Crystallographic studies on cation substitutions in the system (Na,K) (V,P)O3

Three compounds in the system (Na,K) (V,P)O₃ were synthesized and their structures were refined by full matrix least squares method in the space group $\text{C2}\text{c}$. Their compositions were shown by site population analysis to be Na(V_0.66P_0.34)O₃ (I), (Na_0.88K_0.12)VO₃ (II), and (Na_0.5K_0.5)VO₃ (III). All are related to the structure of α-NaVO₃ which in turn is related to the clinopyroxene structure characterized by infinite chains of SiO₄ tetrahedra sharing vertices and two inequivalent metal cation sites M1 and M2. Both sites feature sixfold coordination in compounds I and II, while the Na and K are ordered into M1 and M2 sites, respectively in III, with the latter showing eightfold coordination. The pentavalent cations are randomly distributed in tetrahedral sites in I, and in II the K was found to occupy the M2 sites only. Changes in the α-NaVO₃ structure upon cation substitution are discussed in terms of rotation and displacement of the tetrahedral chains. Parameters for measuring these chain movements are proposed and found to exhibit an almost linear relationship with the ratio $\text{〈X?0〉}\text{〈M2?0〉}$ in cases where the M1 site is exclusively occupied by Na.     

Etude des equilibres solide-liquide des systems MIPO3Sm(PO3)3 (MI = Li,Na, Ag)

The M^IPO₃Sm(PO₃)₃(M^I = Li, Na, Ag) systems were studied. Differential thermal analysis and X-ray diffraction were used to investigate the liquidus and solidus relations. Three compounds LiSm(PO₃)₄, NaSm(PO₃)₄, and AgSm(PO₃)₄ were obtained which melt incongruently at 1248, 1143, and 1078 K, respectively. These compounds are isomorphous with their homologs LiLn(PO₃)₄, NaLn(PO₃)₄, AgLn(PO₃)₄ (Ln = Ce, La, Nd). They belong to the monoclinic system. The LiSm(PO₃)₄ unit cell parameters refined by least squares method are a = 16.43(3) Å, b = 7.16(1) Å, c = 9.65(3) Å, β = 125,9°(1), with the space group $\text{C2}\text{c}$ and Z = 4. NaSm(PO₃)₄ and AgSm(PO₃)₄ are isotypic; they cristallize in the $\text{P2}{}_1\text{c}$ space group, Z = 4; their unit cell parameters are, respectively, a = 12.18(1) Å, b = 13.05(1) Å, c = 7.25(5) Å, β = 126,53°(4), $\text{a = 12.25(1)}\text{A}\text{?}$, b = 13.06(1) Å, c = 7.201(9) Å, β = 126,57°(7). The ir spectra of the last two compounds indicate that these phosphates are chain phosphates.     

Na-Li-[V3O8] insertion electrodes: Structures and diffusion pathways

The potential insertion-electrode compounds Na_1.2[V₃O₈] (NaV) and Na_0.7Li_0.7[V₃O₈] (NaLiV) were synthesized from mixtures of Na₂CO₃, Li₂CO₃ and V₂O₅, which were melted at 750° and subsequently cooled to room temperature. The structures of NaV and LiV contain sheets of polymerized (VO_n) polyhedra, which are topologically identical to the sheet of polymerized polyhedra in Li_1.2[V₃O₈] (LiV). Vanadium occurs in three different coordination environments: [2+3] V(1), [2+2+2] V(2) and [1+4+1] V(3). Calculated bond-valence sums indicate that V⁴⁺ occurs preferentially at the V(3) site, which agrees with the general observation that [6]-coordinated V⁴⁺ prefers [1+4+1]-rather than [2+2+2]-coordination. The M-cations Na and Li occur at three distinct sites, M(1), M(2) and M(3) between the vanadate sheets. The M(1)-site is fully occupied and has octahedral coordination. The M(2) sites are partly occupied in NaV and NaLiV, in which they occur in [4]- and [6]-coordination, respectively. Li partly occupies the M(3) site in NaLiV, in which it occurs in [3]-coordination. The M(2) and M(3) sites in NaLiV occur closer to the vanadate sheets than the M(2) sites in NaV and LiV. The shift in these cation positions is a result of the larger distance between the vanadate sheets in NaLiV than in LiV, which forces interstitial Li to move toward one of the vanadate sheets to satisfy its coordination requirements. Bond-valence maps for the interstitial cations Na and Li are presented for NaV, NaLiV and LiV. These maps are used to determine other potential cation positions in the interlayer and to map the regions of the structure where the Na and Li have their bond-valence requirements satisfied. These regions are potential pathways for Na and Li diffusion in these structures, and are used to explain chemical diffusion properties of Na and Li in the Na-Li-[V₃O₈] compounds.     

