Copper Bismuth Chalcogenide Halogenides with Extensively Disordered and Mobile Copper(I) Cations

A new family of quaternary phases with the general sum formula Cu_3+δBi_5–δSe_8–2δX_2+2δ (X = Cl, Br) was discovered by slow cooling of high temperature melts. Cu_3.58(1)Bi_4.42(1)Se_6.84(2)Cl_3.16(2) (δ = 0.58) and Cu_4.52(1)Bi_3.48(1)Se_4.96(2)Br_5.04(2) (δ = 1.52) crystallize isostructural in the orthorhombic space group type Pnnm with a = 1332.3(1)/1340.2(3) pm, b = 1683.7(2)/1717.2(1) pm, and c = 406.2(1)/407.1(2) pm. The new structure type resembles in some aspects the hollandite as well as the pavonite type. A framework of face‐ and edge‐sharing anion polyhedra around Bi³⁺ cations hosts Cu⁺ cations. The characteristic motif is an infinite band of polyhedra that has the width of five polyhedra, with three octahedra being enclosed by capped trigonal prisms. The octahedrally coordinated Bi³⁺ cations are partially substituted by Cu⁺ (in octahedra faces), while Se^2– anions are replaced by X^–. The sulfide iodide Cu_3.33(2)Bi₂S_3.33(2)I_2.67(2) crystallizes in the monoclinic space group C2/m with a = 2803.6(9) pm, b = 409.9(1) pm, c = 1058.0(3) pm, and β = 110.68(2)°. Double strands of face‐sharing [BiS_1/1S_2/2I_4/4] as well as [BiS_3/3I_2/2(S_0.33/I_0.67)_2/2] polyhedra run along [010]. In between them, the Cu⁺ cations are spread over numerous closely spaced sites. They define a ladder‐shaped continuous path for ion conduction along [010].     

Syntheses, optical properties and electronic structures of copper(I) tantalates: Cu5Ta11O30 and Cu3Ta7O19

Two copper tantalates, Cu₅Ta₁₁O₃₀ (1) and Cu₃Ta₇O₁₉ (2), were synthesized by solid-state and flux synthetic methods, respectively. A synthetic route yielding 2 in high purity was found using a CuCl flux at 800^oC and its structure was characterized using powder X-ray diffraction (XRD) data (P6₃/m (no. 176), Z=2, a=6.2278(1) Å, and c=20.1467(3) Å). The solid-state synthesis of 1 was performed using excess Cu₂O that helped to facilitate the growth of single crystals and their characterization by XRD (P6¯2c (no. 190), Z=2, a=6.2252(1) Å, and c=32.516(1) Å). The atomic structures of both copper tantalates consist of alternating single and double layers of TaO₇ pentagonal bipyramids that are bridged by a single layer of isolated TaO₆ octahedra and linearly-coordinated Cu⁺. Measured optical bandgap sizes of ∼2.59 and ∼2.47 eV for 1 and 2 were located well within visible-light energies and were consistent with their orange-yellow colours. Each also exhibits optical absorption coefficients at the band edge of ∼700 and ∼275 cm⁻¹, respectively, and which were significantly smaller than that for NaTaO₃ of ∼1450 cm⁻¹. Results of LMTO calculations indicate that their visible-light absorption is attributable mainly to indirect bandgap transitions between Cu 3d¹⁰ and Ta 5d⁰ orbitals within the TaO₇ pentagonal bipyramids.     

Molten salt synthesis (MSS) of Cu2Mo6S8—New way for large-scale production of Chevrel phases

The Chevrel phase (CP), Mo₆S₈, was found to be an excellent cathode material for rechargeable magnesium batteries. Mo₆S₈ is obtained by a leaching process of Cu₂Mo₆S₈, which removes the copper. A new method of Cu₂Mo₆S₈ production was developed. In contrast to the well-known solid-state synthesis of CP, the method is based on the reaction in a molten salt media (KCl). A fast kinetics of this reaction allows using less active, but more convenient precursors (sulfides instead of sulfur), decreasing temperature and synthesis duration, as well as operation in the inert atmosphere instead of dynamic evacuated systems. It was shown that the composition and the electrochemical behavior of the products obtained by MSS and by the solid-state synthesis are identical. Thus, the molten salt method is extremely attractive for the large-scale production of the active materials for Mg batteries.     

