High-pressure synthesis and crystal structures of two new polyphosphides, NaP5 and CeP5

Two novel polyphosphides, NaP₅ and CeP₅, were prepared in a BN crucible by the reaction of elemental components under a high pressure of 3 GPa at 800–950 °C. The X-ray structural analysis showed that NaP₅ crystallizes in an orthorhombic space group Pnma with a=10.993(2) Å, b=6.524(1) Å, c=6.903(1) Å, Z=4 and CeP₅ in the monoclinic group P2₁/m with a=4.9143(5) Å, b=9.6226(8) Å, c=5.5152(4) Å, β=104.303(6)°, Z=2. The crystal structure of NaP₅ consists of a three-dimensional framework _∞³[P₅]¹⁻ constructed by P---P bonds among four crystallographically inequivalent phosphorus sites, with large channels hosting the sodium cations, while CeP₅ is a layered compound containing _∞²[P₅]³⁻ polyanionic layers that are separated by Ce³⁺ ions. NaP₅ exhibits the diamagnetic behavior, while the temperature-dependent magnetic susceptibility of CeP₅ essentially follows the Curie–Weiss law.     

Synthesis and crystal structure of Ba3Si4C2

SiC powder prepared by the Na flux method at 1023 K for 24 h and Ba were used as starting materials for synthesis of tribarium tetrasilicide acetylenide, Ba₃Si₄C₂. Single crystals of the compound were obtained by heating the starting materials with Na at 1123 K for 1 h and by cooling to 573 K at a cooling rate of −5.5 K/h. The single crystal X-ray diffraction peaks were indexed with tetragonal cell dimensions of a = 8.7693(4) and c = 12.3885(6) Å, space group I4/mcm (No.140). Ba₃Si₄C₂ has the Ba₃Ge₄C₂ type structure which can be described as a cluster-replacement derivative of perovskite (CaTiO₃), and contains isolated anion groups of slightly compressed [Si₄]⁴⁻ tetrahedra and [C₂]²⁻ dumbbells. The electrical conductivity measured for a not well-sintered polycrystalline sample was 2.6 × 10⁻²–7 × 10⁻³ S cm⁻¹ in the temperature range of 370–600 K and slightly increased with increasing temperature. The Seebeck coefficient showed negative values of around −200 to −300 μV K⁻¹.     

Electronic structure and linear optical property of BaSi2N2O2 crystal

The electronic structure and linear optical property of BaSi₂N₂O₂ (BSNO) have been calculated by density functional method with the local density approximation. A direct band gap of 5.17 eV at G is obtained for BSNO. The calculated total and partial densities of states indicate that the top valence band is mainly constructed from the N 2p and O 2p states, the low conduction band mostly originates from Ba 4d and Si 3p states. The calculated linear optical property of BSNO is in good agreement with the experimental measurement.     

Ba3YB3O9: phase transition and crystal structure

A new modification of the compound Ba₃YB₃O₉, β phase, has been attained through solid phase transition from phase at 1125–1134 °C. β-Ba₃YB₃O₉ crystallizes in the hexagonal space group with cell parameters a=13.0529(8) Å, c=9.5359(9) Å. The crystal structure of -Ba₃YB₃O₉ has been determined from powder X-ray diffraction (XRD) data. The refinement was carried out using the Rietveld methods and the final refinement converged with R_p=8.8%, and R_wp=11.8% with R_exp=5.65%. In its structure, the isolated [BO₃]³⁻ anionic groups are parallel to each other and distributed layer upon layer along the c-axis. The Y atoms are six-coordinated by the O atoms to form octahedra. The result of IR spectrum confirmed the existence of [BO₃]³⁻ triangular groups.     

Single crystal preparation and crystal structure of the Cu2Zn/Cd,Hg/SnSe4 compounds

Single crystals of Cu₂Zn/Cd/SnSe₄ were grown using a solution-fusion method. The crystal structure of the Cu₂Zn/Cd,Hg/SnSe₄ compounds were investigated using X-ray powder diffraction. These compounds crystallize in the stannite structure (space group I 2m) with the lattice parameters: a=0.56882(9), c=1.13378(9) nm, c/a=1.993 (Cu₂ZnSnSe₄), a=0.58337(2), c=1.14039(4) nm, c/a=1.955 (Cu₂CdSnSe₄) and a=0.58288(1), c=1.14179(2) nm, c/a=1.959 (Cu₂HgSnSe₄). Atomic parameters were refined in the isotropic approximation (R_I=0.0517, R_I=0.0511 and R_I=0.0695 for Cu₂ZnSnSe₄, Cu₂CdSnSe₄ and Cu₂HgSnSe₄, respectively).     

