Showing papers on "Perovskite (structure) published in 1976"
TL;DR: In this paper, a new type of quantitative ethanol sensor making use of the perovskite oxides' resistivity increases in proportion to gas concentration with a comparatively short response time, and it recovers to the initial value when the gas is removed.
220 citations
TL;DR: In this article, the authors explore the relationship between the catalytic activity and the defect chemistry of perovskitelike cobaltites, manganites, chromites, and ruthenates.
Abstract: The high expectations present-day society has for catalysis in solving the energy crisis, in coping with environmental pollution, and in providing fertilizers and food have made research in catalysis the focus of interest in many adjacent fields. As an example, the science of solid surfaces in vacuum is explored for its relevance to and experimentally, a link has indeed been e ~ t a b l i s h e d . ~ Perhaps of even more importance, new interest has been stimulated in the links between solid-state physics and chemistry and the characteristics of solid catalysts. In earlier years, this connection had of course been explored on the heels of the spectacular development of semiconductor physics,\" but the fact that the best-studied semiconductors were poor catalysts has impeded progress in the establishment of detailed relationships between collective electrical properties and catalysis. Even so, a general relation between catalytic activity and the width of the band gap of a semiconductor has been recognized,' notwithstanding the frequent exceptions. Not only collective electrical properties, but also collective magnetic properties and ferroelectric properties have in those early years been explored in relation to catalytic characteristics. The relation was indeed established in work on the ferromagnetic man anese perovskite La~,6sSro,3sMn039 and on the ferroelectric perovskite KNbO,,' but the effects were small, which is perhaps not surprising. I ' The study of collective electron effects in metallic catalysts, I2-I4 which was initially partly based on the now ~ u p e r s e d e d ~ ~ . ' ~ rigid-band model of alloy systems such as Cu-Ni and Ag-Pd, has recently taken an interesting turn in the proposed relation between spin fluctuations connected with ma netic interactions and the momentum transfer t o a desorbing or reacting adatom. Surveying the relations between solid-state chemistry and catalysis, it becomes evident that in particular the number and type of localized defects in the solid have been successfully correlated with catalytic activity, e.g., for dislocations and steps on metal surface^,^^.^^ for surface states split off from the conduction band in semiconductors,21 and for anion vacancies or cation vacancies in insulators22 and s e m i c ~ n d u c t o r s . ~ ~ ~ ~ ~ In the present series of lectures on solid-state chemistry and catalysis, further examples of the role of anion and cation vacancies are given by Sleight, Schuit, and Longo. The topic of the present paper, defect chemistry of perovskite-type catalysts for oxidation-reduction processes, has received some stimulus from the suggestions that LaCo03, LaMn03, and their derivatives might be interesting catalysts for application in fuel cell electrodes2' and in the conversion of N O and C O from automotive e x h a ~ s t . ~ ~ ~ ~ In the following, the reduction of N O with CO and H2, and the oxidation of CO with O2 will be used as test reactions. We will explore the relationships between the catalytic activity and the defect chemistry of perovskitelike cobaltites, manganites, chromites, and ruthenates. The crystal structure of perovskite (CaTi03) is shown in FIGURE 1. The 97.1,
211 citations
TL;DR: In this article, a trigonal pyramid was constructed for the selenites and tellurites, where the structure was described as a distorted perovskite or a salt of M2+ and SeO32− or TeO 32− ions.
118 citations
TL;DR: In this article, the orthorhombic perovskite structure of Ferromagnesian silicate olivines, pyroxenes and garnets with Mg/(Mg + Fe)≳0.3 (molar) have been found to transform to high-pressure phases characterized by the orthorehombicity perovsite structure when compressed to pressures above 250 kbar in a diamond-anvil press and heated to temperatures above 1,000°C with a YAG laser.
108 citations
TL;DR: Based on the description of the brownmillerite structure, a model of oxygen vacancy ordering in the AMO 3-x phases along the direction of the cubic perovskite cell is proposed in this article.
