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 geordnete Perowskite mit Kationenfehlstellen. X. Verbindungen vom Typ ABB□1/4MVIO6 ≙ ABIIB□MO24 mit AII,BII = Ba,Sr, Ca und MVI = U,W

On Ordered Perovskites with Cationic Vacancies. X. Compounds of Type A B B □_1/4M^VIO₆ ? A B^IIB □M O₂₄ with A^II, B^II = Ba, Sr, Ca and M^VI = U, W Perovskites of type Ba₈B^IIB₂^III□UO₂₄ show polymorphic phase transformations of order disorder type. An 1:1 ordered orthorhombic HT form is transformed into a higher ordered LT modification with a fourfold cell content (four formula units Ba₈B^IIB□U₄O₂₄), compared to cubic 1:1 ordered perovskites A₂BMO₆. In the series Ba₈BaB□W₄O₂₄ and Sr₈SrB□W₄O₂₄ different ordering phenomena are observed. In comparison with 1:1 ordered cubic perovskites A₂BMO₆, the cell contains eight formula units AB^IIB□W₄O₂₄. The higher ordered cells with U^VI and W^VI are face centered, which has its origin in an ordering of cationic vacancies.     

Die Photolumineszenz der dreiwertigen Seltenen Erden in den Perowskitstapelvarianten Ba2La2−xSE MgW2□O12, Ba6Y2−xSEW3□O18 und Sr8SrGd2−x SEW4□O24

Photoluminescence of Trivalent Rare Earths in Perovskite Stacking Polytypes Ba₂La_2?x RE MgW₂□O₁₂, Ba₆Y_2?x RE W₃□O₁₈, and Sr₈SrGd_2?xRE W₄□O₂₄ Rhombohedral 12 L stacking polytypes Ba₂La_2?xREMgW₂□O₁₂ show with RE³⁺ = Pr, Sm, Eu, Tb, Dy, Ho, Er, Tm; the 18 L stacking polytypes Ba₆Y_2?xREW₃□O₁₈ and the polymorphic perovskites Sr₈SrGd_2?xREW₄□O₂₄ with RE³⁺ = Sm, Eu, Dy, Ho, Er visible photoluminescence. The concentration dependence and the influence of the coordination number of the rare earth are reported.     

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 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. 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.     

Perovskite Phases in the Systems AIIO–UVIO3. II. On The System ABIIUVIO6, with AII,BII = Ba,Sr, Ca

Studies on the system AB^IIU^VIO₆ with A^II, B^II = Ba, Sr, Ca or combinations of these have shown that the alkaline earth ions cannot substitute each other in all proportions. The perovskites were studied by X-ray diffraction and vibrational spectroscopic methods. The lattice vibration region of the far infrared spectra proved to be of particular value in providing information on the occupancy of the A and B sites. Analysis of the spectra shows that, in the majority of cases, contary to the geometrical predictions some of the larger alkaline earth ions occupy the six-coordinated B sites and some smaller ions the A positions. The number of ions that take in this A ? B site-exchange can amount to 20%, but in normally smaller.     

Barium‐deficient celsian,Ba1−xAl2−2xSi2+2xO8 (x = 0.20 or 0.06)

Barium‐deficient forms of celsian (barium aluminium silicate) with the formula Ba_1−xAl_2−2xSi_2+2xO₈ (x = 0.20 and 0.06) have been identified. In contrast with the celsian–orthoclase solid solutions which have been reported previously, these forms, refined in the space group C2/m, with Ba and one O atom in the 4i sites with m site symmetry, and a further O atom in a 4g site with twofold axial symmetry, suggest a slight solid solution with silica. The serendipitous preparation of the compounds represents a possible hazard associated with solid‐state synthesis.     

Über Das System Ba2Gd2/3□1/3U1−xWxO6 sowie hexagonale Perowskite vom 18-

On the System Ba₂Gd_2/3□_1/3U_1?xW_xO₆ and Hexagonal Perovskites of an 18-Layer Type In the system Ba₂Gd_2/3□_1/3U_1?xW_xO₆ the formation of a continuous solid solution series is observed. With x ? 0.9 the mixed crystals have a cubic 1:1 ordered perovskite structure. With x ≥ 0.95 the compounds are polymorphic: besides an cubic 1:1 ordered perovskite type for x = 0.95; 0.99 and 1.00 one hexagonal layer structure exists. This lattice is in all cases rhombohedral (space group R3 m) and represents an 18 L-type. Likewise the compounds Ba₂B□_1/3W^VIO₆ with B^III = Tb-Lu and Y belong to the 18 L-type.     

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.     

