Rare earth substituted fluoride-phosphate apatites

Compositions with the general formula Ln_xM_10?2xNa_x(PO₄)₆F₂ (Ln = La, Pi, Nd, Sm, Eu, Dy, Er, Lu, andY;M = Ca, Sr, and Ba) have been prepared and studied by X-ray diffraction methods. The hexagonal apatite like structure was indicated by the powder patterns of all the compounds (with Ba compounds only when Ln = La through Sm). Single crystal precession data reveal that the crystal lattice of all the compositions in the Ca and Sr system have space group P6₃/m, the Ln₂Ba₆Na₂(PO₄)₆F₂ compounds crystallize in space group P6 and the Ln₃Ba₄Na₃(PO₄)₆F₂ compounds in the trigonal space group P3. Order and disorder mechanisms of the substitution and its dependence on size and polarization effects are discussed.     

A study of magnetic interactions in M2EuRuO6 (M = Ca,Sr, Ba) by 151Eu Mössbauer spectroscopy

The series of compounds M₂EuRuO₆ (M = Ca, Sr, Ba) has been studied by ¹⁵¹Eu Mössbauer spectroscopy. X-Ray data show them to be structurally derived from the ABO₃ perovskite lattice, but only the Ba compound gives positive evidence to suggest ordering of the $\text{Eu}{}^{\mathrm{3+}}\text{Ru}{}^{\mathrm{5+}}$ cations. The ¹⁵¹Eu resonance shows magnetic hyperfine splitting at 4.2 K. The Ru⁵⁺OEu³⁺ORu⁵⁺ exchange takes place by admixture of low-lying excited states into the diamagnetic J = 0 ground-state of the Eu³⁺. The Curie temperatures are approximately 18, 31, and 42 K for the Ca, Sr, and Ba compounds. Detailed analysis shows that substantial disorder of cations occurs, being quite large for Ca, <8% for Sr, and <5% for Ba. However, it appears that considerable canting of the Ru⁵⁺ spins takes place in the Ba compound immediately below the Curie temperature as a result of the disorder and low anisotropy at the Ru sites. This effect is much reduced in the more distorted Sr compound.     

Analogs of the Rose center in the alkaline earth fluorides: Production by hydrolysis and identification by Raman spectroscopy

A family of molecular centers of the type (RO₂M)²⁺ is shown to exist in the alkaline earth fluorides MF₂ (M = Ca, Sr, Ba) doped with R = Sc, Y, Lu, Ho when these crystals have been hydrolyzed and subsequently X-rayed. The centers were identified with the aid of Raman spectroscopy and, in the past, with electron paramagnetic resonance (EPR).     

M(SCN)2 (M = Eu,Sr, Ba): Kristallstruktur,thermisches Verhalten,Schwingungsspektroskopie

M(SCN)₂ (M = Eu, Sr, Ba): Crystal Structure, Thermal Behaviour, Vibrational Spectroscopy Single crystals of M(SCN)₂ (M = Eu, Sr, Ba) have been obtained via metathesis of NaSCN and MCl₂ (M = Eu, Sr, Ba) at 340 °C. The isotypic crystal structures of the thiocyanates M(SCN)₂ (C2/c, Z = 4, Eu: a = 979.3(2), b = 660.8(1), c = 815.7(2) pm, β = 91.58(3)°, R_all = 0.0245, Sr: a = 985.5(2), b = 662.9(2), c = 819.6(2) pm, β = 91.29(3)°, R_all = 0.0435, Ba: a = 1018.8(2), b = 687.2(1), c = 852.2(1) pm, β = 92.43(2)°, R_all = 0.0392) contain alternating layers of M²⁺ and SCN^–. According to M(SCN)_4/4(NCS)_4/4 M²⁺ is eight‐coordinated by four sulfur and four nitrogen atoms forming a square antiprism. Thermal investigations show that the compounds melt without decomposition. Vibrational spectroscopic investigations are presented and discussed.     

Role of interlayer M k atoms and H2O molecules in the structure formation of M k (VUO6) k · nH2O uranovanadates

M ^k (VUO₆) _k · nH₂O uranovanadates of alkali (Li, Na, K, Rb, Cs), alkaline-earth (Mg, Ca, Sr, Ba), 3d transition (Mn, Fe, Co, Ni, Cu, Zn), and rare-earth (Y, La, Ln) elements were prepared by precipitation from solutions under hydrothermal conditions and in solid-phase reactions. The composition and structure of these compounds and the role of M ^k atoms and H₂O molecules in the formation of their structure were studied by X-ray diffraction, IR-spectroscopy, thermal analysis, and chemical analysis.     

