Space Group P3m1 Research Articles

Synthesis of a Ferrolite: A Zeolitic All-Iron Framework.

Crystals of the first sodalite-type zeolite containing an all-iron framework, a ferrolite, Ba8 (Fe12 O24 )Nay (OH)6 ⋅x H2 O, were synthesized using the hydroflux method in nearly quantitative yield. Ba8 (Fe12 O24 )Nay (OH)6 ⋅x H2 O crystallizes in the cubic space group Pm3‾m with a=10.0476(1) Å. Slightly distorted FeO4 tetrahedra are linked to form Fe4 O4 and Fe6 O6 rings, which in turn yield channels and internal cavities that are characteristic of the sodalite structure. Barium, sodium, and hydroxide ions and water molecules are found in the channels and provide charge balance. Magnetic measurements indicate that the ferrolite exhibits magnetic order up to at least 700 K, with the field-cooled and zero-field-cooled curves diverging. Analysis of the 57 Fe Mössbauer spectra revealed two spectral components that have equal spectral areas, indicating the presence of two subsets of iron centers in the structure. Dehydrated versions of the ferrolite were also prepared by heating the sample.

Nanocage containing metal-organic framework constructed from a newly designed low symmetry tetra-pyrazole ligand

1368-Tetra(1H-pyrazol-4-yl)-9H-carbazole (H4CTP), a tetra-pyrazole ligand with Cs symmetry, has been synthesized based on a carbazole core. A solvothermal reaction of this ligand with NiCl2·6H2O gave a three-dimensional (3-D) metal-organic framework (MOF), [Ni(H4CTP)Cl2]·nS (BUT-41), which crystallized in the cubic space group Pm-3 in spite of H4CPT with a central carbazole core and four peripheral pyrazole rings has low symmetry. The framework of BUT-41 can be regarded as a four-connected 3-D net with the rhr topology when both the organic ligand and the metal center are considered as four-connected nodes. Nanocages with internal diameter of 2 nm are present in the framework of BUT-41, which are formed by interconnecting 12 H4CTP ligands and 20 Ni(II) ions. Each nanocage connects with six adjacent cages through sharing hexagonal windows with diameter over 7 Å, resulting in 3-D intersecting channels of the MOF. Although the tetra-pyrazole ligand is not deprotonated after coordination with the metal ions, powder X-ray diffraction and N2 adsorption experiments reveal that the framework of BUT-41 is rigid and permanently porous with the Brunauer-Emmett-Teller surface area up to 1551 m2 g−1. Furthermore, gas adsorption experiments show that this MOF selectively adsorbs CO2 over N2 and CH4.

Strong magnetic correlations to 900 K in single crystals of the trigonal antiferromagnetic insulatorsSrMn2As2andCaMn2As2

Crystallographic, electronic transport, thermal and magnetic properties are reported for SrMn2As2 and CaMn2As2 single crystals grown using Sn flux. Rietveld refinements of powder x-ray diffraction data show that the two compounds are isostructural and crystallize in the trigonal CaAl2Si2-type structure (space group P-3m1), in agreement with the literature. Electrical resistivity rho versus temperature T measurements demonstrate insulating ground states for both compounds with activation energies of 85 meV for SrMn2As2 and 61 meV for CaMn2As2. In a local-moment picture, the Mn^{+2} 3d^5 ions are expected to have high-spin S = 5/2 with spectroscopic splitting factor g = 2. Magnetic susceptibility chi and heat capacity measurements versus T reveal antiferromagnetic (AFM) transitions at TN = 120(2) K and 62(3) K for SrMn2As2 and CaMn2As2, respectively. The anisotropic chi(T < TN) data indicate that the hexagonal c axis is the hard axis and hence that the ordered Mn moments are aligned in the ab plane. The chi(T) for both compounds and Cp(T) data for SrMn2As2 show strong dynamic short-range AFM correlations from TN up to at least 900 K, likely associated with quasi-two-dimensional connectivity of strong AFM exchange interactions between the Mn spins within the corrugated honeycomb Mn layers parallel to the ab plane.

