Modulated structure of the composite crystal InCr1−xTixO3+x/2

Incommensurately modulated structure of the composite crystal InCr_1−xTi_xO_3+x/2 was refined by the profile fitting of powder X-ray diffraction based on the four-dimensional superspace group. The crystal consists of two monoclinic subsystems mutually incommensurate in b. The first subsystem is the alternate stacking of an edge-shared InO₆ octahedral layer and a Cr/Ti triangle-lattice plane along c^*. A sheet of oxygen atoms constructing the second subsystem is also extending on the Cr/Ti plane. The whole structure is the alternate stacking of an edge-shared InO₆ octahedral layer and a Cr/Ti-O plane, where displacive modulation of O ions is prominent. Metal ions on the Cr/Ti-O plane are surrounded by three or four oxygen ions on the plane and, in addition, two axial ones.     

Crystal structure, thermal expansion and conductivity of anisotropic La1−xSrxGa1−2xMg2xO3−y (x=0.05, 0.1) single crystals

Crystal structure and anisotropy of the thermal expansion of single crystals of La_1−xSr_xGa_1−2xMg_2xO_3−y (x=0.05 and 0.1) were measured in the temperature range 300-1270 K. High-resolution X-ray powder diffraction data obtained by synchrotron experiments have been used to determine the crystal structure and thermal expansion. The room temperature structure of the crystal with x=0.05 was found to be orthorhombic (Imma, Z=4, a=7.79423(3) Å, b=5.49896(2) Å, c=5.53806(2) Å), whereas the symmetry of the x=0.1 crystal is monoclinic (I2/a, Z=4, a=7.82129(5) Å, b=5.54361(3) Å, c=5.51654(4) Å, β=90.040(1)°). The conductivity in two orthogonal directions of the crystals has been studied. Both, the conductivity and the structural data indicate three phase transitions in La_0.95Sr_0.05Ga_0.9Mg_0.1O_2.92 at 520-570 K (Imma-I2/a), 770 K (I2/a-R3c) and at 870 K (R3c-R-3c), respectively. Two transitions at 770 K (I2/a-R3c) and in the range 870-970 K (R3c-R-3c) occur in La_0.9Sr_0.1Ga_0.8Mg_0.2O_2.85.     

Laser Ablation Deposition of CeO2−x Epitaxial Domains on Glass

Laser ablation of CeO₂ target in vacuum (5×10⁻⁴ Pa) was used to produce nanometer-size condensates, which deposited as yellowish top coating and whitish bottom coating on a soda-lime glass substrate. The top coating consists of optically anisotropic columnar domains conformable to monoclinic Ce₆O₁₁ phase coexisting with cubic (c) CeO_2−x, whereas the bottom coating is optically isotropic c-CeO_2−x due to oxygen uptake from the substrate. Transmission electron microscopy indicated that the columnar domains are made up of defective fluorite-type nanoparticles, which tended to coalesce over (111) plane to form dislocations and (111)-preferred orientation, an artificial epitaxy owing to rotation-coalescence of (111) faceted CeO_2−x condensates on the amorphous substrate and/or within the coating.     

Enzyme mimics of spinel-type CoxNi1−xFe2O4 magnetic nanomaterial for eletroctrocatalytic oxidation of hydrogen peroxide

