Preparation of SrCe0.95Yb0.05O3−α perovskite for use as a membrane material in hollow fibre fabrication

In this study, a pure orthorhombic perovskite SrCe_0.95Yb_0.05O_3−α (SCYb) ceramic powder was prepared using a chelated water-soluble complex method at relatively low temperatures. Common chelating ligands such as citric acid and EDTA were employed for the synthesis of complex-based precursors, followed by thermal decomposition of the precursors at high temperatures. Thermal behaviour, crystal phases, and structures of the prepared ceramic powders were characterised by TGA/DTA, XRD and SEM techniques, respectively. Clean and single-phase SCYb submicron-sized powders were obtained after sintering at a temperature of 1000 °C for 4 h. Gas-tight hollow fibre having a maximum bending strength of 60 MPa have been fabricated from the SCYb powders synthesised from the chelated water-soluble complex method.     

Microwave-hydrothermal synthesis of perovskite bismuth ferrite nanoparticles

Hydrothermal microwave method (HTMW) was used to synthesize crystalline bismuth ferrite (BiFeO₃) nanoparticles (BFO) in the temperature of 180 °C with times ranging from 5 min to 1 h. BFO nanoparticles were characterized by means of X-ray analyses, FT-IR, Raman spectroscopy, TG-DTA and FE-SEM. X-ray diffraction results indicated that longer soaking time was benefit to refraining the formation of any impurity phases and growing BFO crystallites into almost single-phase perovskites. Typical FT-IR spectra for BFO nanoparticles presented well defined bands, indicating a substantial short-range order in the system. TG-DTA analyses confirmed the presence of lattice OH⁻ groups, commonly found in materials obtained by HTMW process. Compared with the conventional solid-state reaction process, submicron BFO crystallites with better homogeneity could be produced at the temperature as low as 180 °C. These results show that the HTMW synthesis route is rapid, cost effective, and could be used as an alternative to obtain BFO nanoparticles in the temperature of 180 °C for 1 h.     

Preparation, characterization, and stability of calcium zinc hydrophosphate

Calcium zinc hydrophosphate phases with different Zn/(Zn + Ca) molar ratios (x_Zn, from 0 to 1) were synthesized using co-precipitation method at pH 10, 25 °C. X-ray diffraction, FT-IR spectroscopy and field emission scanning electron microscopy (FE-SEM) were used to characterize the synthesized products. Thermal behavior of the products was examined by thermal analytical instruments (TG-DSC-MS), while the chemical stability of the products was tested by toxicity characteristic leaching procedure (TCLP).The results showed that the phase constituents of formed calcium zinc hydrophosphate phases were related to the molar contents of Zn²⁺. With the increase of x_Zn, it formed calcium-deficient hydorxyapatite (CaHap), calcium zinc hydorxyapatite (CaZnHap), CaZn₂(PO₄)₂·2H₂O, and Zn₃(PO₄)₂·4H₂O, respectively. All the calcium zinc hydrophosphates were thermally stable up to 600 °C, and less Zn²⁺ leached in a wide pH range of 2-11, which indicated that calcium zinc hydrophosphate could effectively hold Zn²⁺ in their crystal phases with stabilization ratios of over 99.99%.     

Preparation and characterization of In(I)-β″-alumina

In(I)-β″-alumina has been prepared by ion exchange from Na-β″-alumina. It is stable on heating in air up to 400 °C. Its structure was determined by Rietveld analysis using high-resolution X-ray powder diffraction data [R-3m, a = 5.6044(1) Å, c = 34.4807(1) Å, Z = 3]. The coordination of In(I) in this material is asymmetric, as indicated by the distortion index for this cation, suggesting some stereochemical activity for the lone pair on the cation. However, the distortion is not as pronounced as that seen in the Ga(I) analogue.     