Concentration-driven structural stability and dielectric dispersion in lead free (Ba1−xSc2x/3)Zr0.3Ti0.7O3 ceramics

Lead free scandium doped barium zirconate titanate (Ba1−xSc2x/3)(Zr0.3Ti0.7)O3 abbreviated as (BScZT) (x = 0.02, 0.04, 0.06, 0.08, 0.10) ceramics were prepared by the conventional solid state reaction route and their structural, microstructural and electrical properties were investigated experimentally. X-ray diffraction and Rietveld refinement analysis are indexed by considering cubic symmetry having space group Pm-3 m. Scandium ion (Sc3+) substitution induced A-site vacancies and distortion in three dimensional cation-oxygen networks leads to disorder in the local symmetry as identified in Raman spectra. The microstructural image shows formation of smaller grains of irregular shape and sizes along with aggregative characteristic with successive increase in Sc concentration. Lorentz type quadratic behavior in dielectric dispersion follows modified Curie–Weiss law and indicates a relaxor behavior with diffuse type of phase transition. A non-Debye type of relaxation behavior is observed in these materials. Variation of relaxation strength and diffuse parameters obey the Vogel–Fulcher relation. The ac conductivity highlights the hopping of bound charge carriers between the localized environment at lower temperature and translation hopping at higher temperature is modeled through universal dielectric response.

Sc2S3–Cu2S phase diagram

A phase diagram is constructed for the Sc2S3–Cu2S system. The system forms two incongruently melting complex sulfides: hexagonal CuScS2 (1Cu2S: 1Sc2S3): a = 0.3734 nm, c = 0.6102 nm, space group P3m1, Т m = 1635 K, ΔH m = 1670 kJ/mol; and cubic CuSc3S5 (1Cu2S: 3Sc2S3), a = 1.0481 nm, space group Fd3m, Т m = 1835 K. In the 45–62 mol % Cu2S solid solution (ss) range, there is a singular point corresponding to the composition of compound CuScS2 (50 mol % Cu2S). The Sc2S3-based solubility at 1070 K is 14 mol % Cu2S. In the γ-Cu2S-based solid solution range, there is a peritectic point at 7 mol % Sc2S3, 1423 K.

Crystal structures and magnetic properties of the honeycomb-lattice antiferromagnet M2(pymca)3(ClO4), (M = Fe, Co, Ni)

We report on the syntheses, crystal structures, and magnetic properties of a series of transition metal coordination polymers M2(pymca)3(ClO4), (pymca = pyrimidine-2-carboxylic acid, M = Fe (1), Co (2), and Ni (3)). These compounds are found to crystallize in a trigonal crystal system, space group P31m, with the lattice constants a = 9.727 Å and c = 5.996 Å for 1, a = 9.608 Å and c = 5.996 Å for 2, and a = 9.477 Å and c = 5.958 Å for 3 at room temperature. In these compounds, each pymca ligand connects to two M2+ ions, forming a honeycomb network in the ab plane. The temperature dependences of magnetic susceptibilities in these compounds show broad maxima, indicating antiferromagnetic interactions within two-dimensional honeycomb layers. We also observed an antiferromagnetic phase transition at low temperatures by magnetic susceptibility and heat capacity measurements. From the crystal structures and magnetic properties, we conclude that the compounds 1, 2, and 3 are good realizations of honeycomb-lattice antiferromagnets.

Global structure search and physical properties of Os2C

The crystal structures of Os2C were extensively investigated using the structure search method from the first-principles calculations. In contrast to the P63/mmc phase previously proposed as the ground state at ambient pressure, an energetically favorable structure with space group P-6m2 was found more stable at ambient condition. The structural stabilities of the new phase are confirmed by the phonon dispersion and elastic constants. Further calculations indicate that the newly predicted P-6m2 phase is ultra-incompressible with a high bulk modulus of 387 GPa and has a larger ideal shear strength than the P63/mmc phase.

Subsolidus phase equilibria in the La2O3–Fe2O3–Sb2O5 system and characterization of layered ternary oxide LaFe0.5Sb1.5O6

Phase equilibria in the La2O3-Fe2O3–Sb2O5 system have been studied. The isothermal section was constructed at T=900°С. The existence of the ternary oxide LaFe0.5Sb1.5O6 was confirmed. The structure of this compound was solved using Rietveld refinement of synchrotron radiation-based powder XRD data. LaFe0.5Sb1.5O6 crystallizes in a trigonal layered structure relating to PbSb2O6 type (space group P-31m, a=b=5.2446(3)Å, c=5.1930(3)Å, Z=1). The fine powder of LaFe0.5Sb1.5O6 was prepared by molten salt synthesis. The compound was characterized by diffuse reflection and Mossbauer spectroscopy, magnetic measurements, scanning electron microscopy and photocatalytic tests. The magnetic behavior of LaFe0.5Sb1.5O6 in the applied magnetic field H=5000Oe is entirely paramagnetic. By contrast, in the small magnetic field H=100Oe the magnetic data of LaFe0.5Sb1.5O6 indicates an unusual critical behavior near phase transition at T<2K.