A series of spinel-type Co_xNi_1−xFe₂O₄ (x = 0, 0.2, 0.4, 0.5, 0.6, 0.8, 1.0) magnetic nanomaterials were solvothermally synthesized as enzyme mimics for the eletroctrocatalytic oxidation of H₂O₂. X-ray diffraction and scanning electron microscope were employed to characterize the composition, structure and morphology of the material. The electrochemical properties of spinel-type Co_xNi_1−xFe₂O₄ with different (Co/Ni) molar ratio toward H₂O₂ oxidation were investigated, and the results demonstrated that Co_0.5Ni_0.5Fe₂O₄ modified carbon paste electrode (Co_0.5Ni_0.5Fe₂O₄/CPE) possessed the best electrocatalytic activity for H₂O₂ oxidation. Under optimum conditions, the calibration curve for H₂O₂ determination on Co_0.5Ni_0.5Fe₂O₄/CPE was linear in a wide range of 1.0 × 10⁻⁸–1.0 × 10⁻³ M with low detection limit of 3.0 × 10⁻⁹ M (S/N = 3). The proposed Co_0.5Ni_0.5Fe₂O₄/CPE was also applied to the determination of H₂O₂ in commercial toothpastes with satisfactory results, indicating that Co_xNi_1−xFe₂O₄ is a promising hydrogen peroxidase mimics for the detection of H₂O₂.     

Series of compositions Bi2(M′xM1−x)4O9 (M′, M=Al, Ga, Fe; 0≤x≤1) with mullite-type crystal structure: Synthesis, characterization and O/O exchange experiment

Series of compositions Bi₂(M′_xM_1−x)₄O₉ with x=0.0, 0.1,…, 1.0 and M′/M=Ga/Al, Fe/Al and Fe/Ga were synthesized by dissolving appropriate amounts of corresponding metal nitrate hydrates in glycerine, followed by gelation, calcination and final heating at 800 °C for 24 h. The new compositions with M′/M=Ga/Al form solid-solution series, which are isotypes to the two other series M′/M=Fe/Al and Fe/Ga. The XRD data analysis yielded in all cases a linear dependence of the lattice parameters related on x. Rietveld structure refinements of the XRD patterns of the new compounds, Bi₂(Ga_xAl_1−x)₄O₉ reveal a preferential occupation of Ga in tetrahedral site (4 h). The IR absorption spectra measured between 50 and 4000 cm⁻¹ of all systems show systematic shifts in peak positions related to the degree of substitution. Samples treated in ¹⁸O₂ atmosphere (16 h at 800 °C, 200 mbar, 95% ¹⁸O₂) for ¹⁸O/¹⁶O isotope exchange experiments show a well-separated IR absorption peak related to the M-¹⁸O_c-M vibration, where O_c denotes the common oxygen of two tetrahedral type MO₄ units. The intensity ratio of M-¹⁸O_c/M-¹⁶O_c IR absorption peaks and the average crystal sizes were used to estimate the tracer diffusion coefficients of polycrystalline Bi₂Al₄O₉ (D=2×10⁻²² m²s⁻¹), Bi₂Fe₄O₉ (D=5×10⁻²¹ m²s⁻¹), Bi₂(Ga/Al)₄O₉ (D=2×10⁻²¹ m²s⁻¹) and Bi₂Ga₄O₉ (D=2×10⁻²⁰ m²s⁻¹).     

Structural and magnetic characterization of BiFexMn2-xO5 oxides (x=0.5, 1.0)

The title compounds have been synthesized by a citrate technique followed by thermal treatments in air (BiFe_0.5Mn_1.5O₅) or under high oxygen pressure conditions (BiFeMnO₅), and characterized by X-ray diffraction (XRD), neutron powder diffraction (NPD) and magnetization measurements. The crystal structures have been refined from NPD data in the space group Pbam at 295 K. These phases are isostructural with RMn₂O₅ oxides (R=rare earths) and contain infinite chains of Mn⁴⁺O₆ octahedra sharing edges, linked together by (Fe,Mn)³⁺O₅ pyramids and BiO₈ units. These units are strongly distorted with respect to those observed in other RFeMnO₅ compounds, due to the presence of the electronic lone pair on Bi³⁺. It is noteworthy the certain level of antisite disorder exhibited in both samples, where the octahedral positions are partially occupied by Fe cations, and vice versa. BiFe_xMn_2−xO₅ (x=0.5, 1.0) are short-range magnetically ordered below 20 K for x=0.5 and at 40 K for x=1.0. The main magnetic interactions seem to be antiferromagnetic (AFM); however, the presence of a small hysteresis in the magnetization cycles indicates the presence of some weak ferromagnetic (FM) interactions.     

