Synthesis, structure and properties of new chain cuprates, Na3Cu2O4 and Na8Cu5O10

Na₃Cu₂O₄ and Na₈Cu₅O₁₀ were prepared via the azide/nitrate route from stoichiometric mixtures of the precursors CuO, NaN₃ and NaNO₃. Single crystals have been grown by subsequent annealing of the as prepared powders at 500 °C for 2000 h in silver crucibles, which were sealed in glass ampoules under dried Ar. According to the X-ray analysis of the crystal structures (Na₃Cu₂O₄: P2₁/n, Z=4, a=5.7046(2), b=11.0591(4), c=8.0261(3) Å, β=108.389(1)°, 2516 independent reflections, R₁(all)=0.0813, wR₂ (all)=0.1223; Na₈Cu₅O₁₀: Cm, Z=2, a=8.228(1), b=13.929(2), , β=111.718(2)°, 2949 independent reflections, R₁(all)=0.0349, wR₂ (all)=0.0850), the main feature of both crystal structures are CuO₂ chains built up from planar, edge-sharing CuO₄ squares. From the analysis of the Cu-O bond lengths, the valence states of either +2 or +3 can be unambiguously assigned to each copper atom. In Na₃Cu₂O₄ these ions alternate in the chains, in Na₈Cu₅O₁₀ the periodically repeated part consists of five atoms according to Cu^II-Cu^II-Cu^III-Cu^II-Cu^III. The magnetic susceptibilities show the dominance of antiferromagnetic interactions. At high temperatures the compounds exhibit Curie-Weiss behaviour (Na₃Cu₂O₄: , , Na₈Cu₅O₁₀: , , magnetic moments per divalent copper ion). Antiferromagmetic ordering is observed to occur in these compounds below 13 K (Na₃Cu₂O₄) and 24 K (Na₈Cu₅O₁₀).     

Synthesis and crystal structure of the palladium oxides NaPd3O4, Na2PdO3 and K3Pd2O4

NaPd₃O₄, Na₂PdO₃ and K₃Pd₂O₄ have been prepared by solid-state reaction of Na₂O₂ or KO₂ and PdO in sealed silica tubes. Crystal structures of the synthesized phases were refined by the Rietveld method from X-ray powder diffraction data. NaPd₃O₄ (space group Pm3¯n, a=5.64979(6) Å, Z=2) is isostructural to NaPt₃O₄. It consists of NaO₈ cubes and PdO₄ squares, corner linked into a three-dimensional framework where the planes of neighboring PdO₄ squares are perpendicular to each other. Na₂PdO₃ (space group C2/c, a=5.3857(1) Å, b=9.3297(1) Å, c=10.8136(2) Å, β=99.437(2)°, Z=8) belongs to the Li₂RuO₃-structure type, being the layered variant of the NaCl structure, where the layers of octahedral interstices filled with Na⁺ and Pd⁴⁺ cations alternate with Na₃ layers along the c-axis. Na₂PdO₃ exhibits a stacking disorder, detected by electron diffraction and Rietveld refinement. K₃Pd₂O₄, prepared for the first time, crystallizes in the orthorhombic space group Cmcm (a=6.1751(6) Å, b=9.1772(12) Å, c=11.3402(12) Å, Z=4). Its structure is composed of planar PdO₄ units connected via common edges to form parallel staggered PdO₂ strips, where potassium atoms are located between them. Magnetic susceptibility measurements of K₃Pd₂O₄ reveal a Curie-Weiss behavior in the temperature range above 80 K.     

Synthesis and Properties of Rb6Mn2O6

Rb₆Mn₂O₆ was prepared via the azide/nitrate route. Stoichiometric mixtures of the precursors (Mn₃O₄, RbN₃ and RbNO₃) were heated in a special regime up to 500 °C and annealed at this temperature for 75 h in silver crucibles. Single crystals have been grown by annealing a mixture with a slight excess of rubidium components at 450 °C for 500 h. According to the single crystal structure analysis, Rb₆Mn₂O₆ is isotypic to K₆Mn₂O₆, and crystallizes in the monoclinic space group P2₁/c with a = 6.924(1) Å, b = 11.765(2) Å, c = 7.066(1) Å, β = 99.21(3)°, 2296 independent reflections, R₁ = 5.23 % (all data). Manganese is tetrahedrally coordinated and two tetrahedra are linked by sharing a common edge, forming a dimer [Mn₂O₆]⁶⁻. The magnetic behavior has been investigated.     

