Synthese et structure du sulfate double MSbF2SO4 (M = Rb,Cs)

The crystal structure of RbSbF₂SO₄ has been determined on a single crystal (R = 0.078 for 710 reflections). The structure shows sulfate anions distorted by the SOSb bonds. The antimony atom is from an SbF₂ unit. This antimony dihalogen is from the family of the $\text{1}\text{1}$ compounds which are in MX₃SbX₃ (M = Al, Ga, In) (X = Cl, Br) systems.     

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.     

New pseudo-one-dimensional metals: M2Mo6Se6 (M = Na,In, K,TI), M2Mo6S6 (M = K,Rb, Cs), M2Mo6Te6 (M = In,TI)

We present a new series of ternary chalcogenides, derived from divalent molybdenum: M₂Mo₆X₆. These compounds crystallize in a hexagonal lattice with a ≈ 9 Å, c ≈ 4.5 Å, and space group $\text{P6}{}_3\text{m}$. The compounds are characterized by clusters (Mo₃)¹_∞ in the form of linear chains, resulting from a linear condensation of Mo₆ octahedral clusters. The (Mo₃)¹_∞ clusters are well separated from each other, with the shortest MoMo intercluster distance larger than 6 Å. The resulting pseudo-one-dimensional structures show remarkable anisotropy of physical properties.     

Ln(GaM2+)O4 and Ln(AlMn2+)O4 compounds having a layer structure [Ln = Lu,Yb, Tm,Er, Ho,and Y,and M = Mg,Mn, Co,Cu, and Zn]

A series of new compounds Ln(GaM²⁺)O₄ and Ln(AlMn²⁺)O₄ having a layer structure were successfully prepared [Ln = Lu, Yb, Tm, Er, Ho, and Y, and M = Mg, Mn, Co, Cu, and Zn]. The synthesis conditions and the unit cell parameters for 23 compounds have been determined. These compounds are isostructural with YbFe₂O₄ (space group $\text{R}\text{3}\text{m, a = 3.455(1)}$ Å, and c = 25.109(2) Å).     

Les phases SrLnMnO4 (Ln = La,Nd, Sm,Gd), BaLnMnO4 (Ln = La,Nd) et M1+xLa1−xMnO4 (M = Sr,Ba)

The phases SrLnMnO₄ (Ln = La, Nd, Sm, Gd), BaLnMnO₄ (Ln = La, Nd) and the solid solutions M_1+xLa_1?xMnO₄ (M = Sr: 0 ? x ? 1; M = Ba: 0 ? x ? 0.50) have a K₂NiF₄-type structure. The $\text{c}\text{a}$ ratio of the unit cell is related to the electronic configuration of the Mn³⁺ ions.     

Intergrowth of hexagonal tungsten bronze and perovskite-like structures: The oxides ACu3M7O21 (A = K,Rb, Cs,TI; M = Nb,Ta)

Seven oxides ACu₃M₇O₂₁ have been isolated with A = K, Rb, Tl, Cs for M = Ta and A = K, Rb, Cs for M = Nb. These phases are orthorhombic: $\text{a ? 28}$ Å, $\text{b ? 7.50}$ Å, and $\text{c ? 7.55}$ Å, probable space group Cmmm. Their structure has been established from an X-ray diffraction study and from high-resolution microscopy observations. The structure consists of an intergrowth of single hexagonal tungsten bronze AM₃O₉ slices and double distorted perovskite Cu₃M₄O₁₂ slabs (M = Nb, Ta) in which copper has a square coordination. The host lattice of these compounds can be considered as the member “n = 1; n′ = 2” of a series of intergrowths corresponding to the formulation |M₃O₉|^H_n|M₂O₆|^P_n′.     

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.     