105 citations
TL;DR: Powder neutron diffraction studies of Li0.36WO3, Na0.73 WO3 and La0.14WO 3 showed them to be isostructural with cubic D0.53 WO 3.
88 citations
82 citations
TL;DR: In this article, the spinels of Co 2 GeO 4 and Ni 2 geO 4 have been found to disproportionate into their isochemical oxide mixtures at about 250 kbar and 1400-1800°C in the same manner as their silicate analogues.
73 citations
TL;DR: In this paper, the luminescence of several titanium-activated stannates and zirconates with spinel, perovskite, K2NiF4, pyrochlore, and fluorite structure is reported.
73 citations
67 citations
TL;DR: The formation of strontium hexaferrite SRFE 12 O 19 from pure iron oxide and carbonate has been studied by means of dynamic high temperature X-ray diffraction, thermal analysis, and thermogravimetry as mentioned in this paper.
Abstract: The formation of strontium hexaferrite SRFE 12 O 19 from pure iron oxide and strontium carbonate has been studied by means of dynamic high temperature X-ray diffraction, thermal analysis, and thermogravimetry. The formation in air passes through two endothermal reactions: SrCo 3 +6α-Fe 2 O 3 +(0.5-x) \frac{1}{2} O 2 → SrCo 3 +5.5α-Fe 2 O 3 +CO 2 (A) SrFeO 3-x +5.5α-Fe 2 O 3 → SrFe 12 O 19 +(0.5-x) \frac{1}{2} O 2 (B) The solid state reaction of the formation of the perovskite SrFeO 3-x starts between 660 C (0.13°/min) and 730 C (20°/min) depending on the heating rate. Above 810 C or 1000 C, resp., the perovskite reacts with the excess iron oxide forming the hexaferrite. During the process a part of the iron becomes tetravalent and is again reduced into the trivalent state. The phase Sr 7 Fe 10 O 22 or Sr 4 Fe 6 O 13 , resp., observed in quenched samples could not be detected during the formation in air.
TL;DR: In this article, the electrical properties of perovskite-related oxides were studied in the form of dense single phase sintered specimens, and the following materials were prepared: CaTi 0.7 Al 0.85 Mg 0.9 □ 0.1, SrZr 0.8 Yb 0.2 O 2.2
Patent•
15 Oct 1976TL;DR: In this paper, the catalytic activity of metal oxides is enhanced through application of the metal oxide to a second metal oxide having a perovskite crystal structure, which is obtained by applying the metal oxide to a single metal oxide with a similar crystal structure.
Abstract: Catalytic activity of metal oxides is enhanced through application of the metal oxide to a second metal oxide having a perovskite crystal structure.
TL;DR: In this article, the magnetic behavior of the (CnH2n+1NH3)2MnCl4-family has been studied and the room temperature phase of members with odd numbers of carbon atoms is orthorhombic whereas even numbers lead to monoclinic structures.
TL;DR: In this article, single crystals of [ThCu3](Mn3+2Mn4+2]O12, a ferrimagnetic perovskite-like compound, were synthesized by hydrothermal conditions at 600°C and 2 kbar.
TL;DR: Raman scattering from mixed ordered and disordered crystals with perovskite structure has been investigated in this article, where first-order lines were observed with symmetry properties forbidden for an ideal permutation structure.
Abstract: Raman scattering from mixed ordered and disordered crystals with perovskite structure has been investigated. In the paraelectric phase of the ordered crystal first-order lines were observed with symmetry properties forbidden for an ideal perovskite structure. Also, Raman line in the high frequency region is attributed to local mode associated with charge inequivalency of ions at B positions.
TL;DR: In this article, a hexagonal version of the LuMnO3 structure was obtained at atmospheric pressure of 0.34 kbar, 1000°C, where the In3+ ions are located in fivefold-coordinated trigonal-bipyramidal sites, and the Ln3+ ion are sevenfold coordinated.
Patent•
15 Dec 1976TL;DR: Perovskite catalysts of the general formula ABO 3 have increased stability through the incorporation of metals having low first ionization potentials, and their use in oxidation and reduction reactions as mentioned in this paper.