Group IB organometallic chemistry: XXIX. Synthetic and structural aspects of polynuclear arylcopperlithium compounds Ar4Cu2Li2 (“arylcuprates”) and interaggregate exchange phenomena in Ar4Cu4/Ar4Li4/Ar4Cu2Li2 systems

The thermally stable arylmetal-IB-lithium compounds (2-Me₂NCHZC₆H₄)₄M₂Li₂ (M = Cu, Ag or Au; Z = H or Me) and (2-Me₂NC₆H₄)₄M₂Li₂ have been prepared by a $\text{2}\text{1}$ molar reaction of the aryllithium compounds with the corresponding metal-IB halide (Cu or Ag) or metal-lB halide phosphine complex (BrAuPPh₃). These tetranuclear complexes were also made by an interaggregate exchange reaction of the pure arylmetal-IB clusters with the aryllithium compound.The structure of these compounds in solution consists of aryl groups bridging one metal-lB and one lithium atom of a trans M₂Li₂ core. The four built-in ligands coordinate to lithium resulting in two-coordination at M and four-coordination at Li. These conclusions were based on ¹H and ¹³C NMR spectroscopic data (J(AgC(1)), J(LiC(1)) of solutions of these tetranuclear compounds as well as on the ¹⁹⁷Au Mössbauer data of solid (2-Me₂NC₆H₄)₄Au₂Li₂ (IS 5.65 mm/s and QS 12.01 mm/s).The interaggregate exchange between the tetranuclear species is discussed in terms of an associative mechanism involving formation of an octanuclear intermediate in which the aryl groups can migrate via (3c-2e)edge-(2c-2e)corner(3c-2e)edge movements without M₂Ar bond cleavage.Some aspects of the organic reactions in which organocuprates are involved as intermediates are discussed in terms of the novel structural information.     

Neutron and X-ray powder diffraction study of LixRuO2 and LixIrO2: The crystal structure of Li0.9RuO2

Compounds formed by the insertion of lithium into the rutile structure hosts RuO₂ and IrO₂ were studied by X-ray and neutron powder diffraction techniques. Compositions in the range Li_xMO₂, M = Ru or Ir, 0 < x < 1 are two-phase materials consisting of unreacted host, x = 0, and limiting compositions x = 0.9 in both cases. Preparation of compounds with x > 1 was unsuccessful. Li_0.9RuO₂ and Li_0.9IrO₂ have orthorhombic cells with a = 5.062(3), b = 4.967(4), c = 2.771(4) and a = 4.962(4), b = 4.758(4), c = 3.108(6), respectively. Compared to the host rutile (tetragonal) cells those of the insertion compounds are greatly expanded along [100] and [010], ～0.5 Å for both, and contracted along [001], by ～0.3 Å for Li_0.9RuO₂ and 0.05 Å for Li_0.9IrO₂. The space group for both insertion phases appears to be Pnnm, a subgroup of the rutile space group $\text{P4}{}_2\text{mnm}$. The structure of Li_0.9RuO₂ was solved from neutron diffraction data. Lithium exists as Li⁺ in octahedral sites. The LiO coordination is highly regular with two bonds at 2.05(1) Å and four at 2.08(2) Å. The overall structure is essentially an ordered NiAs-type very similar to but more regular than the previously reported LiMoO₂. Attempts to solve the structure of Li_0.9IrO₂ from both X-ray and neutron powder data were unsuccessful due, presumably, to severe preferred orientation.     

