Zur Darstellung und Struktur neuer Modifikationen von CeTa3O9

Preparation and Structure of New CeTa₃O₉ Modifications The modifications M? , O? and P? CeTa₃O₉ could be prepared by chemical transport reactions (T₂ → T₁; T₂ = 1100°C; T₁ = 1000°C) with chlorine as transport agent. M? CeTa₃O₉ crystallizes in the monoclinic space group C 2/m with a = 12.415(1) Å, b = 7.6317(8) Å, c = 6.5976(8) Å, β = 93.31(1)°; Z = 4; R = 4.88%, R_w = 3.67%. The structure consists of two types of Ta? O-polyhedra. Especially remarkable are chains of edge sharing pentagonal TaO₇-bipyramids which are connected by TaO₆-octahedra at opposite sides. Tunnels running along [010] are created by the framework of Ta? O-polyhedra and are filled with Ce in levels of y = 1/2 and y = 0. O? CeTa₃O₉ crystallizes orthorhombically with a = 6.5429(7) Å, b = 7.6491(7) Å, c = 12.583(1) Å and is isostructural to O? LaTa₃O₉ (space group: Pnma). O? CeTa₃O₉ contains the same characteristic structural units namely pentagonal TaO₇-bipyramides and TaO₆-octahedra. The difference between O? and M? CeTa₃O₉ is based on the orientation of the tunnels: in the orthorhombic modification they are arranged zigzag-like, in the latter parallel. Both modifications of CeTa₃O₉ can be irreversibly converted into the well-known perovskite-related P? CeTa₃O₉ structure with a lower density by heating in air to 1200°C.     

Zur Kenntnis von Zn4Ta2O9

About the New Compound Zn₄Ta₂O₉ The hitherto unknown compound Zn₄Ta₂O₉was prepared by high temperature reaction (CO₂-LASER technique). The X-ray investigation of single crystal shows monoclinic symmetry (space group C? C2/c) with a = 15.002(6), b = 8.954(1), c = 10.345(4)Å and β = 93.64(3)°. Zn₄Ta₂O₉ consists of a Zn/O-network with incorporated one-dimensional TaO₆-chains. The edge connected TaO₆-octahedrals are occupied by Ta⁵⁺ and 0.5 Zn²⁺ respectively. The crystal chemistry of this compound in respect to other Zn-oxotantalates are discussed.     

Zur Kenntnis ‘Kationen-reicher’ Tantalate Über Li7[TaO6]

On Tantalates ‘rich in Cations’ On Li₇[TaO₆] For the first time, colourless single crystals of Li₇[TaO₆] were grown by annealing intimate mixtures of Li₂O and Ta₂O₅ (Li:Ta = 7,7:1) in closed Ni-cylinders (1 000°C, 156 d). [Trigonal-rhomboedral with a = 535.8(1) pm, c = 1 507.3(3) pm, c/a = 2.81/Guinier-Simon-powder data; Z = 3. Space group R3 for the part Li(1)₆TaO₆ and presumably P3 for Li₇TaO₆, including Li(2)]. The crystal structure was solved by four-cycle-diffractometer data [Mo? Kα , 331 from 331 I_o(hkl), R = 1.99%, R_w = 1.96%], parameters see text. The positions of anions correspond to the motif of a hexagonal closest packing of spheres, obviously deformed (with MEFIR of O^2? space filling corresponds to 69.8% instead of expected 73.2%. 1/3 of the octahedron holes are ordered occupied by Ta and Li(2), 1/2 of the tetrahedral holes likewise ordered by Li(1). All polyhedra of coordination of the anions are trigonal prisms. The Madelung Part of Lattice Energy, MAPLE, and Effective Coordination Numbers, ECoN, these calculated via Mean Fictive Ionic Radii, as well as charge distribution ‘CHARDI’ are calculated and discussed.     