Transmission electron microscopy study of Ruddlesden-Popper Can+1MnnO3n+1n=2 and 3 compounds

Two Ruddlesden-Popper compounds Ca_n+1Mn_nO_3n+1 with n=2 and 3 synthesized by a citrate gel technique have been studied by TEM. The structure of Ca₄Mn₃O₁₀ is consistent with the previously determined structure having the space group Pbca and a⁻ a⁻ c⁺/a⁻ a⁻ c⁺ tilt system. The presence of defects suggests the possible high-temperature phase transition from untilted I4/mmm to Pbca. The structure of Ca₃Mn₂O₇ was found to be different from the previously suggested I4/mmm symmetry. Ca₃Mn₂O₇ forms with an orthorhombic structure with either Cmcm or Cmc2₁ space group. A structural model for Cmc2₁ based on the tilting of almost-rigid octahedra with a⁺ c⁻ c⁻/a⁺ c⁻ c⁻ tilt system is proposed. The lamellar defects were shown to be twin variants of the Cmc2₁ structure with the (001)_t interfaces, which suggests the possible tilting phase transition from the ideal I4/mmm to Cmc2₁ following the maximal group-subgroup symmetry tree: I4/mmm→Fmmm→Bbmm(Cmcm)→Bb2₁m(Cmc2₁).     

Structure and magnetic order in the series BixRE1−xFe0.5Mn0.5O3 (RE=La,Nd)

The influence of Bi³⁺ on the structural and magnetic properties of the rare-earth-containing perovskites REFe_0.5Mn_0.5O₃ (RE=La,Nd) was studied, and the limit of bismuth substitution was determined to be x≤0.5 in Bi_xRE_1−xFe_0.5Mn_0.5O_3+δ (RE=La,Nd) at ambient pressure. Crystal structures in both La and Nd series were determined to be GdFeO₃-type Pnma with the exception of the Bi_0.3La_0.7Fe_0.5Mn_0.5O₃ sample, which is monoclinic I2/a in the a⁻b⁻b⁻ tilt scheme. The samples undergo a transition to G-type antiferromagnetic order along with a weak ferromagnetic component, mixed with cluster-glass type behavior. The substitution of bismuth into the lattice results in a drop in T_N relative to the lanthanide end-members. Long range ordering temperatures T_N in the range 240-255 K were observed, with a significantly lower ordered magnetic moment in the case of lanthanum (M∼1.7-1.9 μ_B) than in the case of neodymium (M∼2.1 μ_B).     

O MAS NMR study of the oxygen local environments in the anionic conductors Y2(B1−xB′x)2O7(B, B′=Sn, Ti, Zr)

The local environments for oxygen in yttrium-containing pyrochlores and fluorites, Y₂(B_1−xB′_x)₂O₇ (B=Ti, B′=Sn, Zr) are investigated by using solid state ¹⁷O MAS NMR spectroscopy. The quadrupolar coupling constants of the nucleus, ¹⁷O are sufficiently small for these ionic oxides, that high-resolution spectra are obtained from the MAS spectra. Different oxygen NMR resonances are observed due to local environments with differing numbers of metal cations (Y³⁺, Sn⁴⁺, Ti⁴⁺ and Zr⁴⁺), allowing the numbers of different local environments to be quantified and cation mixing to be investigated. Evidence for pyrochlore-like local ordering is detected for Y₂Zr₂O₇, which nominally adopts the fluorite structure.     

