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. 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. 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.     

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. 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. 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. 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 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. 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. XXX. 5 L-Stapelvarianten in den Systemen BaO?Re2O7?Sb2O5 und BaO?WO3?Sb2O5

On Hexagonal Perovskites with Cationic Vacancies. XXX. 5 L Stacking Polytypes in the Systems BaO — Re₂O₇? Sb₂O₅ and BaO? WO₃? Sb₂O₅ In the systems BaO? Re₂O₇? Sb₂O₅ and BaO? WO₃? Sb₂O₅ phases of composition Ba₅BaRe Sb□O_15?x□_x (x = 0 up to x ? 3/4) and Ba₅BaWSb□O_15?x/2□_x/2 (x ? 3/2 up to x ? 2) are existent, which have an orthorhombic distorted 5 L structure. The pure Sb compound has to be formulated as Ba₃BaSb₂O₉ and crystallize in an orthorhombic variant of the hexagonal BaTiO₃ type.     

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.     

Synthese und Kristallstruktur von Ba6Lu4Zn10O22 mit [OBa6]-Oktaedern

On the Synthesis and Crystal Structure of Ba₆Lu₄Zn₁₀O₂₂ with [OBa₆] Octahedra Single crystals of Ba₆Lu₄Zn₁₀O₂₂ have been prepared by high temperature reactions and investigated by X-ray techniques. This compound is isotypic to Ba₃In₂Zn₅O₁₁ and the first member of the Rare Earth elements. Ba₆Lu₄Zn₁₀O₂₂ crystallizes with cubic symmetry, space group T-F4 3m, a = 13.452(1) Å and Z = 4. Zn²⁺ shows a tetrahedral, Lu³⁺ an octahedral and Ba²⁺ a three-fold capped trigonal prismatic coordination by O^2?. The ZnO₄ tetrahedra and LuO₆ octahedra are forming macro polyhedra of the type Zn₁₀O₂₀ and Lu₄O₁₆. A discussion is given for the Ba₆O₃₃ and Ba₆O₄₂ groups.     

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.     

Strukturbestimmungen an geordneten Perowskiten des Typs Ba2BMVIO6

Determination of Structures of Ordered Perovskites of the Ba₂B M^VIO₆ Type Intensity calculations on powder patterns of Ba₂Y□_0.33M^VIO₆ with M^VI = U, W, Te und Ba₂Gd_0.67□_0.33UO₆ lead for the space group Fm3m/O with 8 Ba in 8c, 8/3 B^III and 4/3 □ in 4b, 4 M^VI in 4a and 24 O in 24e to R values between 4.3 and 7.6%. Two further models are discussed.     

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 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 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 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).     

Ba3Lu4O9: Synthese und Strukturuntersuchung

Ba₃Lu₄O₉: Synthesis and Crystal Structure Determination Single crystals of Ba₃Lu₄O₉ were prepared by high temperature reactions (CO₂-Lasertechnique). The single crystal X-ray work leads to a rhombohedral symmetry with a = 8.96 Å and α = 39.42° (space group C—R3). Characteristic features of this crystal structure are shown and 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.