Synthesis,Crystal Structure and Properties of RbMnO2

RbMnO₂ was prepared via the azide/nitrate route. Stoichiometric mixtures of the precursers (Mn₂O₃, RbN₃ and RbNO₃) were heated in a special regime up to 600 °C and annealed at this temperature for 30 h in specially designed silver crucibles. Single crystals have been grown by annealing a 1:1 mixture of Rb₂O and MnO_x at 585 °C for 1200 h. According to the crystal structure determination Mn³⁺ is in a square‐pyramidal coordination by oxygen. These [MnO₅] units form double chains extending along the crystallographic c‐axis. RbMnO₂ shows Curie‐Weiss behaviour down to ～ 100 K. A fit of the susceptibility data yields an average value of the magnetic moment (per manganese atom) of μ_eff = 5.33 μ_B, and θ_p = –820 K. At 50 K and low field strength onset of ferromagnetic order due to spin canting has been observed.     

Synthesis and Crystal Structure of Na7Cu3O8, Containing a New Type of Oxocuprate(III) Oligoanion

Na₇Cu₃O₈ was prepared through oxidation of a Na₃CuO₂/NaCuO mixture (2:1) in dried oxygen at 450 °C. Single crystals have been grown by annealing of Na₇Cu₃O₈, in the presence of Na₂O₂, at 450 °C for 2000 h in silver crucibles, which were sealed in glass ampoules under dried Ar. According to the X-ray analysis of the crystal structure ( , Z = 1, a = 5.5891(2), b = 6.0945(2), c = 7.8890(3) Å, α = 110.059(2), β = 108.669(2), γ = 90.237(2)°) a new Cu₃O₈^7- oxocuprate anion, consisting of three edge sharing CuO₄ squares, is the prominent structural feature. These anions are aligned parallel to the space diagonal of the unit cell and can be regarded as infinite chains from which every fourth copper atom has been removed. This new representative of an oxocuprate(III) anion gives support to the expectation that the gap between dimeric and infinite edge sharing units of square planar cuprate anions can be closed, in principle.     

Synthesis, structure and magnetic properties of the new mixed-valence vanadate Na2SrV3O9

The new complex oxide Na₂SrV₃O₉ was synthesized and investigated by means of X-ray diffraction, electron microscopy and magnetic susceptibility measurements. This oxide has a monoclinic unit cell with parameters a=5.416(1) Å, b=15.040(3) Å, c=10.051(2) Å, β=97.03(3)°, space group P2₁/c and Z=4. The crystal structure of Na₂SrV₃O₉, as determined from X-ray single-crystal data, is built up from isolated chains formed by square V⁴⁺O₅ pyramids. Neighboring pyramids are linked by two bridging V⁵⁺O₄ tetrahedra sharing a corner with each pyramid. The Na and Sr atoms are situated between the chains. Electron diffraction and HREM investigations confirmed the crystal structure. The temperature dependence of the susceptibility indicates low-dimensional magnetic behavior with a sizeable strength of the magnetic intra-chain exchange J of the order of 80 K, which is very likely due to superexchange through the two VO₄ tetrahedra linking the magnetic V⁴⁺ cations.     

Structure and basic magnetic properties of the honeycomb lattice compounds Na2Co2TeO6 and Na3Co2SbO6

The synthesis, structure, and basic magnetic properties of Na₂Co₂TeO₆ and Na₃Co₂SbO₆ are reported. The crystal structures were determined by neutron powder diffraction. Na₂Co₂TeO₆ has a two-layer hexagonal structure (space group P6₃22) while Na₃Co₂SbO₆ has a single-layer monoclinic structure (space group C2/m). The Co, Te, and Sb ions are in octahedral coordination, and the edge sharing octahedra form planes interleaved by sodium ions. Both compounds have full ordering of the Co²⁺ and Te⁶⁺/Sb⁵⁺ ions in the ab plane such that the Co²⁺ ions form a honeycomb array. The stacking of the honeycomb arrays differ in the two compounds. Both Na₂Co₂TeO₆ and Na₃Co₂SbO₆ display magnetic ordering at low temperatures, with what appears to be a spin-flop transition found in Na₃Co₂SbO₆.     

