Trigonal Prismatic Sites Research Articles

Phase diagram of SrO–InO 1.5–CoO x and a new compound Sr 3In 0.9Co 1.1O 6

Sr 3In 0.9Co 1.1O 6, isostructural to Ca 3Co 2O 6, is revealed by the study of the phase relations in the system SrO–InO 1.5–CoO x (1000 °C). The structure of Sr 3In 0.9Co 1.1O 6 is refined by the combination of powder X-ray and neutron diffraction. Sr 3In 0.9Co 1.1O 6 crystallizes in a trigonal lattice with the cell parameters a= b=9.59438(3) Å, c=11.02172(4) Å with the space group R-3 c. Its structure possesses 1D (In/Co)O 3 chains running along the c-axis constructed by alternating face-sharing CoO 6 octahedra and (In 0.9Co 0.1)O 6 trigonal prisms. The co-occupation of In 3+ and Co 3+ at the trigonal prismatic site is evidenced by elementary analysis and determined by the structure refinement. Sr 3In 0.9Co 1.1O 6 is paramagnetic, and the susceptibility is consistent with the occupation of Co 3+ at 10% of the trigonal prismatic positions in a high spin state (HS, S=2). The HS Co 3+ is well separated by diamagnetic CoO 6 octahedra and InO 6 trigonal prisms and shows a g factor of 2.0 in the magnetic measurements.

Structural studies of a mixed-valence state in the incommensurate composite crystal Sr1.261CoO3

The incommensurate modulated crystal structure of the hexagonal cobalt oxide Sr1.261CoO3 has been studied using a four-dimensional (4D) superspace profile analysis of neutron powder diffraction data. Sr1.261CoO3 is a composite crystal that consists of the [CoO3] and [2Sr] subsystems. The [CoO3] subsystem forms 1D chains that run parallel to the c-axis and consist of face-sharing CoO6 polyhedra with octahedral (Oh) and trigonal prismatic (TP) coordinations. The structure analysis reveals that the [CoO3] chains contain 73.9% Oh and 26.1% TP sites, and that the TP sites have longer Co–O bonds than the Oh sites:dav. =2.039(4) Å (TP) and 1.895(3) Å (Oh). The averaged Co bond valences are Co3.56(3)+ in the Oh sites and Co2.45(3)+ in the TP sites, suggesting that a considerable amount of Co3+ ions are mixed with Co4+ions in the Oh sites and with Co2+ ions in the TP sites. The observed magnetic susceptibility can be well explained assuming that the compound has the Co mixed-valence state with the spin configurations of S=0 low-spin state for Co3+(dε6), S=1/2 low-spin state for Co4+(dε5) and S=3/2 high-spin state for Co2+(dε5dγ2). The Weiss temperature, approximately 0.8 K, implies that Sr1.261CoO3 naturally assumes a Curie paramagnetic state, probably owing to the obstruction of the intrachain magnetic interaction by the nonmagnetic Co3+ ions. These results suggest that the nonmagnetic Co3+ ions play an essential role in the magnetism of Sr2γCoO3 systems.

ChemInform Abstract: The Related Compounds MThTe3 (M: Mn, Mg) and ACuThSe3 (A: K, Cs): Syntheses and Characterization.

