20281-00-9Relevant academic research and scientific papers
Electron microscopy, spectroscopy, and first-principles calculations of Cs2O
Gemming,Seifert,Muehle,Jansen,Albu-Yaron,Arad,Tenne
, p. 1190 - 1196 (2005)
Oxides of cesium play a key role in ameliorating the photoelectron emission of various opto-electronic devices. However, due to their extreme reactivity, their electronic and optical properties have hardly been touched upon. With the objective of better understanding the electronic and optical properties of Cs2O in relationship to its structure, an experimental and theoretical study of this compound was undertaken. First-principles density functional theory calculations were performed. The preferred structural motif for this compound was found to be anti-CdCl2. Here three Cs-O-Cs molecular layers are stacked together through relatively weak van-der-Waals forces. The energy bands were also calculated. The lowest transition at 1.45 eV, was found to be between the K point in the valence band to the Γ point in the conduction band. A direct transition at 2 eV was found in the center (Γ) of the Brillouin zone. X-ray powder diffraction, transmission electron microscopy and selected area electron diffraction were used to analyze the synthesized material. These measurements showed good agreement with the calculated structure of this compound. Absorption measurements at 4.2 K indicated two optical transitions with somewhat higher energy (indirect one at 1.65 and a direct transition at 2.2 eV, respectively). Photoluminescence measurements also showed similar transitions, suggesting that the lower indirect transition is enhanced by three nearby minima at 1.5 eV in the Brillouin zone.
Homoatomic Stella Quadrangula [Tl8]6 in Cs 18Tl8O6, Interplay of SpinOrbit Coupling, and JahnTeller Distortion
Wedig, Ulrich,Saltykov, Vyacheslav,Nuss, Juergen,Jansen, Martin
, p. 12458 - 12463 (2010)
Cs18Tl8O6 was synthesized reacting the binary compounds CsTl and Cs2O. According to single crystal X-ray analysis, the title compound crystallizes as a novel structure type in the cubic space group I23 and is diamagnetic. The electronic structure of the extended solid and of excised Cs6Tl8 clusters has been examined by relativistic density functional calculations including spin-orbit coupling. Cs18Tl8O6 comprises a clusteranion [Tl 8]6- in the shape of a tetrahedral star. An isoelectronic cluster was found previously in Cs8Tl8O, however, with the shape of a parallelepiped. Both clusteranions can be derived from a homocubane unit by displacive distortions. It has been shown by quantum mechanical analyses that the closed-shell electronic structure of the parallelepiped is the result of a Jahn-Teller distortion, while in contrast the tetrahedral star in Cs 18Tl8O6 would still exhibit an open-shell degenerate HOMO within a scalar relativistic approximation. Only if spin-orbit coupling is considered, a closed-shell electronic system is obtained in accordance with the diamagnetic behavior of Cs18Tl8O 6.
