Anti-fluorite Type Research Articles

Ternary nitrides prepared in the Li 3N–Mg 3N 2 system at 900–1000 K

Three phases, (Li x Mg 1− x ) 3N 2− x (0< x<0.20), LiMgN and (Li x Mg 1− x ) 2N (2− x)2/3 (0.5< x<0.6), were prepared in Li 3N – Mg 3N 2 system at 900 and 1000 K, and their crystal structures were investigated by applying the Rietveld method to the X-ray powder diffraction patterns. (Li x Mg 1− x ) 3N 2− x crystallizes in a cubic superlattice ( a=9.9767(5) Å at x=0.17). Mg atoms in the Mg 3N 2 structure (space group Ia3) were found to be partially replaced by Li atoms and the resultant structure was distorted with a lower symmetry space group I213. The crystal structure of LiMgN (orthorhombic, a=7.1586(2), b=3.5069(8), c=5.01424(13) Å, space group Pnma) was determined ab initio from the X-ray powder diffraction data. It revealed a cation-ordered antifluorite-type structure. (Li x Mg 1− x ) 2N (2− x)2/3 was prepared by rapid cooling from 1000 K to room temperature. It was also found to be stable at 900 and 1000 K and decomposed into LiMgN and Li 3N on slow cooling in the furnace. Broad tails of the X-ray diffraction peaks suggest a modulated structure. A cation-disordered simple antifluorite type (space group Fm3̄m, a=4.99559(11) Å at x=0.57) was proposed as the fundamental structure of (Li x Mg 1− x ) 2N (2− x)2/3 .

Anti-fluorite type Li6CoO4, Li5FeO4, and Li6MnO4 as the cathode for lithium secondary batteries

Abstract The anti-fluorite type materials Li6CoO4, Li5FeO4 and Li6MnO4 were synthesized and studied as a cathode for lithium secondary batteries. One equivalent Li was deintercalated from Li6CoO4 and reversibly intercalated, while only 0.5 Li extraction and insertion was possible for Li5FeO4 and no Li was extracted from Li6MnO4. The cell performance of Li/Li6CoO4 with 1 M LiClO4/EC-DME was relatively good in the shallow region 0≤x≤0.75 in Li6−xCoO4 and the large hysteresis with the charge and discharge curves showed a different mechanism between Li deintercalation and intercalation.

Neutron diffraction study of (ND4)2SeCl6, (ND4)2PtCl6, and (ND4)2PtBr6 crystals: The origin of the strong deuterium substitution effect on the phase transitions

Neutron powder diffraction experiments of (ND4)2SeCl6, (ND4)2PtCl6, and (ND4)2PtBr6 were performed to investigate the mechanism of the strong deuterium substitution effect on the phase transitions of the (NH4)2MX6 family. The isotope effect is strong in the first and second compounds and weak in the third. The data were collected in the d-spacing range 0.5–4.3 Å by using a time-of-flight powder diffractometer VEGA installed at the pulsed cold neutron source in KEK. The intensity data of high-temperature phases (HTP) were measured at the temperatures corresponding to 1.3Tc (Tc: transition temperature), and the low-temperature phases (LTP) at 4 K. The HTPs of the three compounds have an antifluorite type cubic structure (a≈9.8 Å and Z=4) as previously reported while the LTPs of (ND4)2PtCl6 and (ND4)2PtBr6 are tetragonal with a tentative space group P42/n and unit cell dimensions similar to those of the HTPs. The LTP of (ND4)2SeCl6 may have an orthorhombic structure with a larger unit cell. The Rietveld refinement and Fourier analysis for the HTPs revealed that the D atoms in (ND4)2SeCl6 and (ND4)2PtCl6 are broadly distributed around the crystallographic threefold rotation axis with three weak overlapping maxima, while that of (ND4)2PtBr6 is more strongly localized at three positions away from the threefold rotation axis. These results indicate that the transitions are due to orientational ordering of the ND4+ ions and that the strong isotope effects may be quantum effects associated with the ND4+ motion in a shallow rotational potential.