Single crystals of MnThTe{sub 3} (1) and MgThTe{sub 3} (2) grow as small black plates from the stoichiometric reaction of the elements, the former at 1,000 C and the latter at 900 C with the aid of a Sn flux. Both compounds crystallize in the space group Cmcm of the orthorhombic system with four formula units in cells of dimensions a = 4.2783(6){angstrom}, b = 13.8618(11){angstrom}, and c = 9.9568(15){angstrom} for 1 and a = 4.2854(6){angstrom}, b = 14.042(2){angstrom}, and c = 9.9450(14){angstrom} for 2 at T - 153(2) K. KCuThSe{sub 3} (3) forms as red blocks from a stoichiometric mixture of K{sub 2}Se, Cu, Th, and Se at 800 C, and CsCuThSe{sub 3} (4) forms as yellow blocks from a stoichiometric mixture of Cs{sub 2}Se{sub 3}, Cu, Th, and Se at 850 C. Compounds 3 and 4 also crystallize in the space group Cmcm of the orthorhombic system with four formula units in cells of dimensions a + 4.1832(8){angstrom}, b = 14,335(3){angstrom}, and c = 10.859(2){angstrom} for 3 and 1 = 4.2105(7){angstrom}, b = 15.715(3){angstrom}, and c = 10.897(2){angstrom} for 4 at 153(2) K. Compounds 1 and 2 are isostructural with each other as well as with several uraniummore » analogues and comprise pseudolayered structures with slabs of corner-shared MTe{sub 6} octahedra alternating with slabs of cap- and edge-shared ThTe{sub 8} bicapped trigonal prisms. the slabs are bonded together through the sharing of edges and vertices of the various polyhedra to form three-dimensional structures. Compounds 3 and 4 are two-dimensional layered structures that are closely related to 1 and 2. In 3 and 4, ThSe{sub 6} octahedra form the same slabs as MTe{sub 6} in 1 and 2 and Cu atoms occupy the tetrahedralholes in the layers. Alkali metal cations occupy bicapped trigonal prismatic sites between the layers. Neither structure type has short Q-Q interactions, and therefore the oxidation states of all atoms are straightforwardly assigned on the assumption of Th{sup 4+}. Magnetic susceptibility measurements on compound 1 show a ferromagnetic translation at 70 K and a magnetic moment of 5.9(2) {mu}{sub {Beta}} per Mn ion, indicating low-spin Mn{sup 2+}.« less

THE CRYSTAL STRUCTURE OF ANGELAITE, Cu2AgPbBiS4

The crystal structure of angelaite, ideally Cu 2 AgPbBiS 4 , a 12.734(5), b 4.032(1), c 14.633(5) A, V 751.2(5) A 3 , space group Pnma, Z = 4, D calc = 6.89 g.cm −3 , from the Angela mine, Los Manantiales district, province of Chubut, Argentina, has been solved by direct methods and refined to R 1 = 6.47% on the basis of 606 unique reflections [ F o > 4σ( F o )]; these were collected on a Bruker P3 diffractometer with a CCD detector and Mo K α radiation from a fragment consisting of an intergrowth of angelaite and galena. Angelaite contains a capped trigonal prismatic Pb site, a quasi-octahedral Bi site, a linearly coordinated Cu site, and three triangular sites, one occupied by Ag and two partially occupied by Cu. Angelaite is a homeotype of galenobismutite with the Pb and Bi1 sites of galenobismutite preserved, and the Bi2 site replaced by the combination of Ag and Cu sites described above, which represent a novel type of substitution: (Ag + + 2Cu + )-for-Bi 3+ . Selenium-free galenobismutite from Felbertal (Austria) was refined to the R 1 value of 2.49% to serve as a reference structure related to that of angelaite.

Magnetism of the spin-chain compound Ca3Co1.9Fe0.1O6: Magnetization and neutron diffraction study

We report the results of the dc magnetization and neutron diffraction studies of the quasi-one-dimensional spin-chain compound Ca3Co1.9Fe0.1O6. Rietveld refinement of neutron powder diffraction pattern at 100 K confirmed that Fe ion was located at trigonal prism site 6a (0, 0, 1/4). The dc susceptibility obeys the Curie-Weiss law. The appearance of additional magnetic Bragg peaks in the low temperature neutron powder diffraction patterns mainly indicates an antiferromagnetic ordering. The magnetic reflections can be indexed with a propagation vector K = (0, 0, 1), referred to the space group R3̄c (hexagonal setting), and indicate that the centering translations have been lost in the magnetic structure.

X-ray diffraction and vibrational Raman spectra of the Li2−xNaxCo2(MoO4)3 (0 ⩽ x ⩽ 1.4) solid solution with a lyonsite structure

Synthesis, X-ray diffraction and Raman spectroscopy studies of Li2–xNaxCo2(MoO4)3 (0⩽x⩽2) compositions have been investigated. These alkali–cobalt molybdates crystallize in the orthorhombic system (space group Pnma (D2h)) with a lyonsite structure (Z=4). The cell parameters are determined by DICVOL04 software and confirmed by Rietveld refinements. The structure is formed by a framework of MoO4 tetrahedra and (Li/Na/Co)O6 octahedra, the tetrahedra provide links between sheets and columns formed by the octahedra. The structure shows that while octahedra share corners and edges in the sheets, they share faces columns. Alkali and cobalt are distributed statically in both the octahedral and trigonal prism sites. X-ray diffraction shows the presence of a solid solution in the range of compositions (0⩽x<1.4). These results are in agreement with Raman studies where the spectra of all the compositions are similar and show linear shifts of the frequencies as a function of the composition toward low values due to the substitutions of Li+ by Na+ with a larger radius.

