Determination of the enthalpy of fusion of K3TaF8 and K3TaOF6

The areas of the fusion and crystallization peaks of K₃TaF₈ and K₃TaOF₆ have been measured using the DSC mode of the high-temperature calorimeter (SETARAM 1800 K). On the basis of these quantities and the temperature dependence of the used calorimetric method sensitivity, the values of the enthalpy of fusion of K₃TaF₈ at temperature of fusion 1039 K: Δ_fusH_m(K₃TaF₈; 1039 K) = (52 ± 2) kJ mol⁻¹ and of K₃TaOF₆ at temperature of fusion 1055 K: Δ_fusH_m(K₃TaOF₆; 1055 K) = (62 ± 3) kJ mol⁻¹ have been determined.     

The mercury chromates Hg6Cr2O9 and Hg6Cr2O10—Preparation and crystal structures, and thermal behaviour of Hg6Cr2O9

The basic mercury(I) chromate(VI), Hg₆Cr₂O₉ (=2Hg₂CrO₄·Hg₂O), has been obtained under hydrothermal conditions (200 °C, 5 days) in the form of orange needles as a by-product from reacting elemental mercury and K₂Cr₂O₇. Hydrothermal treatment of microcrystalline Hg₆Cr₂O₉ in demineralised water at 200 °C for 3 days led to crystal growth of red crystals of the basic mercury(I, II) chromate(VI), Hg₆Cr₂O₁₀ (=2Hg₂CrO₄·2HgO). The crystal structures were solved and refined from single crystal X-ray data sets. Hg₆Cr₂O₉: space group P2₁2₁2₁, Z=4, a=7.3573(12), b=8.0336(13), , 3492 structure factors, 109 parameters, R[F²>2σ(F²)]=0.0371, wR(F² all)=0.0517; Hg₆Cr₂O₁₀: space group Pca2₁, Z=4, a=11.4745(15), b=9.4359(12), , 3249 structure factors, 114 parameters, R[F²>2σ(F²)]=0.0398, wR(F² all)=0.0625. Both crystal structures are made up of an intricate mercury-oxygen network, subdivided into single building blocks [O-Hg-Hg-O] for the mercurous compound, and [O-Hg-Hg-O] and [O-Hg-O] for the mixed-valent compound. Hg₆Cr₂O₉ contains three different Hg₂²⁺ dumbbells, whereas Hg₆Cr₂O₁₀ contains two different Hg₂²⁺ dumbbells and two Hg²⁺ cations. The Hg^I-Hg^I distances are characteristic and range between 2.5031(15) and 2.5286(9) Å. All Hg₂²⁺ groups exhibit an unsymmetrical oxygen environment. The oxygen coordination of the Hg²⁺ cations is nearly linear with two tightly bonded O atoms at distances around 2.07 Å. For both structures, the chromate(VI) anions reside in the vacancies of the Hg-O network and deviate only slightly from the ideal tetrahedral geometry with average Cr-O distances of ca. 1.66 Å. Upon heating at temperatures above 385 °C, Hg₆Cr₂O₉ decomposes in a four-step mechanism with Cr₂O₃ as the end-product at temperatures above 620 °C.     

K2B12F12: A rare A2X structure for an ionic compound at ambient conditions

The anhydrous salt K₂B₁₂F₁₂ crystallized from aqueous solution and its structure was determined by single crystal X-ray diffraction. The Ni₂In-type structure it exhibits is rare for an A₂X ionic compound at 25 °C and 1 atm., consisting of an expanded hexagonal close-packed array of B₁₂F₁₂²⁻ centroids (cent?cent distances: 7.204-8.236 Å) with half of the K⁺ ions filling all of the O_h holes and half of the K⁺ ions filling all of the D_3h trigonal holes in the close-packed layers that are midway between two “empty” T_d holes. The structure is also unusual in that the bond-valence sum for the K⁺ ions in O_h holes is less than or equal to 0.73 (the bond-valence sum for the other type of K⁺ ion is 1.16). A variation of the Ni₂In structure is exhibited by the previously published monohydrate Cs₂(H₂O)B₁₂F₁₂, for which an improved structure is also reported here. For K₂B₁₂F₁₂: monoclinic, C2/c, a = 8.2072(8), b = 14.2818(7), c = 11.3441(9) Å, β = 92.832(5)°, Z = 4, T = 120(2) K. For Cs₂(H₂O)B₁₂F₁₂: orthorhombic, P2₁2₁2₁, a = 9.7475(4), b = 10.2579(4), c = 15.0549(5) Å, Z = 4, T = 110(1) K.     