Bis[tris(2-hydroxyethyl)ammonium] Hexachloroplatinate(IV)

The title compound, [HN(C2H4OH)3]2[PtCl6], comprises [HN(C2H4OH)3]+ and [PtCl6]2− ions. In the cation, the ammonium-H atom forms an intramolecular bifurcated hydrogen bond with two O atoms. The anions and cations are joined in polymeric chains through hydrogen bonds involving the hydroxyl H atom and the coordinated Cl atoms. The crystal structure is of antifluorite type.

Crystal Structure of the Oxidenitride, Li16Nb2N8O

Crystals of rhombohedral Li16Nb2N8O (space groupR3(h), No. 148,Z= 3,a= 5.984(4) Å,c= 25.484(8) Å) were obtained during a study of the Li–Ba–Nb–N system when a mixture of Li, Ba, and Nb confined in quartz was heated at 850°C under flowing N2. Refinement of single crystal data based uponF2yieldedR2 = 0.024 andwR2 = 0.047. Li16Nb2N8O crystallizes isotypically with Li16Ta2N8O in an anti-fluorite type superstructure. The Nb and two of the four independent Li ions are tetrahedrally coordinated by nitrogen anions; the remaining two Li ions are tetrahedrally coordinated by one oxygen and three nitrogen anions. The compound can also be prepared by heating a Li3N:Nb2O5:NbN = 16/3:1/5:8/5 molar mixture under flowing Ar/N2at 900°C for 24 h. Magnetic susceptibility data between 10 and 300 K exhibit temperature independent paramagnetism.

Synthesis and crystal structure of barium copper fluochalcogenides:[BaCuFQ (Q=S,Se)

Two new copper fluochalcogenides BaCuFQ (Q=S,Se) have been synthesized. They crystallize in a tetragonal crystal structure with space group P4/nmm and lattice parameters a=4.1230(1) A ̊ , c=9.0327(2) A ̊ for BaCuFS and a=4.2391(1) A ̊ , c=9.1217(2) A ̊ for BaCuFSe. The structure can be viewed as the intergrowth of a fluorite type layer [Ba 2F 2] and an anti-fluorite type layer [Cu 2Q 2].

Synthesis and crystal structure of new rare-earth copper oxyselenides: RCuSeO (R=La, Sm, Gd and Y)

A new series of copper oxyselenides RCuSeO (R=La, Sm, Gd and Y) have been prepared and studied by X-ray powder diffraction. The Sm-containing phase was determined to have a tetragonal crystal structure with the lattice parameters a=3.9512(1) A ̊ and c=8.7157(2) A ̊ , the space group of which is P4/nmm. Its structure is built of a fluorite type layer [Sm 2O 2] and an anti-fluorite type layer [Cu 2Se 2] stacking alternatively along c direction. The similarity of the diffraction patterns for the samples with R=La, Gd and Y to that of SmCuSeO suggests their assuming the same crystal structure.

Darstellung und Struktur des Lithiumnitridotantalats(V) Li 7TaN 4

The previously reported compound “Li 7TaN 4” [1–4] is a mixture of two phases. In addition to the already described Li 16 Ta 2N 8O [5], single crystals of the second phase identified as Li 7TaN 4 were obtained. Li 7TaN 4 ( a = 9.825(2) A ̊ , Z = 8, spacegroup Pa3̄) crystallizes in a superstructure of antifluorite type. Thereby tantalum is coordinated tetrahedrally by nitrogen (first coordination sphere (CS)) and octahedrally (second CS) and cubooctahedrally (third CS) by lithium.

Darstellung und struktur eines neuen nitridoxides mit lithium und tantal: Li 16Ta 2N 8O

The substance often previously described as “Li 7TaN 4” is a mixture of several phases. We obtained single crystals of one of these phases, which were suitable for X-ray structure determination. Li 16Ta 2N 8O ( a=5.984(1) A ̊ ; c=25.515(3) A ̊ ; Z=3; space group R3) crystallizes in an ordered superstructure of the antifluorite type. Another phase with an as yet unknown but similar composition is cubic ( a=9.828(1) A ̊ ).

