Crystal structures and magnetic properties of CeAu4Si2 and CeAu2Si2

Single crystals of CeAu₄Si₂ and CeAu₂Si₂ have been grown out of ternary fluxes rich in Au, and the former, also by sintering the stoichiometric composition at 750 °C. The single-crystal X-ray refinement result for CeAu₄Si₂ is orthorhombic, Cmmm (No. 65, Z=2), different from a tetragonal result found from an X-ray powder diffraction refinement [H. Nakashima, et al., J. Alloys Compds. 424 (2006) 7]. For CeAu₂Si₂, this is the first report of the stoichiometric crystalline phase, in the known tetragonal I4/mmm structure. The anisotropic field- and temperature-dependent magnetizations, as well as specific heat and resistivity data are compared. Although both compounds have related structural packing, they present unique magnetic features. CeAu₂Si₂ is a typical antiferromagnet with T_N=8.8(1) K and CeAu₄Si₂ features a ferromagnetic component below T_c=3.3(1) K. Both phases have effective moments close in value to that of free Ce³⁺.     

Crystal structure and magnetic properties of the UFe7Al5 uranium-iron aluminide

The ternary compound UFe₇Al₅ was synthesized by arc melting, followed by annealing at 850°C. The crystal structure was determined by single-crystal X-ray diffraction and refined to a residual value of R=0.039 (S=1.030), with lattice parameters a=8.581(2) Å and c=4.946(1) Å. This compound is a new extreme composition in the family of intermetallics with general formula UFe_xAl_12−x crystallizing in the tetragonal ThMn₁₂-type structure, space group I4/mmm. In contrast to UFe_xAl_12−x within the composition range 4?x?6, in UFe₇Al₅ the additional iron atom is found in the 8i equipositions. Magnetization measurements versus temperature show two magnetic transitions at 363 and 275 K, respectively, with a ferromagnetic behavior below the highest temperature transition. ⁵⁷Fe Mössbauer data indicate that the high-temperature transition is related to the ordering of the iron atoms. The dependence of the isomer shifts and magnetic hyperfine fields on the crystallographic site and on the number of the iron nearest neighbors is similar to that observed in the other UFe_xAl_12−x and rare-earth analogues. The magnetic hyperfine field values of iron atoms on 8i sites is larger than in the other sites, in agreement with previous data obtained for other ThMn₁₂-type compounds.     

Crystal structures, unusual magnetic properties and electronic band structures of Cr5−xTixTe8

The effect of substitution of the cation Cr by Ti in Cr₅Te₈ has been investigated with respect to its crystal structure, magnetic properties, and electronic structure. The compounds Cr_5−xTi_xTe₈ (x=0, 0.5, 1, 1.5, 1.85, 2, 3, 4, 5) were synthesized at elevated temperatures followed by slow cooling the samples to room temperature. The crystal structures have been refined with X-ray powder diffraction data with the Rietveld method. Three structural modifications are identified: monoclinic with space group F2/m for Cr_5−xTi_xTe₈ (x=0, 0.5, 1, 1.5, 1.85), trigonal supercell with space group P-3m1 for Cr_5−xTi_xTe₈ (x=2, 3), and trigonal basic cell with space group P-3m1 for Cr_5−xTi_xTe₈ (x=4, 5). The structures of all these phases are related to the NiAs structure with full and deficient metal layers stacking alternatively along the c-axis.The irreversibility in the field-cooled/zero-field-cooled magnetization with low field depends strongly on the Ti concentration x. Four types of magnetic states are distinguished: re-entrant ferromagnet for m-Cr₅Te₈, cluster-glass for m-Cr_4.5Ti_0.5Te₈ and m-Cr₄TiTe₈, antiferromagnetic for m-Cr_3.5Ti_1.5Te₈, and spin-glass for tr-Cr₃Ti₂Te₈, tr-Cr₂Ti₃Te₈, and Cr_0.25TiTe₂.Accompanying spin polarized scalar-relativistic Korringa-Kohn-Rostoker band-structure calculations strongly support the observation that the crystallographic sites in the full metal layers are preferentially occupied and predict that Ti atoms have the preference to occupy the full metal layers. These compounds are predicted metallic. Results for the spin-resolved DOS and magnetic moments on each crystallographic sites are presented.     

