Die Kristallstruktur des Hexakaliumdigermanats,K6Ge2O7

The title compound is monoclinic, space group Pc (No. 7),a=6.549 (1),b=9.094 (1),c=11.426 (2) Å, =126.78 (1)° andZ=2. Its crystal structure has been refined from 1 323 single crystal X-ray reflections toR=0.131. The structure of K₆Ge₂O₇ is very similar to that of K₆Co₂O₇ and K₆Si₂O₇ both of which have been reported to be centrosymmetric, space group P2₁/c. While the angle at the bridging oxygen atom is 180° in the latter compounds, it is 157° in K₆Ge₂O₇.

     

Spektrochemische Analyse der Mischpentoxide Nb2O5 + Ta2O5

Zusammenfassung Zur spektrochemischen Analyse der Mischpentoxide von Niob und Tantal wurde ein Verfahren ausgearbeitet, das die Anregung im Gleichstrom-Kohlebogen nach Addink u. Mitarb. benutzt. Für die Niobbestimmung werden die bekannten K-Werte verwendet, während die K-Werte für Ta 2681,87, Ta 2684,28 sowie einige schwächere Nb- und Ta-Linien erst gefunden werden mußten. Die Reproduzierbarkeit des Verfahrens beträgt 10–11%; es erlaubt eine bequeme und rasche Analyse, besonders in Verbindung mit einer chemischen Isolierung von (Nb, Ta)₂O₅.

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Summary A spectrochemical method utilizing the Addink's Constant Temperature D.C. Arc Method has been worked out for the determination of Nb₂O₅ and Ta₂O₅ in combined pentoxides. For the determination of niobium the known K-values are employed, while the K-values for Ta 2681.87, Ta 2684.28 and for some weaker niobium and tantalum lines had to be found. The reproducibility being 10–11%, the method has proved to be convenient for a rapid and simple niobium and tantalum analysis, especially in combination with a chemical isolation of (Nb,Ta)₂O₅.

     

Die kristallstruktur des kaliumtetragermanats K2[Ge4O9]

Zusammenfassung Die Kristallstruktur des Kaliumtetragermanats, K₂[Ge₄O₉], wurde mit Hilfe dreidimensionaler Röntgendaten bestimmt. K₂[Ge₄O₉] kristallisiert trigonal mit der Raumgruppe P033034c1 (Nr. 165) und den Gitterparametern:a=11.84 undc=9.80 Å. Die vorgeschlagene strukturchemische Beziehung zum Wadeit, K₂Zr[Si₃O₉], wird durch die Existenz tetraedrischer [Ge₃O₉]-Ringe, die über [GeO₆]-Oktaeder zu einem dreidimensionalen Gerüst verknüpft sind, bestätigt. Es wurden folgende mittlere Ge–O-Abstände gefunden: 1.762 (Tetraeder) und 1.886 Å (Oktaeder).

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The crystal structure of potassium tetragermanate K₂[Ge₄O₉]

The crystal structure of potassium tetragermanate K₂[Ge₄O₉] has been determined by means of three-dimensional x-ray data. K₂[Ge₄O₉] crystallizes trigonal with space group P033034c1 (No. 165) and lattice parametersa=11.84 andc=9.80 Å. The proposed structural relationship to wadeite K₂Zr[Si₃O₉] is confirmed by the existence of [Ge₃O₉] rings built by tetrahedra, which are linked by [GeO₆] octahedra forming a three-dimensional network. The mean Ge–O distances are found to be: 1.762 (tetrahedra) and 1.886 Å (octahedra).

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Mit 2 Abbildungen

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Herrn Prof. Dr.H. Nowotny in Verehrung gewidmet.     

Röntgenographische Untersuchungen in den Systemen GeO2-{K2O,Rb2O,Cs2O}

Zusammenfassung Folgende GeO₂-reiche Alkaligermanate wurden aufgefunden und röntgenographisch hinsichtlich der Gitterparameter charakterisiert: K₂Ge₈O₁₇ und Rb₂Ge₈O₁₇ (isotyp), Rb₂Ge₇O₁₅ und Cs₂Ge₅O₁₁. Die Existenz der seinerzeit als Pentagermanate beschriebenen isotypen Verbindungen von K, Rb, Cs und Tl sowie deren Gitterparameter werden bestätigt, doch ergab eine ausführliche Prüfung an gut kristallisierten Produkten zusammen mit den genau bestimmten Dichtewerten eine geringfügige Verschiebung im Verhältnis Me₂O/GeO₂, entsprechend einer Formel Me₂Ge₆O₁₃.