Structure cristalline de [(CH 3) 3CNH 3] 2SnCl 6 · 2H 2O

The crystal structure of [(CH 3) 3CNH 3] 2SnCl 6 · 2H 2O with orthorhombic symmetry and lattice parameters a = 10.9074(8)Å, b = 10.1322(7)Å, c = 19.148(2)Å, α = β = γ = 90°, D calc = 1.56g/cm 3, and Z = 4 has been determined by Patterson and Fourier techniques at room temperature, using 1290 reflections. The agreement factors for these calculations are R F = 0.036 and R WF = 0.039 in space group Pcab. The structure is derived from the antifluorite type and consists of layers of SnCl 2− 6 octahedra. In the remaining tetrahedral holes the H 2O and (CH 3) 3CNH + 3 molecules are situated. The last two entities are nearly isolated and interconnected by hydrogen bonds of the type N H ... Cl and O H ... Cl to the SnCl 2− 6 layers. Characteristic lengths of these distances are N Cl ∼3.6Åand O Cl ∼3.4Å.

Synthesis and crystal structure of lithium phosphorus nitride Li 7PN 4: The first compound containing isolated PN 4-tetrahedra

Single phase Li 7PN 4 was synthesized under nitrogen atmosphere at 620°C by solid state reaction of Li 3N and P 3N 5 with molar ratio 7:1. Li 7PN 4 has cubic symmetry, P 43n, a = 936.48(3) pm, Z = 8 . (Rietveld profile refinement method; X-ray powder diffraction data; R(wp) = 0.099 and R( I, hkl) = 0.0744; 77 nonzero reflections observed, 9 positional parameters refined.) Li 7PN 4 is an ionic solid containing both lithium cations and isolated PN 4 anions. Atomic arrangement in the solid derives from an anti-fluorite type of structure. The PN bond lengths (average: 171 pm) correspond to a bond order of approximately 1 1 4 in the PN 4-tetrahedra. In the cubic unit cell the phosphorus atoms resemble β-tungsten analogous arrangement.

Vibronische Kopplung und dynamisch verzerrte Strukturen in Hexahalogenotelluraten(IV): Ergebnisse aus Tieftemperatur-Röntgenbeugungsuntersuchungen (300—160 K) und aus FTIR-spektroskopischen Experimenten (300—5 K) [1] / Vibronic Coupling and Dynamically Distorted Structures in Hexahalogenotellurates(IV): Low Temperatur X-Ray Diffraction (300—160 K) and FTIR-Spectroscopic (300—5 K) Results [1

Abstract From theoretical considerations a dynamically distorted octahedron as a result of vibronic coupling between the ground state and the first excited state should exist for 14 electron AX6E systems like TeX6 2- . A high symmetry crystal field yielding at least a center of symmetry for the Te position stabilizes this fluctuating structure, otherwise statical distortion will be observed. From X-ray diffraction experiments on antifluorite type compounds A2TeX6 (A = Rb. Cs: X = Cl, Br) the averaged structure (m3̅m symmetry) of the anions was found even at very low temperatures. The thermal parameters are not significantly different from those of similar SnX6 2 compounds. Distortions therefore are very small and are evident from FTIR spectroscopic meas­urements only. Here very broad T1u-deformation vibration bands are observed down to tempera­tures &lt;10 K without splitting: Astatically distorted species could not be frozen out. In contrast to XeF6 for TeX6 2- the energy gap between the threefold, fourfold or sixfold minima of the potential surface (according to the symmetry of one component of the T1u-vibration) is very small and shifted to temperatures lower than reached with the devices used for these experiments.

On the Stereochemistry of the Lone-Pair Electrons in AX6E-Systems: Dynamically Distorted Anion in (NH4)2SeBr6, Statically Distorted Anion in 1,3-Propanediammonium-Hexabromoselenate(IV) (C3N2H12)SeBr6

Abstract Using 293 K diffractometer intensity data, the crystal structures of (NH4)2SeBr6 (1) and [H3N(CH2)3NH3]SeBr6 (2) have been determined by single crystal X-ray technique and refined to a final Rw of 0.049 and 0.040, respectively. The dark red crystals of 1 are cubic (space group Fm3m) with a = 10.478(2) Å and Z = 4. This structure contains SeBe6 2- octahedra (point symmetry m3̄m, distance Se-Br: 2.577(2) Å in an antifluorite type arrangement of cations and anions. In contrast, the SeBr fi 2-ion in 2 is statically distorted (approximate point symmetry 3m, distance Se-Br min. 2,547(2), max. 2.595(2) Å. The dark red crystals are orthorhombic (space group Pnma) with a = 17.795(3), b = 7.5037(6), c = 10.476(1) Å and Z = 4. The results agree with the rules for the appearance of a static/dynamic stereochemical effect of the lone pair electrons given for TeX6 2- (X = Cl, Br, I) species (W. Abriel, Acta Crystallogr. B 42, 449 (1986)). Consequently these rules can be extended considering SeX6 2- as well. Basic structural data for all compounds containing AX6 2- ions (A = Se, Te; X = Cl, Br, I) known to date are given including the ⊿-values (R. D. Shannon, Acta Crystallogr. A 32, 751 (1976)) as a measure for the distortion of the octahedral anion.

