Experimental evidence of an electronic transition in CeP under pressure using Ce L3 XAS.

Cerium phosphide undergoes a unit-cell volume discontinuity without any structural phase transitions upon application of a high pressure of ∼10 GPa. This phenomenon is attributed to a change in the electronic charge distribution of the cerium in CeP, but to date no direct experimental verification for this hypothesis has been presented. Here, we report a Ce L3-edge X-ray absorption spectroscopy study under pressure, which provides direct compelling evidence of an electronic transition associated with the above-mentioned isostructural volume discontinuity. The present results should be relevant to the understanding of the phenomenon of pressure induced isostructural transitions involving unit-cell volume collapse.

Strong intermolecular antiferromagnetic verdazyl-verdazyl coupling in the solid state.

Strong magnetic couplings are generally observed intramolecularly in organic diradicals or in systems in which they are promoted by crystal engineering strategies involving, for example, transition metal ligation. We herein present a strong intermolecularly coupling verdazyl radical in the solid state without the use of such design strategies. The crystal structure of an acetylene-substituted verdazyl radical shows a unique antiparallel face-to-face orientation of the neighboring verdazyl molecules along with verdazyl-acetylene interactions giving rise to an alternating antiferromagnetic Heisenberg chain. Single crystal structural data at 80, 100, 173, and 223 K show that one of the π-stacking distances depends on temperature, while heat capacity data indicate the absence of a phase transition. Based on this structural input, broken symmetry DFT calculations predict a change from an alternating linear Heisenberg chain with two comparable coupling constants J1 and J2 at higher temperatures towards dominant pair interactions at lower temperatures. The predicted antiferromagnetic coupling is confirmed experimentally by magnetic susceptibility, solid-state EPR and NMR spectroscopic results.

Anosovite-type V3O5: a new binary oxide of vanadium.

The reaction of either V(2)F(6)·4H(2)O or a mixture of 60 wt % VF(2)·4H(2)O and 40 wt % VF(3)·3H(2)O with a water-saturated gaseous mixture of 15-20 vol % hydrogen in argon leads to the formation of a new polymorph of V(3)O(5) crystallizing in the orthorhombic anosovite-type structure. Quantum-chemical calculations show that the anosovite-type structure is about 15 kJ/mol less stable than the corresponding monoclinic Magnéli phase. In addition, there are no imaginary modes in the phonon density of states, supporting the classification of the anosovite-type phase as a metastable V(3)O(5) polymorph. Susceptibility measurements down to 3 K reveal no hint for magnetic ordering.

Bixbyite-type V2O3--a metastable polymorph of vanadium sesquioxide.

A metastable polymorph of vanadium sesquioxide was prepared by the reaction of vanadium trifluoride with a water-saturated gaseous mixture of 10 vol % hydrogen in argon. The new polymorph crystallizes in the bixbyite-type structure. At temperatures around 823 K a transformation to the well-known corundum-type phase is observed. Quantum-chemical calculations show that the bixbyite-type structure is about 9 kJ/mol less stable than the known corundum-based one. This result, in combination with the absence of imaginary modes in the phonon density of states, supports the classification of the bixbyite-type phase as a metastable V(2)O(3) polymorph. At ~50 K a paramagnetic to canted antiferromagnetic transition is detected.

Complex magnetic order from multiple Ce-sites in Ce3Pd4Sn6.

Polycrystalline [Formula: see text] [Formula: see text] [Formula: see text] samples were synthesized by arc-melting and subsequent annealing at 970 K. Specific heat, electrical resistivity and magnetic susceptibility measurements are performed over a wide range in temperature and provide hints for the presence of a complex magnetic ordering below 3 K arising from three crystallographically independent Ce sites. This behaviour is driven by a complex interplay between ferro-, ferri-, and antiferromagnetic correlations among the Ce atoms.

Distorted bcc indium cubes as structural motifs in Ca

The title compounds were prepared from the elements by reactions in water-cooled glassy carbon crucibles under an argon atmosphere in a high-frequency furnace. CaPdIn4 crystallizes with the YNiAl4-type structure: Cmcm, a=446.7(3), b=1665(1), c=754.3(5) pm, wR2=0.0465 with 646 F2 values and 24 variables. The structure is built up from a complex three-dimensional [PdIn4] polyanion in which the calcium atoms occupy distorted pentagonal tubes formed by indium and palladium atoms. CaRhIn4 and CaIrIn4 adopt the LaCoAl4-type structure: Pmma, a=867.6(1), b=422.91(8), c=745.2(1) pm, wR2=0.0583 with 468 F2 values and 24 variables for CaRhIn4; a=869.5(1), b=424.11(6), c=746.4(1) pm, wR2= 0.0614 471 F2 values with 24 variables for CaIrIn4. This structure type, too, has a three-dimensional [RhIn4] polyanion which is related to the structure of binary RhIn3. The calcium atoms fill distorted pentagonal prismatic channels formed by indium atoms. Semi-empirical band structure calculations for Ca-RhIn4 and CaPdIn4 reveal strongly bonding In-In, Rh-In and Pd-In interactions but weaker Ca-Rh, Ca-Pd and Ca-In interactions. CaRhIn4 and Ca-PdIn4 are compared with other indium-rich compounds such as YCoIn5 and Y2CoIn8, and with elemental indium. Common structural motifs of the indium-rich compounds are distorted bcc-like indium cubes.