Structural and magnetic properties of Pr 18Li 8Fe 5−xM xO 39 ( M=Ru, Mn, Co)

A polycrystalline sample of Pr 18Li 8Fe 4RuO 39 has been synthesized by a solid state method and characterized by neutron powder diffraction, magnetometry and Mössbauer spectroscopy; samples of Pr 18Li 8Fe 5− x Mn x O 39 and Pr 18Li 8Fe 5− x Co x O 39 ( x=1, 2) have been studied by magnetometry. All these compounds adopt a cubic structure (space group Pm 3 ¯ n , a 0∼11.97 Å) based on intersecting 〈111〉 chains made up of alternating octahedral and trigonal-prismatic coordination sites. These chains occupy channels within a Pr–O framework. The trigonal-prismatic site in Pr 18Li 8Fe 4RuO 39 is occupied by Li + and high-spin Fe 3+. The remaining transition-metal cations occupy the two crystallographically-distinct octahedral sites in a disordered manner. All five compositions adopt a spin-glass-like state at 7 K (Pr 18Li 8Fe 4RuO 39) or below.

Optical and electronic properties of one-dimensional Ca3Co2O6 thin films: Influence of the oxygen pressure

Thin films of Ca3Co2O6 were fabricated on c-cut sapphire substrates by pulsed laser deposition. The films are polycrystalline and can be grown in a large interval of oxygen pressure with significant influence on the film texture. X-ray photoelectron spectroscopy analyses indicated that only Co3+ ions are present in our samples for both octahedral and trigonal prismatic sites. The band gap measured by ultraviolet-visible light absorption experiments was found about 1.35 eV and slightly larger when the oxygen partial pressure during the deposition is increased from 10−3 to 7×10−2 mbar. Temperature dependent transport measurements showed a semiconducting behavior of the films and the associated band gap was found similar to the one evaluated by optical measurements and reported by theoretical studies.

Structural Chemistry and Magnetic Properties of Nd18Li8Fe5−xMxO39(M = Mn, Co)

Polycrystalline samples of Nd(18)Li(8)Fe(5-x)M(x)O(39) (M = Mn, 0 < x < or = 4; M = Co; 0 < x < or = 3) have been synthesized using a solid-state method and have been studied using a combination of dc and ac magnetometry, neutron diffraction, and Mössbauer spectroscopy. All compositions adopt a cubic structure (space group Pm3n, a(0) approximately 11.9 A) based on intersecting <111> chains made up of alternating octahedral and trigonal-prismatic coordination sites. These chains occupy channels within a Nd-O framework. The trigonal prismatic site is occupied by Li(+) and, in some cases, high-spin Fe(3+). When M = Mn, the smaller of the two distinct octahedral sites in the structure is occupied by a disordered distribution of Mn(4+) and low-spin Fe(4+), but in Nd(18)Li(8)Fe(4)CoO(39), this site is occupied exclusively by Fe(4+). The larger of the octahedral sites is occupied by a disordered distribution of M(3+), high-spin Fe(3+), and, in some cases, Li(+). Unusually, the Mn(3+) cations in Nd(18)Li(8)Fe(5-x)M(x)O(39) adopt a low-spin state. This is attributed to the presence of an internal chemical pressure generated by the Nd-O framework. Competing magnetic superexchange interactions lead to the formation of a spin-glass-like phase in all compositions below T(f) approximately 5 K; the transition temperature decreases with increasing cobalt content but is relatively insensitive to the composition when M = Mn.