The crystal structure of Li2WO4II: A structure related to spinel

Li₂WO₄II, synthesized at 3 kbar and 630°C, has tetragonal symmetry, $\text{I4}{}_1\text{amd}\text{, a = 11.954(2)}$ and c = 8.410(1)Å, Z = 16, D_calc = 5.78 g cm^?3. The structure was determined by countermeasuring 469 independent reflections from a single crystal and was refined up to R = 0.032 by the full-matrix least-squares method. It is based on cubic closest packing of oxygen atoms and is closely related to the β-phase structure of Mg₂SiO₄. W and Li(2) are in octahedral sites and Li(1), in tetrahedral sites. Four Li(1)O₄ tetrahedra form a Li₄O₁₂ group, WO₆ and Li(2)O₆ construct a octahedral double chain along the a axis, and four WO₆ octahedra build a W₄O₁₆ group by sharing their octahedral edges.     

Polyèdre de coordination de l'etain(II) dans SnC2O4: Relations structurales entre SnC2O4, Na2C2O4 et Na2Sn(C2O4)2

The crystal structure of SnC₂O₄ has been determined by X-ray single-crystal techniques and refined to R = 0,018 for 1139 reflections. The cell is monoclinic, space group $\text{C2}\text{c}$ with Z = 4 formula units, the parameters being a = 10,375(3)Å. b = 5,504(2)Å, c = 8,234(3)Å, β = 125,11(2)°. The oxalato groups, located on symmetry centers, are chelated to two Sn atoms through one oxygen on each carbon atom, giving rise to an infinite string (SnC₂O₄)_n. The Sn(II) atom is one-side bonded to four oxygen atoms with two SnO bonds of 2,232(2) Å and two of 2,393(2) Å. The tin atom is in a distorted trigonal bipyramid SnO₄E, the lone pair E occupying one of the apices of the equatorial trigonal base of the polyhedron. Crystal structure comparison with disodium bisoxalatostannate(II), Na₂Sn(C₂O₄)₂, permits one to deduce SnC₂O₄ by crystallographic shear operation $\text{1}\text{8}\text{[34}\text{2}\text{](001)}$ of $\text{c}\text{2}$ periodicity. Na₂Sn(C₂O₄)₂ can be described as an intergrowth of SnC₂O₄ and Na₂C₂O₄ structures and consldered as the first member of a new series Na₂Sn_1+n(C₂O₄)_2+n with n integer ? 0.     

Substitution in barium-fluoride apatite: The crystal structures of Ba10(PO4)6F2, Ba6La2Na2(PO4)6F2 and Ba4Nd3Na3(PO4)6F2

The crystal structures of the apatites Ba₁₀(PO₄)₆F₂(I), Ba₆La₂Na₂(PO₄)₆F₂(II) and Ba₄Nd₃Na₃(PO₄)₆F₂ (III) have been determined by single-crystal X-ray diffraction. All three compounds crystallize in a hexagonal apatite-like structure. The unit cells and space groups are: I, a = 10.153(2), c = 7.733(1)Å, $\text{P6}{}_3\text{m}\text{; a = 9.9392(4), c = 7.4419(5)}$Å, $\text{P}\text{6}$; III, a = 9.786(2), c = 7.281(1)Å, $\text{P}\text{3}$. The structures were refined by normal full-matrix crystallographic least squares techniques. The final values of the refinement indicators R_w and R are: I, R_w = 0.026, R = 0.027, 613 observed reflections; II, R_w = 0.081, R = 0.074, 579 observed reflections; III, R_w = 0.062, R = 0.044, 1262 observed reflections.In I, the Ba(1) atoms located in columns on threefold axes, are coordinated to nine oxygen atoms; the Ba(2) sites form triangles about the F site and are coordinated to six oxygen atoms and one fluoride ion. The fluoride ions are statistically displaced ～0.25 Å from the Ba(2) triangles. This displacement of the F ions is analogous to the displacement of OH ion in Ca₁₀(PO₄)₆(OH)₂.The structures of II and III contain disordered cations. In II there is disorder between La and Na in the column cation sites as well as triangle sites. In III, Nd and Na ions are ordered in the column sites, but there is disorder among Ba and the remaining Nd and Na ions in the triangle sites to give an average site population of $\text{2}\text{3}\text{Ba}\text{,}\text{1}\text{6}\text{Nd}\text{,}\text{1}\text{6}\text{Na}$. The coordination of the rare earth ions and Na ions in the ordered column sites are nine and six oxygens, respectively, in accord with the greater charge of the rare earth ions as compared with Na. The F ions in both II and III suffer from considerable disorder in position, and their locations are not precisely known.     