Gd5Ni0.96Sb2.04 and Gd5Ni0.71Bi2.29: Crystal structure, magnetic properties and magnetocaloric effect. Structural transformation and magnetic properties of hexagonal Gd5Bi3

Nickel was successfully introduced into the Gd₅Sb₃ and Gd₅Bi₃ binaries to yield the Gd₅Ni_0.96(1)Sb_2.04(1) and Gd₅Ni_0.71(1)Bi_2.29(1) phases. Both Ni-substituted compounds adopt the orthorhombic Yb₅Sb₃-type structure. While the Gd₅Ni_0.71Bi_2.29 phase is thermodynamically stable at 800 °C and decomposes at lower temperatures upon annealing, it can be easily quenched to room temperature by rapid cooling from 800 °C. The Gd₅Ni_0.96Sb_2.04 phase is found to be thermodynamically stable till room temperature. Through annealing at different temperatures, Gd₅Bi₃ was proven to undergo the Mn₅Si₃-type (LT)↔Yb₅Sb₃-type (HT) transformation reversibly, whereas Gd₅Sb₃ was found to adopt only the hexagonal Mn₅Si₃-type structure. Orthorhombic Gd₅Ni_0.96Sb_2.04 and Gd₅Ni_0.71Bi_2.29 and low-temperature hexagonal Gd₅Bi₃ order ferromagnetically at 115, 162 and 112 K, respectively. In Gd₅Bi₃, the ferromagnetic ordering is followed by spin reorientation below 64 K. Magnetocaloric effect in terms of ΔS was evaluated from the magnetization data and found to reach the maximum values of −7.7 J/kgK for Gd₅Ni_0.96Sb_2.04 and −5.6 J/kgK for Gd₅Ni_0.71Bi_2.29 around their Curie temperatures.     

Crystal structures of V3S4 and V5S8

Crystal structures of the ordered phases of V₃S₄ and V₅S₈ were refined with single crystal data. Both are monoclinic. Chemical compositions, space groups and lattice constants are as follows: VS_1.47, $\text{I2}\text{m}$ (No. 12), a = 5.831(1), b = 3.267(1), c = 11.317(2)Å, β = 91.78(1)° and VS_1.64, $\text{F}\text{2}\text{m}$ (No. 12), a = 11.396(11), b = 6.645(7), c = 11.293(4), Å, β = 91.45(6)°. In both structures, short metal-metal bonds were found between the layers as well as within them. In comparison with the structure of Fe₇S₈, the stability of NiAs-type structure was discussed based on the detailed metal-sulfur distances.     

Crystal growth and anisotropic magnetic properties of V3O7

Needle-like crystals of V₃O₇ up to 2 mm in length were grown by a chemical vapor transport method using NH₄Cl as a transport agent. The anisotropic magnetic susceptibility was measured for the first time. At 2 K, a spin-flop transition occurs under a magnetic field of 0.1 T. V₃O₇ is proved to be a uniaxial antiferromagnet with its easy axis parallel to the b-axis of monoclinic structure. A spin structure with antiferromagnetic interaction between layers and ferromagnetic interaction in the layers below the Néel temperature (5.2 K) is suggested.     

Crystal structures of [Rh(η-C5H5)(C3S5)] and [Rh(η-C5Me5)(C3S5)]2 and properties of their oxidized species

[Rh(η⁵-C₅H₅)(C₃S₅)] and [Rh(η⁵-C₅Me₅)(C₃S₅)]₂ [C₃S₅²⁻=4,5-disulfanyl-1,3-dithiole-2-thionate(2-)] were prepared by reactions of [NMe₄]₂[C₃S₅] with [Rh(η⁵-C₅H₅)Cl₂]₂ and [Rh(η⁵-C₅Me₅)Cl₂]₂, respectively. Their X-ray crystal structural analyses revealed a monomeric form for the former complex and a dimeric geometry containing bridging S-Rh-S bonds for the latter in the solid state. They were reacted with bromine to afford [RhBr(L)(C₃S₅)] (L=η⁵-C₅H₅ and η⁵-C₅Me₅) with the Rh-Br bond and one electron-oxidation on the C₃S₅ ligand. ESR spectra and spin densities for these oxidized species are discussed.     