Crystal structure of new Li+ ion conducting perovskites: Li2xCa0.5−xTaO3 and Li0.2[Ca1−ySry]0.4TaO3

Two new solid solutions—Li_2xCa_0.5−xTaO₃ (0.05⩽x⩽0.25) and Li_0.2[Ca_1−ySr_y]_0.4TaO₃ (0<y⩽0.15)—based on the A defective ABO₃ perovskite structural type, are synthesized. The crystal structures of these Li⁺ ion conducting compounds are solved from synchrotron radiation and conventional X-ray powder diffraction data. The unit cells exhibit a classical orthorhombic distortion of the cubic perovskite model (space group Pnma No. 62) with parameters close to $\text{2}\text{a}{}_{\mathrm{<mtext>p</mtext>}}$, 2a_p, $\text{2}\text{a}{}_{\mathrm{<mtext>p</mtext>}}$ (a_p, primitive cubic cell parameter). The distortion of the cubic aristotype arises from the three tilts system a⁺b⁻b⁻ of the TaO₆ octahedra. For the same lithium content (x=0.10), the Sr²⁺ substitution to Ca²⁺ is found to enhance the electrical conductivity by quasi-one order of magnitude (at 200 °C, bulk dc conductivity values are close to 2.3×10⁻⁶ and 1.1×10⁻⁵ S cm⁻¹ for Li_0.2Ca_0.4TaO₃ and Li_0.2[Ca_0.9Sr_0.1]_0.4TaO₃, respectively).     

Eine weitere Oxovanadat-Phase mit Granatstruktur: Ca5Mg3ZnV6O24

An Additional Oxovanadate Phase with Garnet Structure: Ca₅Mg₃ZnV₆O₂₄ Single crystals of Ca₅Mg₃ZnV₆O₂₄ were prepared by solid state reactions some degree below the melting point of the reaction mixture. It crystallizes with cubic symmetry, space group T-I4 3 d with a = 12.429 Å, Z = 4. The crystal structure is nearly related to the Garnet structure showing Ca²⁺ within distorted cubes (C.N. = 8) of O^2? on a partly unfilled position. the octahedra position are occupied by Mg²⁺ and Zn²⁺ statistically.     

Structural Variations in the Solid‐Solution Series LnxCa2−xAl[Al1+xSi1−xO7] with 0 ≤ x ≤ 1 and Ln = La,Eu, Er

Gehlenite, Ca₂Al[AlSiO₇], has melilite‐type structure with space group . It contains two topologically distinct positions coordinated tetrahedrally by oxygen. One is completely occupied by Al³⁺, whereas the other one contains Al³⁺ and Si⁴⁺. Normally, the Al³⁺ molar fraction in the second tetrahedrally coordinated position does not exceed x_Al = 0.5, i.e. the so‐called Loewenstein‐rule is obeyed. In this contribution the structural variations in the melilite‐type compounds of the compositions La_xCa_2?xAl[Al_1+xSi_1?xO₇], Eu_xCa_2?xAl[Al_1+xSi_1?xO₇] and Er_xCa_2?xAl[Al_1+xSi_1?xO₇] are discussed. All members of the solid solution except the end‐members violate Loewenstein's rule. Rietveld refinements against X‐ray powder diffraction patterns confirm that the compounds have space group , without changes in the Wyckoff‐positions of the ions compared to gehlenite.     

Electrochemical behavior of single crystals of nonstoichiometric cerium(III) fluorides

The electrochemical properties of single crystals of cerium fluoride alloyed with bivalent cations Sr²⁺, Ca²⁺, Ba²⁺, Sr²⁺ + Ca²⁺, Sr²⁺ + Ba²⁺, Ba²⁺ + Ca²⁺ and also with La³⁺ and La³⁺ + Ba²⁺ cations are studied using the dynamic voltammetry and impedance spectroscopy. The conductivity of symmetrical cells with Ag electrodes is determined using the method of impedance spectroscopy in the frequency range from 450 to 5 kHz at the temperatures from 20 to 100°C: for CeF₃: Sr²⁺ (0.5 mol %) + Ba²⁺ (0.5 mol %), σ = σ₀ exp[(?0.284 ± 0.005/kT]; for CeF₃:Ca²⁺ (0.5 mol %) + Sr²⁺ (0.5 mol %), σ = σ₀ exp[(?0.292 ± 0.017/kT]. The steady-state and dynamic voltammogams of symmetrical electrochemical cells with nonpolarizable reference electrodes and CeF₃ single crystals alloyed with Sr²⁺, Ca²⁺, and Ba²⁺ bivalent cations exhibited ohmic polarization. For cells with CeF₃ containing La³⁺ as an admixture, a hysteresis was observed, which could not be eliminated by chemical and electrochemical treatment of crystals. In the dynamic voltammetric curves of asymmetric cells with nonpolarizable and silver electrode and CeF₃ crystals alloyed with Sr²⁺, Ca²⁺, and Ba²⁺, a range of ideal polarizability (from 0 to ～?2.7 V), and also cerium redox processes and silver fluorination-boundary regeneration were observed. In the dynamic voltammetric curves of asymmetric cells with CeF₃ containing La³⁺ admixture, no range of ideal polarizability was observed; however, the reactions of silver fluorination and reduction of solid-electrolyte cerium were well pronounced at the corresponding potentials.     