Abstract: Perovskite catalysts of the general formula ABO 3 having increased stability through the incorporation of metals having low first ionization potentials, and their use in oxidation and reduction reactions.
TL;DR: In this paper, a deformed oxygen octahedra model was proposed for the BaTiO 3 crystal, and the electro-optical and second optical harmonic coefficients were calculated without introducing any adjustable parameters.
Abstract: In order to elucidate the relationship between the structure and the electro-optical and nonlinear optical effects in crystals of the perovskite type, we have here proposed a deformed oxygen-octahedra model for these crystals. On the basis of quasi-molecular orbitals and ionic bond orbitals for the ionic grouping TiO 6 formulated under the imposed crystal field, we have calculated the various electro-optical and second optical harmonic coefficients for the BaTiO 3 crystal without introducing any adjustable parameters. It is gratifying to note that the calculated values of the electro-optical and second optical harmonic coefficients agree satisfactorily with the experimental values. As is to be expected, the quasi-molecular orbitals contribute very little to these optical effects. We have been led to the following conclusions:1) The electro-optical and second optical harmonic effects of the BaTiO 3 crystal arise as a direct consequence of the deformation of the TiO 6 oxygen-octahedra. The more these octahedra are deformed, the larger are these optical effects.2) When BaTiO 3 is present as the ferroelectric phase, a strong odd ordered-term crystal field arises as a result of the spontaneous polarization within the crystal. This explains why BaTiO 3 possesses such large electro-optical and second harmonic optical effects. The covalent bonds in the ionic group TiO 6 tend to cancel each other in their contribution to these effects.3) The electro-optical and second harmonic optical coefficients are directly proportional to the degree of spontaneous polarization.
TL;DR: In this article, the effect of carburation on the hyperfine parameters and the different contributions to the internal magnetic field are thoroughly discussed, and a model of itinerant magnetism can account for the various observed magnetic anomalies: first-order transitions, unresolved magnetic Mossbauer spectra, deviation from unity of the ratio of the magnetic moment deduced from the Curie constant to the magnetic moments at saturation, deviations from the linear moment-field relation.
Abstract: Mossbauer spectra on 57Fe and 119Sn in perovskite carbides with formula M3M'C (where M is Fe or Mn, and M', Al, Ga, Ge, Zn, Sn) have been observed. All those compounds are characterized by a large quadrupole coupling amounting to 1.3 mm s-1 and by low internal magnetic fields, around 70 kOe, at M atom. The effect of carburation on the hyperfine parameters and the different contributions to the internal magnetic field are thoroughly discussed. Only a model of itinerant magnetism can account for the various observed magnetic anomalies: first-order transitions, unresolved magnetic Mossbauer spectra, deviation from unity of the ratio of the magnetic moment deduced from the Curie constant to the magnetic moment at saturation, deviation from the linear moment-field relation.
TL;DR: In this paper, LixNa1-xNbO3 was hot pressed to densities greater than 99% of the theoretical density and their dielectric and electromechanical properties measured as functions of density and composition.
Abstract: Specimens of LixNa1-xNbO3 where 0.02 ≤ x ≤ 0.15 have been hot pressed to densities greater than 99% of the theoretical density and their dielectric and electromechanical properties measured as functions of density and composition. An enhancement of electromechanical properties has been observed for composition with x = 0.12, where kp = 0.395, Qm = 755 and fRr = 1760 Hz m have been realized.
TL;DR: The Eu 2+ luminescence of the compounds ABF 3 :Eu 2 + (A = Na, K, Rb, Cs: B = Mg, Ca, Sr) depends strongly on the choice of A and B and on the temperature as discussed by the authors.
TL;DR: The dielectric properties of (CH3NH3)2CdCl4, NH3(CH2)5NH3, and CnH2n+1NH3 were investigated as a function of temperature between 77 and 373°K as mentioned in this paper.
TL;DR: The structure of the orthorhombic perovskite BaPbO3 at 4.2K has been determined by profile analysis of powder neutron diffraction data.