A molecule based on polyoxometalate acid and crown ether: synthesis and characterization of [(H3O)(C20H24O6)]2[HPMo12O40]·C20H24O6·3MeCN·H2O (C20H24O6=dibenzo-18-crown-6)

The new molecule based on 12-molybdophosphate acid and dibenzo-18-crown-6, [(H₃O)(C₂₀H₂₄O₆)]₂[HPMo₁₂O₄₀]·C₂₀H₂₄O₆·3MeCN·H₂O 1, was synthesized in acetonitrile and characterized by elemental analyses, IR, ¹H NMR, electrospray mass spectra and single crystal X-ray diffraction, indicating that it contains [(H₃O)(dibenzo-18-crown-6)]⁺ cations, where oxonium ions are out of the planes defined by crown ether oxygen atoms, and disordered PMo₁₂O₄₀³⁻ anions with α-Keggin structure where the crystal has high lattice energy so that it is difficult to dissolve it. The crystallographic disorder averages Mo-Mo distances and Mo-O_b/c-Mo angles between the M₃ triplets and within the M₃ triplet. The interactions between crown ether molecules and oxonium ions are hydrogen-bonding with the O(crown ether)-OH₃⁺ distances of 2.510(10)-2.783(7) Å. The interactions between [(H₃O)(dibenzo-18-crown-6)]⁺ cations and PMo₁₂O₄₀³⁻ anions are dominantly electrostatic. The electrical conductivity is <10⁻⁷ S.cm⁻¹.     

Syntheses, crystal structures and Raman spectra of Ba(BF4)(PF6), Ba(BF4)(AsF6) and Ba2(BF4)2(AsF6)(H3F4); the first examples of metal salts containing simultaneously tetrahedral BF4 and octahedral AF6 anions

In the system BaF₂/BF₃/PF₅/anhydrous hydrogen fluoride (aHF) a compound Ba(BF₄)(PF₆) was isolated and characterized by Raman spectroscopy and X-ray diffraction on the single crystal. Ba(BF₄)(PF₆) crystallizes in a hexagonal space group with a=10.2251(4) Å, c=6.1535(4) Å, V=557.17(5) Å³ at 200 K, and Z=3. Both crystallographically independent Ba atoms possess coordination polyhedra in the shape of tri-capped trigonal prisms, which include F atoms from BF₄⁻ and PF₆⁻ anions. In the analogous system with AsF₅ instead of PF₅ the compound Ba(BF₄)(AsF₆) was isolated and characterized. It crystallizes in an orthorhombic Pnma space group with a=10.415(2) Å, b=6.325(3) Å, c=11.8297(17) Å, V=779.3(4) Å³ at 200 K, and Z=4. The coordination around Ba atom is in the shape of slightly distorted tri-capped trigonal prism which includes five F atoms from AsF₆⁻ and four F atoms from BF₄⁻ anions. When the system BaF₂/BF₃/AsF₅/aHF is made basic with an extra addition of BaF₂, the compound Ba₂(BF₄)₂(AsF₆)(H₃F₄) was obtained. It crystallizes in a hexagonal P6₃/mmc space group with a=6.8709(9) Å, c=17.327(8) Å, V=708.4(4) Å³ at 200 K, and Z=2. The barium environment in the shape of tetra-capped distorted trigonal prism involves 10 F atoms from four BF₄⁻, three AsF₆⁻ and three H₃F₄⁻ anions. All F atoms, except the central atom in H₃F₄ moiety, act as μ₂-bridges yielding a complex 3-D structural network.     

The study of Bi3B5O12: synthesis, crystal structure and thermal expansion of oxoborate Bi3B5O12

