Etienne Gaudin

Synthesis and characterization of the crystal structure and magnetic properties of the ternary manganese vanadate NaMnVO4.

A new ternary manganese vanadate, NaMnVO(4), was synthesized by solid state reaction route, and its crystal structure and magnetic properties were characterized by X-ray diffraction, magnetic susceptibility and specific heat measurements, and by density functional calculations. NaMnVO(4) crystallizes in the maricite-type structure with space group Pnma, a = 9.563(1) A, b = 6.882(1) A, c = 5.316(1) A, and Z = 4. NaMnVO(4) contains MnO(4) chains made up of edge-sharing MnO(6) octahedra, and these chains are interlinked by VO(4) tetrahedra. The magnetic susceptibility has a broad maximum at T(max) = 24 K and follows the Curie-Weiss behavior above 70 K with θ = -62 K. NaMnVO(4) undergoes a three-dimensional antiferromagnetic ordering at T(N) = 11.8 K. The spin exchanges of NaMnVO(4) are dominated by the intrachain antiferromagnetic exchange, and the interchain spin exchanges are spin-frustrated. The most probable magnetic structure of the ordered magnetic state below T(N) was predicted on the basis of the extracted spin exchanges.

On the strongly correlated electron hydride Ce2Ni2MgH7.7.

The intermediate valence compound Ce 2Ni 2Mg absorbs irreversibly hydrogen when exposed under 1 MPa of H 2 pressure at room temperature. The resulting hydride Ce 2Ni 2MgH 7.7 is stable in air and crystallizes as the deuteride La 2Ni 2MgD 8 in a monoclinic structure (space group P2 1 /c) with the unit cell parameters a = 11.7620(2), b = 7.7687(2), and c = 11.8969(2) A and beta = 92.75 degrees . The H-insertion in Ce 2Ni 2Mg induces a structural transition from a tetragonal to a monoclinic symmetry with an unit cell volume expansion Delta V m/ V m approximately 24.9%. The investigation of the hydride by magnetization, electrical resistivity, and specific heat measurements indicates a change from an intermediate valence behavior to a non-magnetic strongly correlated electron system. This transition results from a change of the coupling constant J cf between 4f(Ce) and conduction electrons induced by the hydrogenation.

(3 + 1)D superspace structural determination of two new modulated composite phases: Sr1+x(CuxMn1-x )O3; x = 3/11 and x = 0.3244

Abstract We report the structure determination of two new phases belonging to the A1+x(A′xB1−x)O3 family of oxides with A=Sr, A′=Cu, and B=Mn, where x=3/11 and x=0.3244, corresponding to a commensurate and incommensurate composite structure, respectively. These two compounds are the first examples of oxides belonging to the Sr1+x(CuxMn1−x)O3 family. Their structures were solved in the (3+1) dimensional superspace formalism as modulated composite structures with two subsystems [(Cu,Mn)O3] and [Sr]. The superspace group used to solve the structures is R 3 m(00γ)0s . The first phase (x=3/11), corresponding to the chemical formula Sr14Cu3Mn8O33, was obtained as a single crystal with unit cell parameters of a=9.6025(3) A and c1=2.5660(8) A ( q =7/11 c 1 ∗ , Z=3), where c1 is the lattice parameter corresponding to the c-axis of the trigonal subsystem [(Cu,Mn)O3]. The second phase (x=0.3244(1)), is a polycrystalline sample with unit cell parameters of a=9.5933(7) and c1=2.5933(3) ( q =0.6622 c 1 ∗ , Z=3). In both structures, one dimensional chains run along the c-axis which contain octahedra and trigonal prisms occupied by manganese and copper atoms, respectively. The refinement results show that in both cases copper occupies the rectangular faces of the trigonal prism while manganese occupies the octahedral sites. The magnetic measurements of the polycrystalline phase (Sr1+x(CuxMn1−x)O3, x=0.3244(2)) and the Curie constant obtained from the high temperature susceptibility are in agreement with a spin state configuration of S=3/2 for Mn4+ and S=1/2 for Cu2+.

Tetrastrontium dimanganese copper nonaoxide, Sr4Mn2CuO9

Single crystals of Sr(4)Mn(2.09)Cu(0.91)O(9) have been grown by flux synthesis and the structure, closely related to the hexagonal perovskite 2H, was solved from single-crystal X-ray data in space group P321. The structure of Sr(4)Mn(2)CuO(9) is composed of chains of face-sharing polyhedra with a sequence of two octahedra and one trigonal prism. The octahedra are filled by Mn atoms and the Cu atoms are randomly distributed at the centres of the square faces of the trigonal prism. A stacking fault is observed within one of the two chains, which can be attributed to a shifting of the chain along the c axis.

Preparation, structural, Raman and impedance spectroscopic characterisation of the silver ion conductor (AgI)2Ag3SbS3

Pale yellow (AgI)2Ag3SbS3 was synthesized by the reaction of stoichiometric amounts of AgI and Ag3SbS3 (2 ∶ 1) at 683 K. It is air stable for several months. The crystal structure was determined at different temperatures in the range from 173 K to 573 K by single crystal X-ray diffraction. (AgI)2Ag3SbS3 crystallizes in the orthorhombic system, space group Pnnm (no. 58) with a = 10.9674(8) A, b = 13.5200(12) A, c = 7.7460(5) A, V = 1156.3(5) A3, and Z = 4 (data at 298 K). The title compound is isotypic with (CuI)2Cu3SbS3, at least for the positions of I, Sb, and S. The silver atoms are highly disordered and therefore their displacement parameters were refined using a Gram–Charlier non-harmonic development. No phase transition is observed between 173 K and the melting point at 720 K (DSC, onset temperature). The distribution of silver changes drastically with temperature and the localization of silver increases at low temperature. A high ionic conductivity is observed in combination with a pronounced disorder of the silver atoms. Impedance spectroscopic measurements reveal specific conductivity data of σ = 8.15 × 10−5 Ω−1 cm−1 at 332 K and of σ = 1.52 × 10−3 Ω−1 cm−1 at 478 K. The activation energy is EA = 0.29 eV. Raman spectra are dominated by the stretching modes of the [SbS3]3− units at 357, 327 and 316 cm−1 at room temperature.