Crystal structure, magnetic, and dielectric properties of Aurivillius-type Bi3Fe0.5Nb1.5O9

Bi₃Fe_0.5Nb_1.5O₉ was synthesized using conventional solid state techniques and its crystal structure was refined by the Rietveld method using neutron powder diffraction data. The oxide adopts an Aurivillius-type structure with non-centrosymmetric space group symmetry A2₁am (a=5.47016(9) Å, b=5.43492(9) Å, c=25.4232(4) Å), analogous to other Aurivillius compounds that exhibit ferroelectricity. The Fe and Nb cations are disordered on the same crystallographic site. The [(Fe,Nb)O₆] octahedra exhibit tilting and distortion to accommodate the bonding requirements of the Bi cations located in the perovskite double layers. Magnetic measurements indicate non-Curie-Weiss-type paramagnetic behavior from 300 to 6 K. Measurements of dielectric properties and electrical resistivity exhibited changes near 250-260 °C and are suggestive of a ferroelectric transition.     

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.     

Synthesis and Crystal Structure of CsCu3O2, Containing a New Type of Oxocuprate(I) Polyanion

CsCu₃O₂ was prepared via the azide route. Stoichiometric mixtures of the precursors (CsN₃, Cu₂O and CuO) were heated in a special regime up to 450 °C and annealed at this temperature for 50 h in silver crucibles. Single crystals have been grown by subsequent annealing of as prepared powders at 450 °C for 2000 h in silver crucibles, which were sealed in glass ampoules under dried Ar. According to the X‐ray analysis of the crystal structure (P3¯m1, Z = 1, a = 5.250(1), c = 5.442(1)Å, γ = 120°) copper is linearly coordinated by oxygen atoms. The CuO₂‐dumb‐bells are connected to an infinite two‐dimensional Cu₃O₂‐network. CsCu₃O₂ is isostructural with CsCu₃S₂, CsAu₃S₂, CsAu₃Se₂ and RbAu₃Se₂.     

Original close-packed structure and magnetic properties of the Pb4Mn9O20 manganite

The crystal structure of the Pb₄Mn₉O₂₀ compound (previously known as “Pb_0.43MnO_2.18”) was solved from powder X-ray diffraction, electron diffraction, and high resolution electron microscopy data (S.G. Pnma, a=13.8888(2) Å, b=11.2665(2) Å, c=9.9867(1) Å, R_I=0.016, R_P=0.047). The structure is based on a 6H (cch)₂ close packing of pure oxygen “h”-type (O₁₆) layers alternating with mixed “c”-type (Pb₄O₁₂) layers. The Mn atoms occupy octahedral interstices formed by the oxygen atoms of the close-packed layers. The MnO₆ octahedra share edges within the layers, whereas the octahedra in neighboring layers are linked through corner sharing. The relationship with the closely related Pb₃Mn₇O₁₅ structure is discussed. Magnetization measurements reveal a peculiar magnetic behavior with a phase transition at 52 K, a small net magnetization below the transition temperature, and a tendency towards spin freezing.     

Synthesis, band structure, and optical properties of Ba2ZnV2O8

A novel compound Ba₂ZnV₂O₈ has been synthesized in high temperature solution reaction and its crystal structure has been characterized by means of single crystal X-ray diffraction analysis. It crystallizes in monoclinic system and belongs to space group P2₁/c with a=7.9050(16), b=16.149(3), , β=90.49(3). It builds up from 1-D branchy chains of [ZnV₂O₈⁴⁻]_∞, and the Ba²⁺ cations are located in the space among these chains. The IR spectrum, ultraviolet-visible diffuse reflection integral spectrum and fluorescent spectra of this compound have been investigated. The calculated results of energy band structure by the density functional theory method show that the solid-state compound of Ba₂ZnV₂O₈ is an insulator with direct band gap of 3.48 eV. The calculated total and partial density of states indicate that the top valence bands are contributions from the mixings of O-2p, V-3d, and Zn-3d states and low conduction bands mostly originate from unoccupied antibonding states between the V-3d and O-2p states. The V-O bonds are mostly covalence characters and Zn-O bonds are mostly ionic interactions, and the ionic interaction strength is stronger between the Ba-O than between the Zn-O. The refractive index of n_x, n_y, and n_z is estimated to be 1.7453, 1.7469, and 1.7126, respectively, at wavelength of 1060 nm for Ba₂ZnV₂O₈ crystal.     

