baroda, P.O. Box No 51, Kalabhavan, Vadodara – 390001, IndiaSearch for more papers by this authorG. K. Shivakumar, G. K. Shivakumar Metallurgical Engineering Department, Faculty of Technology and Engineering, M.S. University of Baroda, P.O. Box No 51, Kalabhavan, Vadodara – 390001, IndiaSearch for more papers by this author First published: 1991 https://doi.org/10.1002/crat.2170260733Citations: 1AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Citing Literature Volume26, Issue71991Pages K163-K168 RelatedInformation

Heat of transport of tritium in vanadium: General characteristics of of hydrogen isotopes in group V metals

Abstract The heat of transport Q ∗ of tritium in the α phase of vanadium has been measured at average temperatures of 343, 423 and 523 K, and an isotope dependence of Q ∗ has been ascertained by comparing the present data with those of protium and deuterium reported by other investigators. The following characteristics of Q ∗ common to the group V metals have been pointed out by summarizing the experimental data of Q ∗ of hydrogen isotopes in vanadium, niobium and tantalum reported by the present authors and other investigators, 1. (i) Q ∗ (Ta) > Q ∗ (Nb) > Q ∗ (V) for each hydrogen isotope. 2. (ii) Q T ∗ > Q D ∗ > Q H ∗ in each metal. 3. (iii) There is a definite relation between the heat of transport Q ∗ and the activation energy of diffusion ΔHm concerning their element and isotope dependence. 4. (iv) The bias effect of the biased-jump diffusion model approaches zero with temperature. The atomic origin of the bias effect has been ascribed to the lattice distortion energy and electronic polarization energy localized in the neighbourhood of the hydrogen isotopes and the isotope dependence of the heat of transport Q ∗ has been interpreted in terms of the isotope dependence of the lattice distortion energy.

Correlations in the electron subsystem of a ferroelectric and the electron-phonon interaction

Abstract In a vibronic ferroelectric, besides the phonon order parameter also an electronic one is induced. The correlation properties of the latter are investigated, The density of the coupled electron-hole pairs in a condensate characterizing the ordered state is calculated to be proportional to the vibronic lattice distortion energy squared, The total momentum of the condensate equals to the momentum of the vibration driving the structural transition. The electronic correlation length is of the same order as for the phonon order parameter. Electronic contribution to the latent heat is possible.

Possibility of off-center-exciton formation in BaFBr.

Extended-ion calculations have been performed in order to test the possibility of spontaneous off-center motion of excitons in BaFBr. The off-center motion is a mode of decay to F,H centers in the material. The lattice distortion energy is computed self-consistently with the extended-ion method. It is energetically favorable to form off-center excitons displaced roughly 2 a.u. along the molecular axis for fluorine and bromine centers. The fluorine center is stabilized most due to its low-energy F-center ground state.

New evidence of small lattice relaxation for the D X center in AlxGa1−xAs

Local structure of isolated Si impurity in GaAs and AlAs is studied using a parameter-free semi-empirical tight binding method. It is predicted that nearest neighbor As atom around the impurity moves toward SiGa(Al) causing a 6.54% (5.73%) change in GaAs(AlAs) bond length. An estimation of lattice distortion energy 0.02±0.003 eV (0.025±0.003 eV) for GaAs:Si (AlAs:Si) is found in good qualitative agreement with the value obtained by J. C. M. Henning and J. P. M. Ansems [Semicond. Sci. Technol. 2, 1 (1987)] from the photoionization of the DX center in lightly doped Si impurities in Al0.33Ga0.67As. The fits for the observed maxima in the optical cross section and the calculation of the pressure-dependent thermal barrier energy lend support for the small lattice relaxation models and cast doubt on the validity of those with the large lattice relaxation usually recommended for this class of centers.

Properties of Indium Film Deposited at Liquid Nitrogen Temperature

Irreversible resistivities of as-deposited indium films during annealing process were measured. Using Vand's theory, an activation energy of defect, E , and the initial lattice distortion energy function, F 0 ( E ), were evaluated. The spectrum of F 0 ( E ) showed two peaks, one at the activation energy E max1 =0.30 eV, and the other at E max2 =0.45 eV. The dependence of the activation energies on the film thickness were not observed. But the values of F 0 ( E max1 ) and F 0 ( E max2 ) were dependent on the film thickness. It is suggested that the peak at E max2 is related to the stress introduced during the annealing process.

Regular-dimerized stack and neutral-ionic interfaces in mixed-stack organic charge-transfer crystals.

Using diagrammatic valence-bond calculations, we have investigated the interplay between neutral-ionic (N-I) and regular-dimerized stack interfaces in mixed-stack organic charge-transfer (CT) crystals. The interactions relevant to the above two interfaces, that is, the intersite Coulomb and the electron-lattice phonon couplings, are introduced via a mean-field approach and a perturbative Herzberg-Teller expansion, respectively. The k=0 results for finite chains (up to scrN=12 sites) and rings (up to scrN=14 sites) are extrapolated to scrN\ensuremath{\rightarrow}\ensuremath{\infty}, obtaining an appropriate description of the electronic structure of a mixed, regular chain. The calculations distinguish the N and I phases as characterized, respectively, by nondegenerate and degenerate singlet ground states, the crossing point being found at a degree of ionicity (\ensuremath{\rho}) of about 0.63. Also the singlet-triplet gap vanishes in the I phase. The explicit consideration of the intersite Coulomb interactions changes the N-I interface from a continuous to a discontinuous one (first-order phase transition), whereas the electron-lattice phonon coupling makes the singlet degenerate (or quasidegenerate) ground state subject to the Peierls instability. The results are summarized in terms of a three-dimensional phase diagram relating \ensuremath{\rho}, the lattice-distortion energy, and the stabilization energy of the ionic stack due to intersite Coulomb interactions. This phase diagram is shown to nicely account for several experimental observations relevant to mixed-stack CT crystals and to their phase transitions.

Lattice distortion energy spectra of thin evaporated silver films

Thin silver films (thickness, 12.5–160 nm) were evaporated under ultrahigh vacuum conditions onto clean glass substrates (substrate temperature, 225 K). During the growth process a large number of lattice defects were incorporated (condensation rate, 0.2 and 0.01 nm s -1). The films were subjected to heat treatment (constant heating rate, 0.1 K s -1) and the variation in the electrical resistance was measured as a function of temperature. Using Vand's theory the initial lattice distortion energy spectra of the films were determined from the resistance-temperature data. The lattice distortion energy function has maximum values. While the number of distortions with a decay energy of about 0.8 eV increases rapidly with decreasing film thickness, the number of distortions with a decay energy of about 0.93 eV varies only slightly.

DX center: Crossover of deep and shallow states in Si-doped AlxGa1-xAs.

A new microscopic model for the origin of the DX center in Si-doped ${\mathrm{Al}}_{\mathrm{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$As is proposed based on discrete variational X\ensuremath{\alpha} cluster calculations. The calculated level structure shows that the antibonding ${A}_{1}$ state of Si, which lies in the conduction bands as a resonance state in the case of GaAs, shifts downwards into the energy gap upon distortion of the neighboring four As atoms in the case of ${\mathrm{Al}}_{\mathrm{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$As. The formation energy of this distorted configuration is estimated from the shift of the level of the antibonding ${A}_{1}$ state along with the Keating-model calculation for the lattice distortion energy. As a result, the distorted configuration is found to be stable in Si-doped ${\mathrm{Al}}_{\mathrm{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$As.