Synthesis and crystal structure of Sr10Al6O19: a derivative of the perovskite structure type in the system SrO-Al2O3

Sr₁₀Al₆O₁₉ is monoclinic, space group C12/c1, a=34.5823(21) Å, b=7.8460(6) Å, c=15.7485(9) Å, β=103.68(1)°, V=4151.9(7) Å³, Z=8. The structure has been solved from a single crystal diffraction dataset by direct methods and subsequently refined by a full-matrix least-squares process to a residual index of R(|F|)=0.038 for 2537 observed reflections with I>2σ(I). The compound is an oligoaluminate containing highly puckered [Al₆O₁₉]-groups of corner-sharing tetrahedra; it is the first purely aluminate cluster of this type, but it resembles the [□₆O₁₉]-group recently found in α-Sr₁₀□₆O₁₉. Linkage between the hexamers is provided by 11 crystallographically different strontium atoms located in planes parallel (1 0 0). They are coordinated by six-eight next oxygen neighbours. The structure can be derived from perovskite, ABO₃, by introducing ordered vacancies into the substructure of the oxygen atoms. The A-sites in Sr₁₀Al₆O₁₉ are exclusively occupied by Sr atoms, whereas strontium and aluminum atoms reside on the B-positions in the ratio 1:3. The relationship with perovskite can be expressed in the crystal chemical formula Sr(Al_3/4Sr_1/4)(O_19/8□_5/8).     

Synthesis, crystal structure, and properties of novel perovskite oxychalcogenides, Ca2CuFeO3Ch (Ch = S, Se)

Two new perovskite oxychalcogenides, Ca₂CuFeO₃S and Ca₂CuFeO₃Se, have been synthesized in evacuated quartz tubes. They crystallize in P4/nmm space group with lattice parameters a = 3.8271(1), c = 14.9485(2) Å and a = 3.8605(1), c = 15.3030(2) Å for Ca₂CuFeO₃S and Ca₂CuFeO₃Se, respectively. They appear to be the first layered chalcogenide perovskites involving calcium and are structural analogs of the corresponding Sr and Ba compounds. The new compounds exhibit semiconducting properties with energy gap decreasing from the oxysulfide to the oxyselenide. Possibility of introducing Ca²⁺ into structures of known layered oxychalcogenides and oxypnictides is discussed.     

Structural phase transition in the perovskite-type tantalum oxynitrides, Ca1−xEuxTa(O,N)3

Pure Ca_1−xEu_xTa(O,N)₃ were successfully synthesized in the whole range of Ca/Eu compositions by means of ammonia nitridation via a citrate precursor route. As-nitrided products with x < 0.4 were apparently orthorhombic, while those with x ≥ 0.4 crystallized in a cubic structure. The anionic composition was found to be essentially O₂N and independent of Eu content (x). The as-nitrided EuTaO₂N possessed a cubic perovskite-type structure, while high-temperature post-annealing led to a tetragonal EuTaO₂N phase with better crystallinity. The re-nitridation transformed the post-annealed product into the original cubic lattice, which might be an average of the tetragonal micro-domains.     

Magnetic properties of nanocrystalline ɛ-Fe3N and Co4N phases synthesized by newer precursor route

Nanocrystalline ɛ-Fe₃N and Co₄N nitride phases are synthesized first time by using tris(1,2-diaminoethane)iron(II) chloride and tris(1,2-diaminoethane)cobalt(III) chloride precursors, respectively. To prepare ɛ-Fe₃N and Co₄N nitride phases, the synthesized precursors were mixed with urea in 1:12 ratio and heat treated at various temperatures in the range of 450–900 °C under the ultrapure nitrogen gas atmosphere. The precursors are confirmed by FT-IR study. The ɛ-Fe₃N phase crystallizes in hexagonal structure with unit cell parameters, a = 4.76 Å and c = 4.41 Å. The Co₄N phase crystallizes in face centred cubic (fcc) structure with unit cell parameters, a = 3.55 Å. The estimated crystallite size for ɛ-Fe₃N and Co₄N phases are 29 nm and 22 nm, respectively. The scanning electron microscopy (SEM) studies confirm the nanocrystalline nature of the materials. The values of saturation magnetization for ɛ-Fe₃N and Co₄N phases are found to be 28.1 emu/g and 123.6 emu/g, respectively. The reduction of magnetic moments in ultrafine materials compared to bulk materials have been explained by spin pairing effect, lattice expansion, superparamagnetic behaviour and canted spin structures at the surface of the particles.     

