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Topic: Perovskite


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In the News (Wed 21 Aug 19)

  
  Perovskite - Wikipedia, the free encyclopedia
Perovskite is found in contact metamorphic rocks and associated mafic intrusives, nepheline syenites, and rare carbonatites.
Perovskite was discovered in the Ural mountains of Russia by Gustav Rose in 1839 and named for Russian mineralogist, L. Perovski (1792-1856).
The perovskite structure shares the property of ferroelectricity with garnet and olivine.
www.wikipedia.org /wiki/Perovskite   (196 words)

  
 Method for plasma etching of a perovskite oxide thin film - US Patent 5849207   (Site not responding. Last check: 2007-10-21)
Another problem has been noted in that the perovskite oxide which has been removed by the sputtering is liable to be re-attached on the side faces of the pattern or the inner walls of an etching chamber, thereby causing an intended dimension to be varied and contamination with the oxide particles.
The perovskite oxide thin film which is to be plasma etched according to the invention includes a thin film made of a material selected from lead titanate, barium titanate, strontium titanate, PZL and PLZT.
The perovskite oxide thin film 12 made of PZT is formed, for example, as having a thickness of 50 nm by reactive sputtering of multiple targets.
www.patentstorm.us /patents/5849207.html   (2354 words)

  
 Double layer perovskite oxide electrodes - US Patent 6426536   (Site not responding. Last check: 2007-10-21)
Perovskite oxides exhibit a wide range of behavior depending on chemical composition, temperature, electric fields, and magnetic fields.
Because the latter deposition is performed with the substrate at a temperature (T)>500° C., and because of their physical proximity to the electrodes, the reactivity and epitaxial compatibility of gate oxide 200 and channel oxide 195 with the electrodes is an important parameter that affects the performance of these complex devices.
The preferred method of patterning the upper conductive oxide material is ion milling, and the preferred method of removing the lower conductive oxide material is wet chemical etching by which the upper conductive oxide layer and the substrate are unaffected.
www.patentstorm.us /patents/6426536.html   (4135 words)

  
 Winter Workshop for Undergraduates   (Site not responding. Last check: 2007-10-21)
The general chemical formula for a oxide perovskite is ABO3, where by taking the origin at the position of the A atom, the motif coordinates are: A at (0,0,0); B at (1/2,1/2,1/2); and O at (1/2,1/2,0), (1/2,0,1/2), (0, 1/2, 1/2)1.
A common example is the cubic perovskite Barium Titanate (BaTiO3), where its Barium ions reside at the corners of the unit cell, while the Titanium ion sits in the center of the cell surrounded by the Oxygen ions located in the middle of each of the six planes.
Some perovskites are piezoelectric meaning that applying stress or strain will shift the central atom, creating a big enough dipole moment to produce an electrical potential.
mrsec.la.asu.edu /workshop/ww2001/reports/ww2001-lin.html   (895 words)

  
 Process for regenerating perovskite catalysts and hydrocarbon treating processes utilizing the regenerated catalyst - ...
The ideal perovskite crystalline structure is defined by the empirical formula ABO.sub.3 in which A and B are cations of at least two different metals and in which the A cation is coordinated to 12 oxygen atoms while the B cation occupies octahedral sites and is coordinated to 6 oxygen atoms.
Thus, the catalyst may be an unsupported perovskite, that is, 100% perovskite or the catalyst may be a composite catalyst comprising a perovskite.
The regenerated perovskite catalyst is particularly suited for use in catalytic cracking and catalytic fluid coking, including in integrated fluid coking and gasification processes, using high boiling point hydrocarbonaceous feeds having a high content of metallic contaminants and a high Conradson carbon residue.
www.freepatentsonline.com /4446011.html   (4549 words)