Crystal structure and magnetic properties of Sr4Mn2NiO9

The crystal structure of Sr₄Mn₂NiO₉ has been refined on single crystal. This phase belongs to the series A_1+x(A^′_xB_1–x)O₃ (x=1/3) related to the 2H-hexagonal perovskite. The structure contains transition metals in chains of oxide polyhedra (trigonal prisms and octahedra); neighboring chains are separated from each other by the Sr atoms. The sequence of the face sharing polyhedra along the chains is two octahedra + one trigonal prism. Mn occupies the octahedra and Ni is disordered in the trigonal prism with ≈80% in the pseudo square faces of the prism and ≈20% at the centre. This result has been confirmed by XANES experiments at Mn K and Ni K edges, respectively. Sr₄Mn₂NiO₉ is antiferromagnetic with a Néel temperature at T=3 K. The Curie constant measured at high temperature is in good agreement with ≈80% of the Ni²⁺ ions in the spin state configuration S=0.     

Crystal structure and magnetic properties of Ba2Ni3F10

Ba₂Ni₃F₁₀ is monoclinic (space group $\text{C2}\text{m}$), a = 18.542(7) Å, b = 5.958(2) Å, c = 7.821(3) Å, β = 111°92(10). Ba₂Co₃F₁₀ and Ba₂Zn₃F₁₀ are isostructural. The structure has been refined from 995 reflections by full-matrix least-squares refinement to a weighted R value of 0.048 (unweighted R, 0.047). The three-dimensional network can be described either by complex chains connected to each other by octahedra sharing corners or with an 18L dense-packing sequence. The basic unit (Ni₃F₁₀)^4? is discussed and compared to the different unit existing in Cs₄Mg₃F₁₀. Antiferromagnetic properties of Ba₂Ni₃F₁₀ (T_N = 50 K are described.     

Crystal structure, magnetic properties and conductivity of CuSbTeO3Cl2

CuSbTeO₃Cl₂ has been isolated during an investigation of the system Cu₂O:TeCl₄:Sb₂O₃:TeO₂. The new compound is light yellow and crystallises in the monoclinic system, space group C2/m, a=20.333(5) Å, b=4.0667(9) Å, c=10.778(2) Å, Z=6. The structure is layered and is built up from corner and edge sharing [(Sb,Te)O₄E] trigonal bipyramids that have the lone pair (E) directed towards one of the equatorial positions, those groups build up [(Sb,Te)₂O₃E₂⁺]_n layers. The copper and the chlorine atoms are located in between those layers. There are two different Cu positions. The [Cu1Cl₄] group is a slightly distorted tetrahedron and these tetrahedra make up chains by corner sharing. The electron density for the half occupied Cu2 atom is spread out in the structure like a worm that run along the b-axis in the space in between two chains of [Cu1Cl₄] tetrahedrons. Analysis of the diamagnetic response in magnetic susceptibility measurements is in perfect agreement with a Cu⁺ valence. Conductivity measurements in the temperature range 355–590 K gives an activation energy of 0.55 eV. The delocalised Cu2 position in the structure suggests that the compound is a Cu⁺ ionic conductor along the b-axis.     

