Self‐Activated Vanadate Compounds Toward Realization of Rare‐Earth‐Free Full‐Color Phosphors

Rare‐earth‐free phosphors based on vanadate compounds were investigated, where the vanadates included chloride vanadates (M^II₂VO₄Cl), pyrovanadates (M^II₂V₂O₇), orthovanadates (M^II₃(VO₄)₂) with divalent cations M^II of Mg, Sr, Ba, and Zn, and oxofluorovanadates (A^IVOF₄) with an alkali metal A^I. A chloride pyrolysis method and a liquid phase precipitation method were proposed for preparing the chloride vanadates and pyro‐ and orthovanadates, respectively. These vanadate compounds showed self‐activated photoluminescence (PL) based on the VO₄ clusters against the ultraviolet (UV) light irradiation. The colors of PL covered almost the whole visible‐light region from blue to yellow as Sr₂VO₄Cl (deep blue), Ca₂VO₄Cl (sky blue), Ba₂V₂O₇ (green), Sr₂V₂O₇ (yellowish green), Zn₃(VO₄)₂ (yellow), and Mg₃(VO₄)₂ (yellow). A correlation was suggested from these compounds between the luminescent colors and the structural feature as the longer V–O distances in the VO₄ tetrahedra in the crystal structures led to the longer wavelength in PL. This seemed to be also applicable for the oxofluorovanadates A^IVOF₄ (A^I = K and Cs) which contain the VOF₄ polyhedra with one O^2? ion and four F^‐ ions as the ligands, as they exhibited the reddish PL.     

Energetic Effects of Substitution of La–Nd and Si–Ge Oxyapatite‐Type Materials

A series of lanthanide oxyapatites, neodymium silicates (Nd_9.33?xM_3x/2(SiO₄)₆O₂; x = 0.0 and 2.0 and M = Ca, Sr, and Ba), and lanthanum germanate (La₁₀(GeO₄)₆O₃) were prepared by a variety of heat treatments and characterized. High‐temperature oxide melt solution calorimetry in molten 2PbO–B₂O₃ solvent at 1078 K was performed to determine their enthalpies of formation from constituent oxides at room temperature. The energetics of these materials is discussed in terms of the effects of doping on two crystallographic sites, the lanthanide and tetrahedral sites. The enthalpy of formation from oxides becomes less exothermic by substituting La with Nd throughout the whole series, in both doped and undoped compositions, reflecting the smaller radius and lower basicity of Nd compared with La. Cation stoichiometric lanthanum germanate apatite (La₁₀(GeO₄)₆O₃) shows a more endothermic enthalpy of formation than the corresponding silicate, reflecting the larger radius and lower acidity of Ge than Si.     

Tunable photoluminescence of apatite phosphor Ca5.95−xSrxLa4(SiO4)2(PO4)4O2:0.05Eu2+ and its application in light-emitting diodes

A series of new apatite phosphors Ca_5.95−xSr_xLa₄(SiO₄)₂(PO₄)₄O₂:0.05Eu²⁺ (x = 0-5.95) were prepared with the solid-state method. The variations of the occupation rate and cell parameters were investigated in detail, demonstrating that the phosphors are pure phases and that the different occupation rates of La³⁺, Ca²⁺, and Sr²⁺ ions are due to the different electrostatic bond strengths. The reflectance and photoluminescence excitation spectra prove that the phosphors can be efficiently excited with near-ultraviolet (n-UV) light. The broad redshift (50 nm) in the photoluminescence spectra is attributed to the increase in the crystal field splitting when the Ca²⁺ ion is replaced by the larger Sr²⁺ ion. At 150°C, the obtained phosphors maintain an emission intensity of ~67%-77% of that at room temperature (25°C), which indicates relatively the high performance of apatite phosphors in the temperature-dependence experiment. Because of the substitution of the small Ca²⁺ ion by the large Sr²⁺ ion, the emission color changes from green to yellow. Finally, a series of self-made light emitting diodes lamps were fabricated by coating the Ca_5.95−xSr_xLa₄(SiO₄)₂(PO₄)₄O₂:0.05Eu²⁺ phosphors with commercial blue and red phosphors on an n-UV chip (λ_ex = 370 nm). The self-made white-emitting lamps display a continuous changing correlated color temperature (4053-9353 K) or commission international de L'eclairgae (from [0.29, 0.28] to [0.38, 0.37]), implying that the series apatite phosphors have great potential to meet the different requirements of applications.     