  
 Bismuth-containing mixed oxides of perovskite structure in oxidation of acyclic hydrocarbons - Patent 4472314
Mixed oxides of bismuth with other metals of the perovskite structure and having vacant lattice sites in the same lattice positions occupied by bismuth are disclosed as partial oxidation and ammoxidation catalysts.
Perovskites are a well-studied class of crystals having two types of cation lattice sites, having A ions occupying dodecahedral coordination sites (12-coordination sites) and B ions occupying octahedral coordination sites (6-coordination sites).
It was determined that such mixed oxide had assumed a perovskite configuration as described in F. Galasso, Structure, Properties and Preparation of Perovskite Type Compounds (Pergamon Press 1969) with barium or barium and some bismuth in the dodecahedral coordination sites as indicated by the column "A-site Metals" in Table 1.
www.freepatentsonline.com /4472314.html   (2324 words)

  
 Stable perovskite catalysts - United States Patent 4,126,580
Perovskite catalysts of the general formula ABO.sub.3 having increased stability through the incorporation of metals having low first ionization potentials, and their use in oxidation and reduction reactions.
The A site metals used in the preparation of such perovskite compositions can be from the periodic table groups 1A, 1B, 2A, 2B, 3B, 4A, 5A lanthanide rare earth metals (atomic numbers 58 through 71) and from the actinide rare earth metals (atomic numbers 90 through 104).
The perovskite compositions of the invention can be used as catalysts in the form of free-flowing powders, for example, in fluid-bed reaction systems, or in the form of shaped structures providing efficient contact between the catalyst and reactant gases.
xrint.com /patents/us/4126580   (5741 words)

  
 Lee et al.: Perovskite phase developments...   (Site not responding. Last check: 2007-10-21)
So far, perovskite PZN powders could only be prepared under high pressures over 2.5 GPa [1], while single crystalline forms were prepared by flux-growth methods [2-6].
Perovskite powders were prepared using a B-site precursor method [16,17], where precursor powders were synthesized separately and reacted later with PbO, in order to promote perovskite phase developments and thereby to improve dielectric properties.
Perovskite phase contents were estimated by comparing major peak intensities between (110) and (222) of perovskite and pyrochlore structures, respectively.
www1.elsevier.com /gej-ng/10/32/37/43/33/30/article.html   (1853 words)

  
 SrTiO3 (Perovskite)
Among ternary and quarternary oxides and fluorides the perovskite structure class is probably the most common structural arrangement.
- Derived from the perovskite structure by layered ordering of the A-site cations (one is usually Ba and the other typically a smaller rare-earth ion) and removal of the oxygens which lie in the same plane as the rare-earth ion.
It is this copper which is said to belong to the copper-oxygen sheets which are thought to be responsible for the high temperature superconductivity of this compound and some of its relatives.
www.chemistry.ohio-state.edu /%7Ewoodward/ch754/struct/SrTiO3.htm   (741 words)

  
 Structure
Perovskites are a large family of crystalline ceramics that derive their name from a specific mineral known as perovskite.
The parent material, perovskite, was first described in the 1830's by the geoologist Gustav Rose, who named it after the famous Russian mineralogist Count Lev Aleksevich von Perovski.
Superconducting perovskites were first discovered by IBM researchers Bednorz and Mueller who were examining the electrical properties of a family of materials in the Ba-La-Cu-O system.
www.engr.sjsu.edu /WofMatE/Structure.htm   (1896 words)

  
 PEROVSKITE (Calcium Titanium Oxide)
Perovskite is an increasingly economically important, and in some rocks a rather common, mineral.
Often perovskite is enriched in cerium, niobium, thorium, lanthanum, neodymium and other rare earth metals.
Perovskite is actually pseudocubic (or "falsely shaped" in a loose translation from the Greek).
mineral.galleries.com /minerals/OXIDES/perovski/perovski.htm   (392 words)

  
 [Rockhounds] Perovskite, Magnet Cove
We also noticed the perovskites tended to be much more lustrous and sharper crystals.
I know there are different of diffeent dark garnets including kimzeyite for which it is the type locaare (which arer very scarce by the way).
Perovskite typically is very > dark brown, often with some yellow streaks that > probably represent alteration to anatase, and > usually is (pseudo)cube-octahedral.
lists.drizzle.com /pipermail/rockhounds/2003-January/002535.html   (331 words)