The crystal and magnetic structures of Ca2YRuO6 and the electronic properties of the series M2+2X3+Ru5+O6 (M = Ca,Sr, Ba; X = La,Y)

Profile analysis of constant-wavelength powder neutron diffraction data has been used to refine the crystal structure of the ordered perovskite Ca₂YRuO₆. The material is monoclinic (space group $\text{P2}{}_1\text{n}$) with a disordered arrangement of calcium and yttrium on the A site and one of the B sites, such that the formula is best written as Ca_1.43Y_0.57[(Ca_0.57Y_0.43)Ru]O₆. Low-temperature neutron diffraction experiments showed that the material is a Type I antiferromagnet at 2.5 K with an ordered magnetic moment of 1.2(1)μ_B per Ru⁵⁺. It is suggested that the dominant factor in determining the electronic properties of the series M²⁺₂X³⁺Ru⁵⁺O₆ (M = Ca, Sr, Ba; X = La, Y) is the Ru-Ru separation distance.     

Crystal Structures and Magnetic Properties of 6H-Perovskites Ba3MRu2O9 (M=Y, In, La, Sm, Eu, and Lu)

Magnetic properties of quaternary oxides Ba₃MRu₂O₉ (M=Y, In, La, Sm, Eu, and Lu) are reported. Rietveld analyses of the X-ray diffraction data indicate that they adopt the 6H-perovskite structure and have the valence state of Ba₃M³⁺ Ru^4.5+₂O₉. All compounds are nonmetallic at least over the temperature range of 100-400 K. The magnetic susceptibilities show a broad maximum at 135-370 K except for the La compound, which shows a plateau around 22 K. In addition, another magnetic anomaly is observed at 4.5-12.5 K by the magnetic susceptibility and specific heat measurements for any compound. It is considered that this magnetic behavior is ascribed to the antiferromagnetic coupling between two Ru ions in a Ru₂O₉ dimer and to the magnetic interaction between the Ru₂O₉ dimers.     

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.     

Lead phosphate apatites substituted by rare earth,sodium, and potassium ions

Rare earth-substituted lead apatites of the Pb_10?2xLn_xM_x(PO₄)₆Y₂(Ln = La, Nd, Eu, Gd, Dy, and Y: M = Na and K; Y = F and Cl) systems were prepared and studied by X-ray diffraction and infrared methods. The powder patterns of all the compounds show the apatite-like hexagonal structure. Singlecrystal precession data reveal that the space group of the Pb₆Ln₂Na₂(PO₄)₆F₂ compounds is probably $\text{P}\text{6}$ while that of Pb₆Ln₂K₂(PO₄)₆F₂ is $\text{P6}{}_3\text{m}$. Analysis of the ir spectra of substituted Ca, Ba, and Pb compounds show the effect of substituted ions on the spectra and support the assumption that substitution in the Ba and Pb systems is an ordered process. Ordering of the substituted ions in the systems studied is discussed in view of changes in lattice parameters, size conditions, and polarizing properties of the ions.     

Modeling of formula types of fluorite-like isomorphism products in MF2-RF3 systems

A new conceptual model of heterovalent isomorphism is advanced for use in the theoretical investigations of compositions of solid solutions (hereafter, ss) known as nonstoichiometric phases of variable composition M_{1 ? x} R_xF_{2 + x} with a distorted fluorite structure. This model is based on several postulates and starting conditions; the schemes of reciprocal heterovalent substitutions following from them allow one to calculate formula types for theoretically possible isomorphism products. Ignoring the chemical individuality of atomic species at the sites of the crystal lattice, this simplest model is mostly hypothetical. However, this approach allows us to interpret from the general standpoint and systematize the experimental data of many researchers; it also allows us to explain some phenomena associated with heterovalent isomorphism in the systems MF₂-RF₃, where M = Ca, Sr, or Ba and R = Y, La, or Ln(III).     

Über den Einfluß von Temperatur,Druck und Substitution auf die Kristallstruktur von ARh2P2 (A = Ca,Sr, Eu,Ba)

About the Effect of Temperature, Pressure, and Substitution on the Crystal Structure of ARh₂P₂ (A = Ca, Sr, Eu, Ba) Four compounds ARh₂P₂ (A = Ca, Sr, Eu, Ba) were prepared by heating mixtures of the elements and investigated by means of single crystal X-ray methods. They crystallize in the ThCr₂Si₂ type structure (I4/mmm; Z = 2) with P? P distances along [001] reaching from 2.26 Å (CaRh₂P₂) to 3.74 Å (BaRh₂P₂). With increasing temperature (EuRh₂P₂) or increasing pressure (SrRh₂P₂) a first order phase transition occurs with strong changes of the P? P distances. Substitution of the atoms changes the bond lengths of the compounds too.     

