35 research outputs found
Layered double hydroxide based active corrosion protective sealing of plasma electrolytic oxidation/sol-gel composite coating on AA2024
This work reports a novel approach for growing layered double hydroxide (LDH) films on any plasma electrolytic oxidation (PEO) coated AA2024 independently of the nature of the PEO coating. The specific PEO coating chosen to carry out this work is considered to be not suitable for direct LDH growth because of phase composition and morphological features. In this paper, we describe a new methodology that consists of covering the PEO coating with a thin layer of aluminum oxide based xerogel as the source of aluminate ions for subsequent in-situ LDH growth. X-ray diffraction (XRD) and scanning electron microscope (SEM) images showed a successful formation of LDHs on the surface. An improvement in terms of active corrosion protection was also demonstrated by electrochemical impedance spectroscopy (EIS) and scanning vibrating electrode technique (SVET).publishe
Ab Initio Evidence for the Formation of Impurity d(3z^2-r^2) Holes in Doped La_{2-x}Sr_xCuO_4
Using the spin unrestricted Becke-3-Lee-Yang-Parr density functional, we
computed the electronic structure of explicitly doped La_{2-x}Sr_xCuO_4 (x =
0.125, 0.25, and 0.5). At each doping level, an impurity hole band is formed
within the undoped insulating gap. This band is well-localized to CuO_6
octahedra adjacent to the Sr impurities. The nature of the impurity hole is
A_{1g} in symmetry, formed primarily from the z^2 orbital on the Cu and p_z
orbitals on the apical O's. There is a strong triplet coupling of this hole
with the intrinsic B_{1g} Cu x^2-y^2/O1 p_{sigma} hole on the same site.
Optimization of the c coordinate of the apical O's in the doped CuO_6
octahedron lead to an asymmetric anti-Jahn-Teller distortion of the O2 atoms
toward the central Cu. In particular, the O2 atom between the Cu and Sr is
displaced 0.26 A while the O2 atom between the Cu and La is displaced 0.10 A.
Contrary to expectations, investigation of a 0.1 A enhanced Jahn-Teller
distortion of this octahedron does not force formation of an x^2-y^2 hole, but
instead leads to migration of the z^2 hole to the four other CuO_6 octahedra
surrounding the Sr impurity. This latter observation offers a simple
explanation for the bifurcation of the Sr-O2 distance revealed in x-ray
absorption fine structure data.Comment: Submitted to Phys. Rev. B. See http://www.firstprinciples.com for
more informatio
An Ethnohistorical Perspective on Cheyenne Demography
Administrative censuses of the Southern Cheyenne Indians from 1880,1891, and 1900 permit family reconstitution, identification of residence groups, and comparisons of fertility between monogamous and polygynous women, when the records are approached by ethnohistori cal methods. This approach includes an awareness of the aboriginal adoption practices, kinship system, and naming practices. It is argued that the biases and distortions of administrative records can be effectively corrected to add to our store of information on band and tribal societies.Yeshttps://us.sagepub.com/en-us/nam/manuscript-submission-guideline