Reverse Group–Subgroup Relation at the Ferroelastic Phase Transition in [(C2H5)4N][(CH3)4N]MnBr4

Exceptional physical properties have been revealed in a newly synthesized hybrid organic–inorganic compound, [(C2H5)4N][(CH3)4N]MnBr4. At elevated temperatures, above 460 K, the crystal exhibits two-dimensional negative thermal expansion. These properties occur as a consequence of the fast temperature-induced motions of the disordered methylammonium and ethylammonium cations, and the layered crystal structure. Moreover, the crystal undergoes two successive first-order phase transitions at 484 and 565 K. The mechanism of the transition at 484 K involves an order–disorder contribution coupled with a rearrangement of the anionic framework, but the most unusual is the symmetry lowering on heating the crystal. The low-temperature tetragonal phase III of space group P421m transforms into the orthorhombic P21212-symmetric phase II, which satisfies the temperature-reversed group–subgroup relation. Ferroelastic domains consistent with Aizu’s species 42mF222 have been evidenced in the crystal phase II. Another un...

Transport properties and magnetic behaviour of Ce8Pd24Alx (0.1≤x≤2)

Measurements are presented on the resistivity ρ(T), magnetoresistivity MR, dc susceptibility χ(T) and magnetization σ(μ0H), of the alloy series Ce8Pd24Alx with 0.1 ≤ x ≤ 2. Rietveld analysis of the X-ray diffraction (XRD) data indicates that Ce8Pd24Al crystallizes in the cubic structure with space group Pm3¯m (No. 221). The crystal structure of this compound is composed of 8 cubes of CePd3 in which the Al atoms occupy the centres of only certain octahedrons of Pd atoms. The CAILS - Pawley (cell and intensity least square) analysis of XRD data of all compositions show that the cubic structure of the parent compound CePd3 is retained. The XRD analysis indicate a linear increase in the cubic unit cell volume up to x = 1, followed by a curvature for larger Al concentrations and a tendency towards saturation on approaching x = 2. Measurements in the Al-poor alloy in the temperature range 4.2–300 K indicate an evolution from the intermediate valence state of Ce8Pd24 to Kondo behaviour with increased Al concentration. MR measurements on selected alloys are interpreted within the single-ion Bethe ansatz description and values of the Kondo temperature are calculated. χ(T) follows a Curie-Weiss behaviour with high-temperature effective moment values slightly reduced from the expected value of 2.54 μB of the free Ce3+-ion. The paramagnetic Weiss constant temperature −θp decreases rapidly with increasing Al content x, in line with the evolution from intermediate valence state to Kondo state. Low-temperature χ(T) data indicate antiferromagnetic ordering for the concentration range of 0.96 ≤ x ≤ 2. A Kondo and magnetic phase diagram for the Ce8Pd24Alx system is presented.

Structural phase transitions in EuNbO3 perovskite

The crystal structures of europium niobate, EuNbO3, have been examined over a wide temperature range between 20 and 500K using synchrotron X-ray diffraction. We have observed two successive structural phase transitions at 360 and 460K. Below 350K, EuNbO3 adopts an orthorhombic perovskite structure (space group Imma), which is characterized by NbO6 octahedral tilting about the pseudocubic two-fold axis. The result differs from previous reports in which EuNbO3 was assigned to a cubic aristotype (space group Pm3¯m) of perovskite at room temperature. At around 360K, EuNbO3 undergoes a first-order phase transition to a tetragonal symmetry (space group I4/mcm) with the NbO6 octahedral tilting about the pseudocubic four-fold axis. As the temperature is further increased, the I4/mcm tetragonal phase changes into the Pm3¯m cubic aristotype at 460K. The tetragonal-to-cubic transformation is characterized as a continuous phase transition.

Theoretical and experimental investigations on the magnetic and related properties of RAgSn2 (R=Ho, Er) compounds

Polycrystalline RAgSn2 (R=Ho, Er) compounds, synthesized by arc melting method are found to crystallize in cubic crystal structure with the space group Pm3 m. The dc and ac magnetic susceptibility data show that the compounds are antiferromagnetic at low temperatures. The absence of magnetic hysteresis reveals the soft magnetic nature. Magnetocaloric effect has been estimated from magnetization data that show moderate value for these compounds. The structure of the electronic states and corresponding inter-band transitions calculated for these compounds within the LSDA+U method are found in good agreement with experimental optical conductivity. The theoretical calculations also confirm antiferromagnetic ordering in RAgSn2 (R=Ho, Er). The values of the effective magnetic moments of holmium and erbium are found to be close to the experimental ones.