Ein neues Erdalkalimetall-Oxoplatinat-Cuprat Ca3,5Cu0,5PtO6

A new Alkaline-Earth Platinum Copper Oxide: Ca_3.5Cu_0.5PtO₆ Ca_3.5Cu_0.5PtO₆ was prepared and investigated by single crystal X-ray work. (Space group C? C12/m1; a = 9.0743; b = 9.2527; c = 6.4840 Å; β = 91.448°; Z = 4). The crystal structure of the previously unknown compound is closely related to the structure of Sr₃PtCuO₆ and Sr₃IrCuO₆ as well as the rhombohedral phases M₄PtO₆ (M = Ba, Sr, Ca). Typical features of the crystal chemistry are isolated chains of PtO₆ octahedra, alternately allyed by square CuO₄ polygones and trigonal prisms of O^2? around Ca²⁺.     

Zur Darstellung und Struktur von M1?LnTa3O9 (Ln = Pr,Nd) Röntgenographische und elektronenmikroskopische Untersuchungen

Preparation and Structure of M1? LnTa₃O₉ (Ln = Pr, Nd), X-Ray and Electronmicroscopical Investigations New ternary compounds M1? LnTa₃O₉ (Ln = Pr, Nd) could be prepared by chemical transport reaction in a temperature gradient T₂ → T₁ (T₂ = 1100°C; T₁ = 1000°C; CI₂ as transport agent). M1 NdTa₃O₉ crystallizes in the monoclinic space group P 2₁/m with a = 5.3840(9) Å, b = 7.550(1) Å, c = 8.1911(9) Å and β = 92.46(1)°. The structure was refined to give R = 6.29% and R_w = 6.20%. It is built of double and single chains of corner-sharing TaO₆ octahedra extended along the b-axis. Tunnels running along [010] are created by the framework of TaO₆ octahedra. Ln (Ln = Pr, Nd) is located in these tunnels to levels of y = 1/4 and 3/4. A structure refinement for isostructural M1? PrTa₃O₉ led to a = 5.4051(7) Å, b = 7.5680(2) Å, c = 8.1964(9) Å, β = 92.38(2)° and R = 7.72%, R_w = 7.57%. By grinding in an agate mortar M1? LnTa₃O₉ transforms into M2? LnTa₃O₉, a new modification with a higher density. High resolution transmission electron microscopy images of the M1? PrTa₃O₉ structure were made along the [010] direction. They could be interpreted by comparing them with images calculated on the basis of the multi-slice method.     

Photoluminescence Properties of a Promising Red-emitting Phosphor CaNb2O6:EU3+for Trichromatic White Light Emitting Diodes Application

Motivated by the need for new phosphors of white light emitting diode (WLED) application, Ca_0.95Nb₂ O₆:Eu³⁺_0.05 phosphors were synthesized by high temperature solid‐state reaction. Increasing the content of doped‐Eu³⁺ and adding the co‐activator Bi³⁺ to improve the photoluminescence (PL) intensity of Ca_1?xNb₂ O₆Eu³⁺_x phosphors were investigated in detail. The effects of Eu³⁺ were better than that of Bi³⁺ on the PL intensity of Ca_1?xNb₂ O₆Eu³⁺_x phosphors. Compared with Y₂O₂ S:0.05Eu³⁺ the Ca_0.70Nb₂ O₆:Eu³⁺_0.03 phosphor could be excited efficiently by UV (395 nm) light and emit the red light at 614 nm with line spectra, which were coupled well with the characteristic emission from UV‐Near UV LED. The CIE (International Commission on Illumination) chromaticity coordinates (x?0.654, y?0.348) of Ca_0.70Nb₂O₆:Eu³⁺_0.03 were close to the NTSC (National Television Standard Committee) standard values. Therefore Ca_0.70Nb₂ O₆:Eu³⁺_0.03 might find application to UV‐Near UV InGaN chip‐based white light emitting diodes, which is further proved by the LED fabrication with the Ca_0.70Nb₂ O₆:Eu³⁺_0.03 phosphor.     