The paper presents a new data on the crystal structure, thermal expansion and IR spectra of Bi₃B₅O₁₂. The Bi₃B₅O₁₂ single crystals were grown from the melt of the same stoichiometry by Czochralski technique. The crystal structure of Bi₃B₅O₁₂ was refined in anisotropic approximation using single-crystal X-ray diffraction data. It is orthorhombic, Pnma, a=6.530(4), b=7.726(5), c=18.578(5) Å, V=937.2(5) Å³, Z=4, R=3.45%. Bi³⁺ atoms have irregular coordination polyhedra, Bi(1)O₆ (d(B-O)=2.09-2.75 Å) and Bi(2)O₇ (d(B-O)=2.108-2.804 Å). Taking into account the shortest bonds only, these polyhedra are considered here as trigonal Bi(1)O₃ (2.09-2.20 Å) and tetragonal Bi(2)O₄ (2.108-2.331 Å) irregular pyramids with Bi atoms in the tops of both pyramids. The BiO₄ polyhedra form zigzag chains along b-axis. These chains alternate with isolated anions [B₂^IVB₃^IIIO₁₁]⁷⁻ through the common oxygen atoms to form thick layers extended in ab plane. A perfect cleavage of the compound corresponds to these layers and an imperfect one is parallel to the Bi-O chains. The Bi₃B₅O₁₂ thermal expansion is sharply anisotropic (α₁₁≈α₂₂=12, α₃₃=3×10⁻⁶ °C⁻¹) likely due to a straightening of the flexible zigzag chains along b-axis and decreasing of their zigzag along c-axis. Thus the properties like cleavage and thermal expansion correlate to these chains.     

Non-centrosymmetric Ba3Ti3O6(BO3)2

The compound previously reported as Ba₂Ti₂B₂O₉ has been reformulated as Ba₃Ti₃B₂O₁₂, or Ba₃Ti₃O₆(BO₃)₂, a new barium titanium oxoborate. Small single crystals have been recovered from a melt with a composition of BaTiO₃:BaTiB₂O₆ (molar ratio) cooled between 1100°C and 850°C. The crystal structure has been determined by X-ray diffraction: hexagonal system, non-centrosymmetric space group, a=8.7377(11) Å, c=3.9147(8) Å, Z=1, wR(F²)=0.039 for 504 unique reflections. Ba₃Ti₃O₆(BO₃)₂ is isostructural with K₃Ta₃O₆(BO₃)₂. Preliminary measurements of nonlinear optical properties on microcrystalline samples show that the second harmonic generation efficiency of Ba₃Ti₃O₆(BO₃)₂ is equal to 95% of that of LiNbO₃.     

Synthesis, optical properties and electronic structures of polyoxometalates K3P(Mo1−xWx)12O40 (0?x?1)

Various compositions of solid solutions K₃P(Mo_1−xW_x)₁₂O₄₀ (0?x?1) were prepared using two solid state synthetic routes. The crystallite size was determined by linewidth refinements of X-ray diffraction patterns using the Warren-Averbach method, and the grain size distribution by laser scattering experiments. Optical properties were determined by diffuse reflectance measurements in the UV-visible range. The optical gap E_g was found to increase exponentially from ∼2.5 to ∼3.30 eV with increasing x, and is systematically shifted to a higher energy when the grain size decreases. The relation between E_g and x was analyzed by calculating the HOMO-LUMO gaps of the [P(Mo_1−xW_x)₁₂O₄₀]³⁻ anions on the basis of tight-binding electronic structure calculations.     

Synthesis, structure characterization and optical properties of a new tripotassium cadmium pentaborate, K3CdB5O10

A new ternary borate oxide, K₃CdB₅O₁₀, has been synthesized by solid-state reaction at 580 °C. The compound crystallizes in the monoclinic space group P2₁/n with a=7.6707 (7) Å, b=19.1765 (17) Å, c=7.8784 (6) Å, β=115.6083 (49)°, and Z=4. The crystal structure consists of a two-dimensional infinite [CdB₅O₁₀] layer, which forms by connecting isolated double ring [B₅O₁₀] groups and CdO₄ tetrahedra. K atoms filling in the interlayer and intralayer link the layers together and balance charge. The IR spectrum has been studied and confirmed the presence of both BO₃ and BO₄ groups, and the UV-vis-IR diffuse reflectance spectrum exhibits a band gap of about 3.4 eV. The DSC analysis proves that K₃CdB₅O₁₀ is a congruent melting compound.     

Synthesis, structure and electrical properties of Cu3.21Ti1.16Nb2.63O12 and the CuOx-TiO2-Nb2O5 pseudoternary phase diagram

Subsolidus phase relations in the CuO_x-TiO₂-Nb₂O₅ system were determined at 935 °C. The phase diagram contains one new phase, Cu_3.21Ti_1.16Nb_2.63O₁₂ (CTNO) and one rutile-structured solid solution series, Ti_1−3xCu_xNb_2xO₂: 0<x<0.2335 (35). The crystal structure of CTNO is similar to that of CaCu₃Ti₄O₁₂ (CCTO) with square planar Cu²⁺ but with A site vacancies and a disordered mixture of Cu⁺, Ti⁴⁺ and Nb⁵⁺ on the octahedral sites. It is a modest semiconductor with relative permittivity ∼63 and displays non-Arrhenius conductivity behavior that is essentially temperature-independent at the lowest temperatures.     