Crystal structure and magnetic properties of Na2Ni(HPO3)2

Na₂Ni(HPO₃)₂, obtained as light yellow-green crystals under mild hydrothermal conditions, crystallizes in the orthorhombic Pnma space-group with lattice parameters: a=11.9886(3), b=5.3671(2), c=9.0764(3) Å, V=584.01 Å³, Z=4. The structure consists of zig-zag chains of NiO₆ octahedra bridged by two HPO₃²⁻ and the chains are further connected through HPO₃²⁻ to four nearest chains to form a three dimensional framework, delimiting intersecting tunnels in which the sodium ions are located. The Na cations reside in the irregular Na(1)O₅, Na-O of 2.276-2.745 Å, and Na(2)O₉, Na-O of 2.342-2.376 Å, environments. The presence of the phosphite monoanion has been further confirmed by IR spectroscopy. Due to the 3D framework of Ni connected by O-P-O bridges, the magnetic susceptibility behaves as a paramagnet above 100 K (C=1.49(2) emu K mol⁻¹, μ_eff=3.45 μ_B, Θ=−39(2) K) and below 6 K, it orders antiferromagnetically as confirmed the sharp drop and the non-Brillouin behavior of the isothermal magnetization at 2 K.     

The new ternary pnictides Er12Ni30P21 and Er13Ni25As19: Crystal structures and magnetic properties

The new ternary pnictides Er₁₂Ni₃₀P₂₁ and Er₁₃Ni₂₅As₁₉ have been synthesized from the elements. They crystallize with hexagonal structures determined from single-crystal X-ray data for Er₁₂Ni₃₀P₂₁ (space group P6₃/m, a=1.63900(3) nm, c=0.37573(1) nm, Z=1, R_F=0.062 for 1574 F-values and 74 variable parameters), and for Er₁₃Ni₂₅As₁₉ (Tm₁₃Ni₂₅As₁₉-type structure, space group P6?, a=1.6208(1) nm, c=0.38847(2) nm, Z=1, R_F=0.026 for 1549 F-values and 116 variable parameters). These compounds belong to a large family of hexagonal structures with a metal-metalloid ratio of 2:1. HRTEM investigations were conducted to probe for local ordering of the disordered structure at the nanoscale. The magnetic properties of the phosphide Er₁₂Ni₃₀P₂₁ have been studied in the temperature of range 2<T<300 K and with applied fields up to 5 T. The magnetic susceptibility follows the Curie-Weiss law from 4 to 300 K. The measured value of μ_eff=9.59 μ_B corresponds to the theoretical value of Er³⁺.     

Crystal structures and magnetic properties of fluorite-related oxides Ln3NbO7 (Ln=lanthanides)

Crystal structures and magnetic properties of the ternary oxides Ln₃NbO₇ (Ln=La, Pr, Nd, Sm-Lu) are reported. Their powder X-ray diffraction measurements and Rietveld analyzes show that they have the fluorite-related structures with space group Pnma (Ln=La, Pr, Nd), C222₁ (Ln=Sm-Tb), or Fm-3m (Ln=Dy-Lu). Magnetic susceptibility measurements were carried out from 1.8 to 400 K. The Ln₃NbO₇ compounds for Ln=Pr, Gd, Dy-Yb show Curie-Weiss paramagnetic behavior, and Sm₃NbO₇ and Eu₃NbO₇ show van Vleck paramagnetism. On the other hand, two magnetic anomalies were observed for both Nd₃NbO₇ (0.6 and 2.7 K) and Tb₃NbO₇ (2.0 and 3.2 K). From the results of specific heat measurements, it was found that these anomalies are due to the antiferromagnetic ordering of Ln ions in two different crystallographic sites (the 8-coordinated and 7-coordinated sites).     

Crystal structures and magnetic properties of two-dimensional antiferromagnets Co1−xZnxTeMoO6

Crystal structures and magnetic properties of metal telluromolybdates Co_1−xZn_xTeMoO₆ (x=0.0, 0.1,…,0.9) are reported. All the compounds have an orthorhombic structure with space group P2₁2₁2 and a charge configuration of M²⁺Te⁴⁺Mo⁶⁺O₆. In this structure, M ions form a pseudo-two-dimensional lattice in the ab plane. Their magnetic susceptibility measurements have been performed in the temperature range between 1.8 and 300 K. The end member CoTeMoO₆ shows a magnetic transition at 24.4 K. The transition temperature for solid solutions rapidly decreases with increasing x and this transition disappears between x=0.4 and 0.5, which is corresponding to the percolation limit for the square-planer lattice. From the magnetization, specific heat, and powder neutron diffraction measurements, it is found that the magnetic transition observed in the CoTeMoO₆ is a canted antiferromagnetic ordering of Co²⁺ ions. The antiferromagnetic component of the ordered magnetic moment (3.12(3)μ_B at 10 K) is along the b-axis. In addition, there exists a small ferromagnetic component (0.28(3)μ_B) along the a-axis.     