A novel copper diphosphonate complex Cu4(aedp)2(4,4′-bpy)(H2O)4 with three-dimensional framework structure

A novel copper organodiphosphonate complex containing a second ligand 4,4′-bipyridine (4,4′-bpy) based on 1-aminoethylidenediphosphonic acid (H₄aedp), Cu₄(aedp)₂(4,4′-bpy)(H₂O)₄ (1), has been synthesized under hydrothermal conditions. Complex 1 adopts a three-dimensional framework structure assembled from {Cu₄(aedp)₂(H₂O)₄} layers and 4,4′-bpy bridges. Each {Cu₄(aedp)₂(H₂O)₄} unit consists of three crystallographically distinct Cu atoms. The Cu(1) atom has a distorted square pyramidal geometry, whereas the Cu(2) and Cu(3) atoms have a distorted elongated tetragonal octahedral geometry. The magnetic studies indicate that complex 1 show typical antiferromagnetic behaviors at low temperature, which is attributed to the superexchange couplings between Cu(II) centers through μ-O bridge in the phosphonate layers. Crystal data for 1: triclinic, space group , a=8.0931(16), b=13.567(3), c=6.2185(12)Å, α=90.55(3), β=96.97(3), γ=78.50(3)°, V=664.1(2)ų, Z=2.     

Synthesis of Li(x)Na(2−x)Mn2S3 and LiNaMnS2 through redox-induced ion exchange reactions

Na₂Mn₂S₃ was oxidatively deintercalated using iodine in acetonitrile to yield Na_1.3Mn₂S₃, with lattice constants nearly identical to that of the reactant. Lithium was then reductively intercalated into the oxidized product to yield Li_0.7Na_1.3Mn₂S₃. When heated, this metastable compound decomposed to form a new crystalline compound, LiNaMnS₂, along with MnS and residual Na₂Mn₂S₃. Single crystal X-ray diffraction structural analysis of LiNaMnS₂ revealed that this compound crystallizes in P-3m1 with cell parameters a=4.0479(6) Å, c=6.7759(14) Å, V=96.15(3) Å³ (Z=1, wR2=0.0367) in the NaLiCdS₂ structure-type.     

Phase relations in the system K2MoO4–KPO3–MoO3–Bi2O3: A new phosphate K3Bi5(PO4)6

Phase equilibrium in the pseudo-quaternary system K₂O–MoO₃–P₂O₅–Bi₂O₃ was studied as three-component solvent K₂MoO₄–KPO₃–MoO₃ containing 15 mol% Bi₂O₃ during slow cooling and spontaneous crystallization. The results of the investigation were shown on a composition diagram, which indicates the crystallization fields of K₂Bi(PO₄)(MoO₄), K₅Bi(MoO₄)₄, BiPO₄ and K₃Bi₅(PO₄)₆. New phosphate K₃Bi₅(PO₄)₆ was characterized by single-crystal X-ray diffraction (space group C2/c, a=17.680(4), b=6.9370(14), c=18.700(4) Å, β=113.79(3)°) and FTIR spectroscopy. The possibility of lone electron pair stereoactivity of bismuth was suggested using the calculations of characteristics of the Voronoi–Dirichlet polyhedra for K₃Bi₅(PO₄)₆ and K₂Bi(PO₄)(MoO₄).     