High-pressure transitions in MgAl 2O 4 and a new high-pressure phase of Mg 2Al 2O 5

Phase transitions in MgAl 2O 4 were examined at 21–27 GPa and 1400–2500 °C using a multianvil apparatus. A mixture of MgO and Al 2O 3 corundum that are high-pressure dissociation products of MgAl 2O 4 spinel combines into calcium–ferrite type MgAl 2O 4 at 26–27 GPa and 1400–2000 °C. At temperature above 2000 °C at pressure below 25.5 GPa, a mixture of Al 2O 3 corundum and a new phase with Mg 2Al 2O 5 composition is stable. The transition boundary between the two fields has a strongly negative pressure–temperature slope. Structure analysis and Rietveld refinement on the basis of the powder X-ray diffraction profile of the Mg 2Al 2O 5 phase indicated that the phase represented a new structure type with orthorhombic symmetry ( Pbam), and the lattice parameters were determined as a=9.3710(6) Å, b=12.1952(6) Å, c=2.7916(2) Å, V=319.03(3) Å 3, Z=4. The structure consists of edge-sharing and corner-sharing (Mg, Al)O 6 octahedra, and contains chains of edge-sharing octahedra running along the c-axis. A part of Mg atoms are accommodated in six-coordinated trigonal prism sites in tunnels surrounded by the chains of edge-sharing (Mg, Al)O 6 octahedra. The structure is related with that of ludwigite (Mg, Fe 2+) 2(Fe 3+, Al)(BO 3)O 2. The molar volume of the Mg 2Al 2O 5 phase is smaller by 0.18% than sum of molar volumes of 2MgO and Al 2O 3 corundum. High-pressure dissociation to the mixture of corundum-type phase and the phase with ludwigite-related structure has been found only in MgAl 2O 4 among various A 2+B 3+ 2O 4 compounds.

Neutron diffraction study of quasi-one-dimensional spin-chain compounds Ca3Co2–x Fe x O6

We report the results of the DC magnetization, neutron powder diffraction and neutron depolarization studies on the spin-chain compounds Ca3Co2–x Fe x O6 (x = 0, 0.1, 0.2 and 0.4). Rietveld refinement of neutron powder diffraction patterns at room temperature confirms the single-phase formation for all the compounds in rhombohedral structure with space group R\( \bar 3 \)c. Rietveld refinement also confirms that Fe was doped at the trigonal prism site, 6a (0, 0, 1/4) of Co. The high temperature magnetic susceptibility obeys the Curie-Weiss law; the value of the paramagnetic Curie temperature (θ p) decreases as the concentration of iron increases and it becomes negative for x = 0.4. No extra Bragg peak as well as no observable enhancement in the intensity of the fundamental (nuclear) Bragg peaks has been observed in the neutron diffraction patterns down to 30 K. No depolarization of neutron beam has been observed down to 3 K confirming the absence of ferro- or ferrimagnetic-like correlation.

Structural Chemistry and Magnetic Properties of Nd18Li8Fe5O39 and Nd18Li8Co4O39: the Interplay of Cation and Spin Ordering

Polycrystalline samples of Nd(18)Li(8)Fe(5)O(39) and Nd(18)Li(8)Co(4)O(39) have been synthesized using a solid-state method and studied by a combination of neutron diffraction, direct and alternating current magnetometry, and, in the case of Nd(18)Li(8)Fe(5)O(39), Mossbauer spectroscopy. Both compounds adopt a cubic structure (space group Pm3n, a(0) approximately 11.9 A) based on intersecting 111 chains made up of alternating octahedral and trigonal-prismatic coordination sites. The Fe(4+) cations in Nd(18)Li(8)Fe(5)O(39) are found on only the smaller of the two distinct octahedral sites in the structure; Fe(3+) and Li(+) are disordered over the larger octahedral site and the trigonal-prismatic site. The Nd(3+) cations occupy sites between the chains. The smaller octahedral site is fully occupied by cobalt in Nd(18)Li(8)Co(4)O(39), with 25% of the larger octahedral sites being vacant; Li(+) is only found on the prismatic sites. Nd(18)Li(8)Fe(5)O(39) shows spin-glass-like behavior with a spin-freezing temperature of 5.75 K, whereas Nd(18)Li(8)Co(4)O(39) appears to order antiferromagnetically at 2.3 K. In both cases, the magnetic coupling involves the Nd(3+) sublattice.