Synthesis and structure of Ba6Co6ClO16, a new cobalt oxychloride with a layered perovskite-related structure

Well-developed single crystals of the title compound were prepared using a BaCl₂ flux and investigated by X-ray diffraction methods using Mo(Kα) radiation and a Charge Coupled Device (CCD) detector. The crystal structure was solved and refined in the hexagonal symmetry with space group, a=5.6698(2) Å and c=14.4654(5) Å to a final R₁=0.022 for 44 parameters with 1418 individual reflections. The structure of Ba₆Co₆ClO₁₆, which is related to the 6H-perovkite-type structure of BaMnO_2.88, is formed by the periodic stacking along [001] of five [BaO₃] layers separated by a [BaOCl] with a (hhhchc) stacking sequence. The [BaO₃] stacking creates tetranuclear face sharing octahedra units Co₄O₁₅ containing Co(III) connected by dimers of corner-sharing CoO₄ tetrahedra. This new oxychloride belongs to the family of compounds formulated as [BaOCl]M′₂[Ba_n+1M_nO_3n+3] where n represents the thickness of the octahedral string in hexagonal perovskite slabs.     

New germanates RCrGeO5 (R=Nd-Er, Y): Synthesis, structure, and properties

The new complex germanates RCrGeO₅ (R=Nd-Er, Y) have been synthesized and investigated by means of X-ray powder diffraction, electron microscopy, magnetic susceptibility and specific heat measurements. All the compounds are isostructural and crystallize in the orthorhombic symmetry, space group Pbam, and Z=4. The crystal structure of RCrGeO₅, as refined using X-ray powder diffraction data, includes infinite chains built by edge-sharing Cr⁺³O₆ octahedra with two alternating Cr−Cr distances. The chains are combined into a three-dimensional framework by Ge₂O₈ groups consisting of two edge-linked square pyramids oriented in opposite directions. The resulting framework contains pentagonal channels where rare-earth elements are located. Thus, RCrGeO₅ germanates present new examples of RMn₂O₅-type compounds and show ordering of Cr⁺³ and Ge⁺⁴ cations. Electron diffraction as well as high-resolution electron microscopy confirm the structure solution. Magnetic susceptibility data for R=Nd, Sm, and Eu are qualitatively consistent with the presence of isolated 3d (antiferromagnetically coupled Cr⁺³ cations) and 4f (R⁺³) spin subsystems in the RCrGeO₅ compounds. NdCrGeO₅ undergoes long-range magnetic ordering at 2.6 K, while SmCrGeO₅ and EuCrGeO₅ do not show any phase transitions down to 2 K.     

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.     

A sodium gadolinium phosphate with two different types of tunnel structure: Synthesis, crystal structure, and optical properties of Na3GdP2O8

A sodium gadolinium phosphate crystal, Na₃GdP₂O₈, has been synthesized by a high-temperature solution reaction, and it exhibits a new structural family of the alkali-metal-rare-earth phosphate system. Although many compounds with formula M₃LnP₂O₈ have been reported, but they were shown to be orthorhombic [R. Salmon, C. Parent, M. Vlasse, G. LeFlem, Mater. Res. Bull. 13 (1978) 439] rather than monoclinic as shown in this paper. Single-crystal X-ray diffraction analysis shows the structure to be monoclinic with space group C2/c and the cell parameters: a=27.55 (25), b=5.312 (4), c=13.935(11) Å, β=91.30(1)°, and V=2038.80 Å³, Z=4. Its structure features a three-dimensional GdP₂O₈³⁻ anionic framework with two different types of interesting tunnels at where Na atoms are located by different manners. The framework is constructed by Gd polyhedra and isolated PO₄ tetrahedra. It is different from the structure of K₃NdP₂O₈ [R. Salmon, C. Parent, M. Vlasse, G. LeFlem, Mater. Res. Bull. 13 (1978) 439] with space group P2₁/m that shows only one type of tunnel. The emission spectrum and the absorption spectrum of the compound have been investigated. Additionally, the calculations of band structure, density of states, dielectric constants, and refractive indexes have been also performed with the density functional theory method. The obtained results tend to support the experimental data.     