(3 + 1)-dimensional crystal and antiferromagnetic structures in CeRuSn.

At 320 K, the crystal structure of CeRuSn is commensurate with the related CeCoAl-type of structure by the doubling of the c lattice parameter. However, with lowering the temperature it becomes incommensurate with x and z position parameters at all three elemental sites being modulated as one moves along the c-axis. The resulting crystal structure can be conveniently described within the superspace formalism in (3 + 1) dimensions. The modulation vector, after initially strong temperature dependence, approaches a value close to qnuc = (0 0 0.35). Below TN = 2.8 (1) K, CeRuSn orders antiferromagnetically with a propagation vector qmag = (0 0 0.175), i.e. with the magnetic unit cell doubled along the c-axis direction with respect to the incommensurate crystal structure. Ce moments appear to be nearly collinear, confined to the a-c plane, forming ferromagnetically coupled pairs. Their magnitudes are modulated between 0.11 and 0.95 µB as one moves along the c-axis.

Crystal structure of BaFe2Se3 as a function of temperature and pressure: phase transition phenomena and high-order expansion of Landau potential.

BaFe2Se3 (Pnma, CsAg2I3-type structure), recently assumed to show superconductivity at ~11 K, exhibits a pressure-dependent structural transition to the CsCu2Cl3-type structure (Cmcm space group) around 60 kbar, as evidenced from pressure-dependent synchrotron powder diffraction data. Temperature-dependent synchrotron powder diffraction data indicate an evolution of the room-temperature BaFe2Se3 structure towards a high-symmetry CsCu2Cl3 form upon heating. Around 425 K BaFe2Se3 undergoes a reversible, first-order isostructural transition, which is supported by the differential scanning calorimetry data. The temperature-dependent structural changes occur in two stages, as determined by the alignment of the FeSe4 tetrahedra and corresponding adjustments of the positions of Ba atoms. On further heating, a second-order phase transformation into the Cmcm structure is observed at 660 K. A rather unusual combination of isostructural and second-order phase transformations is parameterized within phenomenological theory assuming high-order expansion of the Landau potential. A generic phase diagram mapping observed structures is proposed on the basis of the parameterization.

New high temperature modification of CeTiGe: structural characterization and physical properties.

The new high temperature form (HT) of the ternary germanide CeTiGe was prepared by annealing at 1373 K. The investigation of HT-CeTiGe by x-ray powder diffraction shows that the compound crystallizes in the tetragonal CeScSi type structure (space group I4/mmm; a=414.95(2) and c=1590.85(10) pm as unit cell parameters). Electrical resistivity, thermoelectric power, magnetization and specific heat measurements performed down to 2 K on HT-CeTiGe reveal a non-magnetic strongly correlated electron system; the specific heat divided by temperature attains a value of 0.635 J mol(-1) K(-2) at 2 K. The comparison of the physical properties of the two crystallographic modifications of CeTiGe suggests a decrease of the hybridization J(cf) between 4f(Ce) and conduction electrons in the sequence LT-CeTiGe [Formula: see text]-CeTiGe (CeScSi type).

A study on the antiferromagnetic behavior of the hydride CeRuGeH adopting the ZrCuSiAs-type structure.

The non-magnetic heavy fermion behavior of CeRuGe is destroyed by hydrogen insertion. The resulting hydride CeRuGeH, investigated by magnetization, thermoelectric, electrical resistivity and specific heat measurements, exhibits an antiferromagnetic ordering below T(N) = 4.0(2) K weakly influenced by the Kondo effect. Below T(N), a metamagnetic double transition induced by an applied magnetic field was evidenced for CeRuGeH. This hydride presents a simple field-temperature phase diagram in comparison to that determined for the equivalent compound CeRuSiH.

Two-dimensional [TIn2] polyanions in BaTIn2 (T=Rh, Pd, Ir, Pt)--the collapse of the three-dimensional indium polyanion of BaIn2.

