Über Das System Ba2Sm0,67U1−xWxO6

On the System Ba₂Sm _0.67U_1?xW_xO₆ The ordered perovskites Ba₂Sm_0.67UO₆ and Ba₂Sm_0.67 WO₆ are forming a complete serie of solid solutions with 4 formula units Ba₂Sm_0.67U_1?xW_xO₆ in the unit cell. By diffuse reflectance and i.r.-spectroscopic measurements the relations between color and constitution are shown.     

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. 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 Perowskitphasen des Systems Ba2Y0,67U1−xWxO6

On Perovskite Phases of the System Ba₂Y_0,67U_1?xW_xO₆ A solid solution series is formed between the polymorphic perovskites Ba₂Y_0.67UO₆ and Ba₂Y_0.67WO₆ (cubic: a = 8.37₂ Å; hexagonal: a = 4× 5.88₁ Å and c = 4× 7.77₈ Å). The structure is cubic between x = 0.1 and 0.99 and for x > 0.95 hexagonal as well. Strong deviations from the ideal behaviour are detectabel with spectroscopic methods. The shape of the UO₆ and WO₆ octahedrons experiences only minor changes within the series.     

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 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. XXVIII. Die Struktur der rhomboedrischen 9 L-Stapelvarianten Ba3WNb□O9−x/2□x/2

On Hexagonal Perovskites with Cationic Vacancies. XXVIII. Structure of Rhombohedral 9 L Stacking Polytypes Ba₃W Nb □O_9?x/2□_x/2 According to the intensity calculations for Ba₃W_4/3Nb_2/3□O_26/3□_1/3 and Ba₃Nb₂□O₈□(II) these rhombohedral 9 L compounds crystallize in the space group R3m, sequence (hhc)₃. The refined, intensity related R′ values are 6.9% (Ba₃W_4/3Nb_2/3□O_26/3□_1/3) and 7.2% (Ba₃Nb₂□O₈□(II)). The relations between the rhombohedral 9 L structure (A₃M₂□O₉) and the palmierite type (A₃M₂□O₈□) are discussed.     

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 Perowskite Ba2BBTeVIO6

On Perovskites Ba₂B B Te^VIO₆ Compounds of composition Ba₂BBTe^VIO₆ with B^I = Li, Na; B^III = La, Pr, Nd, Sm, Eu, Gd, Tb, Ho, Yb, Y, In, Sc crystallize in a cubic 1:1 ordered perovskite structure. The vibrational spectroscopic investigations show, that more species of TeO₆ octahedra are present in the lattice.     

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. XXXII. Die Photolumineszenz der dreiwertigen Seltenen Erden in den Systemen Ba2−ySryLa2−xSExMgW2□O12

On Hexagonal Perovskites with Cationic Vacancies. XXXII. Photoluminescence of Trivalent Rare Earth in the Systems Ba_2?ySr_yLa_2?xRE_xMgW₂□O₁₂ In the series Ba_2?ySr_yLa_2?xRE_xMgW₂□O₁₂ the Ba²⁺ can be completely substituted by Sr²⁺. All compounds crystallize in the rhombohedral 12 L-type (space group R3 m; sequence (hhcc)₃). By doping the stacking polytypes with some of the trivalent rare earths efficient visible photoluminescence is obtained. The simultaneous incorporation of two different rare earth ions leads to two-color-phosphors, which, according to the excitation energy used, emit either mainly the typical spectrum from one or the other activator; the corresponding luminescence mechanism 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. XXIV. Rhomboedrische 9 L-Stapelvarianten in den Systemen Ba3W M □ O9−x/2□x/2 mit MV = Nb,Ta

On Hexagonal Perovskites with Cationic Vacancies. XXIV. Rhombohedral 9 L Stacking Polytypes in the Systems Ba₃W M □O_9?x/2□_x?2 with M^V = Nb, Ta In the system Ba₃WNb□O_9?x/2□_x/2 stacking polytypes of rhombohedral 9 L type (sequence (hhc)₃; space group R3 m) can be prepared with ～1/3 ? × ? 2. For x = 2(Ba₃Nb₂□O₈□) two modifications are formed. In the corresponding Ta system the phase with is reduced to a smaller region with x ? 1/3.     