Crystal Structure and Microwave Dielectric Properties of LiRE9(SiO4)6O2 Ceramics (RE = La,Pr, Nd,Sm, Eu,Gd, and Er)

The crystal structure and microwave dielectric properties of apatite‐type LiRE₉(SiO₄)₆O₂ ceramics (RE = La, Pr, Nd, Sm, Eu, Gd, and Er) have been investigated. The densification of lithium apatites has been greatly improved with the addition of 1 wt% LiF. Selected area electron diffraction and X‐ray diffraction (XRD) Rietveld analysis confirm that these compounds belong to the P6₃/m (No. 176) space group with hexagonal crystal symmetry. The porosity‐corrected relative permittivity was found to decrease with decreasing ionic polarizability of RE³⁺ ions. Relationships between the structural parameters and microwave dielectric properties have been examined. The observed variation in the quality factor of LiRE₉(SiO₄)₆O₂ + 1 wt% LiF ceramics (RE = La, Pr, and Nd) was correlated with average cation covalency (%). The temperature coefficient of resonant frequency was found to depend on the bond valence sum of cations. LiEr₉(SiO₄)₆O₂ + 1 wt% LiF ceramics showed good microwave dielectric properties with ε_r = 12.8, Q_u × f = 13000 GHz and τ_f = +17 ppm/°C. All the compositions showed low coefficient of thermal expansion with thermal conductivity in the range 1.3–2.8 W (m K)^?1.     

Synthesis and Characterization of Eu3+‐Doped Transparent Glass–ceramics Containing Nanocrystalline SrIINbIVO3

The glass–ceramics containing a rarely achievable nanocrystalline Sr^IINb^IVO₃ phase in the 53.75SiO₂–18.25K₂O–9Bi₂O₃–9SrO–9Nb₂O₅–0.5CeO₂–0.5Eu₂O₃ (mol%) glass system were prepared by the melt‐quench technique followed by a two‐stage controlled heat treatment. The unusual oxidation state of Nb in Sr^IINb^IVO₃ crystal is 4+ and upon heat treatment of the samples at lower temperature of 500°C for several hours, the glass composition and chemical environment around Nb ions played a key role for the formation of Sr^IINb^IVO₃ in the glass–ceramics. The microstructure of the glass–ceramics was studied using TEM and FESEM. The TEM images advocate 10–40 nm crystallite size of Sr^IINb^IVO₃. FTIR study confirms that all the samples consist of SiO₄, BiO₃, BiO₆, and NbO₆ structural units. The refractive index at different wavelengths was found to vary in the range 1.7105–1.7905 and increase with increase in heat‐treatment time. The luminescence spectra of Eu³⁺‐doped glass and glass–ceramics were recorded at 465 nm excitation wavelength and the luminescence intensity is found to be increased with heat‐treatment time due to increase in crystallinity. The high intensity ratio of ⁵D₀→⁷F₂ to ⁵D₀→⁷F₁ indicates that the Eu³⁺‐doped nanocrystalline Sr^IINb^IVO₃ glass–ceramics are promising candidate materials as red‐light source.     

Luminescence Mechanism and Thermal Stabilities of a White Silicate Phosphor for Multifunctional Applications

A series of Dy³⁺‐doped Sr_2(1?y)Ca_2yY₈(SiO₄)₆O₂ (0 ≤ y ≤ 1) white phosphors were synthesized by the solid‐state reaction. All samples crystallize into a hexagonal crystal system with space group P6₃/m (176) by the determination of XRD Rietveld refinements. With the change in Ca/Sr ratio, the crystal environment of active ions is lightly affected. Upon excitation by UV/VUV/cathode ray sources, the samples present an efficient white light emission with significant differences in the blue/yellow ratio of Dy³⁺ characteristic transitions. Based on luminescence properties, decay times and thermal properties, the interesting phenomenon with excitation energy increasing from UV to electron beam can be reasonably explained by a potential mechanism we proposed. With the introduction of Bi³⁺, the white emission intensity is rapidly enhanced and the optimal intensity reaches to 3.75 times compared with the single doped Dy³⁺ sample. To evaluate the applicability of this phosphor, we packaged two light‐emitting diode devices and measured the actual luminescence efficacies and CIE chromaticity coordinates. These results indicate that the silicate phosphors have the potential for multifunctional application in ultraviolet‐based light‐emitting diodes, mercury‐free lamps, and field‐emission displays.     

Crystal structure and luminescence properties of novel Sr10−x(SiO4)3(SO4)3O:xEu2+ phosphor with apatite structure

In this paper, a series of novel luminescent Sr_10−x(SiO₄)₃(SO₄)₃O:xEu²⁺ phosphors with apatite structure were synthesized by a high temperature solid-state reaction. The phase structure, photoluminescence (PL) properties, as well as the PL thermal stability were investigated. Sr_9.92(SiO₄)₃(SO₄)₃O:0.08Eu²⁺ phosphor exhibits better thermal quenching resistance, retaining the luminance of 66.55% at 150 °C compared with that at 25 °C. The quenching concentration of Eu²⁺ in Sr₁₀(SiO₄)₃(SO₄)₃O was about 0.08 (mol) with the dipole–quadrupole interaction. The Sr_10−x(SiO₄)₃(SO₄)₃O:xEu²⁺ phosphors exhibited a broad-band green emission at 538 nm upon excitation at 396 nm. The results indicate that Sr_10−x(SiO₄)₃(SO₄)₃O:xEu²⁺ phosphors have potential applications as near UV-convertible phosphors for white-light UV LEDs.     

