Über geordnete Perowskite mit Kationenfehlstellen. XI. Verbindungen vom Typ ABB□1/4WVIO6 ≙ ABIIB□WO24 mit AII,BII = Ba,Sr

On Ordered Perovskites with Cationic Vacancies. XI. Compounds of Type A B B □_1/4W^VIO₆ ? A B^IIB □W O₂₄ with A^II, B^II = Ba, Sr Depending on the ionic radii of the two and three valent cations in the perovskites of type ABB □_1/4W^VIO₆ ?; AB^IIB □WO₂₄ order disorder phenomena are present. The results of the x-ray and vibrational spectroscopic investigations as well as the diffuse reflectance spectra and the visible photoluminescence are reported.     

Über Hexagonale Perowskite mit Kationenfehlstellen. I. Verbindungen vom Typ Ba2B□2/3ReVIIO6

On Hexagonal Perovskites with Cationic Vacancies. I. Compounds of the Type Ba₂B □_2/3Re^VIIO₆ Compounds of Type Ba₂B□_2/3Re^VIIO₆ are formed with B^III = Sm? Gd Ho? Lu, Y, Sc, In (yellow); Tb (black-brown); Dy (yellow-orange). They crystallize with B^III = Sm? Lu, Y and Sc in a rhombohedral layer structure of 12 L-type (space group R3 m; sequence: cchhcchhcchh) with 6 formula units in the unit cell.     

Über hexagonale Perowskite mit Kationenfehlstellen. III Strukturbestimmungen an Verbindungen vom Typ Ba2B □2/3 ReVIIO6

On Hexagonal Perovskites with Cationic Vacancies. III. Structure Determination on Compounds of Type Ba₂B □_2/3 Re^VIIO₆ Compounds of Type Ba₂B □_2/3 Re^VIIO₆ with B^III = rare earth, Y. Sc, In belong to the group of hexagonal perovskite stacking polytypes. For B^III = Gd, Y structure determinations with powder data have been performed. The refined R′ factors are 9.11% for Ba₂Gd1/3□_2/3ReO₆ and 12.07% for Ba₂Y1/3□_2/3ReO₆. The structure represents a rhombohedral 12 L type (space group R3 m) with the sequence hhcchhcchhcc. The lattice contains groups of three octahedra connected by common faces which are linked together by a single octahedron via common vertices. In the block of three face-sharing octahedra the central octahedral lattice site is vacant and the two outer positions are occupied by the rhenium atoms. According to this distribution direct contact of occupied face-sharing octahedra is absent.     

Über Hexagonale Perowskite mit Kationenfehlstellen. X. Verbindungen vom Typ Ba4BIII(ReW□O12) – neue rhomboedrische 12 L-Stapelvarianten

On Hexagonal Perovskites with Cationic Vacancies. X. Compounds of Type Ba₄B^III(ReW□O₁₂) – New Rhombohedral 12 L-Stacking Polytypes Compounds of type Ba₄B^III(ReW□O₁₂) are described for B^III = Sc, In, Lu, Yb. They crystallize in the rhombohedral 12 L-stacking poly/type (space group R3 m, sequence (3)(1) ? hhcc).     

Über Geordnete Perowskite mit Kationenfehlstellen. IX. Verbindungen vom Typ Sr2Sr1/4B□1/4WO6≙Sr8SrB□W4O24 (BIII  La,Pr, Nd,Sm – Tm,Y)

On Ordered Perovskites with Cationic Vacancies. IX. Compounds of the Type Sr₂Sr_1/4B □_1/4WO₆?Sr₈SrB ?W₄O₂₄ (B^III ? La, Pr, Nd, Sm–Tm, Y) The compounds Sr₂Sr_1/4B□_1/4WO₆?Sr₈SrB?W₄O₂₄ belong to the group of perovskites with octahedral cationic vacancies (cation/vacancy ratio (CN 6) ?:1). For the larger B^III ions (La, Pr, Nd, Sm–Dy) different ordering effects are observed. The perovskites with B^III ? Sm, Eu, Gd are polymorphic too (HT modification: higher ordered cubic perovskite (B^III ? Gd: a = 2X8.23₄ Å); LT modification: hexagonal perovskite stacking polytype (B^III ? Gd: a = 9.95₄ Å; c = 19.0₄ Å)). With the smaller B^III ions (Ho, Er, Tm and Y) a cubic, 1:1 ordered perovskite type is observed.     