TL;DR: In this paper, the crystal structure of cubic CsPbCl 3 was investigated by neutron diffraction technique at 55°C and two structure models were examined: (i) perovskite structure with anisotropic thermal vibration and (ii) disordered structure having several potential minima for the Cs and Cl atoms, originally proposed by Moller.
Abstract: The crystal structure of cubic CsPbCl 3 was reinvestigated by neutron diffraction technique at 55°C. Two structure models were examined: (i) perovskite structure with anisotropic thermal vibration and (ii) disordered structure having several potential minima for the Cs and Cl atoms, originally proposed by Moller (1959). Both models explain the present neutron data equally well with a reliability index of about 9%. A set of parameters refined on the basis of the structure factor proposed by Moller is, however, revealed to be simply another representation of the perovskite model. As for the perovskite model, anomalously large thermal vibrations were obtained for the Cs and Cl atoms. It is concluded that such anomalous thermal vibrations are characteristics of the phase transitions of this substance.
01 May 1976
TL;DR: The Eu/sup 2 +/ luminescence of the compounds ABF/sub 3/:Eu/Sup 2+/ (A=Na, K, Rb, Cs: B=Mg, Ca, Sr) depends strongly on the choice of A and B and on the temperature.
Abstract: The Eu/sup 2 +/ luminescence of the compounds ABF/sub 3/:Eu/sup 2 +/ (A=Na, K, Rb, Cs: B=Mg, Ca, Sr) depends strongly on the choice of A and B and on the temperature. The wavelength of maximum emission varies from 360 nm to 610 nm. The compounds with B=Mg show 5d-4f band emission and 4f-4f line emission, both located in the ultra-violet. The other compounds show only 5d-4f band emission in the blue, green or red.
Patent•
13 Apr 1976
TL;DR: In this article, a high surface area perovskite catalyst is proposed, which is composed of a transition metal and a spinel-coated metal oxide support, followed by calcination at a temperature of at least 540° C.
Abstract: A high surface area perovskite catalyst comprises a perovskite containing at least one transition metal composited with a spinel-coated metal oxide support The catalyst is prepared by forming a surface spinel on a metal oxide and subsequently co-impregnating or co-depositing the appropriate perovskite precursor component on the spinel coated metal oxide, followed by calcination at a temperature of at least 540° C A preferred catalyst is LaCoO 3 supported on a spinel-covered alumina
TL;DR: In this article, single-phase regions have been detected in the ternary uranium-europium-oxygen system at 1250°C, and the first lanthanide-actinide perovskite compounds, orthorhombic EuUO3, and EuNpO3 could be prepared by different methods.
TL;DR: In this paper, the phase transformations of FeSiO3 were investigated in a diamond-anvil press coupled with laser heating from loading pressures of 80-280 kbar at temperatures of approximately 1200-1600°C.
TL;DR: In this paper, the deviations from the ideal behaviour are studied by x-ray, diffuse reflectance and vibrational methods by using a vibrational method and the ordered perovskite Ba2SrUO6 forms a solid solution series with Ba2Gd067UOO6 and Ba2Y0,67O6 respectively.
Abstract: Die geordneten Perowskite Ba2SrUO6 und Ba2Gd0,67UO6 bzw Ba2Y0,67UO6 bilden eine luckenlose Reihe von Mischkristallen Die Abweichungen vom idealen Verhalten werden rontgenographisch sowie an Hand der diffusen Reflexionsspektren und Schwingungsspektren untersucht
On Perovskite Phases in the Systems AOSe2O3UO2,x with A = Alkaline Earth Metal and SE = Rare Earths, La, and Y IX The Systems Ba2SrUo6Ba2Gd067UO6 and Ba2SrUO6Ba2Y067UO6
The ordered perovskite Ba2SrUO6 forms a solid solution series with Ba2Gd067UO6 and Ba2Y0,67UO6 respectively The deviations from the ideal behaviour are studied by x-ray, diffuse reflectance and vibrational methods