2D Cu(I) and 3D mixed-valence Cu(I)/Cu(II) coordination polymers: Synthesis and structural characterization of [CuCl(pyz-H)2]·2H2O and [Cu2Cl2(pyz)(H2O)]·H2O (pyz-H = pyrazinic acid)

Two new coordination polymers of copper(I) chloride and pyrazinic acid (pyz-H), namely [CuCl(pyz-H)₂]·2H₂O (1) and [Cu₂Cl₂(pyz)(H₂O)]·H₂O (2) have been prepared and characterized by spectroscopic, magnetic and crystallographic methods. The overall physical measurements suggest that 1 is diamagnetic and contains monodentate N-pyrazinic acid, whereas 2 is paramagnetic and contains tridentate N,N′,O- chelating bridging pyrazinato anion. In the structure of 1 as elucidated by X-ray single crystal analysis, the asymmetric units [CuCl(pyz)₂] are linked together forming a zigzag chain with tetrahedral copper(I) environment. The two lattice water molecules form hydrogen bonds with the uncoordinated N atom and carboxylate group O atom of pyz-H molecules. The Cu–N bond lengths are 2.009(6) Å and Cu–Cl distances are 2.337(2) Å. Complex 2 has a three-dimensional structure with the chains [Cu(I)Cu(II)(C₅H₃N₂O₂)Cl₂(H₂O)] interconnected by [Cu(I)Cl₂N] tetrahedral unit and [Cu(II)NO₂Cl₂] polyhedra. The Cu(I)–Cl and Cu(I)–N distances are 2.327(2)–2.581(2) Å and 1.988(6) Å, respectively, whereas the Cu(II)–Cl and Cu(II)–N bond lengths are 2.258(2), 2.581(2) Å, and 2.017(6) Å, respectively. Hydrogen bonds of the type O–HO are formed between lattice and coordinated water, and carboxylate oxygens of pyrazinato ligand giving rise to a three-dimensional network. The Cl⁻ anions act as bridging ligands in both complexes. The magnetic data of complex 2 have been measured from 2 to 300 K and discussed.     

Ferromagnetic exchange coupling in phosphonato-bridged dinuclear copper(II) compound with monoethyl (pyridyn-2-ylmethyl)phosphonate ligand (2-mpmpe): Cu2(2-mpmpe)2(H2O)2(NO3)2

The interaction of diethyl (pyridyn-2-ylmethyl)phosphonate (2-pmpe) with Cu(NO₃)₂ · 6H₂O leads to a partial hydrolysis of the starting ligand and formation of the compound of the formula Cu₂(2-mpmpe)₂(H₂O)₂(NO₃)₂, where 2-mpmpe = monoethyl (pyridyn-2-ylmethyl)phosphonate. The crystal and molecular structure of a copper(II) compound was determined by single X-ray diffraction method. Its structure consists of five-coordinated in distorted square planar geometry (CuNO₄ chromophore) copper(II) ions doubly bridged by OPO from phosphonate. The Cu?Cu distance is 4.69 Å. The crystal packing is determined by the interdinuclear hydrogen bond system, which leads to a three-dimensional (3D) H-bonds network. The compound was characterized by infrared, ligand field, EPR spectroscopy, and magnetic studies. The magnetic properties of the title compound investigated over the 1.8–300 K, revealed the occurrence of a weak ferromagnetic coupling through phosphonate bridge (J = 1.86 cm⁻¹) and interdimer superexchange coupling through H-bond network (zJ′ = −0.17 cm⁻¹). Spectroscopic and magnetic properties are presented in the light of crystal structure.     