Über hexagonale Perowskite mit Kationenfehlstellen. XXXIII. Verbindungen vom Typ Ba6−xSrxB2−y3+SEy3+W3□O18

On Hexagonal Perovskites with Cationic Vacancies. XXXIII. Compounds of Type Ba_6?xSr_xB_2?y³⁺SE_y³⁺W₃□O₁₈ In the series Ba_6?xSr_xLu_2?ySE_y³⁺W₃□O₁₈ a substitution of Sr²⁺ for Ba²⁺ is possible. According to intensity calculations on powder data of BaSr₅Lu_1,6Ho_0,4W₃□O₁₈ the compounds crystallize in a rhombohedral 18 L type with the sequence (hhcccc)₃; space group R3 m. The refined, intensity related R' value is 11.5%. The differences in properties (diffuse reflectance spectra, photoluminescence) between the hexagonal modifications Ba₆B_2?y³⁺SE_y³⁺W₃□O₁₈ (B³⁺ ? Gd, Y, Lu; SE³⁺ ? Sm, Eu, Tb, Dy, Ho, Er, Tm) and the corresponding cubic HT modifications are discussed.     

Über Hexagonale Perowskite mit Kationenfehlstellen. XI. Die Stapelvariante Ba6W4□2O18

On Hexagonal Perovskites with Cationic Vacancies. XI. Stacking Polytype Ba₆W₄□₂O₁₈ The white Ba₆W₄□₂O₁₈, with a cation/vacancy ratio of 2:1 for the octahedral holes, is the first representative of a new stacking polytype for this formula type. It crystallizes in a rhombohedral six layer-structure with a_hex = 10.13₀ Å c_hex = 13.96₀ Å Z = 3 (ρ_exp = 7.3₈ g/cm³; ρ_calc = 7.41₈ g/cm³).     

Über hexagonale Perowskite mit Kationenfehlstellen. XII. Strukturbestimmung an Ba6W4□2O18

On Hexagonal Perovskites with Cationic Vacancies. XII. Structure Determination on Ba₆W₄□₂O₁₈ The stacking polytype Ba₆W₄□₂O₁₈ is the first oxidic variant of the Cs₃Tl₂Cl₉-type. The structure determination gave for the space group R3 c with the sequence (h)₆, Z = 3, the refined, intensity related R′ value of 6.8%. The octahedral net consists of groups of two face sharing WO₆ octahedra (W₂O_6/2;O₆), which are in the (110) plane displaced against each other. In the doublé octahedra the tungsten atoms are shifted away from their ideal central position (W–W: 2.32₇ Å) with the result, that the W–W distance has increased to 2.90₅ Å.     

Über Verbindungen vom Typ Ba3BIIMO9 mit BII  Mg,Ca, Sr,Ba und MV  Nb,Ta

Compounds of the Type Ba₃B^IIM O₉ with B^II ? Mg, Ca, Sr, Ba, and M^V ? Nb, Ta The hexagonal perovskites Ba₃B^IIMO₉ (M^V ? Nb, Ta) crystallize with B^II ? Mg Ca in a 3 L structure (sequence (c)₃) and B^II ?; Sr in the hexagonal BaTiO₃ type (6 L; sequence (hcc)₂) with an 1:2 order for the B and M ions. Intensity calculations for Ba₃SrNb₂O₉ and Ba₃SrTa₂O₉ gave in the space group P6₃/mmc a refined, intensity related R′ value of 8.4% (Nb) and 9.0% (Ta) respectively. For B^II ? Ba the perovskite Ba₃BaTa₂O₉ has an orthorhombic distorted 6 L structure and forms with Ba₃SrTa₂O₉ a continuous series of mixed crystals (Ba₃Sr_1?xBa_xTa₂O₉). In the system Ba₃Sr_1?xBa_xNb₂O₉ the range of existence of the hexagonal BaTiO₃ type is confined to the Sr richer end. The pure Ba compound possesses a proper structure type (5 L: Ba₅BaNb₃□O_13.5□_1.5).     

Über hexagonale Perowskite mit Kationenfehlstellen. XIV Die rhomboedrischen 12 L-Stapelvarianten Ba2La2BII(W□O12)

On Hexagonal Perovskites with Cationic Vacancies. XIV. The Rhombohedral 12 L-Stacking Polytypes Ba₂La₂B^II(W □O₁₂) Rhombohedral 12 L-stacking polytypes with cationic vacancies of type Ba₂La₂B^II-(W□O₁₂) are reported for B^II = Mg, Zn (white), Ni(light brown) and Co(brown). They crystallize in the space group R3 m, sequences (3 )(1) ? (hhcc)₃. For B^II = Cu, as a consequence of the Jahn Teller effect, a triclinic distorted lattice is observed.     