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The GeO₂-rich regions of alkaline germanate systems have been examined by X-rays. The compounds K₂Ge₈O₁₇ and Rb₂Ge₈O₁₇ (isostructural), Rb₂Ge₇O₁₅ and Cs₂Ge₅O₁₁ have been detected and characterized by their lattice parameters. The existence as well as the cell dimensions of the isotypic compounds previously described as pentagermanates have been corroborated; a detailed investigation of completely crystallized material gives strong evidence for a lower Me₂O/GeO₂-ratio, in accordance with precise density measurements. Thus a formulaMe ₂Ge₆O₁₃ (Me=K, Rb, Cs, Tl) has to be assumed.

     

Neue Oxocadmate der Alkalimetalle: K6[CdO4],Rb6[CdO4], Rb2CdO2 und Rb2Cd2O3

The crystal structure of K₆[CdO₄] and Rb₂CdO₂ has been determined from single crystal X-ray diffraction data and refined toR=0.058 (K₆[CdO₄]) andR=0.088 (Rb₂CdO₂). K₆[CdO₄] crystallizes hexagonal, space group P6₃mc with lattice constantsa=867.42 (6),c=665.5 (1) pm,c/a=0.767 andZ=2. It is isotypic with Na₆[ZnO₄]. Rb₂CdO₂ is orthorhombic, space group Pbcn witha=1045.0 (2),b=629.1 (1),c=618.3 (1) pm,Z=4, and crystallizes with the K₂CdO₂ structure type. The crystal structures can be deduced from the motif of a closest packed arrangement of O^2– with hexagonal (K₆[CdO₄]) or cubic (Rb₂CdO₂) stacking. The tetrahedra occupied by Cd²⁺ are isolated (K₆[CdO₄]) or edge-shared (formation of infinite SiS₂-like chains [CdO_4/2]) (Rb₂CdO₂). The powder diffraction pattern of Rb₆[CdO₄] [a=906.6 (1),c=694.3 (1) pm] and Rb₂Cd₂O₃ [a=642.6 (2),b=679.0 (1),c=667.9 (2) pm, =115.2 (1)] confirm isotypie with K₆[CdO₄] and K₂Cd₂O₃ respectively.

Herrn Prof. Dr.Gutman zum 65. Geburtstag gewidmet.     

Synthesis and thermal decomposition of potassium peroxotitanate to K2Ti2O5

Potassium peroxotitanate was synthesized by the peroxo method. During the thermal decomposition K₂Ti₂O₅ can be obtained. The isothermal conditions for decomposition of K₂[Ti₂(O₂)₂(OH)₆]·3H₂O were determined on the base of DTA, TG and DSC results. DTA and TG curves were recorded in the temperature range 20 and 900°C at a heating rate of 10°C min^–1. The obtained intermediate compounds were characterized by means of quantitative analysis and IR spectroscopy. The mechanism of thermal decomposition of K₂[Ti₂(O₂)₂(OH)₆]·3H₂O to K₂Ti₂O₅ was studied. The optimal conditions for obtaining K₂Ti₂O₅ were determined (770°C for 10 h).     

Die Kristallstruktur des Tetragermanats K2Ba[Ge4O9]2

The crystal structure of the compound K₂Ba[Ge₄O₉]₂ has been determined by means of three-dimensional X-ray data resulting a finalR-value of 0.034. The lattice constants of the trigonal unit cell ( ) are:a=11.729 (I) andc=19.278 (3) Å. There is a close structural relationship to the tetragermanates K₂Ge₄O₉ and BaGe₄O₉. The new compound also consists of three-membered rings built up by [GeO₄] tetrahedra, which are linked by [GeO₆] octahedra forming a three-dimensional network.According to their powder diagrams the following compounds are isostructural to K₂Ba[Ge₄O₉]₂: Na₂Ba[Ge₄O₉]₂, Rb₂Ba[Ge₄O₉]₂, Na₂Sr[Ge₄O₉]₂ and K₂Sr[Ge₄O₉]₂.     