Magnetic superexchange involving tetrahedral anions: One-dimensional antiferromagnetic interactions via sulfate anions in M(2,9-di-CH3-1,10-phenanthroline)SO4 (M = Mn,Fe, Co,Ni, Cu)

The magnetic susceptibilities of powder samples of the polymeric compounds M(dmp)SO₄ (M = Mn, Fe, Co, Ni, Cu; dmp = 2,9-di-CH₃-1,10-phenanthroline) have now been studied at temperatures between 1.5 and 305 K. There is clear evidence of one-dimensional, antiferromagnetic interactions in the Mn, Fe, Co, and Ni compounds: from $\text{T ? 300}\text{to}\text{1.7}\text{K}$, the magnetic moment decreases steadily from a value that is approximately the spin-only moment of the high-spin configuration to a value that is ～20% of the spin-only moment, and the susceptibility-vs-temperature curve contains a broad maximum atT ≤ 30 K. Cu(dmp)SO₄, however, exhibits almost perfect Curie-Weiss paramagnetism. These results when combined with the results of various spectroscopic studies lead to proposed molecular structures (chainlike polymers of cis-MN₂O₄ chromophores and bridging-chelating sulfates) and estimated energies of intrachain antiferromagnetic exchange ($\text{?0.5}\text{K}\text{≥}\text{J}\text{k}{}_{\mathrm{<mtext>B</mtext>}}\text{≥ ?10}\text{K}$).     

Etude des equilibres solide-liquide des systems MIPO3Sm(PO3)3 (MI = Li,Na, Ag)

The M^IPO₃Sm(PO₃)₃(M^I = Li, Na, Ag) systems were studied. Differential thermal analysis and X-ray diffraction were used to investigate the liquidus and solidus relations. Three compounds LiSm(PO₃)₄, NaSm(PO₃)₄, and AgSm(PO₃)₄ were obtained which melt incongruently at 1248, 1143, and 1078 K, respectively. These compounds are isomorphous with their homologs LiLn(PO₃)₄, NaLn(PO₃)₄, AgLn(PO₃)₄ (Ln = Ce, La, Nd). They belong to the monoclinic system. The LiSm(PO₃)₄ unit cell parameters refined by least squares method are a = 16.43(3) Å, b = 7.16(1) Å, c = 9.65(3) Å, β = 125,9°(1), with the space group $\text{C2}\text{c}$ and Z = 4. NaSm(PO₃)₄ and AgSm(PO₃)₄ are isotypic; they cristallize in the $\text{P2}{}_1\text{c}$ space group, Z = 4; their unit cell parameters are, respectively, a = 12.18(1) Å, b = 13.05(1) Å, c = 7.25(5) Å, β = 126,53°(4), $\text{a = 12.25(1)}\text{A}\text{?}$, b = 13.06(1) Å, c = 7.201(9) Å, β = 126,57°(7). The ir spectra of the last two compounds indicate that these phosphates are chain phosphates.     

Synthesis and Crystal Structure of M11X10 Compounds, M=Sr, Ba and X=Bi, Sb. Electronic Requirements and Chemical Bonding

The intermetallic compounds Sr₁₁Bi₁₀, Ba₁₁Bi₁₀, and (Sr₅Ba₆)Sb₁₀ have been obtained from melts of mixtures of the elements. They crystallize in the tetragonal system, space group I4/mmm, Ho₁₁Ge₁₀ structure type, tI84 Pearson symbol, Z=4, with cell parameters a=12.765(3), 13.230(3), 12.748(2) Å and c=18.407(3), 19.365(3), 18.761(2) Å, respectively. The structures were solved from single-crystal X-ray data and refined by full-matrix least-squares to R1=6.71, 5.44, and 5.73%. The structure of M₁₁X₁₀ contains three discrete anionic moieties: square rings X⁴⁻₄, dumbbells X⁴⁻₂, and isolated X³⁻. Using formal charges the unit cell of M₁₁X₁₀ may be described as containing 44 M²⁺, 2X⁴⁻₄, 8X⁴⁻₂, and 16X³⁻ ions. This structure is discussed in comparison with other Bi or Sb pnictide compounds. Bonding is analyzed therein using molecular orbital (EHMO) calculations for the anions (dumbbell and square units) and also the periodic tight-binding method. Lone pair repulsions inside and between the anionic units are evidenced; they are compensated by strong bonding cation-to-anion interactions. Interatomic distances along the series appear to be more dependent on packing than on electronic effects.     