  
 Bayerisches Geoinstitut - Annual Report 2001 Aluminium diffusion in silicate perovskite and majoritic garnet (N. ...   (Site not responding. Last check: 2007-10-21)
The diffusion of aluminium in majorite and aluminous silicate perovskite plays an important role in determining the longevity of chemical heterogeneity in the Earth’s lower mantle (e.g.
Although measured diffusion profiles in perovskite are less than 1 µm in length, i.e.
Thus diffusion is 1-2 orders of magnitude faster in garnet than in perovskite at 25 GPa and 1750 to 1950 °C. This preliminary result suggests that homogenization of slab heterogeneities and mineral transformations involving an exchange of aluminium for (magnesium + silicon) will occur considerably slower in the lower mantle than in the transition zone.
www.bgi.uni-bayreuth.de /annual_report/2001/c_18.phtml   (313 words)

  
 GdFeO3 (Perovskite)   (Site not responding. Last check: 2007-10-21)
It occurs when the A-site cation is too small for its 12 coordinate cavity in the cubic perovskite structure.
This distortion of the perovskite structure is the predominant for perovskites with tolerance factors smaller than ~0.98 (the best way to calculate tolerance factors is to use 12-coordinate radii for the A-site cation, 6-coordinate radii for the M-site cation, and 2-coordinate radii for the anion).
This distortion decreases orbital overlap and the width of the conduction band when M is a transition metal cation.
www.chemistry.ohio-state.edu /%7Ewoodward/ch754/struct/GdFeO3.htm   (335 words)

  
 APS - 2005 APS March Meeting - Event - Strain-induced metal-insulator phase coexistence in perovskite manganites   (Site not responding. Last check: 2007-10-21)
The observed coexistence of distinct metallic and insulating electronic phases within the same sample of a perovskite manganite, such as La$_{1-x-y} $Pr$_y$Ca$_x$MnO$_3$, has been a puzzle to both theorists and experimentalists.
In particular, colossal magnetoresistance in these materials is considered to be closely related to the texture owing to nanometer- and micrometer-scale heterogeneities.
This framework provides a basis for engineering nanoscale patterns of metallic and insulating phases, and for understanding other novel features observed in manganites, such as: precursor short range ordering and quasielastic scattering near the phase transition temperature; hysteretic and glassy dynamics; metastability; and photoinduced insulator-metal transition.
meetings.aps.org /Meeting/MAR05/Event/25705   (230 words)

  
 Compositional Inversion Symmetry Breaking in Ferroelectric Perovskite Compounds   (Site not responding. Last check: 2007-10-21)
We present ultrasoft-pseudopotential LDA calculations on ternary ABO_3 cubic perovskite compounds of the form (A_1/3A'_1/3A''_1/3)BO_3 or A(B_1/3B'_1/3B''_1/3)O_3, in which the three different cations form an ordered layer sequence in the (001) direction.
These are of interest as simple model systems in which the compositional order breaks the inversion symmetry of the cubic perovskite structure, leading to interesting effects on the ferroelectric properties of the material.
In the case of isovalent substitution, the effect is weak enough that a double-well potential still exists, but strong enough so that the material may self-pole.
flux.aps.org /meetings/YR00/MAR00/abs/S6590006.html   (226 words)

  
 Method for Switching the Properties of Perovskite Materials Used In Thin Film Resitors   (Site not responding. Last check: 2007-10-21)
A method for switching properties of perovskite thin film materials, including the colossal magnetoresitive (CMR) and high temperature superconducting (HTSC) materials, is provided.
Short electrical pulses are applied to the materials in thin films to change both reversibly and non-reversibly the electrical, thermal, mechanical and magnetic properties of the material.
Applications of the method and materials to form memory devices, resistors in electronic circuits which can be varied in resistance and other applications are disclosed.
www.svec.uh.edu /pat-6204139-abs.html   (127 words)

  
 (Mg,Fe)SiO3-Perovskite Stability and Lower Mantle Conditions -- Dubrovinsky et al. 285 (5430): 983 -- Science
perovskite was synthesized from a mixture of oxides, and attempts
which decomposition of perovskite was detected earlier (2).
In (13) it is stated, "the only indication of the presence of perovskite is a broad band near 800 cm
www.sciencemag.org /cgi/content/full/285/5430/983a   (2400 words)