Eine neue Verbindung vom M5TiB2O10-Typ mit geordneter Metallverteilung: Ni5SnB2O10

Summary The unknown compound Ni₅SnB₂O₁₀, prepared by using a flux of excess B₂O₃, was investigated by single crystal X-ray technique. It crystallizes with orthorhombic symmetry, space group D _2h ¹⁶ — Pnma witha=9.302,b=6.089,c=12.280 Å,Z=4. The mean result of this investigation is a hitherto unobserved strictly ordered metal distribution. Ni₅SnB₂O₁₀ is not isotypic but related to Ni₅TiB₂O₁₀.

     

β‐K2Cr2O7

The monoclinic modification of dipotassium dichromate, β‐K₂Cr₂O₇, has been synthesized in the K₂Cr₂O₇–H₂O system. The structure consists of K⁺ cations and Cr₂O₇^2? dimers. In contrast with triclinic α‐K₂Cr₂O₇ [Kuz'min, Ilyukhin, Kharitonov & Belov (1969). Krist.Tech. 4 , 441–461], the Cr₂O₇^2? groups in β‐K₂Cr₂O₇ have twofold crystallographic symmetry and are parallel to each other.     

Mise au point d'un dispositif d'analyse thermique haute pression (2 GPa) application a l'etude des systemes quaternaires SiO2-Al2O3-M2O-H2O (M=Li,Na, K)

An apparatus for thermal analysis operating up to 500°C temperature and up to 2 GPa, pressure using a conventional piston-cylinder device, is described.A few results concerning solid phases of the quaternary systems SiO₂-Al₂O₃-M₂O-H₂O (M=Li, Na, K) studied under 2.10⁸ Pa pressure, are discussed.

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Zusammenfassung Es wird eine Apparatur für die Thermoanalyse bis 500°C und bis zum Druck von 2 GPa beschrieben. Dabei wird ein herkömmliches Kolben-Zylinder-Gerät verwendet. Einige Ergebnisse bezüglich der Festphasen des quaternären Systemes SiO₂-Al₂O₃-M₂O-H₂O (M=Li, Na, K) bei einem Druck von 2·10⁸ Pa wurden beschrieben.

     

Spektroskopisches und thermisches Verhalten von K4H2[S2I2O14]

The infrared andRaman spectra of the tittle compound have been recorded and an assignment for the internal vibrations of the H₂S₂I₂O ₁₄ ^4– polyanion is proposed. The thermal behaviour was investigated using TG-, DTA-, IR- and X-ray methods; it is shown that the polyanion breaks down after the release of one mole of H₂O, generating a mixture of -K₂SO₄ and I₂O₅.

     

Study of thermal properties of potassium μ-hydroxo-bis(oxo-diperoxovanadate)(V)

The thermal decomposition of K₃[OH{VO(O₂)₂}₂]·H₂O was studied under dynamic conditions up to 350°C and also isothermally at 150°±3°C in self-generated atmosphere. K₄[V₂O₆(O₂)] is formed as the reaction intermediate. The final products of thermal decomposition of K₃[OH{VO(O₂)₂}₂]·H₂O are KVO₃ and K₄V₂O₇.

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Zusammenfassung Unter dynamischen Bedingungen bis 350°C und isotherm bei 1503°C in selbsterzeugter Atmosphäre wurde die thermische Zersetzung von K₃[OH{VO(O₂)₂}₂]H₂O untersucht. Als Zwischenprodukt der Reaktion wird K₄[V₂O₆(O₂)] gebildet. Die Endzersetzungsprodukte von K₃[OH{VO(O₂)₂}₂]H₂O sind KVO₃ und K₄V₂O₇.