The suboxometallates A9MO4 (A = Rb, Cs; M = Al, Ga, In, Fe, Sc)
Hoch, Constantin,Bender, Johannes,Wohlfarth, Andreas,Simon, Arndt
, p. 1777 - 1782 (2009)
Single crystals of the suboxometallates A9MO4 (A = Rb, Cs; M = Al, Ga, Fe, Sc) were prepared by reaction of stoichiometric mixtures of M2O3 with alkali metals and their oxides A 2O. They crystallize i
Preparation of Cs2ZrO3 and Cs2ThO3 through sol-gel method and their characterization
Mishra,Ali,Bharadwaj,Das
, p. 779 - 784 (2001)
Cesium zirconate and cesium thorate were prepared by sol-gel method following citrate-nitrate route. The compounds were characterized by X-ray diffraction, chemical analysis and simultaneous TG-DTA. The methods of preparation of Cs2ZrO3/s
Alkali Metal Suboxometalates-Structural Chemistry between Salts and Metals
W?rsching, Matthias,Hoch, Constantin
, p. 7058 - 7064 (2015)
The crystal structures of the new cesium-poor alkali metal suboxometalates Cs10MO5 (M = Al, Ga, Fe) show both metallic and ionic bonding following the formal description (Cs+)10(MO45-)(O2-)·3e-. Comparable to the cesium-rich suboxometalates Cs9MO4 (M = Al, Ga, In, Fe, Sc) with ionic subdivision (Cs+)9(MO45-)·4e-, they contain an oxometalate anion [MIIIO4]5- embedded in a metallic matrix of cesium atoms. Columnlike building units form with prevalent ionic bonding inside and metallic bonding on the outer surface. In the cesium-rich suboxometalates Cs9MO4, additional cesium atoms with no contact to any anion are inserted between columns of the formal composition [Cs8MO4]. In the cesium-poor suboxometalates Cs10MO5, the same columns are extended by face-sharing [Cs6O] units, and no additional cesium atoms are present. The terms "cesium-rich" and "cesium-poor" here refer to the Cs:O ratio. The new suboxometalates Cs10MO5 crystallize in two modifications with new structure types. The orthorhombic modification adopts a structure with four formula units per unit cell in space group Pnnm with a = 11.158(3) ?, b = 23.693(15) ?, and c = 12.229(3) ? for Cs10AlO5. The monoclinic modification crystallizes with eight formula units per unit cell in space group C2/c with a = 21.195(3) ?, b = 12.480(1) ?, c = 24.120(4) ?, and β = 98.06(1)° for Cs10AlO5. Limits to phase formation are given by the restriction that the M atoms must be trivalent and by geometric size restrictions for the insertion of [Cs6O] blocks in Cs10MO5. All of the suboxometalate structures show similar structural details and form mixed crystal series with statistical occupation for the M elements following the patterns Cs9(M1xM21-x)O4 and Cs10(M1xM21-x)O5. The suboxometalates are a new example of ordered intergrowth of ionic and metallic structure elements, allowing for the combination of properties related to both ionic and metallic materials. (Figure Presented).
Metal-insulator transition during oxidation of cesium films
Shi,Jacobi
, p. 12 - 20 (1992)
The oxidation of Cs films in the thickness range of 5 to 25 layers was investigated at 95 K using UPS and HREELS combined in situ. The whole film undergoes a metal to insulator transition at an oxygen dose equivalent to the formation of Cs2O, the normal oxide. This state is characterized through a single, somewhat broadened 2p line of O2- in UPS, the opening of a gap around EF (vanishing electronic losses as seen through HREELS), and the appearance of a strong Fuchs-Kliewer phonon intensity. Below this transition, i.e., in the range of suboxides, the Cs surface plasmon is observed with its energy shifting to small values as the metallic electron density gets diluted with O2 dose. Above the transition, the UP spectra change into multiplet spectra well known for Cs dioxygen species. The oxidation process can be described by a Cs → suboxides → Cs2O → peroxides sequence.