Monoclinic phases and stress-relief conditions in (1 − x)Pb(Mg1/3Nb2/3)TiO3–xPbTiO3 solid solutions

A comparative study on heterophase states in perovskite-type solid solutions of (1 − x)Pb(Mg_1/3Nb_2/3)TiO₃–xPbTiO₃ is carried out for compositions near the morphotropic phase boundary. The conditions for mechanical stress relief at elastic matching of phases are analysed at x = const in a wide temperature range. The heterophase states concerned with the presence of the intermediate monoclinic phase are interpreted using the domain state–interface diagrams calculated for x = 0.28, 0.32 and 0.34. It is shown that optimum volume fraction parameters of the domains in the monoclinic phase of the B type are varied in relatively wide ranges and promote complete stress relief with cubic–monoclinic phase coexistence. Two scenarios of stress relief at x = 0.32 are considered in connection with different heterophase states (either tetragonal–monoclinic of the B type or tetragonal–monoclinic of the C type) in a wide temperature range. Possibilities of elastic matching of two polydomain phases (tetragonal–monoclinic of the B type) with almost equal relative widths of the domains in these phases are shown for x = 0.34. The active role of domains of the monoclinic phases in stress relief and forming the planar unstrained interfaces is discussed.     

High pressure study of β-UH3 crystallographic and electronic structure

The crystallographic and electronic structure of β-UH₃ were studied as a function of pressure by combining X-ray diffraction results with the full potential linearized augmented plane wave (LAPW) calculations. No phase transition was observed up to a pressure of 29 GPa, with a total volume contraction of V/V₀=0.87, and a bulk modulus value of B₀=33±5 GPa. The calculated value of the electric field gradient main component at the uranium 6(c) site was found to be linear dependent in the pressure induced volume reduction. This linear dependence is attributed to the increase in the positive p–p contribution to the efg as a function of volume, while the negative s–d, d–d and the lattice contributions to the efg are almost pressure independent.     

Syntheses and characterization of two new selenides Ba5Al2Se8 and Ba5Ga2Se8

Two new barium selenides Ba₅Al₂Se₈ and Ba₅Ga₂Se₈ have been synthesized by solid-state reactions. The structures of Ba₅Ga₂Se₈ and Ba₅Al₂Se₈ were determined by single-crystal X-ray diffraction method and the Rietveld method, respectively. The two isostructural compounds crystallize in space group Cmca of the orthorhombic system with isolated MSe₄ (M = Al, Ga) tetrahedra separated by Ba atoms. The optical band gap of 2.51(2) eV for Ba₅Ga₂Se₈ was deduced from the diffuse reflectance spectrum. Band structure calculation indicates that Ba₅Ga₂Se₈ is a direct-gap semiconductor. The valence band maximum is dominated by Se 4p orbitals, while the Ba 5d orbitals have the largest contribution to bottom of the conduction band.     

An investigation of the structures of the compounds in the tin-rich part of the Dy–Sn system: Crystal structure of Dy5Sn11 and Dy5Sn13

The structural properties of the compounds in the tin-rich part of the dysprosium–tin system have been studied by X-ray powder diffraction. The crystal structures of six compounds DySn_2+x (0 < x < 1) have been characterized. There are four compounds with known structural types: DySn₂ with the ZrSi₂ structure, Dy₃Sn₇ with the Gd₃Sn₇ structure, Dy₂Sn₅ with the Er₂Ge₅ structure, DySn₃ with the DyGe₃ structure and two compounds characterized by new body-centred orthorhombic types (Immm): Dy₅Sn₁₁ (a = 4.411 Å, b = 42.50 Å and c = 4.328 Å) and Dy₅Sn₁₃ (a = 4.341 Å, b = 48.05 Å and c = 4.405 Å) which result from various insertions of AuCu₃ and Po slabs into the ZrSi₂ structure. The relationships and structural evolution are discussed.     

Magnetic properties and electronic structures of GdCo3−xSix compounds

Magnetic measurements and band structure calculations were performed on GdCo_3−xSi_x system with x ≤ 0.3. The experimentally determined magnetizations are in rather good agreement with those obtained from band structure calculations. The composition dependence of cobalt moments, at various lattice sites, are analyzed in correlation with the effects of Co 3d–Si 3p bands hybridization.     