Synthesis, crystal structure, dielectric properties, and potential use of nanocrystalline complex perovskite ceramic oxide Ba2ErZrO5.5

A new member belongs to Ba₂REZrO_5.5 (RE = Rare-Earth) perovskites, viz. Ba₂ErZrO_5.5, is synthesized as nanocrystals using a combustion process. Unlike the other Ba₂REZrO_5.5 perovskites, which are cubic, Ba₂ErZrO_5.5 crystallizes in tetragonal structure having space group P4/mnc (#128). Phase purity and ultrafine morphology of Ba₂ErZrO_5.5 powders were examined using X-ray diffraction (XRD), differential thermal analysis (DTA), thermogravimetric analysis (TGA), Fourier transform of infrared spectroscopy (FT-IR), Brunauer-Emmett-Teller (BET) specific surface area measurements, and transmission electron microscopy (TEM). Nanocrystals of Ba₂ErZrO_5.5 was sintered at ∼1500 °C for 4 h; whereas coarse-grained powders synthesized through solid state reaction could not be sintered even at 1700 °C for prolonged duration. XRD pattern of Ba₂ErZrO_5.5 was refined for atomic coordinates, lattice parameters, occupancies, and thermal factors using Rietveld analysis of XRD. Dielectric constant (?′) of Ba₂ErZrO_5.5 at 10 MHz is 21.62 ± 2 and dielectric loss (tan δ) is 5 × 10⁻³ at room temperature. Similar to the other Ba₂REZrO_5.5 perovskites, Ba₂ErZrO_5.5 is also showed chemically stability with YBa₂Cu₃O_7−δ (YBCO) and Bi₂Sr₂Ca₁Cu₂O_x (Bi-2212) superconductors. Ba₂ErZrO_5.5 can possibly be used as a substrate for high temperature superconductor (HTS) films, or be used as an insulator in the active superconductor-insulator-superconductor (SIS) structures.     

Synthesis and structural characterization of Ce-doped bismuth titanate

Ce-modified bismuth titanate nanopowders Bi_4−xCe_xTi₃O₁₂ (x ≤ 1) have been synthesized using a coprecipitation method. DTA/TG, FTIR, XRD, SEM/EDS and BET methods were used in order to investigate the effect of Ce-substitution on the structure, morphology and sinterability of the obtained powders. The phase structure investigation revealed that after calcinations at 600 °C powder without Ce addition exhibited pure bismuth titanate phase; however, powders with Ce (x = 0.25, 0.5 and 0.75) had bismuth titanate pyrochlore phase as the second phase. The strongest effect of Ce addition on the structure was noted for the powder with the highest amount of Ce (x = 1) having a cubic pyrochlore structure. The presence of pure pyrochlore phase was explained by its stabilization due to the incorporation of cerium ions in titanate structure. Ce-modified bismuth titanate ceramic had a density over 95% of theoretical density and the fracture in transgranular manner most probably due to preferable distribution of Ce in boundary region.     

Influence of the B-site ordering on the magnetic properties of the new La3Co2MO9 double perovskites with M = Nb or Ta

Double perovskites La₃Co₂NbO₉ and La₃Co₂TaO₉ have been prepared by both solid state and sol-gel synthesis. The crystal structures have been studied from X-ray and neutron powder diffraction data. Rietveld refinements show that the crystal structure is monoclinic (P2₁/n), with different degrees of ordering of B′ and B″ cations, with octahedra tilted according to the Glazer notation a⁻b⁻c⁺. Occupancy refinements show that the solid state materials are more B-site ordered than the sol-gel ones. Magnetization measurements show that these perovskites show two magnetic contributions, one with spontaneous magnetization and other with linear behaviour with the magnetic field associated to antiferromagnetic correlations. In the samples synthesized by solid state the spontaneous magnetization is more important than those synthesized by the sol-gel and present T_C of 62 K for Nb and 72 K for Ta. On the other hand, materials prepared by sol-gel have T_C 20 K for Nb and 40 K for Ta, respectively and major presence of the antiferromagnetic contribution. The competition between these magnetic behaviours is interpreted, by a microscopic point of view, as to be due to the different degrees of Co²⁺ ions disorder on the B site of the double perovskite structure. This disorder affects the ratio between the antiferromagnetic Co²⁺-O-Co²⁺ and the ferromagnetic Co²⁺-O-M⁵⁺-O-Co²⁺ couplings proposed for the system.     

Preparation, microstructure and properties of reaction-bonded AlN ceramics

AlN ceramics were prepared via a reaction-bonding technique, using Al and AlN powders as the starting materials. The effects of processing parameters and CaO as an additive were investigated. An AlN ceramic sintered at 1800°C with 0.5 wt.% CaO is highly densified and its dielectric constant and dielectric loss tgδ are 9.4 and 0.002 at 1 MHz, respectively. Its electrical resistivity and Vickers hardness are 2.88×10¹² Ω cm, 1210 kg/mm², respectively.     