Anomalous lattice parameter increase in alkali earth aluminium substituted tungsten defect pyrochlores
Thorogood, Gordon J.,Kennedy, Brendan J.,Peterson, Vanessa K.,Elcombe, Margaret M.,Kearley, Gordon J.,Hanna, John V.,Luca, Vittorio
, p. 457 - 464 (2009)
The structures of the defect pyrochlores AAl0.33W1.67O6 where A=K, Rb or Cs have been investigated using X-ray and neutron powder diffraction methods as well as the ab initio modelling program VASP. The three cubic pyrochl
Preparation and structural characterization of stable Cs2O closed-cage structures
Albu-Yaron, Ana,Arad, Talmon,Popovitz-Biro, Ronit,Bar-Sadan, Maya,Prior, Yehiam,Jansen, Martin,Tenne, Reshef
, p. 4169 - 4172 (2005)
(Figure Presented) Fullerene-like Cs2O nanoparticles were prepared by laser ablation of 3R-Cs2O powder in evacuated quartz ampoules. The Cs2O closed cages, such as the faceted nanoparticle shown in the picture, are remarka
Crystal structures of Rb2U2O7 and Rb 8U9O31, a new layered rubidium uranate
Yagoubi,Obbade,Dion,Abraham
, p. 3218 - 3232 (2005)
Two alkali metal uranates Rb2U2O7 and Rb8U9O31 have been synthesized by solid state reaction at high temperature and their crystal structures determined from single crystal X-ray diffraction data, collected with a three circles Brucker SMART diffractometer equipped by Mo(Kα) radiation and a charge-coupled device (CCD) detector. Their structures were solved using direct methods and Fourier difference techniques and refined by a least-square method on the basis of F2 for all unique reflections, with R1=0.043 for 53 parameters and 746 independent reflections with I≥2σ(I) for Rb2U 2O7, monoclinic symmetry, space group P21/c, a=7.323(2)A, b=8.004(3)A, c=6.950(2)A, β=108.81(1)°, ρmes=6.56(3)g/cm3, ρcal=6.54(2)g/cm3, Z=2 and R1=0.036 for 141 parameters and 2065 independent reflections with I≥2σ(I) for Rb 8U9O31, orthorhombic, space group Pbna, a=6.9925(9)A, b=14.288(2)A, c=34.062(5)A, ρmes=6.47(3)g/ cm3, ρcal=6.48(2)g/cm3, Z=4. The Rb2U2O7 structure presents a strong analogy with that of K2U 2O7 and can be described by layers of distorted UO 2(O4) octahedra built from dimeric units of edge shared octahedra further linked together by opposite corners. In Rb8U 9O31 puckered layers are formed by the association of two different uranium polyhedra, pentagonal bipyramids and distorted octahedra. The structure of Rb8U9O31 is built from a regular succession of ∞1[U4O14]4- infinite ribbons similar to those observed in diuranates M2U2O7 (MK, Rb) and infinite three polyhedra wide ribbons ∞1[U5O21]12-, to create an original undulated sheets ∞2[U9O31]8-. For both compounds Rb+ ions occupy the interlayer space and exhibit comparable mobility with conductivity measurements indicating an Arrhenius-type behavior.
First isolated hypoelectronic [In6]6- cluster in insulating Cs22In6(SiO4)4
Saltykov, Vyacheslav,Nuss, Juergen,Wedig, Ulrich,Prasad, Dasari L. V. K.,Jansen, Martin
, p. 834 - 839 (2011)
Cs22In6(SiO4)4 was synthesized by the reaction of appropriate starting materials at 673 K, followed by slow cooling to room temperature, in arc-welded tantalum ampoules. According to single-crystal X-ray analysis, the compound crystallizes in a new structure type (P21/n(no. 14), a = 14.3533(4), b = 16.1712(4), c = 25.0135(7) A, β = 94.368(1), Z = 4), consisting of [In6]6- clusters with the shape of a distorted octahedron or more appropriately described as a condensate of three face sharing tetrahedra. The cluster is the first example of a hypoelectronic isolated [In6] 6- indium cluster. The oxosilicate indide can be regarded as a double salt , Cs6In6 on one hand and the oxosilicate Cs4SiO4 (× 4) on the other, which form the quaternary structure by inhomogeneous intergrowth of partial structures. The electronic structure of Cs22In6(SiO4) 4 was examined by DFT calculations and compared to the one of Rb 2In3, which exhibits linked In6 polyhedra. According to the DOS the title compound is a semiconductor with a band gap of 0.5 eV, which is in agreement with its observed insulating character. [In 6]6- is an isolated cluster bearing inert electron pairs at each vertex. In contrast, [In6]4- in Rb2In3 only exhibits inert pairs at the apical atoms. The four basal atoms are linked to neighboring clusters by covalent bonds forming a 2D network. These bonding scenarios are supported by the analysis of the projected density of states, the electron localization function and the partitioning of the electron density according to Bader. Copyright