Flux growth and magnetic properties of rare earth cobalt germanide, RE6Co5Ge1+xAl3−x (RE=Pr, Nd; x≈0.8)

The intermetallic compounds RE6Co5Ge1+xAl3−x (RE=Pr, Nd) were synthesized from the reaction of germanium and aluminum in RE/Co eutectic flux. These phases crystallize with the Nd6Co5Ge2.2 structure type in hexagonal space group P-6m2 (a=9.203(2)Å, c=4.202(1) Å, R1=0.0109 for Pr6Co5Ge1.80Al2.20; and a=9.170(3) Å, c=4.195(1) Å, R1=0.0129 for Nd6Co5Ge1.74Al2.26). The structure features chains of face-sharing Ge@RE9 clusters intersecting hexagonal cobalt nets linked by aluminum atoms. Magnetic susceptibility measurements indicate that both phases exhibit ferromagnetic ordering of the cobalt layers with TC in the range of 130–140K. The magnetic moments of the rare earth ions order at lower temperature (30–40K). Magnetic measurements on oriented crystals of Nd6Co5Ge1.74Al2.26 show a strong preference of the moments to order along the c-axis.

Field-insensitive heavy fermion features and phase transition in the caged-structure quasi-skutterudite Sm3 Ru4 Ge13

The robust field-insensitive heavy fermion features in Sm3 Ru4 Ge13 and the magnetic phase transition at TN ≈ 5 K are studied using magnetization M(T), specific heat Cp(T), resistivity ρ(T) and thermal conductivity κT(T). The average crystal structure of Sm3 Ru4 Ge13 conforms to the cubic space group Pm3¯n however, signatures of subtle structural distortions are obtained from the x ray data. The magnetic susceptibility, χ(T), follows a modified Curie–Weiss law indicating the presence of crystal fields of Sm3+ and the significance of van Vleck terms. No sign of ferromagnetism is observed in M(H) of Sm3 Ru4 Ge13 which yields only 0.025 μB/f.u.-Sm at 2 K, 7 T. The Sommerfeld coefficient, γ≈ 220 mJ/mol-Sm K2, estimated from the analysis of low temperature specific heat suggests the formation of heavy quasi particles at low temperature. Though a lnT dependence of ρ(T) is observed till 60 K, the resistivity behavior is accounted for by assuming a two-band model for activated behavior of charge carriers. The field scans of resistivity, ρ(H), below TN display significant nonlinearity while those above the TN are more metal-like. Low values of thermal conductivity, κT(T), are observed in Sm3 Ru4 Ge13 however, displaying an anomaly at TN which signifies magnetoelastic coupling. A fairly high value of Seebeck coefficient, S ≈ 40 μV/K is observed at 300 K. We identify Sm3 Ru4 Ge13 as a low charge carrier density system with unusual field-insensitive heavy fermion features very similar to the filled skutterudites.

Effect of preparation conditions on the indium species in fully indium exchanged zeolite LTA

Three fully indium-exchanged zeolite A (LTA) crystals, In-A, were prepared by the reaction of fully dehydrated Tl-A with indium metal at 623, 673, and 723 K. Three additional crystals were prepared as above and then hydrated, washed with water, and redehydrated (post-treatment). All six structures were determined crystallographically with synchrotron X-radiation and refined in the space group Pm3¯m. Monatomic In+ ions predominate in all crystals: ca. 63–83 atomic % of the In atoms present are monatomic In+ at 6- and 8-ring positions. Tetrahedral In57+ clusters are always found in the sodalite cavities, occupying from 9% to 82% of them. Before post-treatment, only In+, In57+, and In3+ were found, and the In+ population was greatest after the 673 K reaction. The In57+ population decreases monotonically with increasing reaction temperature due to its disproportionation to In+ and In3+. Between 673 K and 723 K, In+ begins to disproportionate also, to In3+ and In0. Post-treatment continues the extent of these disproportionations to In3+ and In0. Some of the In0 atoms produced bridge between remaining In+ ions to form In32+ and In75+. The remainder have moved to the surface of the zeolite crystal.

A first-order antiferromagnetic-paramagnetic transition induced by structural transition in GeNCr3

A first-order antiferromagnetic (AFM)-paramagnetic (PM) phase transition has been confirmed by systematic magnetic measurements in GeNCr3, and it does not depend on the applied magnetic fields. Interestingly, a structural transition from space group P-421m to I4/mcm without breaking tetragonal symmetry appears around this AFM-PM transition temperature, which may be the driving force for the AFM-PM transition. Moreover, obvious exothermic and endothermic peaks in calorimetric measurements, a sharp peak of specific heat Cp(T), and a slope change of resistivity ρ(T) are also observed around structural transition temperature, indicating a strong coupling between structure and electrical as well as thermal properties.