Diffuse neutron scattering study of Cu 2−xSe

We have measured the diffuse neutron scattering in the hkk plane for Cu 2Se and Cu 1.8Se at 180°C and 51°C, respectively, in the cubic antifluorite type phase. The diffuse scattering shows significant structure, indicative of correlated short range mobile ion ordering. The short range order is found to be dependent on the concentration of vacant mobile ion sites.

New fast solid lithium ion conductors at low and imtermediate temperatures

Three approaches for practically useful new solid lithium electrolytes are presented. Combination of two binary lithium salts provides materials which are stable against reaction with lithium and decompose at intermediate values of the decomposition voltages of the two binary salts. Results are given for systems based on the ionic conductor Li 2S and lithium halides. A small number of ternary lithium compounds exist which contain a second type of cations with a higher binding energy to the anion than lithium. These materials are also stable with lithiums. Results obtained for the compounds LiMgN and Li 3AlN 2 which crystallize both in an antifluorite type structure are reported. The third class of solid lithium ion conductors are addition compounds formed from lithium halides and alcoholes. LiI.4CH 3OH shows a room temperature conductivity of 2.2×10 −4 Ω −1cm −1 and an activation enthalpy of 0.51 eV.

Formation and lithuim ionic conduction of the antifluorite type solid electrolytes, Li 2+ x- y- z[(NH) 1- x- y- zN xCl yH z

Antifluorite type solid electrolytes, Li 2+ x- y- z [(NH) 1- x- y- z N x Cl y H z ] have been synthesized from Li 3N, LiCl and LiCl·H 2O or Li 2[( NH) 1 2 N 1 4 H 1 4 ]. Either of the last two compounds introduces NH 2- ions into the product and is indispensable to form the antifluorite type structure. The lattice parameter decreases with increasing amount of NH 2- ions in the compound, reflecting the difference of anion sizes between Cl - and NH 2- ions. Activation energies of Li + diffusive motion, derived from both conductivity and NMR measurements, increase with concentration of NH 2- ions, although the values differ by a factor of ≈2 netween the both methods.

X-ray and pulsed NMR studies of lithium nitride chlorides in anti-fluorite type structures

Lithium nitride chloride, Li 2-2 x N 0.5- x Cl 0.5+x′ have been found to possess anti-fluorite type structures in the range 0.05 < x< 0.1, with Fm3m, and with the lattice parameter in the range 5.354 ≈ 5.375 Å. The 7Li relaxation was studied in the temperature range 178–625 K, and the activation energy for Li + hopping motion, E a = 0.19 eV was obtained for x = 1. Small variation of E a with composition or with occupancy of the Li + site was confirmed.

Diamagnetism and Superexchange Electron Interaction in Cs2Sb (IV) Cl6, Semiconducting Crystals

AbstractCrystals of Cs2Sb SbCl6Sb are diamagnetic and have a cubic structure of the antifluorite type. These facts may be explained either in terms of statistical disorder between Sb(III) and Sb(V) or in terms of electron exchange between SbCl and SbCl. A calculation is presented of the exchange interaction between the nearest SbCl complexes. The exchange integral £ is taken in form £ = (Es − Et)/2 where Es and Et are energies of singlet and triplet states. It is established that CI atoms mainly contribute to the exchange interaction. Sign and value of the exchange integral correspond to an antiferromagnetically ordered state in Cs2SbCl6 at room temperature.

Diffuse transition and melting in fluorite and antifluorite type of compounds. Heat content of potassium sulfide from 298 to 1260.degree.K

Diffuse transition and melting in fluorite and antifluorite type of compounds. Heat content of potassium sulfide from 298 to 1260.degree.K