Defect clusters and precipitation/oxidation of MgO-Co1−xO solid solution

MgO and Co_1−xO powders in 9:1 and 1:9 molar ratio (denoted as M₉C₁ and M₁C₉, respectively) were sintered and homogenized at 1600°C followed by annealing at 850°C and 800°C, respectively to form defect clusters and precipitates. Analytical electron microscopic observations indicated the protoxide remained as rock salt structure with complicated planar diffraction contrast for M₉C₁ sample, however with spinel paracrystal precipitated from the M₁C₉ sample due to the assembly of charge- and volume-compensating defects of the 4:1 type, i.e., four octahedral vacant sites surrounding one Co³⁺-filled tetrahedral interstitial site. The spacing of such defect clusters is 4.5 times the lattice spacing of the average spinel structure of Mg-doped Co_3−δO₄, indicating a higher defect cluster concentration than undoped Co_3−δO₄. The {111} faulting of Mg-doped Co_3−δO₄/Co_1−xO in the annealed M₁C₉ sample implies the possible presence of zinc blend-type defect clusters with cation vacancies assembled along oxygen close packed (111) plane.     

A Novel Boron-Rich Scandium Borocarbide; Sc4.5−xB57−y+zC3.5−z(x=0.27, y=1.1, z=0.2)

A novel ternary boron-rich scandium borocarbide Sc_4.5−xB_57−y+zC_3.5−z (x=0.27, y=1.1, z=0.2) was found. Single crystals were obtained by the floating zone method by adding a small amount of Si. Single-crystal structure analysis revealed that the compound has an orthorhombic structure with lattice constants of a=1.73040(6), b=1.60738(6) and c=1.44829(6) nm and space group Pbam (No. 55). The crystal composition ScB_13.3C_0.78Si_0.008 calculated from the structure analysis agreed with the measured composition of ScB_12.9C_0.72Si_0.004. The orthorhombic crystal structure is a new structure type of boron-rich borides and there are six structurally independent B₁₂ icosahedra I1—I6, one B₈/B₉ polyhedron and nine bridging sites all which interconnect each other to form a three-dimensional boron framework. The main structural feature of the boron framework structure can be understood as a layer structure where two kinds of boron icosahedron network layer L1 and L2 stack each other along the c-axis. There are seven structurally independent Sc sites in the open spaces between the boron icosahedron network layers.     

Structural studies of five layer Aurivillius oxides: A2Bi4Ti5O18 (A=Ca, Sr, Ba and Pb)

The room temperature structures of the five layer Aurivillius phases A₂Bi₄Ti₅O₁₈ (A=Ca, Sr, Ba and Pb) have been refined from powder neutron diffraction data using the Rietveld method. The structures consist of [Bi₂O₂]²⁺ layers interleaved with perovskite-like [A₂Bi₂Ti₅O₁₆]²⁻ blocks. The structures were refined in the orthorhombic space group B2eb (SG. No. 41), Z=4, and the unit cell parameters of the oxides are a=5.4251(2), b=5.4034(1), c=48.486(1); a=5.4650(2), b=5.4625(3), c=48.852(1); a=5.4988(3), b=5.4980(4), c=50.352(1); a=5.4701(2), b=5.4577(2), c=49.643(1) for A=Ca, Sr, Ba and Pb, respectively. The structural features of the compounds were found similar to n=2-4 layers bismuth oxides. The strain caused by mismatch of cell parameter requirements for the [Bi₂O₂]²⁺ layers and perovskite-like [A₂Bi₂Ti₅O₁₆]²⁻ blocks were relieved by tilting of the TiO₆ octahedra. Variable temperature synchrotron X-ray studies for Ca and Pb compounds showed that the orthorhombic structure persisted up to 675 and 475 K, respectively. Raman spectra of the compounds are also presented.     