Crystallography and phase relations of MeOM2O3TiO2 systems (Me = Fe,Mg, Ni; M = Al,Cr, Fe)

Subsolidus phase relations of ternary oxide systems containing divalent Fe, Mg, or Ni, trivalent Al, Cr, or Fe, and tetravalent Ti are characterized by solid solutions at metal/oxygen ratios $\text{3}\text{4}$, $\text{2}\text{3}$, and $\text{3}\text{5}$. At low temperatures only compounds with cubic or hexagonal close-packed oxygen and uniform oxygen coordination remain stable in the crystal structures NaCl, spinel, ilmenite-α-Al₂O₃, TiO₂. The pseudobrookite phases FeTi₂O₅, MgTi₂O₅, Al₂TiO₅, Fe₂TiO₅, the V₃O₅ structure phase Cr₂TiO₅, and the Andersson phases Cr₂Ti_n?2O_2n?1 (n = 4,6,7,8,9) decompose. Additional phases with close-packed oxygen as predicted by a simple structure model for metal/oxygen ratios $\text{7}\text{12}$, $\text{5}\text{6}$, and $\text{11}\text{12}$ do not form but presumably are important for nonstoichiometric solid solutions. Most differences between systems containing transition metals and the MgOAl₂O₃TiO₂ system can be attributed to crystal field effects.     

Luminescent properties of Nd3+ in the NaxNdxM(1−2x)Ga2S4 thiogallates (M = Ca,Sr,Ba; x ≤ 0.5): A family of materials characterized by weak self-quenching and efficient band excitation

As a consequence of the weak phonon energies and the low crystal field, several excited states of Nd³⁺ are emitters in the Na_xNd_xM_1?2xGa₂G₄ thiogallates (x ≤ 0.5 for M = Ca or Sr and ≤0.2 for M = Ba). The infrared ${}^4\text{F}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ emission is little affected by concentration quenching. NaNdGa₄S₈ is the first efficient stoichiometric sulfide so far reported. Unlike other sulfides previously investigated, the neodymium thiogallates show an intense excitation band, ascribed to electron transfer from the valence band to states constituted essentially by neodymium orbitals.     

Etude à haute pression des tétramétaphosphates du type M2P4O12 (M = Ni,Mg, Cu,Co, Fe,Mn, Cd). Données cristallographiques sur tous les composés M2P4O12

Fe₂P₄O₁₂ has been prepared and identified as an isotype of the other M^II₂P₄O₁₂ tetrametaphosphates (M^II = Ni, Mg, Cu, Co, Mn, Cd). Its monoclinic unit cell:

$\text{a=11.952,b=8.359,c=9.932}\text{A}\text{?}$

$\text{β=118°76}$

contains 4 formula units. The space group is $\text{C2}\text{c}$. For tetrametaphosphates with M^II = Ni, Mg, Cu, Co, and Mn we found a new denser phase induced at 80 kbar and 1000°C. In the case of Fe₂P₄O₁₂ the unit cell of this new form is

$\text{a=9.777,b=8.994,c=4.968}\text{A}\text{?}$

$\text{β=107°22}$

with Z = 2 and two possible space groups Cc or $\text{2C}\text{c}$. This dense phase exists at ordinary pressure for the zinc salt.     

Single-Crystal Growth and Classification of EuAlF5 and Solid Solutions M(II)1−xEuxAlF5 (M=Ca, Sr, Ba) within the Structural Family of Tetragonal M(II)M(III)F5 Compounds