Stable tetrahedron of lithium bromide,metavanadate, and molybdate and potassium bromide in the Li,K || Br,VO<Subscript>3</Subscript>, MoO<Subscript>4</Subscript> quaternary reciprocal System

Phase equilibria in the LiBr–LiVO₃–Li₂MoO₄–KBr quaternary system (the stable tetrahedron of the quaternary reciprocal system Li, K || Br, VO₃, MoO₄) were studied by differential thermal analysis. The composition and melting point of a quaternary eutectic were determined: 56.7 mol % LiBr, 1.5 mol % LiVO₃, 4.9 mol % Li₂MoO₄, 36.9 mol % KBr, 321°C.     

Phase equilibrium relations in the binary systems LiPO3CeP3O9 and NaPO3CeP3O9

The LiPO₃CeP₃O₉ and NaPO₃CeP₃O₉ systems have been investigated for the first time by DTA, X-ray diffraction, and infrared spectroscopy. Each system forms a single 1:1 compound. LiCe(PO₃)₄ melts in a peritectic reaction at 980°C. NaCe(PO₃)₄ melts incongruently, too, at 865°C. These compounds have a monoclinic unit cell with the parameters: a = 16.415(6), b = 7,042(6), c = 9.772(7)Å; β = 126.03(5)°; Z = 4; space group $\text{C}{}_2\text{c}$ for LiCe (PO₃)₄; and a = 9.981(4), b = 13.129(6), c = 7.226(5) Å, β = 89.93(4)°, Z = 4, space group $\text{P2}{}_1\text{n}$ for NaCe(PO₃)₄. It is established that both compounds are mixed polyphosphates with chain structure of the type |M^I_IM^III_II (PO₃)₄|_∞M^I_I: alkali metal, M^III_II: rare earth.     

Structure cristalline de NaBaPO4

The crystal preparation of NaBaPO₄ is discussed. The space group and cell dimensions are $\text{C2}\text{m}$; a = 9.743(3), b = 5.622(1), c = 7.260(1) Å, β = 90.10(3)°, Z = 4. The main characteristic of the NaBaPO₄ structure consists in a statistical occupation of some special positions (4i) by Na or Ba atoms. The network is built up with PO₄ tetrahedra, NaO₆ octahedra, BaO₁₂ and MO₁₀ polyhedra (M = Na or Ba). The final R value is 0.058.     

Bismuth substituted calcium,strontium, and lead apatites

Bismuth substituted apatites of two general types have been prepared: M_10?2xBi_xNa_x(PO₄)₆Y₂ (M = Ca, Sr, Pb; Y = F, Cl) and lead apatites with the Y ion completely vacant Pb_10?(2x+2)BixNa_x+2(PO₄)₆. X-ray powder diffraction patterns of all the compounds show the $\text{P6}{}_3\text{m}$ hexagonal apatite type structure. The change of the lattice parameters and $\text{c}\text{a}$ values with compositions indicate the preference of the bismuth ions to occupy the 6h triangular positions. Bi³⁺ tends to incorporate in apatites with unoccupied halide positions.     

Interactions magnétiques dans des groupements binucléaires [Fe2O7]8− au sein de Na8Fe2O7