Phase relations, crystal chemistry, and dielectric properties in sections of the La2O3-CaO-MgO-TiO2 system

Subsolidus phase equilibria and crystal chemistry were studied for the La₂O₃-MgO-TiO₂ system and for the ternary sections LaMg_1/2Ti_1/2O₃-CaTiO₃-La₂O₃ and LaMg_1/2Ti_1/2O₃-CaTiO₃-La_0.833Mg_0.25Ti_0.75O₃ in the quaternary La₂O₃-CaO-MgO-TiO₂ system. Dielectric properties (relative permittivity and temperature coefficient of resonant frequency, τ_f) were measured at 5-10 GHz and mapped onto the phase equilibria relations to reveal the compositions of temperature-stable (τ_f=0) compounds and mixtures. Phase equilibria relations were obtained by X-ray powder diffraction analysis of approximately 80 specimens prepared by solid-state reactions in air at ∼1450°C. Six ternary phases were found to form in the La₂O₃-MgO-TiO₂ system, including the three previously reported compounds LaMg_1/2Ti_1/2O₃, La₅Mg_0.5Ti_3.5O₁₅, and “La₆MgTi₄O₁₈”; and the new phases La₁₀MgTi₉O₃₄, La₉Mg_0.5Ti_8.5O₃₁, and a perovskite-type solid solution (1−x)LaMg_1/2Ti_1/2O₃-xLa_2/3TiO₃ (0?x?0.5). The phase previously reported as “La₆MgTi₄O₁₈” was found to form off-composition, apparently as a point compound, at La₆Mg_0.913Ti_4.04O₁₈. Indexed experimental X-ray powder diffraction patterns are given for LaMg_1/2Ti_1/2O₃, La₅Mg_0.5Ti_3.5O₁₅, La₆Mg_0.913Ti_4.04O₁₈, La₁₀MgTi₉O₃₄, and La₉Mg_0.5Ti_8.5O₃₁. LaMg_1/2Ti_1/2O₃ exhibits a slightly distorted perovskite structure with ordered B-cations (P2₁/n; a=5.5608(2) Å, b=5.5749(3) Å, c=7.8610(5) Å, β=90.034(4)°). La₅Mg_0.5Ti_3.5O₁₅ (Pm1; a=5.5639(1), c=10.9928(5) Å) and La₆Mg_0.913Ti_4.04O₁₈ (R3m; a=5.5665(1), c=39.7354(9) Å) are n=5 and n=6 members, respectively, of the (111) perovskite-slab series A_nB_n−1O_3n. The new phases La₁₀MgTi₉O₃₄ (a=5.5411(2), b=31.3039(9), c=3.9167(1) Å) and La₉Mg_0.5Ti_8.5O₃₁ (a=5.5431(2), b=57.055(1), c=3.9123(1) Å) are n=5 and n=4.5 members, respectively, of the (110) perovskite-slab series A_nB_nO_3n+2, which exhibit orthorhombic subcells; electron diffraction revealed monoclinic superlattices with doubled c-parameters for both compounds. Extensive perovskite-type solid solutions form in the ternary sections LaMg_1/2Ti_1/2O₃-CaTiO₃-La₂O₃ and LaMg_1/2Ti_1/2O₃-CaTiO₃-La_0.833Mg_0.25Ti_0.75O₃. The La₂O₃-MgO-TiO₂ system contains two regions of temperature-stable (τ_f=0) compositions. The quaternary La₂O₃-CaO-MgO-TiO₂ system contains an extensive single-phase perovskite-type volume through which passes a surface of temperature-stable compositions with permittivities projected to be in the 40-50 range. Traces of this surface occur as lines of τ_f=0 perovskite-type phases in the ternary sections LaMg_1/2Ti_1/2O₃-CaTiO₃-La₂O₃ and LaMg_1/2Ti_1/2O₃-CaTiO₃-La_0.833Mg_0.25Ti_0.75O₃.     