Hydrogenation inducing ferromagnetism in the ternary antiferromagnet NdCoSi.

The hydride NdCoSiH obtained by exposure at 523 K of the ternary antiferromagnet NdCoSi under a pressure of 4 MPa of hydrogen crystallizes in the tetragonal ZrCuSiAs-type structure where H atoms occupy the tetrahedral [Nd(4)] site. The hydrogenation induces an increase in the unit cell volume close to 6%. The investigation of NdCoSiH by magnetization measurements reveals its ferromagnetic behavior below T(C) = 20.5(5) K. Neutron powder diffraction shows that the T(C) temperature is associated with a ferromagnetic arrangement of the Nd moments (2.3(2) mu(B) at 1.5 K) parallel to the c axis as observed for NdFeSi. The magnetic properties, magnetic structure, and the value of the Nd ordered magnetic moment evidenced for NdCoSiH are discussed using both band structure calculations and a comparison with the behavior of NdCoSi and NdFeSi.

Huge influence of hydrogenation on the magnetic properties and structures of the ternary silicide NdMnSi

The hydride NdMnSiH obtained by exposure of the ternary silicide NdMnSi under a pressure of 4 MPa of hydrogen at 523 K crystallizes in the tetragonal ZrCuSiAs-type structure where H atom occupies the tetrahedral [Nd4] sites. The hydrogenation of NdMnSi induces an increase in the unit cell volume close to 3.3%. The investigation of NdMnSiH by magnetization and specific heat measurements reveals the existence of two antiferromagnetic ordering, respectively, at TN1=565(5) K and TN2=103(4) K. Neutron powder diffraction shows that these Neel temperatures are associated with an antiferromagnetic arrangement of the (i) Mn substructure (TN1) and (ii) Nd substructure linked to a reorientation of the Mn one (TN2). Comparison of the TN1 and TN2 temperatures of NdMnSiH to those reported for the initial compound NdMnSi indicates a strong increase in TN1 (280 K→565 K) and a significant decrease in TN2 (185 K→103 K). The magnetic properties, magnetic structures, and values of Nd and Mn ordered magnetic moments are discu...

Structural, magnetic and electrical properties of the ternary silicide Gd6Co1.67Si3 derived from the hexagonal Ho4Co3.07 (or Ho6Co4.61) type structure

The title compound was discovered as an impurity phase in many GdCoSi samples. It crystallizes in the hexagonal space group P63/m with a = 11.7787(5) and c = 4.1640(2) Å . Using X-ray powder diffraction, an ordered distribution between Co and Si was found but one site is not fully occupied by Co for steric reasons. Magnetization measurements reveal that Gd6Co1.67Si3 exhibits a ferromagnetic transition at TC = 294(2) K, a Curie temperature similar to that reported for pure gadolinium. This magnetic ordering has been confirmed by electrical resistivity investigations.

Structural and NMR studies of the series of related [H3N(CH2)xNH3]·AlF5 (x=6, 8, 10, 12) hybrid compounds

The series of [H 3 N(CH 2 ) x NH 3 ].AlF 5 (x = 6, 8, 10, 12) compounds is synthesized by solvothermal method. Structure determinations are performed by single crystal (x = 8, 10) and powder (x = 12) techniques. The structures of [H 3 N(CH 2 ) x NH 3 ].AlF 5 (x = 8, 10, 12) are related with the structure of [H 3 N(CH 2 ) 6 NH 3 ].AlF 5 , which was previously described. They are built up from [AlF 5 2- ]∞infinite puckered inorganic chains linked by the diprotonated organic moieties through N-H...F hydrogen bonds. The analogy of the 19 F and 27 Al NMR spectra confirms the strong structural similarity of the series and demonstrates that the hydrogen bond schemes are identical.

NdNiMg5, a New Magnesium-Rich Phase with an Unusual Structural Type

The new intermetallic NdNiMg5 was discovered during the study of the Mg-rich part of the Mg-Nd-Ni system. It was synthetized by melting of the constituent elements in a sealed tantalum tube with subsequent annealing. Its structure was determined by X-ray diffraction on a single crystal. Crystal data: orthorhombic system, Cmcm, Z = 4, a = 4.4799(2) Å, b = 9.9827(3) Å, c = 13.7854(10) Å, d(calc) = 3.49 g·cm(-3). Its structure is made of infinite layers of Mg atoms that form blocks stacked along the c axis. These blocks, with a close-packed array of Mg atoms, are separated by infinite NiNd layers and connected through short Mg-Mg bonds. In the NiNd layer, the Ni and Nd atoms form an ordered graphite-type network. Antiferromagnetic ordering is observed with T(N) = 12 K, and the effective magnetic moment μeff is equal to 3.89(1) μB.