Über hexagonale Perowskite mit Kationenfehlstellen. XXVII. Die Systeme Ba4−xSrxBIIRe2□O12′, Ba4BCaxRe2□O12 und Ba4−xLaxBIIRe2−xWx□O12 mit BII = Co,Ni

On Hexagonal Perovskites with Cationic Vacancies. XXVII. Systems Ba_4?xSr_xB^IIRe₂□O₁₂, Ba₄B Ca_xRe₂□O₁₂, and Ba_4?xLa_xB^IIRe_2?xW_x□O₁₂ with B^II = Co, Ni In the systems Ba_4?xSr_xB^IIRe₂□O₁₂, Ba₄BCa_xRe₂□O₁₂ and Ba_4?xLa_xB^IIRe_2?xW_x□O₁₂ (B^II = Co, Ni) hexagonal perovskites with a rhombohedral 12 L structure (general composition A₄BM₂□O₁₂; sequence (hhcc)₃; space group R&3macr;m) are observed. With the exception of Ba₄NiRe₂□O₁₂ the octahedral net consists of BO₆ single octahedra and M₂□O₁₂ face connected blocks (type 1). In type 2 (Ba₄NiRe₂□O₁₂) the M ions are located in the single octahedra and in the center of the groups of three face connected octahedra. The two outer positions of the latter are occupied by B ions and vacancies in the ratio 1:1. The difference between type 1 and 2 are discussed by means of the vibrational and diffuse reflectance spectra.     

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 hexagonale Perowskite mit Kationenfehlstellen. XXVI. Ba12Ba2 2/3M 1/3□2O33□3 (MV = Nb,Ta) – die ersten Stapelvarianten eines rhomboedrischen 36 L-Typs

On Hexagonal Perovskites with Cationic Vacancies. XXVI. Ba₁₂Ba_{2 2/3}M _1/3□₂O₃₃□₃ (M^V = Nb, Ta) – the First Stacking Polytypes of a Rhombohedral 36 L-Type In the systems BaO? MO₅(M^V = Nb, Ta) for a Ba:M^V ratio of 2:1 polymorphism is observed. Here the low temperature modifications are described. They crystallize in a rhombohedral 36 L structure with three formula units Ba₁₂Ba_{2 2/3}M _1/3□₂O₃₃□₃ for the trigonal setting (M^V = Nb: a = 5.92₂ Å; c = 93.₂₅ Å; Ta: a = 5,92₂ Å; s = 93.4 Å).     

Über hexagonale Perowskite mit Kationenfehlstellen. XVII Strukturbestimmung an Ba9Nb6W□2O27 - der ersten Stapel-variante eines rhomboedrischen 27 L-Typs

On Hexagonal Perovskites with Cationic Vacancies. XVII. Structure Determination on Ba₉Nb₆W□₂O₂₇ – the First Stacking Polytype of a Rhombohedral 27 L-Type The hexagonal stacking polytype of rhombohedral 27 L -type, Ba₉Nb₆W□₂O₂₇, crystallizes in the space group R3 m with the sequence (4)1(3)1 ? (hhccchhcc)₃ and three formula units for the trigonal setting. The refined, intensity related, R'-value is 9.7percnt;. The octahedral net consists of blocks of three face connected octahedra which are linked to each other alternately through one or two octahedra connected exclusively by common vertices. The cationic vacancies are located in the centers of the groups of three octahedra. With this distribution direct contact between occupied face-sharing octahedra is avoided. The niobium and tungsten atoms are distributed statistically between the remaining octahedral holes. In the blocks of three octahedra they are displaced by ≈ 0.29 Å from their ideal positions in the direction of the central void. The Ba atoms neighbouring a vacancy (all in hexagonal packed BaO₃ sheets) are dislocated in the direction of the void, while the cubic packed BaO₃ sheets maintain nearly regular form.     

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. 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. 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.