Electronic structure and magnetic properties of Ca 3Co 2O 6 cobaltites: Intrachain magnetic ordering

The present study is focussed on the intrachain magnetic interactions between the trigonal prismatic (TP) and octahedral (OCT) Co sites in Ca 3Co 2O 6 cobaltites from their electronic structure determined using the first principle full potential linearized augmented plane wave method within the GGA+U approximation. The occurence of various magnetic solutions as a function of the Coulomb integral U of the GGA+U approach is investigated. Various magnetic configurations, corresponding to different total magnetization, are found only when the insulating state is reached for U > 2.5 eV and the most stable solution corresponds to a magnetic spin moment on the TP (respectively OCT) site around 2.6 (respectively 1) Bohr magneton.

Synthesis, Crystal Structure, and Magnetic Properties of Sr1.31Co0.63Mn0.37O3: A Derivative of the Incommensurate Composite Hexagonal Perovskite Structure

We report the synthesis, structural investigation, and magnetic property studies of Sr1.31Co0.63Mn0.37O3 that adopts an incommensurate composite hexagonal perovskite-related structure. The crystal structure has been solved using a (3 + 1)-dimensional superspace approach from powder X-ray and neutron diffraction data (SSG R3̅m(00γ)0s, a = 9.5548(1) Å, c = 2.5599(1) Å, q = 0.65581(4)c*, RB = 0.041, RP = 0.059). The structure consists of face-sharing chains of octahedra and trigonal prisms, wherein the trigonal prismatic sites are preferentially occupied by Co with some cation disorder. A combination of electron diffraction and high-resolution electron microscopic analysis has demonstrated that the compound possesses a complicated microstructure related to the formation of domains with slightly different lengths of the modulation vector. X-ray absorption near-edge spectroscopic (XAS) studies clearly indicate the presence of Mn in the 4+ and Co in the 3+ oxidation state. While the magnetic susceptibility data indicates the presence of antiferromagnetic correlations in the system, the calculation of effective paramagnetic moment (μcal = 3.561 μB), assuming the metal oxidation states as obtained from XAS and the cation distribution as obtained from neutron refinement, is in agreement with the value obtained experimentally (μexp = 3.676 μB).

Hydrostatic compression of galenobismutite (PbBi2S4): elastic properties and high-pressure crystal chemistry

A single-crystal sample of galenobismutite was subjected to hydrostatic pressures in the range of 0.0001 and 9 GPa at room temperature using the diamond-anvil cell technique. A series of X-ray diffraction intensities were collected at ten distinct pressures using a CCD equipped 4-circle diffractometer. The crystal structure was refined to R1(|F0| > 4σ) values of approximately 0.05 at all pressures. By fitting a third-order Birch-Murnaghan equation of state to the unit-cell volumes V 0 = 700.6(2) A3, K 0 = 43.9(7) GPa and dK/dP = 6.9(3) could be determined for the lattice compression. Both types of cations in galenobismutite have stereochemically active lone electron pairs, which distort the cation polyhedra at room pressure. The cation eccentricities decrease at higher pressure but are still pronounced at 9 GPa. Galenobismutite is isotypic with CaFe2O4 (CF) but moves away from the idealised CF-type structure during compression. Instead of the two octahedral cation sites and one bi-capped trigonal-prismatic site, PbBi2S4 attains a new high-pressure structure characterised by one octahedral site and two mono-capped trigonal-prismatic sites. Analyses of the crystal structure at high pressure confirm the preference of Bi for the octahedral site and the smaller one of the two trigonal-prismatic sites.

Characterization and electronic structure calculations of the antiferromagnetic insulatorCa3FeRhO6

We investigate the antiferromagnetic insulating nature of Ca3FeRhO6 both experimentally and theoretically. Susceptibility measurements reveal a Neel temperature T_N = 20 K, and a magnetic moment of 5.3 muB/f. u., while Moessbauer spectroscopy strongly suggests that the Fe ions, located in trigonal prismatic sites, are in a 3+ high spin state. Transport measurements display a simple Arrhenius law, with an activation energy of 0.2 eV. The experimental results are interpreted with LSDA band structure calculations, which confirm the Fe 3+ state, the high-spin/low-spin scenario, the antiferromagnetic ordering, and the value for the activation energy.