Übergangsmetallchalkogenverbindungen. Spectrophotometric evidence for the existence of MoO3Se2− and WO3Se2− in aqueous solution. Electronic Spectra of the Ions MeOxSe4−x2− (Me = Mo,W)

A spectrophotometric investigation of the reaction between MeO₄^2? (Me?Mo, W) and gaseous H₂Se leading to the identification of the unknown monoselenoanions of molybdenum(VI) and tungsten(VI) is reported. The electronic spectra agree well with the theoretically predicted ones. Further a comparative study of the spectra of different seleno- and thio-anions was made. The first band in the electronic spectra of MoO₃Se^2? and WO₃Se^2? is due to the Se → metal charge transfer transition.     

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 die Polymorphie der Perowskite Ba2SE0,67WVIO6. II. Die Systeme Ba2Nd0,67(1−x) Y0,67xWO6 und Ba2Nd0,67W1−xUxO6

Polymorphism of Perovskite Compounds Ba₂SE_0.67W^VIO₆. II. The Systems Ba₂Nd_0.67(1?x)Y_0.67xWO₆ and Ba₂Nd_0.67W_1?xU_xO₆ In the system Ba₂Nd_0.67(1?x)Y_0.67xWO₆ the formation of a continuous series of mixed crystals with cubic 1:1 ordered perovskite structure is observed. The existence of a hexagonal modification is confined to the Y-rich side (x ≥ 0,9). In the Ba₂Nd_0.67W_1?xU_xO₆ series only for x ? 0,25 homogeneous cubic perovskites are obtained. In contrast to systems with other rare earths the Nd series show uncommon optical properties.     

Ternäre Mangan-Verbindungen AMnX (A ≙ Mg,Ca, Sr oder Ba; X ≙ Si,Ge oder Sn): Neutronenbeugungsuntersuchungen zur Charakterisierung der magnetischen Eigenschaften

Ternary Manganese Compounds AMnX (A ≙ Mg, Ca, Sr or Ba; X ≙ Si, Ge or Sn): Characterization of the Magnetic Properties by Neutron Diffraction Experiments Neutron diffraction experiments led to the determination of the antiferromagnetic spin structures of MgMnGe, CaMnSi, CaMnGe, CaMnSn, SrMnGe, SrMnSn, and BaMnGe. For the compounds MgMnGe, CaMnSi, CaMnGe, and CaMnSn an arrangement was found that can be described in the crystallographic cell; in the case of SrMnGe, SrMnSn, and BaMnGe the c-axes have to be doubled. The Shubnikov-groups are P4′/n′m′m and P4′/n′cc′, respectively. The magnetic moments of the maganese atoms are significantly below those values to be expected for Mn²⁺ ions.     

Tetrapnictidotitanate(IV) M4TiX4 (M = Sr,Ba; X = P,As), hierarchische Derivate der KGe-Struktur K4□Ge4

Tetrapnictidotitanates(IV) M₄TiX₄ (M = Sr, Ba; X = P, As), hierarchical Derivatives of the KGe Structure K₄□Ge₄ The four new tetrapnictidotitanates(IV) Sr₄TiP₄, Sr₄TiAs₄, Ba₄TiP₄ and Ba₄TiAs₄ are synthesized from the binary pnictides MX (M = Sr, Ba and X = P, As) and elementary titanium in tantalum ampoules. The compounds are isotypic and isoelectronic with Ba₄SiAs₄ (space group P4 3n (no. 218); cP72; Z = 8; Sr₄TiP₄: a = 1259.0(1) pm; Sr₄TiAs₄: a = 1288.3(4) pm; Ba₄TiP₄: a = 1316.6(2) pm; Ba₄TiAs₄: a = 1346.9(2) pm). The transition metal compounds form cubic, metallic reflecting crystals (Sr₄TiP₄ (green); Sr₄TiAs₄ (silver coloured); Ba₄TiP₄ (silver coloured); Ba₄TiAs₄ (violet). They are semiconducting and very sensitive against air and moisture. The structure is a hierarchical derivative of Cr₃Si (A15) and KGe type: Cr₆Si₂ ? (□Ge₄K₄)₆(□Ge₄K₄)₂ ? (TiX₄M₄)₆(TiX₄M₄)₂, where Ti occupies the positions of the Cr₃Si structure, and the alkaline-earth metal and pnicogen atoms occupy the positions of the KGe structure. Therefore, Ti is surrounded by four X and four more distant M atoms forming a heterocubane. The mean bond lengths are: d (Ti? P) = 238.0(5) pm; 307 ? d(Sr? P) ? 333 pm; d (Ti? As) = 245.9(4); 313 ? d(Sr? As) ? 341 pm; d (Ti? P) = 240.5(5); 324 ? d(Ba? P) ? 348 pm; d (Ti? As) = 248.3(3) pm; 331 ? d(Ba? As) ? 355 pm.