Synthesis, structure refinement and characterization of tetrahydrated acid gadolinium diphosphate HGdP2O7·4H2O

Synthesis and single crystal structure are reported for a new gadolinium acid diphosphate tetrahydrate HGdP₂O₇·4H₂O. This salt crystallizes in the monoclinic system, space group P2₁/n, with the following unit-cell parameters: a = 6.6137(2) Å, b = 11.4954(4) Å, c = 11.377(4) Å, β = 87.53(2)° and Z = 4. Its crystal structure was refined to R = 0.0333 using 1783 reflections. The corresponding atomic arrangement can be described as an alternation of corrugated layers of monohydrogendiphosphate groups and GdO₈ polyhedra parallel to the () plane. The cohesion between the different diphosphoric groups is provided by strong hydrogen bonding involving the W4 water molecule.

IR and Raman spectra of HGdP₂O₇·4H₂O confirm the existence of the characteristic bands of diphosphate group in 980–700 cm⁻¹ area. The IR spectrum reveals also the characteristic bands of water molecules vibration (3600–3230 cm⁻¹) and acidic hydrogen ones (2340 cm⁻¹). TG and DTA investigations show that the dehydration of this salt occurs between 79 and 900 °C. It decomposes after dehydration into an amorphous phase. Gadolinium diphosphate Gd₄(P₂O₇)₃ was obtained by heating HGdP₂O₇·4H₂O in a static air furnace at 850 °C for 48 h.     

Cation disorder in Bi2Ln2Ti3O12 Aurivillius phases (Ln = La, Pr, Nd and Sm)

The synthesis and structure of triple layered Bi₂Ln₂Ti₃O₁₂ Aurivillius phases (Ln=La, Pr, Nd and Sm), prepared from K₂Ln₂Ti₃O₁₀ Ruddlesden-Popper precursors, has been investigated. These materials adopt a body centred tetragonal structure (space group I4/mmm, with unit cell parameters a∼3.8 Å and c∼33 Å) comprising a regular intergrowth of [Bi₂O₂]²⁺ fluorite-type and [Ln₂Ti₃O₁₀]²⁻ perovskite-type layers. A significant degree of cation disorder is present in the Bi₂Ln₂Ti₃O₁₂ system, involving the cross-substitution of Ln/Bi cations onto the Bi/Ln sites in the fluorite- and perovskite-type layers, respectively. As the size of the lanthanide cation is reduced, Bi/Ln disorder is significantly suppressed due to the effect of bond length mismatch in the perovskite-type layer in the crystal structure of Bi₂Ln₂Ti₃O₁₂. This offers a potential strategy for the chemical control of cation disorder in the Bi₂Ln₂Ti₃O₁₂ system.     

Rapid synthesis of room temperature ferromagnetic Ag-doped LaMnO3 perovskite phases by the solution combustion method

We report the rapid solution combustion synthesis and characterization of Ag-substituted LaMnO₃ phases at relatively low temperature using oxalyl dihydrazide, as fuel. Structural parameters were refined by the Rietveld method using powder X-ray diffraction data. While the parent LaMnO₃ crystallizes in the orthorhombic structure, the Ag-substituted compounds crystallize in the rhombohedral symmetry. On increasing Ag-content, unit cell volume and Mn-O-Mn bond angle decreases. The Fourier transform infra red spectrum shows two absorption bands corresponding to Mn-O stretching vibration (ν_s mode) and Mn-O-Mn deformation vibration (ν_b mode) around 600 cm⁻¹ and 400 cm⁻¹ for the compositions, x = 0.0, 0.05 and 0.10, respectively. Electrical resistivity measurements reveal that composition-controlled metal to insulator transition, with the maximum metal to insulator being 280 K for the composition La_0.75Ag_0.25MnO₃. Increase in magnetic moment was observed with increase in Ag-content. The maximum magnetic moment of 35 emu/g was observed for the composition La_0.80Ag_0.20MnO₃.     