The title compounds were prepared from the elements by reactions in sealed tantalum tubes in a high-frequency furnace. The four compounds were investigated by X-ray diffraction both on powders and single crystals, and the structures of the rhodium and platinum compounds were refined from single-crystal data: Cmcm, a = 447.68(8), b = 1131.1(2), c = 805.6(2) pm, wR2 = 0.0561, 354 F2 values for BaRhIn2; a = 452.06(8), b = 1162.4(2). c = 801.5(1) pm, wR2 = 0.1427, 362 F2 values, for BaPtIn2: with 16 variables for each refinement. The structures are isopointal to MgCuAl2 and can be considered to be a transition metal (T) filled CaIn2 type, in which the indium atoms form a distorted network like hexagonal diamond (lonsdaleite). The indium substructure is cut apart in BaTIn2 and resembles together with the transition metal atoms a two-dimensional polyanion rather than a three-dimensional polyanion as found in the compounds CaTIn2, CaTSn2, and SrTIn2. Semiempirical band structure calculations support the assumption of a two-dimensional polyanion in which the strongest interactions are found for the T-In contacts.

Orthonitridoborate ions [BN3]6- in oxonitridosilicate cages: synthesis, crystal structure, and magnetic properties of Ba4Pr7[Si12N23O][BN3], Ba4Nd7[Si12N23O][BN3], and Ba4Sm7[Si12N23O][BN3].

The isotypic title compounds Ba4Pr7[Si12N23O][BN3], Ba4Nd7[Si12N23O][BN3], and Ba4Sm7[Si12N23O][BN3] were prepared by reaction of Pr, Nd, or Sm, with barium, BaCO3, Si(NH)2, and poly(boron amide imide) in nitrogen atmosphere in tungsten crucibles using a radiofrequency furnace at temperatures up to 1650 C. They were obtained as main products (approximately 70%) embedded in a very hard glass matrix in the form of intense dark green (Pr), orange-brown (Sm), or dark red (Nd) large single crystals, respectively. The stoichiometric composition of Ba4Sm7[Si12N23O][BN3] was verified by a quantitative elemental analysis. According to the single-crystal X-ray structure determinations (Ba4Ln7[Si12N23][BN3], Z= , P6 with Ln = Pr: a = 1225.7(1), c = 544.83(9) pm, R1 = 0.013, wR2 = 0.030; Ln = Nd: a = 1222.6(1), c = 544.6(1) pm, R1 = 0.017, wR2 = .039; Ln = Sm: a = 1215.97(5), c = 542.80(5) pm, R1 = 0.047, wR2 = 0.099) all three compounds are built up by a framework structure [Si12N23O]23- of corner-sharing SiX4 tetrahedrons (X = O, N). The oxygen atoms are randomly distributed over the X positions. The trigonal-planar orthonitridoborate ions [BN3]6- and also the Ln(3)3+ are situated in hexagonal cages of the framework (bond lengths Si-(N/O) 169-179 pm for Ln=Pr). The remaining Ba2+ and Ln3- ions are positioned in channels of the large-pored network. The trigonal-planar [BN3]6- ions have a B-N distance of 147.1(6) pm (for Ln = Pr). Temperature-dependent susceptibility measurements for Ba4Nd7[Si12N23O][BN3] revealed Curie-Weiss behavior above 60 K with an experimental magnetic moment of muexp = 3.36(5) microB/Nd. The deviation from Curie-Weiss behavior below 60 K may be attributed to crystal field splitting of the J = 9/2 ground state of the Nd3+ ions. No magnetic ordering is evident down to 4.2 K.

A new 1 --> infinity [Ni7] cluster in LaNi7In6 and distorted bcc indium cubes in LaNiIn4.

LaNiIn4 and LaNi7In, were prepared by reaction of the elements in an arc melting furnace and subsequent annealing at 870 K for five weeks. Both compounds were investigated by X-ray diffraction on powders and single crystals and the structures were refined from single-crystal data: Cmcm, a = 448.2(1), b = 1689.5(4). c = 722.1(1) pm, wR2 = 0.0340, 472 F2 values, 24 variables for LaNiIn4, and Ibam, a = 806.6(2). b = 924.8(2). c = 1246.5(2) pm. wR2 = 0.0681. 726 F2 values and 40 variables for LaNi7In,. LaNiIn4 adopts the YNiAl4-type structure. The nickel and indium atoms form a three-dimensional infinite [NiIn4] polyanion in which the lanthanum atoms fill distorted hexagonal channels. No Ni-Ni contacts occur. The indium substructure consists of distorted bcc-like indium cubes. LaNi7In6 crystallizes with a peculiar new structure type. The nickel atoms build a 1 --> infinity [Ni7] cluster unit with Ni-Ni distances ranging from 249 to 269 pm. The cluster units are enveloped by indium atoms. These larger units show an orthorhombic rod packing with the lanthanum atoms filling the space between the rods. Several nickel clusters in ternary rare earth metal nickel indides and the structural relations of the LaNi7In6 structure with the cubic NaZn13 type are discussed.