A promising molten silicate resistant material: Rare-earth oxy-apatite RE9.33(SiO4)6O2 (RE = Gd,Nd or La)

In this work we reported a new class of rare earth oxy-apatite, RE_9.33(SiO₄)₆O₂, with superior molten silicate resistant capability which shows promising application for thermal barrier coatings (TBCs). Three RE elements with different ion radius, i.e., Gd, Nd and La, were selected to prepare RE_9.33(SiO₄)₆O₂ bulk using co-precipitation and pressless-sintering. After 8-h CMAS attack at 1300 °C, the specimens exhibited a dense, continuous reprecipitated layer at RE-apatite/CMAS interface, which is predominantly controlled by a dissolution-reprecipitation mechanism distinguishing from the sacrificial material which is usually with reaction layer being formed. With an increase of ion radius, apatite is easier to crystallize in the melt.     

The field of solid solutions in ternary system of synthetic apatite-type alkaline earth element-yttrium-silicate oxybritholite phases of the composition: AEEδY10−δ[SiO4]6O3−0.5δ, where AEE=Ca,Sr and Ba

This contribution deals with the synthesis, properties and investigation of the field of solid solutions formed between the three end-members of apatite-type alkaline earth element-yttrium-silicate oxybritholites with the hexagonal structure (P6₃/m). The stoichiometric composition of these compounds corresponds to the formula AEE_δY_10−δ(SiO₄)₆O_3−0.5δ, where AEE=Ca, Sr and Ba and parameter δ→2. These compounds and their solid solutions crystallize from non-equilibrium high temperature flux as the main product of sinter-crystallization process. Increasing ionic radius of AEE cations has significant effect to the lattice parameters, properties and miscibility of apatite phases. While there is non-limited miscibility of solid solutions formed between Ca₂Y₈[SiO₄]₆O₂ and Sr₂Y₈[SiO₄]₆O₂, the highest content of barium in the binary solution with these species is limited to 28% and 38%, respectively. The connecting line of these points marks out the borderline for the field of solid solutions in the ternary system. All attempts for the preparation of pure Ba₂Y₈[SiO₄]₆O₂ end-member via the ceramic method were not successful.     

Effects of crystal structure and cation size on molten silicate reactivity with environmental barrier coating materials

Rare earth (RE) disilicates are utilized in environmental barrier coatings to protect Si-based engine components from destructive reactions with water vapor and other combustion species. These coating materials, however, degrade when exposed to molten silicate deposits in the engine. Four RE-disilicates (RE₂Si₂O₇, RE = Er, Dy, Gd, Nd) are analyzed herein in thermochemical interactions with glassy calcium-magnesium-aluminosilicate (CMAS) compositions at 1400°C. Crystalline reaction products included RE₂Si₂O₇, SiO₂, and a Ca_2+yRE_8+x(SiO₄)₆O_2+3x/2+y apatite-type silicate. RE₂Si₂O₇ formation was favored in interactions with CMAS having low CaO:SiO₂ ratios. Increased reactivity was observed for higher CaO:SiO₂ ratios in CMAS combined with larger RE³⁺ cation size, resulting in apatite formation of varying stoichiometry and changes in lattice parameters. The crystallization of SiO₂ was dependent on both thermodynamic equilibrium at low CaO:SiO₂ ratios and sequestration of silicate modifiers at higher CaO:SiO₂ ratios, although residual amorphous content after CMAS exposure in both cases was still substantial.     

Improvement of Electrical Conductivity of Trivalent Rare‐earth Cation‐doped Neodymium Zirconate by Co‐doping Gadolinium and Ytterbium

Pyrochlore oxides of A₂Zr₂O₇, where A represents trivalent rare‐earth elements, have a high electrical conductivity, which makes them suitable for applications as high‐temperature solid electrolytes. The influence of Gd and Yb cations co‐doping at the Nd site on structure and electrical conductivity of a pyrochlore oxide Nd₂Zr₂O₇ is investigated using X‐ray diffraction and impedance spectra measurements. Different zirconate ceramics of Nd₂Zr₂O₇, Nd_1.8Gd_0.2Zr₂O₇, Nd_1.8Gd_0.1Yb_0.1Zr₂O₇, Nd_1.4Gd_0.6Zr₂O₇ and Nd_1.4Gd_0.3Yb_0.3Zr₂O₇ are prepared by pressureless‐sintering method at 1,973 K for 10 h in air. Nd₂Zr₂O₇ doped with Gd and Yb cations at the Nd site exhibit a single phase of pyrochlore‐type structure. The measured values of the total conductivity obey the Arrhenius relation. Nd₂Zr₂O₇ and its doped zirconate ceramics are oxide‐ion conductors in the oxygen partial pressure range of 1.0 × 10^–4 to 1.0 atm at all test temperature levels. The total conductivity increases with reducing average ionic radii of A‐site rare‐earth cations. The dual Yb+Gd intermix doping causes a distinctly enhanced total conductivity as compared to unmodified Nd₂Zr₂O₇ and singly Gd‐doped zirconate ceramics. The highest total conductivity value obtained in this work is 1.02 × 10^–2 S cm × ¹ at 1,173 K for Nd_1.4Gd_0.3Yb_0.3Zr₂O₇ ceramic.     