Weitere magnetische Untersuchungen an Ti3−xMxO5-Phasen (M = Al3+, Fe2+, Mn2+, Mg2+) mit einem Beitrag über CrTi2O5

Additional Magnetic Examinations of Ti_3?xM_xO₅-Phases (M = Al³⁺, Fe²⁺, Mn²⁺, Mg²⁺) with a Contribution about CrTi₂O₅ Ti_3?xM_xO₅ was prepared with M = Al³⁺, Fe²⁺, Mn²⁺, and Mg²⁺. Die magnetic properties of this phases were examinated by the Faraday method in respect to the temperature. The well known magnetic effect of Ti₃O₅ near 450 K is shifted to lower degrees if Ti is replaced by Al, Fe, Mn, or Mg. Compared to Ti_3?xV_xO₅ and Ti_3?xCr_xO₅ the stability of the low temperature-form of Ti₃O₅ is much more reduced in Ti_3?xM_xO₅ (M = Al, Fe, Mn, Mg). The crystal structure investigation of CrTi₂O₅ explained the anomalous behaviour of the Cr³⁺ and V³⁺ doped Ti₃O₅.     

Zwei neue Erdalkalimetall-Oxoindate: BaCa2In6O12 und BaSr2In6O12

Two New Alkaline-Earth-Oxoindates: BaCa₂In₆O₁₂ and BaSr₂In₆O₁₂ The hitherto unknown compounds (I): BaCa₂In₆O₁₂ and (II): BaSr₂In₆O₁₂ were prepared and examined by single crystal X-Ray work. (I) and (II) crystallize with hexagonal symmetry, space group C? P6₃/m, with (I): a = 9.880, c = 3.211 Å; (II): a = 9.9443; c = 3.2671 Å, Z = 1. Both compounds are isotypic to the metastable oxide AM₂Ln₆O₁₂, but without metastable behavior. The [In₆O₁₂]^6? network is occupied by the alkaline earth ions. One of the tunnels is stuffed by Ca²⁺ and Sr²⁺ respectively, the other one by Ba²⁺ in a statistical distribution on possible point positions. (I) and (II) prove the existence of the AM₂Ln₆O₁₂-type in respect to small Ln³⁺ ions.     

Electroconductivity and transport numbers of solid electrolytes La10−x CaxA6O27−δ and La9.33+δA6−x AlxO26 (A = Si, Ge) with apatite-like structure

The ion-oxygen conductivity of apatite-like compounds based on lanthanum silicates and germanates La₁₀A₆O₂₇ (A = Si, Ge), La_10?x Ca_xSi₆O_27?δ (x = 0.25, 0.5, 1.0), La_9.75Ca_0.25Ge₆O_27?δ and La_9.33+δSi_6?x Al_xO₂₆(x=0.4, 0.8, 1.5) is studied in the interval of partial oxygen pressures pO₂ extending from 10^?16 to 10⁵ Pa, at temperatures of 500–1000°C. The electroconductivity of undoped compounds La₁₀A₆O₂₇ (A = Si, Ge) exceeds that of yttria-stabilized zirconia. The electroconductivity of lanthanum germanate (1.7 × 10^?2 and 8.5 × 10^?2S cm^?1 at 700 and 900°C, respectively) is substantially higher than that of lanthanum silicate (9.8 × 10^?3 and 3.5 × 10^?2 S cm^?1 at 700 and 900°C). Doping lanthanum germanate with calcium raises its electroconductivity (2.7 × 10^?2 and 1.3 × 10^?1 S cm^?1 for La_9.75Ca_0.25Ge₆O_27?δ at 700 and 900°C). Conversely, doping lanthanum silicate with ions of calcium or aluminum reduces the conductivity. In the pO₂ interval studied, the above compounds are ionic conductors and represent a class of solid electrolytes of promise for various electrochemical devices.     