The magnetic interaction in the structural units [Fe₂O₇]^8?, built of two corner-sharing FeO₄ tetrahedra, in Na₈Fe₂O₇ ($\text{Na}{}_2\text{O}\text{Fe}{}_2\text{O}{}_3\text{=}\text{4}\text{1}$) has been studied by magnetic susceptibility measurements (4.2–500 K). An exchange integral $\text{J}\text{K}{}_{\mathrm{<mtext>B</mtext>}}$ of ?37 K is obtained by comparison of the experimental values and the calculated ones using a Heisenberg-Dirac-Van Vleck-type Hamiltonian ? = $\text{?2J}\text{S}\text{?}{}_1\text{S}\text{?}{}_2$. The hypothesis of magnetically isolated [Fe₂O₇]^8? groups is corroborated by Mössbauer spectroscopy between 1.5 and 77 K. The susceptibility measurements of the solid solutions Na₈Fe_2?xM_xO₇ (M = Al, Ga; 0 ≤ x ≤ 0.2 for Al; 0 ≤ x ≤ 2 for Ga) leads to the same conclusion of the existence of isolated Fe³⁺Fe³⁺ pairs in Na₈Fe₂O₇. The type of substitution of Fe by Al or Ga is determined; homonuclear Fe³⁺Fe³⁺ and M³⁺M³⁺ pairs and heteronuclear Fe³⁺M³⁺ pairs are formed.     

Preparation and crystal structure of Li2CaSiO4 and isostructural Li2CaGeO4

Li₂CaSiO₄ and Li₂CaGeO₄ are isostructural. They have body-centered tetragonal unit cells, with dimensions a = 5.047 ± 0.005, c = 6.486 ± 0.006 Å, and a = 5.141 ± 0.002, c = 6.595 ± 0.002 Å, respectively, and space group $\text{I}\text{4}\text{2m}$. Their crystal structures, refined to R = 0.076 and 0.051, respectively, comprise columns, parallel to [001], of alternating (CaO₈) dodecahedra and (SiO₄) [or (GeO₄)] tetrahedra that are linked by sharing edges. Neighboring columns are joined at their corners to form a three-dimensional network, enclosing channels parallel to [001] that contain lithium. The lithium atoms are in distorted (LiO₄) tetrahedra joined at the corners to form sheets perpendicular to [001].     

Synthesis, structure, and ionic conductivity of Na5Li3Ti2S8

The compound Na₅Li₃Ti₂S₈ has been synthesized by the reaction of Ti with a Na/Li/S flux at 723 K. Na₅Li₃Ti₂S₈ crystallizes in a new structure type with four formula units in space group C2/c of the monoclinic system. The structure contains three crystallographically independent Na⁺ cations and two crystallographically independent Li⁺ cations. Na₅Li₃Ti₂S₈ possesses a channel structure that features two-dimensional layers built from Li(1)S₄ and TiS₄ tetrahedra. The layers, which are stacked along c, comprise eight-membered rings and sixteen-membered rings. Na(3)⁺ cations are located between the eight-membered rings and Na(1)⁺, Na(2)⁺, and Li(2)⁺ cations are located between the sixteen-membered rings. These cations are each octahedrally coordinated by six S²⁻ anions. The ionic conductivity σ_T of Na₅Li₃Ti₂S₈ ranges from 8.8×10⁻⁶ S/cm at 303 K to 3.8×10⁻⁴ S/cm at 483 K. The activation energy E_a is 0.40 eV.     

The crystal chemistry of the M+VO3 (M+ = Li,Na, K,NH4, Tl,Rb, and Cs) pyroxenes

The crystal structures of M⁺VO₃(M⁺ = K, NH₄, and Cs) have been refined using three-dimensional counter-diffractometer X-ray data and full-matrix least-squares methods. The structure of these compounds is characterized by a (V⁵⁺O^2?₃)^?_∞ chain extending along the c-axis (Pbcm orientation), with adjacent chains linked by the alkali metal cation. The structure may be considered as a variant of the pyroxene structure, and standard atom nomenclature is proposed in order to facilitate comparison with silicate pyroxenes. Structural variation across this series is discussed in detail and is compared with the analogous M⁺M³⁺Si₂O₆ (M⁺ = Li, Na; M³⁺ = Al, Cr, Fe, Sc, In) series.     

Etude cristallochimique de LiPN2: Une structure derivée de la cristobalite

LiPN₂ has been prepared by reaction between Li₃N and P₃N₅ nitrides. The unit cell is tetragonal with a = 4.567(1) and c = 7.140(4) Å. The space group is $\text{I}\text{4}\text{2d}$. The structure is related to the β cristobalite type and is isostructural with CaGeN₂. It is built up from a PN₄ tetrahedra framework in the holes of which the lithium atoms are localized. The values of the rotation angle ф of tetrahedra, $\text{c}\text{a}$ ratio and θ (NPN) angle have been discussed in relation to the parameter x of the nitrogen atoms.     