     

The first silver bismuth borate,AgBi2B5O11

The first silver bismuth borate, AgBi₂B₅O₁₁ (silver dibismuth pentaborate), has been prepared via glass crystallization in the Ag₂O–Bi₂O₃–B₂O₃ system and characterized by single‐crystal X‐ray diffraction. Its structure is derived from that of centrosymmetric Bi₃B₅O₁₂ by ordered substitution of one Bi³⁺ ion for Ag⁺, which results in the disappearance of the mirror plane and inversion centre. Second harmonic generation (SHG) measurements confirm the acentric crystal structure. It is formed by [Bi₂B₅O₁₁]_∞ layers stretched along c and comprised of vertex‐sharing B₅O₁₀ and BiO₃ groups which incorporate the Ag⁺ cations. The new compound was characterized by thermal analysis, high‐temperature powder X‐ray diffraction, and vibrational and UV–Vis–NIR (near infrared) spectroscopy. Its thermal expansion is strongly anisotropic due to the presence of rigid B₅O₁₀ groups aligned in a parallel manner. The minimal value is observed along their axis [parallel to c, α_c = 3.1 (1) × 10^?6 K^?1], while maximal values are observed in the ab plane [α_a = 20.4 (2) and α_b = 7.8 (2) × 10^?6 K^?1]. Upon heating, AgBi₂B₅O₁₁ starts to decay above 684 K due to partial reduction of silver; incongruent melting is observed at 861 K. According to density functional theory (DFT) band‐structure calculations, the new compound is a semiconductor with an indirect energy gap of 3.57 eV, which agrees with the experimental data (absorption onset at 380 nm).     

Thermal decomposition of potassium carbonatooxoperoxovanadate(V)

The thermal decomposition of K₃[V(CO₃)O(O₂)₂] was studied under isothermal, dynamic and quasi-isobaric-isothermal condition. A mixture of K₄V₂O₇ and K₂CO₃ was identified as the primary product of thermal decomposition. Under experimental conditions not allowing a continuous loss of volatile products, the reaction of K₄V₂O₇ with CO₂ gives KVO₃ and K₂CO₃.

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Zusammenfassung Unter isothermen, dynamischen und quasi-isobaren Bedingungen wurde die thermische Zersetzung von K₃[V(CO₃)O(O₂)₂] untersucht. Als Primärprodukt der thermischen Zersetzungsreaktion wurde ein Gemisch aus K₄V₂O₇ und K₂CO₃ festgestellt. Wird unter experimentellen Bedingungen das Entweichen flüchtiger Produkte verhindert, so gibt die Reaktion von K₄V₂O₇ mit CO₂ die Produkte KVO₃ und K₂CO₃.

     

Syntheses of mixed metaphosphates KY(PO3)4 and K2Y(PO3)5

In the ternary system Y₂O₃-K₂O-P₂O₅ the binary system KPO₃-Y(PO₃)₃ has been examined. There are two intermediate metaphosphates KY(PO₃)₄ and K₂Y(PO₃)₅ in it. On the basis of thermal analysis and powder X-ray diffraction, the methods of synthesizing these compounds were prepared.

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Zusammenfassung Im Dreikomponentensystem Y₂O₃-K₂O-P₂O₅ wurde das binäre System KPO₃-Y(PO₃)₃ untersucht. Darin existieren zwei intermediäre Metaphosphate KY(PO₃)₄ und K₂Y(PO₃)₅. Unter Anwendung thermoanalytischer und röntgenographischer Verfahren wurden die Methoden zur Herstellung dieser Verbindungen ausgearbeitet.

     

Das erste Oxocobaltat des Typs A2CoIIO2: K2CoO2 = K4[OCoO2CoO]

The First Oxocobaltate of the Type A₂Co^IIO₂: K₂CoO₂ = K₄[OCoO₂CoO] By “reaction with the cylinder surface” of intimate mixtures of K₂O and CdO (molar ratio 1:1) in closed Co-Cylinders at 450°C during 73 d dark-red single-crystals of K₂CoO₂ were obtained. Structure solution and refinement (four-circle diffractometer-data, MoKα , 1 567 independent I_o(hkl), none was omitted, R = 3.25%, R_w = 2.67%) result in a monoclinic unit cell containing anions [Co₂O₄]^4? of two connected triangles similar to those of Rb₁₀[Co^IO₂]₂[CoO₄]. MAPLE-values and Charge-distributions are given and discussed.     