Rare-earth-substituted chloro-phosphate apatites

Compositions with the general formula Ln_xM_10?2xNa_x(PO₄)₆Cl₂ (Ln = Pr, Nd, Sm, Eu, Dy, Ho and Y; M = Ca, Sr, Ba, and Pb) have been prepared and studied by X-ray diffraction methods. The limited extent of rare earth substitution observed in chlorapatites in comparison to fluorapatites is attributed to the structural differences of the two systems.     

New Y(La)-M-O Binary Systems (M = Ca,Sr, or Ba): Synthesis,Physicochemical Characterization,and Application As the Supports of Ruthenium Catalysts for Ammonia Synthesis

The effect of the nature of the alkaline-earth metal on the phase composition and specific surface area of new Y(La)-M-O binary oxide compositions (M = Ca, Sr, or Ba) prepared by coprecipitation was studied. These systems were found to contain mixed compounds (M₂Y₂O₅, MY₂O₄, and MLa₂O₄), which are different in thermal stability, in addition to individual La₂O₃ or Y₂O₃ phases. The Y(La)-M-O compositions calcined at 450°C were characterized by a more developed specific surface area, as compared with that of individual La₂O₃ or Y₂O₃. An increase in the calcination temperature to 650°C was accompanied by a decrease in the specific surface area of binary compositions. Catalysts prepared by supporting K₂[Ru₄(CO)₁₃] onto the Y(La)-M-O systems were active in ammonia synthesis at 250-400°C and atmospheric pressure. The most active of these catalysts, K₂[Ru₄(CO)₁₃]/Y-Ba-O, provided a higher yield of NH₃ at 250-300°C than analogous catalysts prepared with the use of well-known supports (Sibunit, CFC-1, and C/MgO).     

Ternary phases MPtSi (M = Ca,Eu, Sr,Ba) with the LalrSi-type structure

Four ternary phases MPtSi (M = Ca, Eu, Sr, Ba) have been shown to crystallize in the LaIrSi-type structure (space group P2₁3). This ternary structure is a derivative structure of the binary SrSi₂-type structure (space group P4₃32 or P4₁32). In the MPtSi series the LaIrSi-type structure has a stability range for metals with radii from r_Ca = 1.973 Å to r_Ba = 2.243 Å in contrast to MSi₂ compounds which exist with the SrSi₂-type structure only from r_Sr = 2.151Å to r_Ba 2.243 Å. From a single-crystal investigation on CaPtSi remarkably short PtSi distances of 2.30 Å (3x) are obtained. Structural relations are discussed.     

A study on mixed halide compounds MFX (M = Ca,Sr, Eu,Ba; X = Cl,Br, I)

MFX (M = Ca, Sr, Eu, Ba; X = Cl, Br, I) compounds have been prepared by solid-state reaction. Lattice parameters and X-ray diffraction patterns are presented for these compounds, which are all isostructural with tetragonal PbFCl. Attempts to synthesize solid solutions of Sr(Eu)FCl and of MFCl compounds with several rare earth oxychlorides are reported. The crystal chemistry of MFX, MHX, and LnOX compounds is briefly discussed in comparison, and the observed $\text{c}\text{a}$ ratios are interpreted on the basis of electrostatic calculations.     

Charge disorder effects in 3d transition metal oxide perovskites

The effects of the random electrostatic potential due to differences in formal charge between A site R³⁺ (lanthanide, Y), M²⁺ (Ca, Sr, Ba) and Th⁴⁺ cations have been investigated in ferromagnetic AMnO₃ and superconducting A₂CuO₄ perovskites. Series of samples in which the mean A site charge and the mean and variance of the A cation radius distribution are held constant, but the A site charge variance increases, show no significant changes of the electronic (Curie or superconducting) transition temperatures. The effect of the A cation random potentials on electronic transitions in the 3d metal oxide perovskites are insignificant in comparison to the lattice effects from the differing cation sizes.     

On the characterization of BiMO2NO3 (M=Pb, Ca, Sr, Ba) materials related with the Sillén X1 structure

The compounds BiMO₂NO₃, with M=Pb, Ca, Sr, and Ba, were obtained as single-phase products from solid-state reactions in an atmosphere of nitrous gases. The oxide nitrates with Pb and Ca crystallize in the tetragonal space group I4/mmm with two formula units per unit cell; the oxide nitrates with Sr and Ba crystallize in the orthorhombic space group Cmmm with four formula units per unit cell. Lattice parameters at room temperature are a=397.199(4), c=1482.57(2) pm for M=Pb; a=396.337(5), c=1412.83(3) pm for M=Ca; a=1448.76(3), b=567.62(1), c=582.40(1) pm for M=Sr and a=1536.50(8), b=571.67(3), c=597.55(3) pm for M=Ba. The structures, which were refined by powder X-ray diffraction, consist of alternating [BiMO₂]⁺ and [NO₃]⁻ layers stacked along the direction of the long axis. IR and thermogravimetric data are also given. The various M²⁺ cations in BiMO₂NO₃ are compatible with each other; therefore and because of their layer-type structure, these compounds are interesting precursors for oxide materials, e.g., the HTSC compounds (Bi,Pb)₂Sr₂Ca_n−1Cu_nO_x.     