Formation of TiB2 by volume combustion and mechanochemical process

Titanium diboride was produced both by volume combustion synthesis (VCS) and by mechanochemical synthesis (MCP) through the reaction of TiO₂, B₂O₃ and Mg. VCS products, expected to be composed of TiB₂ and MgO, were found to contain also side products such as Mg₂TiO₄, Mg₃B₂O₆, MgB₂ and TiN. HCl leaching was applied to the reaction products with the objective of removing MgO and the side products. Formation of TiN could be prevented by conducting the VCS under an argon atmosphere. Mg₂TiO₄ did not form when 40% excess Mg was used. Wet ball milling of the products before leaching was found to be effective in removal of Mg₃B₂O₆ during leaching in 1 M HCl. When stoichiometric starting mixtures were used, all of the side products could be removed after wet ball milling in ethanol and leaching in 5 M HCl when pure TiB₂ was obtained with a molar yield of 30%. Pure TiB₂ could also be obtained at a molar yield of 45.6% by hot leaching of VCS products at 75 °C in 5 M HCl, omitting the wet ball milling step. By MCP, products containing only TiB₂ and MgO were obtained after 15 h of ball milling. Leaching in 0.5 M HCl for 3 min was found to be sufficient for elimination of MgO. Molar yield of TiB₂ was 89.6%, much higher than that of VCS. According to scanning electron microscope analyses, the TiB₂ produced had average grain size of 0.27 ± 0.08 μm.     

Effects of borosilicate glass addition on the structure and dielectric properties of ZnTiO3 ceramics

ZnTiO₃ powders and borosilicate glass were made by sol-gel method, and then mixed for co-firing at low temperatures. The results show that the borosilicate glass was liquefied to improve the density of the ceramic during sintering. However, Zn₄O(BO₂)₆ and TiO₂ were formed if too much borosilicate glass was added (over 10 wt.%). The microwave dielectric properties of the ZnTiO₃ co-fired with borosilicate glass were also improved dramatically. With 5 wt.% borosilicate glass addition, ZnTiO₃ ceramics can be sintered at 850 °C and shows excellent microwave properties: 22.2 for dielectric constant, and 52,460 for Q × f value at a frequency of 6 GHz.     

Synthesis and characterization of thorium phosphate phases by spray pyrolysis: chemistry of thorium phosphates

This paper describes the synthesis of some thorium phosphate compounds with different Th/P ratio (1/2, 2/3 and 3/4) by a spray pyrolysis technique. The so-prepared rough compounds were annealed at different temperatures for 2 h and then analyzed by mainly X-ray diffraction on powder and infrared spectroscopy. Every rough compound is composed by very badly crystallized ThO₂ phase polluted by carbon residue. An annealing treatment at 800 °C leads to the thorium diphosphate phase, α-ThP₂O₇ in every case. At 900 °C, such a phase is decomposed into a thorium phosphate diphosphate phase (Th₄(PO₄)₄P₂O₇, called TPD). However, a thorium excess in the initial mixture (Th/P = 3/4) leads also to observe the ThO₂ phase. The TPD phase is stable up to 1200 °C and does not react with the ThO₂ compound. Beyond 1200 °C, the TPD phase is slowly decomposed into a thorium phosphate compound which should be a thorium oxide phosphate; this compound does not contain any diphosphate species.     

Self-flux synthesis and photoluminescent properties of LiAl5O8

Pure-phase LiAl₅O₈ was selected as an oxide ceramic red phosphor material without dopants (color centers) and was synthesized using a self-flux method. The LiAl₅O₈ was formed by heating a powder mixture consisting of γ-Al₂O₃:Li₂SO₄ = 1:2 (molar ratio) at over 1100 °C for 1 h. Photoluminescence (PL) properties for the synthesized LiAl₅O₈ were investigated. The maximum intensity of the excitation spectrum for the photoluminescent emission of LiAl₅O₈ synthesized was at 274 nm. The peak intensity of the emission spectrum was at a wavelength of 667 nm (red color). The intensity of the peak emission spectrum increased with the heating temperature, i.e., the maximum peak intensity of the red emission spectrum was detected for the LiAl₅O₈ synthesized by heating at 1500 °C for 1 h.     

Preparation and investigation of the quaternary alloy CuTaInSe3

Polycrystalline samples of the quaternary alloy CuTaInSe₃ were prepared by the usual melt and anneal technique. The analysis of the diffraction pattern indicates a single phase which indexes as a tetragonal chalcopyrite-like structure with lattice parameters a = 5.7837 ± 0.0002 Å; c = 11.6208 ± 0.0007 Å and V = 389 ± 1 Å³. Differential thermal analysis shows that the melting transition of CuTaInSe₃ is incongruent with large liquid + solids regions.