Zur Stabilisierung der monoklinen B-Form. II. Umwandlung von C?Er2O3 in B?Er2O3 durch Einbau von CaO bei hohen Temperaturen

Stabilization of the Monoclinic B-Modification. II. Transformation of C? Er₂O₃ into B? Er₂O₃ by High Temperature Reaction with CaO Smale amounts of CaO stabilize the monoclinic B-Type of Er₂O₃. X-Ray single crystal investigations of Ca_o.1Er_1.9O_2.95 show Er³⁺ is replaced by Ca²⁺ only on special lattice points with a 7-fold O^2? coordination.     

Ein neues Alkali-Erdalkalimetall-Kupfer-Oxovanadat: Kba3Ca4Cu3V7O28

A new Alkaline-Alkaline-Earth-Copper-Oxovanadate: Kba₃Ca₄Cu₃V₇O₂₈ . Single crystals of Kba₃Ca₄Cu₃V₇O₂₈ were prepared by solid state reactions below the melting point of the reaction mixture. It crystallizes with hexagonal symmetry, space group C?P6₃mc, a=11.160, c=12.428 Å, Z=2. Kba₃Ca₄Cu₃V₇O₂₈ represents a new structure type with special coordination polyhedra around Ba²⁺, trigonal prisms and octahedra around Ca²⁺ and Cu²⁺ inside square pyramids. The crystal structure will be shown and discussed.     

Interaction of calcium ion with sodium triphosphate determined by potentiometric and calorimetric techniques

The stoichiometry of the interaction of Ca²⁺ with sodium triphosphate was determined using a Ca²⁺ sensitive electrode, divalent ion sensitive electrode, a glass electrode and by titration calorimetry, A 2:1 and 1:1 complex of Ca²⁺ and P₃O^5?₁₀ is found when titrating calcium chloride with sodium triphosphate by the calcium ion sensitive electrode and tritation calorimetry. However, only by titration calorimetry is the 2:1 and 1:1 complex found when titrating sodium triphosphate with calcium chloride. Thermodynamic value (log K, ΔH and ΔS) are reported for the formation of CaP(in3)O^?3₁₀ and Ca₂P₃O^?₁₀ in aqueous solution.     

The crystal and magnetic structures of Ca2NdRuO6, Ca2HoRuO6, and Sr2ErRuO6

The crystal structure of Sr₂ErRuO₆ has been refined from neutron powder diffraction data collected at room temperature; space group P2₁/n, A = 5.7626(2), B = 5.7681(2), C = 8.1489(2) Å, β = 90.19(1)°. The structure is that of a distorted perovskite with a 1:1 ordered arrangement of Ru⁵⁺ and Er³⁺ over the 6-coordinate sites. Data collected at 4.2 K show the presence of long range antiferromagnetic order involving both Ru⁵⁺ and Er³⁺. The temperature dependence of the sublattice magnetizations is described. The crystal structure of Ca₂NdRuO₆ is also that of a distored perovskite (P2₁/n, A = 5.5564(1), B = 5.8296(1), C = 8.0085(1) β = 90.19(1)°. The β = 90.07(1)°) with a random distribution of Ca²⁺ and Nd³⁺ on the A site and a 1:1 ordered arrangement of Ca²⁺ and Ru⁵⁺ on the 6-coordinate B sites. The Ru⁵⁺ sublattice is antiferromagnetic at 4.2 K but there is no evidence for magnetic ordering of the Nd³⁺ ions. Ca₂HoRuO₆ is also a distorted perovskite (P2₁/n, A = 5.4991(1), B = 5.7725(1), C = 7.9381(2), β = 90.18(1)° at 4.2 K) with a cation distribution best represented as Ca_1.46Ho_0.54[Ca_0.54Ho_0.46Ru]O₆. There is no ordering among the Ca³⁺ or Ho³⁺ ions on either the A or the B sites, but the Ca/Ho ions form a 1:1 ordered arrangement with Ru⁵⁺ on the B sites. At 4.2 K the Ru⁵⁺ ions adopt a Type I antiferromagnetic arrangement but there is no evidence of long range magnetic ordering among the Ho³⁺ ions.     