Syntheses, crystal structures, and properties of three new metal selenites Na2Co2(SeO3)3, Na2Co1.67Ni0.33(SeO3)3, and Na2Ni2(SeO3)3

Three new sodium cobalt (nickel) selenite compounds, namely, Na₂Co₂(SeO₃)₃, Na₂Co_1.67Ni_0.33(SeO₃)₃, and Na₂Ni₂(SeO₃)₃ have been hydro-/solvothermally synthesized in the mixed solvents of acetonitrile and water. Single-crystal X-ray diffraction analyses reveal that these isostructural compounds belong to the orthorhombic Cmcm space group and their structures feature three-dimensional open frameworks constructed by the two-dimensional layers of [MSeO₃] pillared by the [SeO₃]²⁻ groups. The two different types of Na⁺ ions reside in the intersecting two-dimensional channels parallel to the a- and c-axes, respectively. Their thermal properties have been investigated via TGA-DSC. The magnetic measurements indicate the existence of the antiferromagnetic interactions in these compounds.     

Synthesis, crystal structure, and nonlinear optical properties of Bi2Cu5B4O14

Bi₂Cu₅B₄O₁₄ crystallizes in the noncentrosymmetric triclinic space group P1 (No. 1) with cell parameters a=10.1381(11) Å, b=9.3917(11) Å, c=3.4566(4) Å, α=105.570(2)°, β=92.275(2)°, γ=107.783(2)°, Z=1 and R₁=0.0401 and wR₂=0.0980. It is a layered structure that is built up from sheets of rectangular CuO₄ and trigonal BO₃ groups. The sheets are connected by infinite chains of edge shared BiO₆ polyhedra that intersect the bc plane at an angle slightly greater than 90°. The second-harmonic generation efficiency of Bi₂Cu₅B₄O₁₄, using 1064 nm radiation, is about one half times that of KH₂PO₄.     

Synthesis,Crystal Structure and Properties of Na2MnO2

Na₂MnO₂ was prepared via the azide/nitrate route. Stoichiometric mixtures of the precursors (Mn₂O₃, NaN₃ and NaNO₃) were heated in an appropriate regime up to 390 °C and annealed at this temperature for 20 h, in specially designed silver containers. As the most prominent feature, the crystal structure of Na₂MnO₂ (C2/c, Z = 12, a = 12.5026(9), b = 12.1006(9), c = 6.0939(4) Å, β = 117.94(0)°, 1556 independent reflections, R₁ = 3.83 % (all data)) forms a three dimensional framework polyanion of corner sharing MnO₄‐tetrahedra. The connectivity pattern of the tetrahedral building units corresponds to the moganite structure, a rare SiO₂ modification. According to measurements of the magnetic susceptibility in the temperature range from 2 to 750 K, Na₂MnO₂ shows antiferromagnetic ordering below 250 K. Evaluation of the high temperature data employing the Curie‐Weiss law revealed a magnetic moment of μ_eff = 5.93 μ_B, confirming the presence of divalent manganese.     

Single-crystal synthesis and structure refinement of the LiCoO2-LiAlO2 solid-solution compounds: LiAl0.32Co0.68O2 and LiAl0.71Co0.29O2

Single crystals of the LiCoO₂-LiAlO₂ solid solution compounds LiAl_0.32Co_0.68O₂ and LiAl_0.71Co_0.29O₂ were synthesized by a flux method using alumina crucibles. A single-crystal X-ray diffraction study confirmed the trigonal space group and the lattice parameters a=2.8056(11) Å, c=14.1079(15) Å, and c/a=5.028 for LiAl_0.32Co_0.68O₂, and a=2.8023(7) Å, c=14.184(4) Å, and c/a=5.061 for LiAl_0.71Co_0.29O₂. The crystal structures have been refined to the conventional values R=3.2% and wR=2.4% for LiAl_0.32Co_0.68O₂, and R=3.6% and wR=3.5% for LiAl_0.71Co_0.29O₂. The evidence of the location of Al atoms in the pseudotetragonal coordination (6c site), reported previously in LiAl_0.2Co_0.8O₂, could not be observed in the present electron density distribution maps in both LiAl_0.32Co_0.68O₂ and LiAl_0.71Co_0.29O₂. The octahedral distortion analysis indicated that the Al-substitution strongly affected the distortion of the LiO₆ octahedron in this solid-solution compound system, but hardly affected that of the (Al.Co)O₆ octahedron.