Synthesis and properties of Ba3NaRu2O9−δ and Ba3(Na, R)Ru2O9−δ (R=rare earth) crystals

Crystals of Ba₃NaRu₂O_9−δ (δ≈0.5) and Ba₃(Na, R)Ru₂O_9−δ (R=Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm and Yb) were grown by an electrochemical method, and their crystallographic, magnetic, and electric properties were studied. All crystals have a hexagonal structure of space group P6₃mmc. Ba₃NaRu₂O_9−δ and Ba₃(Na, R)Ru₂O_9−δ (except Ce) have a negative asymptotic Curie temperature suggesting the existence of an antiferromagnetic order; however, they are paramagnetic at temperatures above 1.7 K. Ba₃NaRu₂O_9−δ has an effective magnetic moment P_eff of 0.91 μ_B, while P_eff of Ba₃(Na, R)Ru₂O_9−δ (except Ce) reflects the large free-ion moment of the rare earth ions. Ba₃(Na, Ce)Ru₂O_9−δ shows peculiar magnetic behavior that differs from the magnetism of other Ba₃(Na, R)Ru₂O_9−δ crystals. The resistivity of all crystals exhibits an activation-type temperature dependence with an activation energy in the range of 0.10.2 eV.     

Phase transitions in Cd3P2 at high pressures and high temperatures

The high-pressure, high-temperature structural behaviour of Cd₃P₂ has been studied using electrical resistance measurements, differential thermal analysis, thermo baric analysis and X-ray diffraction. At room temperature, a phase transformation is observed at 4.0 GPa in compression. The experimental zero-pressure bulk modulus of the low-pressure phase is 64.7(7) GPa, which agrees quite well with the calculated value of 66.3 GPa using the tight-binding linear muffin-tin orbital method within the local density approximation. Tentatively, the high-pressure phase has an orthorhombic crystal structure with space group Pmmn (#59). The relative volume change at the phase transition is ΔV/V = −5.5%. Amorphization of the sample occurs above 25 GPa. A P–T phase diagram of Cd₃P₂ has been constructed. A metastable phase is observed at ambient conditions after heating the sample to above 600 K at about 3 GPa. A hexagonal unit cell can describe the crystal structure of the metastable phase.     

Investigation of cation-deficient quaternary thiospinels: single crystal study of Ag1.4Cr1.47Sn2.53S8

Single crystals of the quaternary thiospinel Ag_1.41(1)Cr_1.47(5)Sn_2.52(5)S₈ have been obtained by heating stoichiometric mixtures of elemental metals and sulfur at 750 °C. Structural analysis by single crystal X-ray diffraction shows that the above phase crystallizes in the space group with a = 10.4142(3) Å (R₁ = 0.0156 and wR₂ = 0.0416). The Ag-deficiency has been confirmed by solving the structures of crystals prepared in different batches and was observed to vary slightly between crystals. Magnetic studies on a monophasic powder sample with a nominal composition of Ag_1.63CrSn₃S₈ indicates anti-ferromagnetic ordering at low temperature. The high temperature susceptibility leads to a magnetic moment of 3.45 B.M. suggesting that chromium exists predominantly in a trivalent state.     

LiSrGe2 and LiBaGe2: One-dimensional chains of in an unusual conformation

Two new isostructural intermetallic germanides, LiSrGe₂ and LiBaGe₂, were synthesized as single crystals from constituent elements in molten Na. They both crystallize in the space group Pnma (no. 62) with a = 7.142(1), b = 4.459(1), c = 11.550(2) Å, Z = 4, and a = 7.381(1), b = 4.617(1), c = 11.837(1) Å, Z = 4, for LiSrGe₂ and LiBaGe₂, respectively. They contain one-dimensional anionic germanide chains, , running along the a-axis. The chains are in an unusual zigzag-like conformation, with weakly alternating Ge–Ge bond lengths of 2.475(1) and 2.498(1) Å, and 2.473(1) and 2.525(1) Å, for LiSrGe₂ and LiBaGe₂, respectively. Extended Hückel calculations suggest that LiSrGe₂ is metallic: the Fermi level lies within bands having anti-bonding character.     

Crystal structures of the Ag4HgGe2S7 and Ag4CdGe2S7 compounds

The crystal structures of the Ag₄HgGe₂S₇ and Ag₄CdGe₂S₇ compounds were investigated using X-ray powder diffraction. These compounds crystallize in the monoclinic Cc space group with the lattice parameters a=1.74546(8), b=0.68093(2), c=1.05342(3) nm, β=93.398(3)° for Ag₄HgGe₂S₇ and a=1.74364(8), b=0.68334(3), c=1.05350(4) nm, β=93.589(3)° for Ag₄CdGe₂S₇. Atomic parameters were refined in the isotropic approximation (R_I=0.0761 and R_I=0.0727, respectively).     