The crystal structures and magnetic properties of Ba2LaRuO6 and Ca2LaRuO6

Profile analysis of high-resolution, powder neutron-diffraction data was used to refine the previously reported structures of the ordered, distorted perovskites Ba₂LaRuO₆ and Ca₂LaRuO₆. Low-temperature neutron diffraction experiments showed that, at 2K, the former is a Type IIIa antiferromagnet while the latter is Type I. Both compounds have an ordered magnetic moment of $\text{μ}{}_{\mathrm{<mtext>Ru</mtext>}}\text{? 1.95μ}{}_{\mathrm{<mtext>B</mtext>}}$ per Ru⁵⁺ ion. The Néel temperature of Ba₂LaRuO₆ was determined to be 29.5K, and the covalent mixing between the ruthenium and nearest-neighbor anions is described by A²_π = 8.2 ± 1% for Ba₂LaRuO₆ and 8.6 ± 1% for Ca₂LaRuO₆. The ionic radius of a Ru⁵⁺ ion is 0.56 Å. These data are consistently interpreted within the framework of a strongly correlated, half-filled π1 band. Extension of this interpretation to the magnetic data for the perovskites CaRuO₃ and SrRuO₃ leads to a fundamental theoretical prediction.     

Synthesis, structures and magnetic properties of the new vanadates AgMnVO4 and RbMnVO4

The new compounds, AgMnVO₄ and RbMnVO₄ have been synthesized by solid state reaction route. Their crystal structures were determined from single-crystal X-ray diffraction data for RbMnVO₄ and powder X-ray diffraction data for AgMnVO₄. AgMnVO₄ crystallizes with the maricite-type structure in space group Pnma, a=9.5778(6) Å, b=6.8518(4) Å, c=5.3734(3) Å and Z=4. RbMnVO₄ crystallizes in space group P6₃ with a stuffed tridymite-type structure, a=11.2584(3), c=8.9893(13) Å and Z=8. A merohedral twinning was taken into account for its structural refinement. To our knowledge this is the first vanadate showing this structural type. AgMnVO₄ and RbMnVO₄ were characterized by magnetic susceptibility and specific heat measurements. AgMnVO₄ is antiferromagnetic with a Néel temperature of 12.3 K determined by specific heat measurements. RbMnVO₄ exhibits canted antiferromagnetism with a Néel temperature of 6.5 K.     

Crystal structure, thermal and magnetic properties of Cr2V4O13

Cr₂V₄O₁₃, a tetravanadate of Cr³⁺ has been prepared by repeated heating of stoichiometric amounts of Cr₂O₃ and V₂O₅ and its crystal structure is refined by Rietveld refinement of the powder XRD data. This compound crystallizes in a monoclinic lattice with unit cell parameters: a=8.2651(3), b=9.2997(3), c=14.5215(5) Å, β=102.618(3)°, V=1089.21(6) Å³ and Z=4 (Space group: P2₁/c). The U shaped (V₄O₁₃)⁶⁻ formed by corner connected VO₄ tetrahedra links the Cr₂O₁₀ (dimers of two edge shared CrO₆ octahedra) forming a three dimensional network structure of Cr₂V₄O₁₃. This compound is stable up to 635 °C and peritectically decomposes to orthorhombic CrVO₄ and V₂O₅ above this temperature. A possible long range antiferromagnetic ordering below 10 K is suggested from the squid magnetometry and electron paramagnetic resonance (epr) spectroscopic studies of Cr₂V₄O₁₃.     