Effect of sintering on the ionic conductivity of garnet-related structure Li5La3Nb2O12 and In- and K-doped Li5La3Nb2O12

Garnet-structure related metal oxides with the nominal chemical composition of Li₅La₃Nb₂O₁₂, In-substituted Li_5.5La₃Nb_1.75In_0.25O₁₂ and K-substituted Li_5.5La_2.75K_0.25Nb₂O₁₂ were prepared by solid-state reactions at 900, 950, and 1000 °C using appropriate amounts of corresponding metal oxides, nitrates and carbonates. The powder XRD data reveal that the In- and K-doped compounds are isostructural with the parent compound Li₅La₃Nb₂O₁₂. The variation in the cubic lattice parameter was found to change with the size of the dopant ions, for example, substitution of larger In³⁺(r_CN6: 0.79 Å) for smaller Nb⁵⁺ (r_CN6: 0.64 Å) shows an increase in the lattice parameter from 12.8005(9) to 12.826(1) Å at 1000 °C. Samples prepared at higher temperatures (950, 1000 °C) show mainly bulk lithium ion conductivity in contrast to those synthesized at lower temperatures (900 °C). The activation energies for the ionic conductivities are comparable for all samples. Partial substitution of K⁺ for La³⁺ and In³⁺ for Nb⁵⁺ in Li₅La₃Nb₂O₁₂ exhibits slightly higher ionic conductivity than that of the parent compound over the investigated temperature regime 25-300 °C. Among the compounds investigated, the In-substituted Li_5.5La₃Nb_1.75In_0.25O₁₂ exhibits the highest bulk lithium ion conductivity of 1.8×10⁻⁴ S/cm at 50 °C with an activation energy of 0.51 eV. The diffusivity (“component diffusion coefficient”) obtained from the AC conductivity and powder XRD data falls in the range 10⁻¹⁰-10⁻⁷ cm²/s over the temperature regime 50-200 °C, which is extraordinarily high and comparable with liquids. Substitution of Al, Co, and Ni for Nb in Li₅La₃Nb₂O₁₂ was found to be unsuccessful under the investigated conditions.     

Cr3+在不同基质Y3Ga5O12或Ga2O3中的荧光特性

以Ga_2O_3、Y_2O_3、Cr(NO_3)_3·9H_2O为原料,柠檬酸为配位剂,通过溶胶-凝胶高温固相合成法制备出Ga_(2-2x)O_3∶2xCr~(3+)(Ga_2O_3∶xCr)与Y_3Ga_(5-5x)O_(12)∶5xCr~(3+)(YGG∶xCr)2种多晶粉体(x=0.01,0.03,0.05,0.07)。并采用X射线衍射(XRD)、红外光谱(IR)、扫描电镜(SEM)、荧光光谱(PL)对样品的结构、组成、形貌和荧光性能进行测试分析。XRD和IR分析结果显示在900℃煅烧后Ga_2O_3∶xCr和YGG∶xCr两种样品均成相。SEM照片显示Ga_2O_3∶xCr样品形貌为柱形多面体,YGG∶xCr为短棒状。PL结果显示Cr~(3+)在Ga_2O_3和YGG两种基质中的最强荧光发射峰分别位于742和740 nm,均属于Cr~(3+)的~2E-~4A_2跃迁,对比发现Cr~(3+)在YGG基质中的荧光发射强度更强,在远红光区的荧光性能更好,能满足温室照明中植物光合作用的需求。     

Crystal chemistry of Co-doped Zn7Sb2O12

Zn₇Sb₂O₁₂ forms a full range of Co-containing α solid solutions, Zn_7−xCo_xSb₂O₁₂, with an inverse-spinel structure at high temperature. At low temperatures for x<2, the solid solutions transform into the low temperature β-polymorph. For x=0, the β→α transition occurs at 1225±25 °C; the transition temperature decreases with increasing x. At high x and low temperatures, α solid solutions are formed but are non-stoichiometric; the (Zn+Co):Sb ratio is >7:2 and the compensation for the deficiency in Sb is attributed to the partial oxidation of Co²⁺ to Co³⁺. From Rietveld refinements using ND data, Co occupies both octahedral and tetrahedral sites at intermediate values of x, but an octahedral preference attributed to crystal field stabilisation, causes the lattice parameter plot to deviate negatively from the Vegard's law. Sub-solidus compatibility relations in the ternary system ZnO-Sb₂O₅-CoO have been determined at 1100 °C for the compositions containing ?50% Sb₂O₅.     