The compound EuAlF₅, as well as the solid solutions Ca_0.19(1)Eu_0.81(1)AlF₅, Sr_0.15(1)Eu_0.85(1)AlF₅, Sr_0.55(1)Eu_0.45(1)AlF₅, Sr_0.77(1)Eu_0.23(1)AlF₅, and Ba_0.62(1)Eu_0.38(1)AlF₅, crystallize in colorless tetragonal columns. These have been prepared by solid state reactions at 900°C, starting from mixtures of the binary fluorides. According to Vegard's rule the solid solution Sr_1−xEu_xAlF₅ shows a linear dependence of the crystal volume on the molar ratio Eu/Sr. All crystal structures have been refined from single-crystal diffractometer data. EuAlF₅ and the M_1−xEu_xAlF₅ (M=Ca, Sr) compounds obtained are isotypic with β-SrAlF₅. They crystallize in a superstructure in space group I4₁/a (no. 88) with 64 formula units and lattice parameters a≈19.9 Å, c≈14.3 Å. The structure is characterized by chains of trans-corner-sharing [AlF_4/2F_2/1] and branched [AlF_5/1F_1/2] octahedra forming a channel structure. Inside the channels isolated ordered dimeric units [AlF_4/1F_2/2]₂ are located. The divalent metal atoms show coordination numbers 8 and 9; they connect the [AlF₆] octahedra into a three-dimensional structure. Ba_0.62(1)Eu_0.38(1)AlF₅ is isotypic with the corresponding Sr compound Ba_0.43(1)Sr_0.57(1)AlF₅, and it crystallizes with 16 formula units and lattice parameters a=14.3860(7) Å, c=7.2778(3) Å in space group I4/m (no. 87). The network structure is identical with that of EuAlF₅. Instead of the dimeric units, infinite chains [AlF_4/1F_2/2]_∞ of trans-corner-sharing [AlF₆] octahedra extending along the c- axis are located inside the channels. The bridging fluorine atoms of this chain show large anisotropic displacement parameters, but no superstructure reflections have been observed for this compound.     

Synthesis and structure of a new family of phases, A2MGe5O12: A = Rb,Cs; M = Be,Mg, Co,Zn

A new family of eight germanate phases, A₂MGe₅O₁₂: A = Rb, Cs; M = Be, Mg, Co, Zn, has been synthesized. They are cubic with a in the range 13.7 to 14.0 Å, Z = 8, and space group $\text{I}\text{4}\text{3d}$. These phases, named the β phases, are isostructural with KBSi₂O₆ which has a structure related to that of pollucite, CsAlSi₂O₆. The structure of one, Rb₂ZnGe₅O₁₂, has been refined to an R value of 0.079 using X-ray powder diffraction data. Several of the new phases are polymorphic. Cs₂ZnGe₅O₁₂, Cs₂CoGe₅O₁₂, and Rb₂MgGe₅O₁₂ form low-temperature, δ polymorphs which have primitive cubic unit cells. Rb₂ZnGe₅O₁₂ forms a low-temperature, ε polymorph which is probably a tetragonal distortion of the β structure.     

Etude structurale des composés MxTiSe2 (M = Fe,Co, Ni)

New compounds M_xTiSe₂ have been prepared with M = Fe (x ? 0.66), M = Co or Ni (x ? 0.50). The metal M is located in vacant octahedral sites of the TiSe₂ host lattice (hexagonal unit cell a′, c′). An ordering of vacancies occurs if x ? 0.20. With M = Co or Ni (x = 0.50) and with M = Fe (0.25 ? x ? 0.66) isotypic compounds of Ti₃Se₄ can be obtained (M₃ □ X₄ type; monoclinic unit cell a ≈ a′ √3, b ≈ a′, c ≈ 2c′). The compounds Fe_0.38TiSe₂ and Co_0.38TiSe₂ (hexagonal unit cell a ≈ a′ √3, c ≈ 2c′) are of the M₂ □ X₃ type, variety 2c′. The Fe_0.25TiSe₂ and Co_0.25TiSe₂ monoclinic unit cells (a ≈ 2a′ √3, b ≈ 2a′, c ≈ 2c′) allow us to assume, for these two compounds, a structure of the M₅ □ ₃X₈ type, variety 2c′, identical to the Ti₅Se₈ one. The compound Ni_0.25TiSe₂ has an hexagonal unit cell (a ≈ 2a′, c ≈ 3c′); it belongs to a so-called 3c′ variety of the M₅ □ ₃X₈ type.     