The plastic crystalline A15 phase of dimethylaminoalane, [N(CH3)2-AlH2]3.

A plastic crystalline phase of dimethylaminoalane has been discovered at T > 332 K. The phase transitions solid - plastic phase - liquid are fully reversible. The plastic crystalline phase exhibits a cubic unit cell, space group Pm3[combining macron]n, in which the dimethylaminoalane molecules rotate and adopt a structural arrangement reminiscent of the A15 phase.

Investigation of formamidinium and guanidinium lead tri-iodide powders as precursors for solar cells

Abstract Formamidinium and guanidinium lead tri-iodide powders (FAPbI3 and GUAPbI3 respectively) were prepared by self-organization processes in solutions. The XRD analysis detected the formation, at room temperature, of a trigonal structure (α-FAPbI3, space group P3m1), of a (non-perovskitic) hexagonal structure (δ-FAPbI3, space group P63mc) for FAPbI3, and the presence of orthorhombic (space group Pnma) and hexagonal structures for GUAPbI3 respectively. The morphological investigation revealed the growth of aggregated (α-FAPbI3 phase) and stripe-like crystallites (GUAPbI3) respectively. The infrared spectra (IR) confirmed the strong influence of additional C–N bonds on vibrational properties of GUA-containing system. Optical absorption measurements indicated that α-FAPbI3 and GUAPbI3 systems reveal direct energy band gaps of 1.42 eV and 1.92 eV respectively at room temperature. Photoluminescence measurements revealed emissions in the infra-red (IR) (for α-FAPbI3) and visible (Vis) ranges (for GUAPbI3). Films formation of GUAPbI3 was demonstrated, and solar cells devices were fabricated with average power conversion of 0.3%.

Luminescent properties of novel red-emitting phosphor: Gd_2O_2CN_2:Eu^3+

Eu3+-doped Gd2O2CN2 was firstly synthesized by a classical solid-state reaction of Li2CO3, Eu2O3 and GdF3 under NH3 gas flow in the presence of graphite at low firing temperature. Powder X-ray diffraction (XRD) analysis indicated that Gd2O2CN2: Eu3+ crystallizes in a trigonal-type structure with space group P-3m1. Gd2O2CN2: Eu3+ shows a sharp red emission band peaking at 626 nm under excitation at 300 nm at room temperature. PL spectra indicates that Eu3+ doped Gd2O2CN2 samples emit the typical emission peaks at 614 nm and 626 nm originated from the hypersensitive electric dipole transition (5D0→7F2) of Eu3+ ions. The optimized doping concentration of Eu3+ ions was found to be 7.5 at. %, and the critical transfer distance was calculated to be 10.907 A.

Synthesis and structure determination of seven ternary bismuthides: crystal chemistry of the RELi3Bi2 family (RE = La-Nd, Sm, Gd, and Tb).

Zintl phases are renowned for their diverse crystal structures with rich structural chemistry and have recently exhibited some remarkable heat- and charge-transport properties. The ternary bismuthides RELi3Bi2 (RE = La-Nd, Sm, Gd, and Tb) (namely, lanthanum trilithium dibismuthide, LaLi3Bi2, cerium trilithium dibismuthide, CeLi3Bi2, praseodymium trilithium dibismuthide, PrLi3Bi2, neodymium trilithium dibismuthide, NdLi3Bi2, samarium trilithium dibismuthide, SmLi3Bi2, gadolinium trilithium dibismuthide, GdLi3Bi2, and terbium trilithium dibismuthide, TbLi3Bi2) were synthesized by high-temperature reactions of the elements in sealed Nb ampoules. Single-crystal X-ray diffraction analysis shows that all seven compounds are isostructural and crystallize in the LaLi3Sb2 type structure in the trigonal space group P-3m1 (Pearson symbol hP6). The unit-cell volumes decrease monotonically on moving from the La to the Tb compound, owing to the lanthanide contraction. The structure features a rare-earth metal atom and one Li atom in a nearly perfect octahedral coordination by six Bi atoms. The second crystallographically unique Li atom is surrounded by four Bi atoms in a slightly distorted tetrahedral geometry. The atomic arrangements are best described as layered structures consisting of two-dimensional layers of fused LiBi4 tetrahedra and LiBi6 octahedra, separated by rare-earth metal cations. As such, these compounds are expected to be valance-precise semiconductors, whose formulae can be represented as (RE(3+))(Li(1+))3(Bi(3-))2.