Energetics of copper diphosphates – Cu2P2O7 and Cu3(P2O6OH)2

Differential scanning calorimetry and high temperature oxide melt solution calorimetry are used to study enthalpy of phase transition and enthalpies of formation of Cu₂P₂O₇ and Cu₃(P₂O₆OH)₂. α-Cu₂P₂O₇ is reversibly transformed to β-Cu₂P₂O₇ at 338–363 K with an enthalpy of phase transition of 0.15 ± 0.03 kJ mol⁻¹. Enthalpies of formation from oxides of α-Cu₂P₂O₇ and Cu₃(P₂O₆OH)₂ are −279.0 ± 1.4 kJ mol⁻¹ and −538.8 ± 2.7 kJ mol⁻¹, and their standard enthalpies of formation (enthalpy of formation from elements) are −2096.1 ± 4.3 kJ mol⁻¹ and −4302.7 ± 6.7 kJ mol⁻¹, respectively. The presence of hydrogen in diphosphate groups changes the geometry of Cu(II) and decreases acid–base interaction between oxide components in Cu₃(P₂O₆OH)₂, thus decreasing its thermodynamic stability.     

Stabilisation of heterobimetallic networks by crown ethers and hydrogen-bonding in [Ni(H2O)6][Cu3Cl8(H2O)2] · (15-crown-5)2 · 2H2O: Structure and magnetism

[Ni(H₂O)₆][Cu₃Cl₈(H₂O)₂] · (15-crown-5)₂ · 2H₂O can be conveniently prepared by the interaction of NiCl₂ · 6H₂O, CuCl₂ · 2H₂O and 15-crown-5 in water. The X-ray crystal structure reveals an ionic complex involved in a hydrogen-bonded two dimensional network with the [Ni(H₂O)₆]²⁺ and [Cu₃Cl₈(H₂O)₂]²⁻ ions sandwiched between the 15-crown-5 macrocycles. The magnetic susceptibility data (4–300 K) and magnetisation isotherms (2–5.5 K; 0–5 T) are best interpreted in terms of intra-trimer ferromagnetic coupling within the [Cu₃Cl₈(H₂O)₂]²⁻ moieties, with J ∼ 6 cm⁻¹, and antiferromagnetic coupling between the trimers, the latter mediated by H-bonding pathways. Comparisons are made to other reported quaternary ammonium salts of [Cu₃Cl₈]²⁻ and [Cu₃Cl₁₂]⁶⁻, most of which display structures that involve close stacking of such Cu(II) trimers, rather than being of the present isolated, albeit H-bonded, types.     

Novel bicyclic hexanuclear copper(I) aggregate: Structure and solid state P CPMAS NMR spectra of [(Cu3L3)2] and [Cu(PPh3)2L] complexes of N-(diisopropoxythiophosphinyl)-N′-phenylthiourea (HL)

A new complex of N-thiophosphorylthiourea PhNHC(S)NHP(S)(OiPr)₂ (HL) of formula [(Cu₃L₃)₂] has been synthesized and characterized by single crystal X-ray diffraction, FT-IR, ¹H, ³¹P NMR in solution and by ³¹P CPMAS NMR spectroscopy in the solid state. A comparison of the structure and the spectral parameters of [(Cu₃L₃)₂] with those of the mononuclear analogue [Cu(PPh₃)₂L] was performed. In the solid state the aggregate [(Cu₃L₃)₂] represents the first example of a spontaneous “side-by-side” association of two neutral cyclic [Cu₃L₃] moieties using two Cu-S-Cu bridges formed by the sulfur atoms of the PS-groups. The values of the ¹J(³¹P-^63,65Cu) and ²J(³¹P-³¹P) coupling constants of the [Cu(PPh₃)₂]⁺ moiety in the solid state spectra are reported.     

Reaction of carboxamide with Cu2Oisonitrile complex; formation of a new chelated copper(I) complex

Reaction of carboxamides with Cu₂O in the presence of t-butyl isocyanide gave new chelated copper(I) complexes, which probably are formed by the insertion of t-butyl isocyanide into the coppernitrogen bond of copper(I) amide isonitrile complexes, which were initially produced from the carboxamides and Cu₂Ot-butyl isocyanide complex. The same chelated copper(I) complexes were prepared more readily by the reaction of the corresponding N-trimethylsilyl-carboxamides with Cu₂Ot-butyl isocyanide complex. Reactions of the copper(I) complexes thus obtained with alkylating agents, such as alkyl halides, alkyl tosylates and triethyloxonium tetrafluoroborate, also were described.     