Über geordnete Perowskite mit Kationenfehlstellen. III. Ba2CeSb4/5□1/5O6, der erste Vertreter einer neuen Perowskitvariante

On Ordered Perovskites with Cationic Vacancies III. Ba₂CeSb_4/5□_1/5O₆, the First Representant of a New Perovskite Variant The lemon coloured Ba₂CeSb_4/5□_1/5O₆ is polymorphic. The HT modification has a cubic face centered (a = 8.53₉ Å) and the TT form a cubic primitive lattice (a = 8.53₁ Å). According to the density measurement there are 4 formula units of Ba₂CeSb_4/5□_1/5O₆ in the unit cell.     

Über hexagonale Perowskite mit Kationenfehlstellen. XVI Die rhomboedrischen 12 L-Stapelvarianten Ba3AIIIM□O12 mit MV = Nb,Ta

On Hexagonal Perovskites with Cationic Vacancies. XVI. Rhombohedral 12 L-Stacking Polytypes Ba₃A^IIIM □O₁₂ with M^V = Nb, Ta The white quaternary oxides Ba₃LaM□O₁₂ with M^V = Nb, Ta belong to the group of hexagonal perovskites with cationic vacancies. They crystallize in a rhombohedral 12 L-structure (sequence (hhcc)₃; space group R3 m) with a = 5.75₁ Å; c = 28.1₁ Å (M^V = Nb); a = 5.74₆ Å; c = 28.2₀ Å (Ta) and Z = 3. Signs for the formation of isotypic compounds with A^III = Pr, Nd could be obtained as well.     

Über Sauerstoffperowskite des fünfwertigen Rutheniums ABIIIRuVO6 mit AII = Ba,Sr

On Oxygen Perovskites with Pentavalent Ruthenium A B^IIIRu^VO₆ with A^II = Ba, Sr The perovskites Ba₂B^IIIRu^VO₆ with B^III = La, Nd, Sm, Eu, Gd, Dy, Y, are cubic (B^III = La: a = 8,54₄ Å; Y: a = 8,33₇ Å); with a partial order for B^III and Ru^V. The Sc compound, Ba₂ScRuO₆, has a hexagonal 6 L structure (a = 5.79₅ Å; c = 14.22₉ Å; sequence (hcc)₂)₂. The lattice of the Sr perovskites, Sr₂B^IIIRu^VO₆, with B^III = Eu, Gd, Dy, Y is rhombic distorted. The IR and FRI spectra are discussed.     

Über hexagonale Perowskite mit Kationenfehlstellen. VII. Schwingungsspektroskopische Untersuchungen an rhomboedrischen 12 L-Stapelvarianten vom Typ Ba4BII(Re2 □ O12) and Ba4B □1/3 (Re2 □ O12)

On Hexagonal Perovskites with Cationic Vacancies. VII. Vibrational Spectroscopie investigations on the Rhombohedral 12 L-Stacking Polytypes Ba₄B^II(Re₂□O₁₂) and Ba₄B □_1/3 (Re₂ □ O₁₂) For the rhombohedral 12 L stacking polytypes Ba₄B^II(Re₂□O₁₂) and Ba₄B□_1/3(Re₂□O ₁₂), space group R3 m, sequence (3)(1), the lattice consists of groups of three face sharing octahedra with the composition Re₂□O₁₂. They are isolated from each other by the Ba and B ions.The vibrational spectra are interpreted according to the factor group analysis. For the Re₂□O₁₂ unit (symmetry D_3d) the results of a complete vibrational analysis and the calculation of the force constants are reported.     

Über geordnete Perowskite mit Kationenfehlstellen. VIII. Strukturuntersuchungen an Ba2Ba7/8□1/8UO57/8□1/8

On ordered perovskites with cationic vacancies. VIII. Structure investigations on Ba₂Ba_7/8□_1/8UO_57/8□_1/8 The reddish brown Ba₂Ba_7/8□_1/8UO_57/8□_1/8 belongs to the group of oxygen perovskites with an ordered distribution of cationic vacancies. It crystallized tetragonally (a = 12.62₄ Å; c = 17.53₄ Å) with 16 formula units in the unit cell: Ba₃₂Ba₁₄□₂U₁₆O₉₄□₂. For the space group I4/mmm intensity calculations on powder data gave a refined, intensity related R′ value of 13.4%. The octahedrally coordinated barium an uranium atoms are 1:1 ordered; both cationic vacancies are located in the barium sublattice and form a body centered arrangement. For the 94 oxygen atoms and the two oxygen vacancies a statistical distribution was chosen. In the lattice all cations neighbouring the cationic vacancies are dislocated: The corresponding barium atoms in the close packed sheets move by ～0.55 Å in direction of the holes, on the contary the uranium atoms concerned are shifted away by ～0.17 Å and ～0.26 Å respectively.     