Etude par RMN de la localisation des cations dans des phases ferroélectriques non-stoechiométriques derivées de LiTaO3

A ⁷Li NMR investigation of nonstoechiometric ferroelectric phases derived from LiTaO₃ has been performed on three solid solutions of formulation $\text{Li}{}_{\mathrm{1+x}}\text{Ta}{}_{\mathrm{<mtext>1?</mtext><mtext>x</mtext><mtext>5</mtext>}}\text{O}{}_3$, Li_1+xTa_1?xTi_xO₃, and Li_1?xTa_1?3x Ti_4xO₃. For the first one, based on the substitution of 1 Ta⁵⁺ by 5 Li⁺, the existence of Li⁺ in both octahedral and tetrahedral sites is confirmed. It is not excluded that the 5 Li⁺ form a small cluster within seven sites (one octahedral position and six tetrahedral ones) in the vicinity of the substituted Ta⁵⁺. For the second solid solution a large variation of the ⁷Li quadrupolar spectrum with composition has been detected, such behavior is related to the great decrease in T_c near the x = 0.10 composition.     

New defect vanadium dioxide phases

Two new monoclinic V₂O₄ phases were prepared at high pressure from the regular monoclinic (M₁) form of V₂O₄. The unit cell dimensions for the unmodified monoclinic (M₂) phase are: a = 9.083, b = 5.763, c = 4.532 Å, and β = 91.30°. The space group $\text{C 2}\text{m}$ is consistent with the crystallographic data. The new vanadium dioxide exhibited a structural transition and an abrupt, reversible change in resistivity (approx. 4 orders of magnitude) at 66°C similar to that observed in M₁-type V₂O₄. This new form of V₂O₄ is believed to be stabilized by chemical and structural defects. Controlled substitution of V⁵⁺ for V⁴⁺ in the structure led to yet another monoclinic (M₃) phase. This phase is closely related to the M₂ phase. The M₃ unit cell dimensions are: a = 4.506, b = 2.899, c = 4.617 Å, and β = 91.79°, having the space group $\text{P 2}\text{m}$. The substitution of V³⁺ yielded only monoclinic (M₁) derivatives. The modified products have varied semiconductor to metal transition temperatures which depend on the type and amount of substitution and defect structure.     

Phase diagram and some physical properties of V2O3+x1 (0 ? x ? 0.080)

The magnetic and electric properties of V₂O_3+x were investigated by measurements of magnetic susceptibility, electrical resistivity, magnetotorque, Mössbauer of doped ⁵⁷Fe, and NMR of ⁵¹V, and the results were compared with those of the (V_1?xTi_x)₂O₃ system or highly pressured V₂O₃. The results obtained are as follows: (1) The metallic state shows an antiferromagnetic ordering at T_N (x). The value of T_N for metallic V₂O₃, obtained by interpolation to x = 0, shows the coincidence between V₂O_3+x and the (V_1?xTi_x)₂O₃ system. (2) Magnetic susceptibility of V₂O_3+x is expressed as χ_M(V₂O_3+x) = (1?x)χ_M(V³⁺) + xχ_M(V⁴⁺). χ_M(V⁴⁺) obeys the Curie-Weiss law $\text{(χ}{}_{\mathrm{<mtext>M</mtext>}}\text{(}\text{V}{}^{\mathrm{4+}}\text{) =}\text{0.77}\text{T}\text{+ 17)}$. (3) In the insulating phase, the electrical resistivity ? is expressed as a common equation: $\text{? = 10}{}^{\mathrm{?1.8}}\text{exp}\text{(}\text{E}\text{kT}\text{)}$. This implies that the substitution of Ti or nonstoichiometry (V⁺⁴ + metal vacancies) has little influence on the carrier mobility (or bandwidth). (4) There is a critical length in the c-axis (? 14.01 Å) where the metal-insulator transition takes place. This suggests that the length of the c-axis plays an important role in the metal-insulator transition of V₂O₃-related compounds.