An evaluation of silver ionic transport in the mixed system (1−x)·CuI-x·Ag2MoO4 (0.15?x?0.6)

The origin and nature of correlation between silver ionic conduction and composition of various phases present in the case of the mixed system CuI-Ag₂MoO₄ were probed in terms of possible solid-state reactions. Detailed X-ray diffraction (XRD), differential scanning calorimetry, Fourier transform infrared, electrical transport studies involving ionic transport number data and electrical conductivity measurement were carried out in order to identify the reaction products. The feasible reaction products identified were found to determine the exact composition resulting from the completion of each solid-state reaction and hence the behavior of effective electric conduction.     

Syntheses and study on nickel and copper complexes with 1,3,5-benzenetricarboxylic acid. Crystal and molecular structure of [Cu3(mdpta)3(btc)](ClO4)3 · 4H2O

Nickel and copper complexes containing 1,3,5-benzenetricarboxylic acid, with a combination of selected N-donor ligands and Schiff bases, of the composition Ni₃(bimz)₆(btc)₂ · 12H₂O (1), Ni₃(btz)₉(btc)₂ · 12H₂O (2), Ni₂(L₁)(btc) · 7H₂O (3), Ni₃(L₂)₂(Hbtc) · 9H₂O (4), Ni₂(L₃)(btc) · 4H₂O (5), Cu₂(L₄)(btc) · 7H₂O (6), [Cu₃(pmdien)₃(btc)](ClO₄)₃ · 6H₂O (7) and [Cu₃(mdpta)₃(btc)](ClO₄)₃ · 4H₂O (8); H₃btc = 1,3,5-benzenetricarboxylic acid, bimz = benzimidazole, btz = 1,2,3-benztriazole, L₁ = 2-[(phenylimino)methyl]phenol, L₂ = N,N′-bis-(salicylidene)propylenediamine, L₃ = 2-{[(2-nitrophenyl)methylene]amino}phenol, L₄ = 2-[(4-methoxy-phenylimino)methyl]phenol, pmdien = N,N,N′,N″,N″-pentamethyldiethylenetriamine, mdpta = N,N-bis-(3-aminopropyl)methylamine, have been synthesized. The complexes have been studied by elemental analysis, IR, UV–Vis spectroscopies, magnetochemical and conductivity measurements and selected compounds also by thermal analysis. The crystal and molecular structure of complex 8 was solved. The complex is trinuclear with btc³⁻-bridge. The coordination polyhedron around each copper atom can be described as a distorted square with a CuON₃ chromophore formed by one oxygen atom of carboxylate and three nitrogen atoms of mdpta. The magnetic properties of 8 have been studied in the 1.8–300 K temperature range revealing a very weak antiferromagnetic exchange interaction with J = −0.56 cm⁻¹ for g = 2.13(9). The antimicrobial activities against selected strains of bacteria were evaluated. It was found that only complex 5 is able to inhibit the growth of Staphylococcus strains.     

Hydrothermal synthesis, crystal structure and third-order non-linear optical property of a discrete decanuclear iodocuprate(I) [Cu10H2I16] with [Ni(phen)3] as a template