A theoretical analysis of zero-field splitting parameters of Mn doped dicadmium diammonium sulfate Cd2(NH4)2(SO4)3 single crystal

The superposition model (SPM) and crystallographic data are utilized to determine the zero-field splitting (ZFS) parameters (ZFSPs) for Mn²⁺ ions in Cd₂(NH₄)₂(SO₄)₃ single crystal, assuming that the Mn²⁺ ions locate at either Cd²⁺ or NH⁴⁺ site. The SPM results has been verified by the fourth-order perturbation formulae analysis. Experimental suggestions about Mn²⁺ ions substituting at Cd²⁺ sites have been confirmed theoretically for the first time.     

X-ray photoemission spectrum, electronic structure, and magnetism of UCu2Si2

The room temperature X-ray photoemission spectrum of the ferromagnetic compound UCu₂Si₂ (T_C = 100 K) was measured using an Al K_α source. Related theoretical spectra were computed from densities of electronic states obtained in the local density approximation (LDA), the generalized gradient approximation (GGA), and using the GGA + U method. The calculated spectrum is in a good agreement with the experimental one. The spin polarized calculations based on the GGA + U approach as well as GGA/LSDA with orbital polarization (OP) corrections taken into account provide values of the total magnetic moment in reasonable agreement with the experimental values ranging between 1.6 and 2.0 μ_B/U atom.     

Crystal structure and magnetic properties of ZnV2O4

We present structural and magnetic data on ZnV₂O₄ single crystals. Single crystal X-ray diffraction shows the measured crystals to be of very high quality, especially with respect to atomic order. The measured magnetic susceptibility resembles to that of a spin glass system, surprising for a translational invariant structure. The results are discussed in the framework of disorder in a magnetically frustrated lattice.     

Studies on structural and electrical properties of Co1−xNixFe1.9Mn0.1O4 ferrite

Nickel-doped iron-deficient cobalt ferrite with small amount of manganese having the chemical composition Co_1−xNi_xFe_1.9Mn_0.1O₄, with x = 0.2, 0.4, 0.6 and 0.8, were prepared by standard double sintering ceramic method. The spinel phase formation was confirmed by X-ray diffraction (XRD). The DC resistivity measurements with temperature indicate a semiconducting behavior showing a linear decrease with increasing temperature and the doping of Ni enhances the resistivity. Maximum resistivity of the order of 10⁹ Ω cm was found for composition x = 0.8. Room temperature dielectric constant measurements with frequency (100 Hz to 1 MHz), show usual dielectric dispersion. Also, the variation of room temperature AC conductivity as a function of frequency were studied and explained by using Maxwell–Wagner two-layer model. The studies on dielectric constant (′), loss tangent (tan δ) and AC conductivity (σ_AC), at four different frequencies (viz., 1, 10, 100 kHz and 1 MHz), with temperature were made.     

Crystal structures and magnetic properties of iron (III)-based phosphates: Na4NiFe(PO4)3 and Na2Ni2Fe(PO4)3

Crystal structures from two new phosphates Na₄NiFe(PO₄)₃ (I) and Na₂Ni₂Fe(PO₄)₃ (II) have been determined by single crystal X-ray diffraction analysis. Compound (I) crystallizes in a rhombohedral system (S. G: R-3c, Z = 6, a = 8.7350(9) Å, c = 21.643(4) Å, R₁ = 0.041, wR₂=0.120). Compound (II) crystallizes in a monoclinic system (S. G: C2/c, Z = 4, a = 11.729(7) Å, b = 12.433(5) Å, c = 6.431(2) Å, β = 113.66(4)°, R₁ = 0.043, wR₂=0.111). The three-dimensional structure of (I) is closely related to the Nasicon structural type, consisting of corner sharing [(Ni/Fe)O₆] octahedra and [PO₄] tetrahedra forming [NiFe(PO₄)₃]⁴⁺ units which align in chains along the c-axis. The Na⁺ cations fill up trigonal antiprismatic sites within these chains. The crystal structure of (II) belongs to the alluaudite type. Its open framework results from [Ni₂O₁₀] units of edge-sharing [NiO₆] octahedra, which alternate with [FeO₆] octahedra that form infinite chains. Coordination of these chains yields two distinct tunnels in which site Na⁺.The magnetization data of compound (I) reveal antiferromagnetic (AFM) interactions by the onset of deviations from a Curie-Weiss behaviour at low temperature as confirmed by Mössbauer measurements performed at 4.2 K. The corresponding temperature dependence of the reciprocal susceptibility χ⁻¹ follows a typical Curie-Weiss behaviour for T > 105 K. A canted AFM state is proposed for compound (II) below 46 K with a field-induced magnetic transition at H ≈ 19 kOe, revealed in the hysteresis loop measured at 5 K. This transition is most probably associated with a spin-flop transition.