Crystal-chemistry of mullite-type aluminoborates Al18B4O33 and Al5BO9: A stoichiometry puzzle

Orthorhombic Al₂O₃-rich aluminoborate is an important ceramic material for which two slightly different compositions have been assumed: Al₅BO₉ (5Al₂O₃:B₂O₃) and Al₁₈B₄O₃₃ (9Al₂O₃:2B₂O₃). The formula Al₁₈B₄O₃₃ (=Al_4.91B_1.09O₉) was derived from results of chemical analyses when crystal structure data were not yet available. Subsequent structural investigations indicated Al₅BO₉ composition. Nevertheless, Al₁₈B₄O₃₃ was still accepted as the correct stoichiometry assuming that additional B replaces 9% Al.Powder samples of both compositions and ones with excess boron were prepared by solid state reactions between α-Al₂O₃ and B₂O₃/H₃BO₃ at temperatures above 1100 °C and single-crystals were grown from flux at 1100 and 1550 °C. Products were investigated by single-crystal and powder XRD, ¹¹B and ²⁷Al solid-state MAS-NMR, Raman and FTIR spectroscopy as well as Laser-ablation ICP-MS. No indication of the predicted 9% B→Al substitution was found. LA ICP-MS indicated 12.36(27) wt% B₂O₃ corresponding to Al_4.97B_1.03O₉. Hence, the suggested Al₁₈B₄O₃₃ stoichiometry can be excluded for all synthesized samples. A very low amount of Al vacancies at a five-fold coordinated site are likely, charge balanced by an additional nearby three-fold coordinated B site. All evidences indicate that the title compound should be reported as Al_5−xB_1+xO₉ with x<0.038(6), which is close to Al₅BO₉.     

Structure and Ionic Conductivity of Bi6Cr2O15, a New Structure Type Containing (Bi12O14)n Columns and CrO4 Tetrahedra

Powder samples of the Cr⁶⁺-containing compound Bi₆Cr₂O₁₅ were prepared by solid state reaction of Bi₂O₃ and Cr₂O₃ in air at 650°C. The structure was solved and refined using high-resolution neutron powder diffraction data in space group Ccc2, with anisotropic thermal displacement parameters a=12.30184(5), b=19.87492(7), and c=5.88162(2) Å, V=1438.0 ų, and 126 variables to R_F=1.8%. Bi₆Cr₂O₁₅ exhibits a new structure type that contains (Bi₁₂O₁₄)⁸ⁿ⁺_n columns, of the kind previously found only for phases isotypic with Bi₁₃Mo₄VO₃₄. Each column is surrounded by eight CrO²⁻₄ tetrahedra. The ionic conductivity of Bi₆Cr₂O₁₅ was determined by impedance measurements to be 3.5×10⁻⁵ (Ω cm)⁻¹ at 600°C.     

Structure and magnetism of rare-earth-substituted Ca3Co2O6

Yttrium- and rare-earth-substituted derivatives of Ca_3−vR_vCo₂O₆ (RY, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Yb, and Lu) have been synthesized and structurally characterized by powder X-ray and neutron diffraction. All phases adopt the K₄CdCl₆-type structure with space group R3¯c), in which the trivalent R³⁺ substituents randomly occupy the Ca²⁺ site. The homogeneity range of Ca_3−vR_vCo₂O₆ extends to v≈0.90 for the substituents concerned. A significant increase in the Co2-O distances within the trigonal-prismatic Co2O₆ co-ordination polyhedra upon introduction of R³⁺ confirms that extra electrons from the R³⁺-for-Ca²⁺ substitution exclusively enter the Co2 site of the quasi-one-dimensional Ca_3−vR_vCo₂O₆ structure, thereby formally reducing its oxidation state. This is furthermore supported by magnetic susceptibility and low-temperature neutron diffraction measurements. The long-range ferrimagnetic ordering temperature is reduced upon R substitution and appears to vanish for v>∼0.30.     

