137 research outputs found
Relative energetics and structural properties of zirconia using a self-consistent tight-binding model
We describe an empirical, self-consistent, orthogonal tight-binding model for
zirconia, which allows for the polarizability of the anions at dipole and
quadrupole levels and for crystal field splitting of the cation d orbitals.
This is achieved by mixing the orbitals of different symmetry on a site with
coupling coefficients driven by the Coulomb potentials up to octapole level.
The additional forces on atoms due to the self-consistency and polarizabilities
are exactly obtained by straightforward electrostatics, by analogy with the
Hellmann-Feynman theorem as applied in first-principles calculations. The model
correctly orders the zero temperature energies of all zirconia polymorphs. The
Zr-O matrix elements of the Hamiltonian, which measure covalency, make a
greater contribution than the polarizability to the energy differences between
phases. Results for elastic constants of the cubic and tetragonal phases and
phonon frequencies of the cubic phase are also presented and compared with some
experimental data and first-principles calculations. We suggest that the model
will be useful for studying finite temperature effects by means of molecular
dynamics.Comment: to be published in Physical Review B (1 march 2000
Boron and Lithium in Calcium Sulfate Veins: Tracking Precipitation of Diagenetic Materials in Vera Rubin Ridge, Gale Crater
The NASA Curiosity roverâs ChemCam instrument suite has detected boron in calciumâsulfateâfilled fractures throughout the sedimentary strata of Gale crater including Vera Rubin ridge (VRR). The presence of elevated B concentration provides insights into Martian subsurface aqueous processes. In this study we extend the dataset of B in Caâsulfate veins across Gale crater, comparing the detection frequency and relative abundances with Li. We report 33 new detections of B within veins analyzed between sols 1548 and 2311 where detections increase in Pettegrove Point and Jura members, which form VRR. The presence of B and Li in the Caâsulfate veins is possibly due to dissolution of preâexisting B in clays of the bedrock by acids or neutral water and redistribution of the elements into the veins. Elevated frequency of B detection in veins of Gale crater correlate with presence of dehydration features such as desiccation cracks, altered clay minerals and detections of evaporites such as Mgâsulfates, chloride salts in the host rocks. The increased observations of B also coincide with decreased Li concentration in the veins (average Li concentration of veins drops by ~15 ppm). Boron and Li have varying solubilities and Li does not form salts as readily upon dehydration as B, causing it to remain in the solution. So, the weak negative correlation between B and Li may reflect the crystallization sequence during dehydration on Vera Rubin ridge
Effect of Dopants on Zirconia StabilizationâAn X-ray Absorption Study: III, Charge-Compensating Dopants
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/66100/1/j.1151-2916.1994.tb05404.x.pd
Cation non-stoichiometry in yttrium-doped barium zirconate: phase behavior, microstructure, and proton conductivity
Low-temperature and low atmospheric pressure infrared reflectance spectroscopy of Mars soil analog materials
Contribution Ă l'Ă©tude de la structure des halloysites et essais de synthĂšse
On a pu obtenir des particules d'halloysite par précipitation à partir d'un mélange d'aluminate et silicate de soude, en proportions convenables. La formation du précipité est favorisée par l'introduction d'une faible quantité d'halloysite naturelle. Le corps obtenu est étudié par l'analyse thermique différentielle et contrÎlé au microscope électronique. Les résultats sont discutés.Karsulin M., Stubican V. Contribution à l'étude de la structure des halloysites et essais de synthÚse. In: Bulletin de la Société française de Minéralogie et de Cristallographie, volume 76, 10-12, 1953. pp. 434-437
The Calcia-Zirconia Phase Diagram Revisited: Stability of the Ordered Phases phi1 and phi2
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