A reagentless DNA biosensor based on cathodic electrochemiluminescence at a C/CxO1−x electrode

A reagentless signal-on electrochemiluminescence (ECL) biosensor for DNA hybridization detection was developed based on the quenching effect of ferrocene (Fc) on intrinsic cathodic ECL at thin oxide covered glassy carbon (C/C_xO_1−x) electrodes. To construct the DNA biosensor, molecular beacon (MB) modified with ferrocene (3′-Fc) was attached to a C/C_xO_1−x electrode via the covalent bound between labeled amino (5′-NH₂) and surface functional groups. It was found that the immobilization of the probe on the electrode surface mainly depended on the fraction of surface carbonyl moiety. When a complementary target DNA (cDNA) was present, the stem-loop of MB on the electrode was converted into a linear double-helix configuration due to hybridization, resulting in the moving away of Fc from the electrode surface, and the restoring of the cathodic ECL signal. The restoration of the ECL intensity was linearly changed with the logarithm of cDNA concentration in the range of 1.0 × 10⁻¹¹ to 7.0 × 10⁻⁸ M, and the detection limit was ca. 5.0 pM (S/N = 3). Additionally, single-base mismatched DNA can be effectively discriminated from the cDNA. The great advantage of the biosensor lies in its simplicity and cost-effective with ECL generated from the electrode itself, and no adscititious luminophore is required.     

Solvothermal Synthesis of Superfine Li1−xMn2O4−σ Powders

Superfine Li_1−xMn₂O_4−σ powders were successfully synthesized by the alcohol-thermal method using 0.01 mol of MnO₂, 0.01mol of LiOH·H₂O, and 0.06mol of NaOH as starting materials at 160-200°C. The products are characterized by XRD, TEM, ED, BET, and ICP. Results show that the Li_0.74Mn₂O_3.74 powder prepared at 200°C has an average size of 180 nm with BET surface areas of 16.44 m²/g. A possible formation mechanism is proposed. It was concluded that the alcohol acts not only as the solvent but also as the reducing agent in the synthesis of Li_1−xMn₂O_4−σ powders. The effects of reaction temperature and the contents of NaOH and LiOH on the formation of single phase Li_1−xMn₂O_4−σ were investigated.     

Investigation of structural and hydrogen absorption properties in the LaNi5−xPtx-H2 system

The substitution of nickel by platinum in the binary LaNi₅ compound (CaCu₅ structure type, a=5.019(1) Å, c=3.981(1) Å, space group P6/mmm) and its effect on the hydrogenation properties was studied. The phase LaNi_5−xPt_x has a homogeneity domain ranging from x=0 to 5. For x<3, platinum substitutes almost exclusively on site 3g and also replaces nickel on site 2c for x>3. Contrary to what is observed in other systems, the hydrogen absorption plateau pressure was found to increase as a function of the cell volume. Powder neutron diffraction experiments were conducted for two deuterated compounds with x=0.25 and 0.75. Deuterium partial ordering occurs in the case of x=0.25 leading to a symmetry decrease to the space group P6mm (LaNi_4.75Pt_0.25D_5.23, a=4.225(1) Å, c=5.357(1) Å, Z=1, R_Bragg=3.3%). For x=0.75, an orthorhombic superstructure based on the CaCu₅-type lattice was found (LaNi_4.25Pt_0.75D_2.61, a_orth=√3a_hex=9.089(1) Å, b_orth=b_hex=5.272(1) Å, c_orth=2c_hex=8.145(1) Å, Z=4, SG Ibam, R_Bragg=6.1%).     

A novel route to synthesize cubic ZrW2−xMoxO8 (x=0-1.3) solid solutions and their negative thermal expansion properties

Cubic ZrW_2−xMo_xO₈ (c-ZrW_2−xMo_xO₈) (x=0-1.3) solid solutions were prepared by a novel polymorphous precursor transition route. X-ray diffraction (XRD) analysis reveals that the solid solutions are single phase with α- and β-ZrW₂O₈ structure for 0?x?0.8 and 0.9?x?1.3, respectively. The optimum synthesis conditions of ZrWMoO₈ are obtained from differential scanning calorimetry-thermal gravimetric analysis (DSC-TGA), XRD and mass loss-temperature/time curves. Following the above experience, the stoichiometric solid solutions of c-ZrW_2−xMo_xO₈ (x=0-1) are obtained within 1 wt% of mass loss. The relationships of lattice parameters (a), phase transition temperatures (T_c) and instantaneous coefficients of thermal expansion (α_i) against the content x of Mo are discussed based on the variation of order degree parameters of ZrW_2−xMo_xO₈.     