Phase stabilities of monoclinic oxoborates LaB3O6 and GdB3O6 in C121 and I12/a1 phase—Energetics and chemical bonds derived from first-principles calculations

The computational study on the relative phase stabilities between two monoclinic polymorphs of the lanthanide-containing oxoborates LaB₃O₆ and GdB₃O₆ is presented at the first-principles density functional theory gradient-corrected B3PW level. The hypothetical monoclinic α-BiB₃O₆-like C121 non-centrosymmetric crystal structures were assumed for LaB₃O₆ and GdB₃O₆ and the corresponding geometries were calculated and compared with their monoclinic I12/a1 centrosymmetric structures. The enthalpy-pressure correlations were calculated and the first-principles chemical bonds based on the crystal orbital overlapping population were quantitatively analyzed for LaB₃O₆ and GdB₃O₆. The chemical bonds between the central cation (La (III)/Gd (III)) and coordinated oxygen atoms rather than the B-O bonds in the borate units are found to stabilize the I12/a1 centrosymmetric LaB₃O₆ and GdB₃O₆ structures with respect to the C121 non-centrosymmetric counterparts.     

Synthesis of MnOOH nanorods by cluster growth route from [Mn12O12(RCOO)16(H2O)n] (R=CH3, C2H5). Rational conversion of MnOOH into Mn3O4 or MnO2 Nanorods

Single-crystalline nanorods of γ-MnOOH (manganite) phase with diameters of 120 nm and lengths of 1100 nm have been prepared using a new cluster growth route under low-temperature hydrothermal conditions starting from [Mn₁₂O₁₂(CH₃COO)₁₆(H₂O)₄]·2CH₃COOH·4H₂O or [Mn₁₂O₁₂(C₂H₅COO)₁₆(H₂O)₃]·4H₂O without any catalyst or template agents. The so-obtained nanorods were studied by X-ray diffraction (XRD), infrared (IR) spectroscopy, Raman spectroscopy and high resolution transmission electron microscopy (HRTEM). Their thermal conversion opens an access to Mn₃O₄ (hausmannite) and β-MnO₂ (pyrolusite) nanorods, respectively, under argon or air atmosphere. A coercive field of 12.4 kOe was obtained for the Mn₃O₄ nanorods.     

Phase transitions in K3AlF6

Phase transitions in the elpasolite-type K₃AlF₆ complex fluoride were investigated using differential scanning calorimetry, electron diffraction and X-ray powder diffraction. Three phase transitions were identified with critical temperatures , and . The α-K₃AlF₆ phase is stable below T₁ and crystallizes in a monoclinic unit cell with a=18.8588(2)Å, b=34.0278(2)Å, c=18.9231(1)Å, β=90.453(1)° (a=2a_c−c_c, b=4b_c, c=a_c+2c_c; a_c, b_c, c_c—the basic lattice vectors of the face-centered cubic elpasolite structure) and space group I2/a or Ia. The intermediate β phase exists only in very narrow temperature interval between T₁ and T₂. The γ polymorph is stable in the T₂<T<T₃ temperature range and has an orthorhombic unit cell with a=36.1229(6)Å, b=17.1114(3)Å, c=12.0502(3)Å (a=3a_c−3c_c, b=2b_c, c=a_c+c_c) at 250 °C and space group Fddd. Above T₃ the cubic δ polymorph forms with a_c=8.5786(4)Å at 400 °C and space group . The similarity between the K₃AlF₆ and K₃MoO₃F₃ compounds is discussed.     

Investigation of the quasi-ternary system LaMnO3-LaCoO3-“LaCuO3”—I: the series La(Mn0.5Co0.5)1−xCuxO3−δ

The La(Mn_0.5Co_0.5)_1−xCu_xO_3−δ series with x=0, 0.05, 0.1, 0.2, 0.4, 0.6, 0.8 and 1 was synthesized by the Pechini method to obtain insight into the phase formation in the quasi-ternary LaMnO₃-LaCoO₃-“LaCuO₃” system caused by the instability of LaCuO₃ under ambient conditions. After sintering at 1100°C some remarkable results were obtained: LaMn_0.3Co_0.3Cu_0.4O_3−δ crystallized as a single phase in the orthorhombic perovskite structure typical of LaCuO₃. Among the synthesized compositions this compound showed the highest electrical conductivity in air at 800°C (155 S cm⁻¹) and also the highest thermal expansion coefficient (α_30−800°C=15.4×10⁻⁶ K⁻¹). The LaCuO_3−δ composition also crystallized as a single phase but in a monoclinic structure although previous investigations have shown that other phases are preferably formed after sintering at 1100°C. The electrical conductivity and thermal expansion coefficient were the lowest within the series of compositions, i.e. 9.4 S cm⁻¹ and 11.9×10⁻⁶ K⁻¹, respectively.