Diffuse scattering from a Li–Mn oxide disorderly stacked through flocculation of exfoliated nanosheets

A new type of layered Li–Mn oxide has been synthesized through flocculation of delaminated MnO2 nanosheets with Li ions. X-ray powder diffraction patterns show remarkable broadening of reflections. Diffuse scattering was simulated using the matrix method, taking into account the probability of stacking with different shift vectors. A satisfactorily good fit of the simulated pattern to the observed one was obtained assuming a layer sequence with (1/3)a + (2/3)b, which produces trigonal prismatic sites for guest species; this had a probability around 24% and the other stacking modes were random.

Ab initiox-ray absorption study of the manganeseK-edge XANES spectra in Mn- and Zn-related hexagonal perovskites

An x-ray absorption spectroscopy study of several Mn-containing one-dimensional-related hexagonal perovskites $\mathrm{Ba}\mathrm{Mn}{\mathrm{O}}_{3}$, ${\mathrm{Ca}}_{3}\mathrm{Zn}\mathrm{Mn}{\mathrm{O}}_{6}$, and ${\mathrm{Sr}}_{4}\mathrm{Zn}{\mathrm{Mn}}_{2}{\mathrm{O}}_{9}$ is reported. A combined analysis of the Mn $K$-edge extended x-ray absorption fine structure and x-ray absorption near-edge structure has been conducted to investigate a possible disordering caused by the cation interchange between crystallographic lattice sites. For ${\mathrm{Ca}}_{3}\mathrm{Zn}\mathrm{Mn}{\mathrm{O}}_{6}$ and ${\mathrm{Sr}}_{4}\mathrm{Zn}{\mathrm{Mn}}_{2}{\mathrm{O}}_{9}$ compounds, ab initio computations based on multiple-scattering theory suggest that Mn is present at two different crystallographic sites: in addition to the expected $\mathrm{Mn}{\mathrm{O}}_{6}$ octahedra, Mn stands also in the trigonal prism site. This cation disordering would explain satisfactorily the observed temperature magnetic behavior of ${\mathrm{Sr}}_{4}\mathrm{Zn}{\mathrm{Mn}}_{2}{\mathrm{O}}_{9}$.

Structural and magnetic properties of spin chain compoundsCa3Co2−xFexO6

We report the structural and magnetic properties of quasi-one-dimensional (1D) spin chain compounds ${\mathrm{Ca}}_{3}{\mathrm{Co}}_{2\ensuremath{-}x}{\mathrm{Fe}}_{x}{\mathrm{O}}_{6}$ ($x=0$, 0.1, 0.2, and 0.4). Simultaneous Rietveld refinement of powder neutron and x-ray diffraction patterns at room temperature confirmed the single-phase formation for all the samples in the rhombohedral structure with space group $R\overline{3}c$. Rietveld refinement and M\ossbauer study confirmed that ${\mathrm{Fe}}^{3+}$ ion was doped at trigonal prism site, $6a$ (0, 0, $1∕4$) of Co. Decrease of intrachain positive exchange constant $J$ and increase of interchain negative exchange constant ${J}^{\ensuremath{'}}$ with iron substitution result in deviation from ``1D character'' in these spin chain compounds. Deviation from the ${H}^{\ensuremath{-}3∕2}$ dependence of magnetization-approach to its saturation value for higher iron concentration $(x=0.4)$ further supports this observation. The observed results have been ascribed to a breaking of the ferromagnetically ordered linear spin chains along the crystallographic $c$ axis with iron doping and strengthening of antiferromagnetic exchange interaction between ${\mathrm{Fe}}^{3+}$ ions.

A hexagonal 2a,csuperstructure of Ba7F12Cl2

Hydrothermal synthesis yielded crystals of heptabarium dodecafluoride dichloride, Ba7F12Cl2, displaying a new 2a,c hexagonal superstructure with P-6 symmetry. The superstructure results from the disorder of Ba2+ cations over two adjacent tricapped trigonal prismatic sites located in channels parallel to the c axis.