Crystal Structure and Property of Perovskite-Type Oxides Containing Ion Vacancy

Studies on the role of oxygen vacancy in structural change of nonstoichiometric perovskites and a property of oxygen-deficient perovskite-related K₂NiF₄ compounds are reviewed.The structural changes on which the authors focused are cation ordering and lattice distortion. The relationship between the distortion and oxygen vacancy was investigated by comparing the structures of Sr₂(Sr_1-xM_x)TaO_6-d (M = Ca²⁺ and Nd³⁺) solid solutions. It was found that distortion of a perovskite-type lattice decreased with an increasing amount of oxygen vacancies. In order to investigate the relationship between the cation ordering on octahedral sites and oxygen vacancy, structures of stoichiometric Sr_2-xLa_xCo_1-yTa_1+yO₆ and oxygen-deficient Sr_2-xLa_xMg_1-yTa_1+yO_6-d solid solutions were compared. The authors' work reveals that the cation ordering affects the amount of oxygen vacancies in addition to cation charge and size.     

Significant enhancement of luminescence intensity of CaTiO3:Eu3+ red phosphor prepared by sol–gel method and co-doped with Bi3+ and Mg2+

In this study, red phosphors Ca_1?n Mg _n TiO₃:Eu³⁺,Bi³⁺ were prepared by the sol?Cgel method and the impact of single dopant, co-dopants and solid solutions on the photoluminescence of the samples has been also investigated. Our results show that the crystal structure of the host does not have distinct changes when doped with Eu³⁺, Bi³⁺ and/or Mg²⁺. The emission intensity at 615?nm of Eu³⁺ increased at the presence of Bi³⁺ ions owing to the energy transfer from Bi³⁺ ion to Eu³⁺ ion. Moreover, with the addition of Mg²⁺, the red emission of the phosphor was further enhanced due to the stronger absorption at 399 and 467?nm, which match well with the emission of near-UV (395?C400?nm) and blue-LED (450?C470?nm), respectively. Under the near-UV (399?nm) or blue light (467?nm) excitation, the fluorescence quantum yield of the optimal composition Ca_0.9Mg_0.1TiO₃:0.18Eu³⁺,0.018Bi³⁺ is 0.36 and 0.41, respectively, which possesses the higher photoluminescence intensity than CaMoO₄:0.2Bi³⁺,0.05Eu³⁺ and the commercially available Y₂O₂S:Eu³⁺ phosphors under near-UV excitation. Based on these results, we are currently considering the potential application of Ca_0.9Mg_0.1TiO₃:Eu³⁺,Bi³⁺ as a near-UV or blue-chip convertible red-emitting phosphor.     

Beiträge zum thermischen Verhalten wasserfreier Phosphate. IX. Darstellung und Kristallstruktur von Cr6(P2O7)4. Ein gemischtvalentes Pyrophosphat mit zwei- und dreiwertigem Chrom

Contributions on the Thermal Behaviour of Anhydrous Phosphates. IX. Synthesis and Crystal Structure of Cr₆(P₂O₇)₄. A Pyrophosphate Containing Di- and Trivalent Chromium Cr₆(P₂O₇)₄ (Cr₂²⁺Cr₄³⁺(P₂O₇)₄) can be obtained reducing CrPO₄ by phosphorus (950°C, 48 h, 100 mg iodine as mineralizer). By means of chemical transport reactions (transport agent iodine; 1050 → 950°C) the compound has been separated from its neighbour phases (Cr₂P₂O₇, CrP₃O₉) and crystallized (greenish, transparent crystals; edge length up to 0.3 mm). The crystal structure of Cr₆(P₂O₇)₄ (Spcgrp.: P-1; z = 1; a = 4.7128(8) Å, b = 12.667(3) Å, c = 7.843(2) Å, α = 89.65(2)°, β = 92.02(2)°, γ = 90.37(2) has been solved and refined from single crystal data (2713 unique reflections, 194 parameter, R = 0.035). Cr²⁺ is surrounded by six oxygen atoms which occupy the corners of an elongated octahedron (4 × d^{Cr? O} ≈? 2.04 Å; 2 × d^{Cr? O} ≈? 2.62 Å). The Cr³⁺ ions are also coordinated octahedraly (1.930 Å ≤ d_{Cr? O} ≤ 2.061 Å). The crystallographically independent pyrophosphate groups show nearly eclipsed conformation. The bridging angles (P? O? P) are 136.5° and 138.9° respectively.