Vacancy ordering and oxygen dynamics in oxide ion conducting La1−xSrxGa1−xMgxO3−x ceramics: Ga, Mg and O NMR

The oxygen vacancies distribution in the rigid lattice and the thermally activated motion of oxygen atoms are studied in La_1−xSr_xGa_1−xMg_xO_3−x (x=0.00; 0.05; 0.10; 0.15 and 0.20) compounds. For that ⁷¹Ga, ²⁵Mg and ¹⁷O NMR was performed from 100 K up to 670 K, and ion conductivity measurements were carried out up to 1273 K. The comparison of the electric field gradients at the Ga- and Mg-sites evidences that oxygen vacancies appear exclusively near gallium cations as a species trapped below room temperature in local clusters, GaO_5/2-□-GaO_5/2. These clusters decay at higher temperature into mobile constituents of the structural octahedra Ga(O_5/6□_1/6)_6/2. At the same time, the nearest octahedral oxygen environment of magnesium cations persists at different doping levels. The case of two adjacent vacant anion sites is found highly unlikely within the studied doping range. The thermally activated oxygen motion starts to develop above room temperature as is observed from both the motional narrowing of ¹⁷O NMR spectra and the ¹⁷O nuclear spin-lattice relaxation rate. The obtained results show that two types of motion exist, a slow motion and a fast one. The former is a long-range diffusion whereas the latter is a local back and forth oxygen jumps between two adjacent anion sites. These sites are strongly differentiated by the probability of the vacancy formation, like the vacant apical site and the occupied equatorial site in the orthorhombic compositions x <0.15.     

Chemical stability of La1−xSrxCrO3 in oxidizing atmospheres

The single-phase region of La_1−xSr_xCrO₃ (x=0.1, 0.2, 0.3) was precisely determined as a function of temperature, P_O2 and Sr content. The powders with the nominal composition of La_1−xSr_xCrO₃ were equilibrated under various conditions, and then identified by XRD analyses. To confirm the equilibration, two independent experiments were performed for each composition observing (i) the precipitation of the second phase from a single-phase solid solution, and (ii) the formation of the single phase from the constituent oxides. Two kinds of second phases, SrCrO₄ and an unknown phase, were observed depending on the conditions. The second phases tended to appear at low temperature, in high P_O2 and with a large Sr content. The single-phase regions obtained via the two equilibration routes were in good agreement with each other. The thermodynamic calculations on the supposition of ideality of the solid solution essentially reproduced the experimental results. When this material is used as the interconnects of solid oxide fuel cells, much attention should be paid to its relatively narrow solubility range of Sr; for example, the solubility limit is approximately 0.1 under a typical cathode-side condition (1273 K, air).     

Room temperature photoluminescence of amorphous BaxSr1−xTiO3 doped with chromium

ABO₃ amorphous materials, such as BaTiO₃ (BT), SrTiO₃ (ST), PbTiO₃ (PT), and Ba_xSr_1−xTiO₃ (BST) have recently attracted a good deal of attention due to their ferroelectric and electro-optical properties. Intense photoluminescence at room temperature was observed in amorphous titanate doped with chromium (Ba_xSr_1−xTi_1−yCr_yO₃) prepared by the polymeric precursor method. Results indicated that substantial luminescence at room temperature was achieved with the addition of small Cr contents to amorphous Ba_xSr_1−xTi_1−yCr_yO₃. Further addition of Cr or crystallization were deleterious to the intensity of the luminescent peak obtained for excitation using λ=488.0 nm.