The title compound [Ni^II(phen)₃]₂[Cu₁₀H₂I₁₆] 1 (phen=1,10-phenanthroline, C₁₂H₈N₂) was hydrothermally synthesized from a simple reaction of CuI-NiCl₂·6H₂O-phen·H₂O-H₂O. X-ray analysis revealed that it consists of NiN₆²⁺ core cation and decanuclear iodocuprate(I) anion together with two dissociative H⁺ ions. In anionic unit, the discrete decanuclear iodocuprate(I) is formed by crystallographically independent five monovalent copper atoms and eight iodine atoms via an inversion center. There exist two types of Cu(I) coordination sites; only one copper(I) atom is in a highly distorted triangular planar site, and the other four copper(I) atoms display the tetrahedral geometries. It deserves to be noted that four types of bridging modes of I⁻ ions in which two are ordinary μ₂- and μ₃-bonding modes can be found. But the other two are the rectangle planar geometry and the novel μ₄-bridge like an “umbrella”, and both of them are rather rare in the halocuprates(I). Compound 1 was crystallized in triclinic space group with a=11.6861(17), b=14.590(2), c=14.649(2) Å, α=76.370(2), β=70.830(2), γ=81.320(3)^o, R=0.075, and was characterized by elemental analysis, IR spectrum and UV-VIS spectrum. The third-order non-linear optical property of 1 was also investigated and the compound exhibits the reverse saturable absorption and self-defocusing performance.     

Synthesis and crystal structure of copper halide complexes with triethylallylammonium (teaa) chloride: [(teaa)Cu3ICl4], [(teaa)Cu3IBr3.86Cl0.14], and (teaa)2CuIICl4

The results of X-ray diffraction analysis of novel triethylallylammonium chloride compounds with copper(I) chloride, copper(I) bromide, and copper(II) chloride are reported. The [(CH₃CH₂)₃(CH₂=CHCH₂xN]Cu ₃ ^I Cl₄ and [(CH₃CH₂)₃(CH₂=CHCH₂Cu ₃ ^I Br_3.86)Cl_0.14 -complexes are isostructural: space group P2₁/a; a= 17.58(1) Å, b = 12.059(8)Å, c = 7.184(4) Å, = 98.37(5)° and a = 17.972(9) Å, b=12.479(8) Å, c = 7.290(5) Å, = 98.81(5)°, respectively. ²-Coordination of the copper atom by the olefinic bond plays a key role in the structural ordering of the tetraalkylammonium cation. In contrast, the structure of {(CH₃CH₂)₃x(CH₂=CHCH₂)N}₂Cu^IICl₄ (P4₂/nmc; a = 8.839(3) Å, c =15.660(9) Å) follows the ionic salt pattern.Original Russian Text Copyright © 2004 by L. M. Babkov, I. I. Gnatyuk, G. A. Puchkovskaya, and S. V. TrukhachevTranslated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 3, pp. 398–405, May–June, 2004.     

Synthesis and coordination chemistry of new tetradentate N2S2 donor Schiff-base ligand ca2-dapte: Mononuclear and dinuclear copper(I) complexes [Cu(ca2dapte)]ClO4 and [{Cu(PPh3)(X)}2(ca2dapte)] (X = I and Br)

A mononuclear copper(I) complex, [Cu(ca₂dapte)]ClO₄ (1), and two dinuclear copper(I) complexes, [{Cu(PPh₃)(X)}₂(ca₂dapte)] (X = I (2) and Br (3)), of a new tetradentate N₂S₂ donor Schiff-base ligand ca₂dapte have been prepared (ca₂dapte = N,N′-bis(trans-cinnamaldehyde)-1,2-di(o-iminophenylthio)ethane). These compounds have been characterized by elemental analyses (CHN), FT-IR, UV–Vis and ¹H NMR spectroscopy. The crystal structures of these copper(I) complexes have been determined by single-crystal X-ray diffraction. The coordination geometry around Cu(I) centers in these complexes is a distorted tetrahedron. The ca₂dapte is coordinated to Cu(I) as a tetradentate ligand in 1, while it acts as a bis-bidentate bridging ligand in 2 and 3.     