Crystal, electronic structures and photoluminescence properties of rare-earth doped LiSi2N3

The crystal and electronic structures, and luminescence properties of Eu²⁺, Ce³⁺ and Tb³⁺ activated LiSi₂N₃ are reported. LiSi₂N₃ is an insulator with an indirect band gap of about 5.0 eV (experimental value ∼6.4 eV) and the Li 2s, 2p states are positioned on the top of the valence band close to the Fermi level and the bottom of the conduction band. The solubility of Eu²⁺ is significantly higher than Ce³⁺ and Tb³⁺ in LiSi₂N₃ which may be strongly related to the valence difference between Li⁺ and rare-earth ions. LiSi₂N₃:Eu²⁺ shows yellow emission at about 580 nm due to the 4f⁶5d¹→4f⁷ transition of Eu²⁺. Double substitution is found to be the effective ways to improve the luminescence efficiency of LiSi₂N₃:Eu²⁺, especially for the partial replacement of (LiSi)⁵⁺ with (CaAl)⁵⁺, which gives red emission at 620 nm, showing highly promising applications in white LEDs. LiSi₂N₃:Ce³⁺ emits blue light at about 450 nm arising from the 5d¹→4f¹5d⁰ transition of Ce³⁺ upon excitation at 320 nm. LiSi₂N₃:Tb³⁺ gives strong green line emission with a maximum peak at about 542 nm attributed to the ⁵D₄→⁷F_J (J=3-6) transition of Tb³⁺, which is caused by highly efficient energy transfer from the LiSi₂N₃ host to the Tb³⁺ ions.     

Crystal and magnetic structures of the brownmillerite compound Ca2Fe1.039(8)Mn0.962(8)O5

The crystal and magnetic structures of the brownmillerite material, Ca₂Fe_1.039(8)Mn_0.962(8)O₅ were investigated using powder X-ray and neutron diffraction methods, the latter from 3.8 to 700 K. The compound crystallizes in Pnma space group with unit cell parameters of a=5.3055(5) Å, b=15.322(2) Å, c=5.4587(6) Å at 300 K. The neutron diffraction study revealed the occupancies of Fe³⁺ and Mn³⁺ ions in both octahedral and tetrahedral sites and showed some intersite mixing and a small, ∼4%, Fe excess. While bulk magnetization data were inconclusive, variable temperature neutron diffraction measurements showed the magnetic transition temperature to be 407(2) K below which a long range antiferromagnetic ordering of spins occurs with ordering wave vector k=(000). The spins of each ion are coupled antiferromagnetically with the nearest neighbors within the same layer and coupled antiparallel to the closest ions from the neighboring layer. This combination of intra- and inter-layer antiparallel arrangement of spins forms a G-type magnetic structure. The ordered moments on the octahedral and tetrahedral sites at 3.8 K are 3.64(16) and 4.23(16) μ_B, respectively.     

Crystal structure and magnetic properties of a new form of NH4MnFeF6

The hydrothermal synthesis at 380°C, 200 MPa of NH₄MnFeF₆, NH₄MnCrF₆, and RbMnFeF₆ leads to a new AM^IIM^IIIF₆ structural type of orthorhombic symmetry with Z = 8. Lattice constants are found to be, respectively, a = 7.844 (4), b = 12.819 (8), c = 10.582 (6); a = 7.808 (5), b = 12.755 (9), c = 10.501 (7); and a = 7.913 (5), b = 12.858 (9), c = 10.619 (5). The structure was solved for NH₄MnFeF₆ from 755 X-Ray reflections and refined to R_ω = 0.029 in the space group Pb2nC⁶_2v. The network is built from edge-sharing MnFeF₁₀ bioctahedra connected to each other by their vertices. RbMnFeF₆ upon heating transforms irreversibly to the modified pyrochlore structure at 881 K. From magnetic and Mössbauer experiments, NH₄MnFeF₆ and NH₄MnCrF₆ are established to be antiferromagnetic with T_N = 117.7 ± 0.5 K and < 6 K, respectively.