Über hexagonale Perowskite mit Kationenfehlstellen. XV Ba9Nb6W□2O27 - die erste Perowskit-Stapelvariante vom rhomboedrischen 27 L-Typ

On Hexagonal Perovskites with Cationic Vacancies. XV. Ba₉Nb₆W□₂O₂₇ – the First Perovskite Stacking Polytype of Rhombohedral 27 L-Type The perovskite stacking polytype Ba₉NbW^VI□₂O₂₇(white) is the first representative of a rhombohedral 27 L-type. The lattice parameters (trigonal setting) are: a = 5.79₃ Å; c = 63.4₁ Å; Z = 3 (?_exp = 6.4₆ g/cm³; ?_calc = 6.51₂ g/cm³). The corresponding Ta^V -compound is isotypic; it tends to develop stacking faults.     

Über hexagonale Perowskite mit Kationenfehlstellen. XX. Ba6Nb4Zr□O18 – eine neue Stapelvariante mit rhomboedrischer 18 L-Struktur

On Hexagonal Perovskites with Cationic Vacancies. XX. Ba₆Nb₄Zr□o₁₈ - a New Stacking Polytype with a Rhombohedra1 18 L Structure The white Ba₆Nb₄Zr□O₁₈ crystallizes in a rhombohedral 18 L structure (a = 5.82₁ Å; c = 42.6₃ Å; space group R3 m) with three formula units for the trigonal setting (?_exp = 6.0₅ g/cm³; ?_calc = 6.27₁ g/cm³). The corresponding Ti^IV and Hf^IV compounds, Ba₆Nb₄Zr□O₁₈ and Ba₆Nb₄Hf□O₁₈, are isotypic.     

Über hexagonale Perowskite mit Kationenfehlstellen. XXXI. Die Systeme BaO?Re2O7?MO5 mit MV = Nb,Ta

On Hexagonal Perovskites with Cationic Vacancies. XXXI. Systems BaO? Re₂O₇? M O₅ with M^V = Nb, Ta In the systems BaO? Re₂O₇? MO₅ three quaternary oxides are formed, which belong to the perovskite stacking polytypes with cationic vacancies: Ba₈Re_7/2M□₃O₂₄ (M^V = Nb, Ta; rhombohedral 24 L type; sequence (hhhhchhc)₃; space group R3 m), Ba₄Re_9/8Ta_13/8□_5/4O₁₂ (rhombohedral 12 L type; sequence (hhcc)₃; space group R3 m) and the phases Ba₅BaRe_3/2?xM □O_15?x□_x (M^V = Nb, Ta; variants of a hexagonal 5 L type).     

Über Geordnete Perowskite mit Kationenfehlstellen. II. Der Ersatz von UVI durch NbV in Ba2Gd0,67□0,33UO6

On Ordered Perovskites with Cationic Vacancies. II. The Incorporation of Nb^V in Ba₂Gd_0,67□_0,33UO₆ In Ba₂Gd_0.67□_0.33UO₆ a complete substitution of U^VI by Nb^V is possible by filling the cationic vacancies (x-phase: Ba₂Gd_0.67+0.33xU_1?xNb_xO₆). For the y-Phase (Ba₂Gd_0.67U_1?yNb_yO_6?0.5y) solid solutions are formed only for y ? 0.5. The properties of both phases are studied by x-ray and spectroscopic methods. In Ba₂GdNbO₆ – in contrary to the complete ordered Ba₂GdTaO₆ – the order of gadolinium and niobium id partial.     

Über hexagonale Perowskite mit Kationenfehlstellen. XXIX. Die Struktur von Ba4ScReW□O12 – zur Funktion von oktaedrischen Kationenfehlstellen in Perowskitstapelvarianten

On Hexagonal Perovskites with Cationic Vacancies. XXIX. Structure of Ba₄ScReW□O₁₂ On the Function of Octahedral Cationic Vacancies in Perovskite Stacking Polytypes The hexagonal perovskite stacking polytype Ba₄ScReW□O₁₂ crystallizes in a rhombohedral 12 L structure (space group R3 m; sequence (hhcc)₃). The refined, intensity related R′ value is 6.6%. The octahedral net consists of blocks of three face connected octahedra with a central vacancy, in the two outer positions the rhenium and tungsten atoms are located; this units are linked via common corners by single octahedra, occupied with scandium.