Crystal structure and magnetic properties of Cu3(TeO3)2Br2—a layered compound with a new Cu(II) coordination polyhedron

The new compound Cu₃(TeO₃)₂Br₂ crystallizes in the monoclinic spacegroup C2/m. The unit cell parameters are a=9.3186(18)Å, b=6.2781(9)Å, c=8.1999(16)Å, β=107.39(2)°, Z=2. The structure is solved from single crystal data, R₁=0.021. The new compound shows a layered structure where only weak van der Waals interactions connect the layers. There are two crystallographically different Cu(II) atoms; one having a square planar [CuO₄] coordination and one showing an unusual [CuO₄Br] trigonal bi-pyramidal coordination, the Br-ion is located in the equatorial plane. The Te(IV) atom has a tetrahedral [TeO₃E] coordination where E is the 5s² lone-pair. Within the layers the Cu-polyhedra are connected by corner- and edge sharing to form chains. The chains are separated by the Te atoms. The magnetic properties are dominated by long range magnetic ordering at . Evidence for a coexistence of ferromagnetic and antiferromagnetic interactions exists.     

Synthesis,spectroscopic properties,structural characterization and electrochemistry of mixed ligand complexes of copper(I) halide with PPh3 and naphthylazoimidazole

The reaction of CuX (X = Cl, Br, I) with a mixture of PPh₃ and 1-alkyl-2-(naphthyl-α/β-azo)imidazole has synthesized mixed ligand complexes of the composition, [Cu(α/β-NaiR)(PPh₃)X]. The spectroscopic characterization (IR, UV–Vis, ¹H NMR) supports this formulation. The single crystal X-ray diffraction study of [Cu((α-NaiMe)(PPh₃)I] (7a) (α-NaiMe = 1-methyl-2-(naphthyl-α-azo)imidazole) shows a distorted tetrahedral geometry about Cu(I). Cyclic voltammograms of the complexes show a high potential Cu(II)/Cu(I) couple and azo reductions. The [Cu(α/β-NaiR)(PPh₃)I] complexes show an additional oxidative response at 0.4 V that is assigned to I/I⁻ A sharp anodic peak at ∼−0.2 V is assigned to the oxidation of metallic Cu, deposited on electrode surface upon scanning to the negative side of the SCE. DFT and TD-DFT computations of [Cu((α-NaiMe)(PPh₃)I] (7a), [Cu((α-NaiMe)(PPh₃)I]⁺ (7a⁺) and [Cu((α-NaiMe)(PPh₃)I]⁻ (7a⁻) were carried out to examine the electronic configuration and to explain the spectral and redox properties of the complexes.     

Oxygen ionic and electronic transport in apatite-type La10−x(Si,Al)6O26±δ

The main factor governing the oxygen ionic conductivity in apatite-type La_10−xSi_6−yAl_yO_{27−3x/2−y/2} (x=0-0.33; y=0.5-1.5) is the concentration of mobile interstitials determined by the total oxygen content. The ion transference numbers, measured by modified faradaic efficiency technique, vary in the range 0.9949-0.9997 in air and increase on reducing oxygen partial pressure due to decreasing p-type electronic conduction. The activation energies for ionic and hole transport are (56-67)±3 kJ/mol and (57-100)±8 kJ/mol, respectively. Increasing oxygen content leads to higher hole conduction in oxidizing atmospheres and promotes minor oxygen losses from the lattice when the oxygen pressure decreases, although the overall level of ionic conductivity is almost constant in the p(O₂) range from 50 kPa down to 10⁻¹⁶ Pa. Under reducing conditions at temperatures above 1100 K, silicon oxide volatilization from the surface layers of apatite ceramics results in a moderate decrease of the conductivity with time. This suggests that the operation of electrochemical cells with silicate-based solid electrolytes should be limited to the intermediate-temperature range, such as 800-1000 K, where the ionic transport in most-conductive apatite phases containing 26.50-26.75 oxygen atoms per unit formula is higher than that in stabilized zirconia. The average thermal expansion coefficients of apatite ceramics, calculated from dilatometric data in air, are (8.7-10.8)×10⁻⁶ K⁻¹ at 300-1300 K.