Phase diagrams of the KF-K<Subscript>2</Subscript>TaF<Subscript>7</Subscript> and KF-Ta<Subscript>2</Subscript>O<Subscript>5</Subscript> systems

The phase diagrams of the systems KF-K₂TaF₇ and KF-Ta₂O₅ were determined using the thermal analysis method. The phase diagrams were described by suitable thermodynamic model. In the system KF-K₂TaF₇ eutectic points at x _KF=0.716 and t=725.4°C and at x _KF=0.214 and t=712.2°C has been calculated. It was suggested that K₂TaF₇ melts incongruently at around 743°C forming two immiscible liquids. The system KF-Ta₂O₅ have been measured up to 8 mol% of Ta₂O₅. The eutectic point was estimated to be at x _KF∼0.9 and t∼816°C. The formation of KTaO₃ and K₃TaO₂F₄ compounds has been observed in the solidified samples.     

Phase equilibria in the system La2O3-Na2O-P2O5

In the ternary system La₂O₃-P₂O₅-Na₂O the partial system La₂O₃-Na₄La₂P₄O₁₅-LaPO₄ has been examined by the thermal, dilatometric X-ray and microscopic analyses and its phase diagram provided. The lanthanum oxyphosphate La₃PO₇ melts incongruently at the 1590°C temperature and crystallizes in a monoclinic systema=11.20 Å,b=11.94 Å,c=7.01 Å,=93.79 andV=936.97 ų.

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Zusammenfassung Mittels Thermo- und dilatometrischer Analyse, Röntgendiffraktionsuntersuchungen und Mikroskopie wurde das Teilsystem La₂O₃ - Na₄La₂P₄O₁₅ - LaPO₄ des ternären Systemes La₂O₃ - P₂O₅ - Na₂O untersucht und ein Phasendiagramm entwickelt. Lanthanoxyphosphat La₃O₇ schmilzt inkongruent bei 1590°C und kristalliert in einem monoklinen System mita=11.20 Ä,b=11.94 Ä,c=7.01 Å,=93.79 undV=936.97 ų.

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The author thanks Mrs. B. Lagódka for the technical assistance (thermogravimetric analyses). The thermal study was supported by grant CPBP.     

Thermal stability and crystallization kinetics of Pb and Bi borate-based glasses

Glasses with compositions 60B₂O₃–40PbO, 60B₂O₃–40Bi₂O₃, and 60B₂O₃–30Bi₂O₃–10PbO have been prepared and studied by differential thermal analysis. The crystallization kinetics of the glasses was investigated under non-isothermal conditions. From dependence of the glass transition temperature (T _g) on the heating rate, the activation energy for the glass transition was derived. Similarly the activation energy of the crystallization process was determined. Thermal stability of these glasses were achieved in terms of the characteristic temperatures, such as the glass transition temperature, T _g, the onset temperature of crystallization, T _in , the temperature corresponding to the maximum crystallization rate, T _p, beside the kinetic parameters, K(T _g) and K(T _p). The results revealed that the 60B₂O₃–40PbO is more stable than the others. The crystallization mechanism is characterized for glasses. The phases at which the glass crystallizes after the thermal process have been identified by X-ray diffraction.     

(Solid+Liquid) Equilibria in the Quaternary System Na2B4O7-MgB4O7-K2B4O7-H2O at 288 K

(Solid+Liquid) phase equilibria in the quaternary system Na₂B₄O₇‐MgB₄O₇‐K₂B₄O₇‐H₂O at 288 K were studied experimentally using the method of isothermal solution saturation. Solubility of any single salt in the solution of the quaternary system was determined experimentally. Based on the experimental data achieved, the phase diagram and water content diagram of the quaternary system were constructed, respectively. In the phase equilibrium diagram of the quaternary system Na₂B₄O₇‐MgB₄O₇‐K₂B₄O₇‐H₂O at 288 K, there are one invariant point E, three univariant curves E1E, E2E and E3E, and three fields of crystallization corresponding to Na₂B₄O₇·10H₂O, K₂B₄O₇·4H₂O and MgB₄O₇·9H₂O. The experimental results show that potassium borate (K₂B₄O₇·4H₂O) have higher solubilities than the magnesium borate and sodium borate in the quaternary system Na₂B₄O₇‐MgB₄O₇‐K₂B₄O₇‐H₂O at 288 K.