99Ru Mössbauer spectra of quaternary ruthenium(V) oxides with the hexagonal barium titanate structure

⁹⁹Ru Mössbauer spectra have been recorded at 4.2 K for the quaternary oxides Ba₃Ru₂MO₉ (M = Mg, Ca, Sr; Co, Ni, Cu, Zn; and Cd), all of which crystallize with the hexagonal barium titanate structure. The Ca, Sr, and Cd compounds give sharp symmetrical singlets with chemical isomer shifts typical of ruthenium in the +5 oxidation state. The absence of magnetic hyperfine splitting is consistent with the published interpretation of magnetic susceptibility data in terms of binuclear intracluster spin pairing which leads to an S = 0 ground state. In contrast, magnetic hyperfine splitting is seen for the Mg, Zn, Co, Ni, and Cu compounds; this can be interpreted only in terms of long-range magnetic order and the absence of such an S = 0 ground state at 4.2 K. This differs from the published interpretation of the magnetic susceptibility data for Ba₃Ru₂MgO₉ in the low-temperature region. The magnetic flux densities at the ruthenium nuclei in the magnetically ordered compounds (32.5–51.6 T) are lower than those normally associated with ruthenium(V), and the spectra cannot be curve fitted satisfactorily with single hyperfine patterns having the natural linewidth. Possible reasons for these observations are discussed.     

Crystal Structure and Electrical Conductivity of Palladium Sulfide BronzesMP3S4(M=La,Nd, and Eu)

Palladium sulfide bronzesMPd₃S₄(M=La, Nd, and Eu) were prepared in single phase. The bronzes are cubic with twoMatoms in (0,0,0; 1/2,1/2,1/2) and six palladium atoms in (1/4,0,1/2⥀) positions. The sulfur positions (x,x,x⥀) were determined with a guide of theRfactors. Thexvalues were 1/4 for La and Nd compounds (i.e., space groupPm3n), while a plot of theRfactors of EuPd₃S₄gave a very broad curve showing thexvalue rather displaced from 1/4. This result is considered to be associated with the mixed valency of europium (Eu²⁺and Eu³⁺) in this compound.MPd₃S₄(M=La, Nd, and Eu) exhibited metallic conductions with the electrical conductivities decreasing with increasing temperature in the experimental range from ∼15 K to room temperature. At 300 K, σ were 2.77, 2.42, and 2.28 S m⁻¹forMPd₃S₄(M=La, Nd, and Eu), respectively. From the Hall coefficient measurements, the carriers were found to be the electrons with their numbers 1.71, 1.68, and 0.82 per unit cell of the crystals ofM=La, Nd, and Eu compounds, respectively. These values suggest the formulas to beM³⁺(Pd²⁺₃e⁻)S²⁻₄for La and Nd compounds, and to be Eu²⁺_0.5Eu³⁺_0.5(Pd²⁺₃e⁻_0.5)S²⁻₄for Eu compound.     

Polymerization by alkaline earth metal compounds—I. Studies on the polymerization of methylmethacrylate by triphenylmethyl metal derivatives and related compounds of calcium,strontium and barium

A series of related organo-alkaline earth metal compounds of formula (Ph₃C)MX(THF)_η, (M = Ca, Sr, Ba; X = Cl: M = Ca, Sr; X = Br: M = Ba; X = CPh₃), has been isolated and characterized using analytical and spectroscopic techniques. The polymerization of methylmethacrylate (MMA) has been studied using these organometallic compounds as initiators. Investigations of the tacticity variations of polymethylmethacrylate (PMMA) produced in 1,2-dimethoxyethane or tetrahydrofuran (THF) at 210 K have shown that the syndiotacticity is higher in the former solvent, decreases with the following changes in initiator composition: Ca > Sr ? Ba; Cl > Br; in THF, it is dependent on the monomer concentration. The molecular weight distributions of the PMMA samples are broad and have distinct bi- or poly-modal features. The polymerization process appears to be anionic in nature but the evidence suggests that more than one type of propagation occurs and mechanistic aspects are discussed. Polymerization of bulk MMA by these same initiators is also reported. The initiators RMX(THF)_n (M = Sr, R = Me, n = 3 or R = Et, n = 2) and (C₃H₅)SrBr(THF)₂ are shown to be inefficient for polymerization of MMA. The glass transition temperatures of a range of PMMA samples of differing tacticity are presented and discussed.