Synthesis, structure and physical properties of layered semiconductors MCuFCh (M=Sr, Eu, Ch=S, Se)

Effects of open shell cations on magnetic, optical and carrier transport properties were examined for layered wide bandgap semiconductors MCuFCh (M=Sr, Eu, Ch=S, Se). Single-phase MCuFCh powder and ceramic samples were synthesized by solid-state reactions. The crystal structures refined by the Rietveld analyzes revealed that all the materials have the space group P4/nmm, indicating that the samples have the same crystal structure as that of layered oxychalcogenides LaCuOCh, and cation vacancies of several percent were present for Cu⁺ and Eu²⁺ sites in EuCuFCh. Thermopower measurements revealed that both SrCuFCh and EuCuFCh were p-type semiconductors. Degenerate conduction was observed for EuCuFCh with conductivities >1 S cm⁻¹, whereas SrCuFCh exhibited thermally activated behavior. The optical band gaps of SrCuFS and SrCuFSe estimated were approximately 3.0 and 2.7 eV, respectively, and those of EuCuFCh were ∼2 eV. Temperature dependence of magnetic susceptibilities of EuCuFCh followed the Curie-Weiss law down to 5 K and the samples did not show any transition to a magnetic ordering phase.     

Magnetic order in AVX3 (A = Rb,Cs, (CD3)4 N; X = Cl,Br, I): A neutron diffraction study

AVX₃ (A = Rb, Cs, (CD₃)₄ N; X = Cl, Br, I) crystallize in the hexagonal system, space group $\text{P6}{}_3\text{mmc}$, with chains of face-sharing VX₆ octahedra along the c-axis. This leads to a pronounced one-dimensional character of their magnetic properties with a strong antiferromagnetic exchange interaction J between nearest neighbor V²⁺ ions along these chains. All compounds except [(CD₃)₄N]VCl₃ order three-dimensionally with ordering temperatures T_c between 13 and 32 K. In the ordered phase the magnetic moments, μ, lie in the basal plane in a triangular arrangement typical for antiferromagnetic interchain interaction J′.     

Application de la spectrometrie vibrationnelle à un probleme de non-stoechiométrie par insertion dans les tunnels pentagonaux des réseaux (M6X4O26) (M = Nb,Ta; X = Si,Ge)

The ir spectra of A₃M₆Si₄O₂₆ (A = Ba, Sr; M = Nb, Ta) and K₆M₆Si₄O₂₆ oxides, whose structure contains linear Si₂O₇ groups, are discussed with particular emphasis on the peculiar behavior of the antisymmetric stretching frequency of the linear SiOSi bridge. In accord with previous data, this frequency is the highest of the spectrum (near 1200 cm^?1), but it is significantly lowered (by about 75 cm^?1) when passing from the A₃M₆Si₂₄O₂₆ to the K₆M₆Si₄O₂₆ compounds. This is readily explained by the peculiar structure of the K₆ compounds, in which three (out of the six) K⁺ cations are located near the bridge oxygen (A₂ sites), these sites remaining empty in the A₃M₆Si₄O₂₆ compounds. The resulting KO bonding weakens the SiO bond, thus leading to a lowering of the corresponding bridge frequency. The same type of explanation holds for the presence of a new band at an intermediate frequency (about 1150 cm^?1) in phases of intermediate composition K_6?2xBa_xM₆Si₄O₂₆, this new band being correlated with a partial occupancy of the A₂ sites. This has been applied to, and is a sensitive means of, detecting nonstoichiometry in the A₂ sites of other compounds with (M₆X₄O₂₆) layers (X = Si, Ge) such as Ba_6+xNb₁₄Si₄O₄₇, K₈M₁₄Si₄O₄₇, and K₁₀M₂₂X₄O₆₈ (M = Nb, Ta).     

Hexagonal-spinel transitions in antimonates Li2Cr3−xMIIIxSbO8 (MIII = Al,Fe, Ga)

A new family of antimonates Li₂Cr_3?xM^III_xSbO₈ (M^III = Al, Fe, Ga) was synthesized and studied by X-ray diffraction and ir spectroscopy. The Al-containing compounds exhibit a hexagonal close-packed structure similar to that of LiFeSnO₄ ($\text{a ? 5.8, c ? 9.5}$ Å. For M = Fe or Ga, two structural forms are isolated: a low-temperature hexagonal form which is isotypic with LiFeSnO₄ and a high-temperature cubic form isotypic with the spinel structure. The hexagonal spinel transformation was observed for the first time, while the reverse transformation cannot be obtained.