  
 "Majorite" and "Silicate Perovskite" Mineral Compositions in Xenoliths from Malaita -- Neal et al. 292 (5519): 1015 -- ...
"Majorite" and "Silicate Perovskite" Mineral Compositions in Xenoliths from Malaita -- Neal et al.
Comparison of "perovskite" mineral compositions (1) with similar compositions in the upper mantle suite (14-20) from Malaitan, Solomon Islands.
Secondary clinopyroxene "sliver" between garnet and spinel in the garnet-spinel peridotites.
www.sciencemag.org /cgi/content/full/292/5519/1015a   (3348 words)

  
 Brewer, Rhett Ty (2003-07-10) Quantitative biaxial texture analysis with reflection high-energy electron diffraction ...
To facilitate ferroelectric-based actuator integration with silicon electronics fabrication technology, we have developed a route to produce biaxially textured ferroelectrics on amorphous layers by using biaxially textured MgO templates.
Biaxially textured perovskite ferroelectrics were grown on biaxially textured MgO templates using sol-gel, metallorganic chemical vapor deposition (MOCVD), and molecular beam epitaxy (MBE).
Through RHEED-based biaxial texture analysis we observed that the heteroepitaxial ferroelectric in-plane orientation distribution, deposited using ex situ techniques (not performed in the same high vacuum growth environment where the MgO was deposited), narrowed significantly with respect to the in-plane orientation distribution of its MgO template (from 11o to 6o FWHM).
resolver.caltech.edu /CaltechETD:etd-08182003-150957   (440 words)

  
 The elasticity of the MgSiO3 post-perovskite phase in the Earth's lowermost mantle : Nature   (Site not responding. Last check: 2007-10-21)
perovskite has been assumed to be the dominant component of the Earth's lower mantle, although this phase alone cannot explain the discontinuity in seismic velocities observed 200−300 km above the core−mantle boundary (the D" discontinuity) or the polarization anisotropy observed in the lowermost mantle
Experimental and theoretical studies that have attempted to attribute these phenomena to a phase transition in the perovskite phase have tended to simply confirm the stability of the perovskite phase
Dislocation creep in MgSiO3 perovskite at conditions of the Earth's uppermost lower mantle
dx.doi.org /10.1038/nature02702   (342 words)

  
 Bayerisches Geoinstitut - Annual Report 2003 - Trace element partitioning between Mg-silicate perovskite and silicate ...
Trace element partitioning between Mg-silicate perovskite and silicate melt – geochemical constraints on a “hidden” perovskitic reservoir in the lower mantle (C. Liebske, D.J. Frost, D.C. Rubie, in collaboration with A. Corgne, B.J. Wood/Bristol)
Fractionation of Mg-silicate perovskite (Mg-pv) at depths > 700 km in such a deep magma ocean could be one explanation as to why the Si/Mg ratio of the Earth’s upper mantle is low when compared to CI chondrites.
Recent findings in seismology and geochemistry suggest a chemically heterogeneous lower mantle and raise again the question of a “hidden” perovskitic reservoir in the deep interior of the Earth.
www.bgi.uni-bayreuth.de /annual_report/2003/c_57.phtml   (677 words)

  
 Perovskite   (Site not responding. Last check: 2007-10-21)
perovskite is a valid word in this word list.
The word "perovskite" uses 10 letters: E E I K O P R S T V.
Words within perovskite not shown as it has more than seven letters.
www.morewords.com /word/perovskite   (182 words)

  
 Technology Summary - WARF: P04320US - Perovskite-based Thin Film Structures on Miscut Semiconductor Substrates
While methods exist for efficiently growing PMN-PT in bulk single crystals, there remains a need to grow this perovskite as an epitaxial thin film, particularly on a silicon substrate for microelectromechanical systems (MEMS).
A perovskite overlayer with a substantially pure perovskite crystal structure can then be epitaxially grown on the SrRuO
The overlayer may comprise a piezoelectric perovskite such as PMN-PT, PZT, or PZN-PT; a magnetic perovskite; or a multi-ferroic perovskite.
www.warf.wisc.edu /technologies.jsp?casecode=P04320US   (271 words)

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