Structural and Crystal Chemical Investigation of Intermediate Phases in the System Ca2SiO4–Ca3(PO4)2–CaNaPO4

Two intermediate compounds of the system Ca₂SiO₄–Ca₃(PO₄)₂–CaNaPO₄ were synthesized by reaction sintering at 1600°C and analyzed structurally, chemically, and optically. The structure of Ca₇(PO₄)₂(SiO₄)₂ nagelschmidtite (space group P6₁, a = 10.7754(1) Å, c = 21.4166(3) Å) was determined by single crystal X‐ray analysis. Its unit cell can be interpreted as a supercell (≈ 2 × a, 3 × c) of the high‐temperature polymorph α‐Ca₂SiO₄. Evidence for pseudo‐hexagonal symmetry is shown. Using electron microprobe, the solid solution Ca_7?xNa_x(PO₄)_2+x(SiO₄)_2?x, (x ≤ 2), of nagelschmidtite was confirmed. Volume thermal expansion coefficients of Ca_6.8Na_0.2(PO₄)_2.2(SiO₄)_1.8 and Ca_5.4Na_1.5(PO₄)_3.7(SiO₄)_0.3 were determined using high‐temperature X‐ray powder diffraction, yielding mean α_V = 3.95 and 5.21 [×10^?5/°C], respectively. Ca₁₅(PO₄)₂(SiO₄)₆ is a distinct phase in the binary section Ca₂SiO₄–Ca₃(PO₄)₂ and was found to extend into the ternary space according to Ca_15?xNa_x(PO₄)_2+x(SiO₄)_6?x, (x ≤ 0.1). Quenching experiments of the latter allowed for structural analysis of a strongly disordered, defective high‐temperature polymorph of the α‐Ca₂SiO₄–α‐Ca₃(PO₄)₂ solid solution. Structural relations between nagelschmidtite, Ca₁₅(PO₄)₂(SiO₄)₆ and the end‐member compounds of the system are discussed.     

Selective binding of an imprinted polymer resulted from controlling cobalt coordination to nitric oxide

In this article, the binding characteristics of the imprinted polymer P‐1[Co^II(salen)] (salen: bis(2‐hydroxybenzaldehyde)ethylenediimine) to nitric oxide (NO) have been reported. P‐1[Co^II(salen)] was characterized by Fourier transform infrared analysis, thermogravimetric analysis, and differential scanning calorimetry. Batch‐mode adsorption studies were carried out to investigate binding thermodynamics, kinetics, and selective recognition behavior of P‐1[Co^II(salen)] to NO. The kinetics study indicates that binding of the polymer to NO fits the first‐order reaction kinetics with the rate constant k₁ of 0.087 min^?1. Langmuir and Freundlich equations were used to explain the equilibrium character of P‐1[Co^II(salen)] binding to NO. The r² and χ² values suggest that total amount of NO bound by P‐1[Co^II(salen)] can be best fitted by the Langmuir equation. The binding capacity (B_max) of P‐1[Co^II(salen)] was calculated to be 76.28 μmol/g, very close to the experimental value, 75 μmol/g. The thermodynamics and selectivity experiments showed that the affinity of P‐1[Co^II(salen)] to NO was much higher than carbon dioxide (CO₂) and oxygen (O₂), suggesting that P‐1[Co^II(salen)] is a promising functional material for NO storage and NO sensing. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Effect of Al/Sr ratio on the luminescence properties of SrAl2O4:Eu2+, Dy3+ phosphors

Recent studies have brought out many phosphors like Eu²⁺, Dy³⁺-doped alkaline earth aluminates. The trivalent Dy³⁺ ions as co-dopants greatly enhance the duration and intensity of persistent luminescence. These phosphors show excellent properties, such as high quantum efficiency, long persistence of phosphorescence, good stability and suitable color emission.In this work the effect of Al/Sr ratio on the afterglow and phosphorescence decay properties of Eu²⁺ and Dy³⁺ co-activated strontium aluminates synthesized by a solid-state process has been investigated. The luminescence properties of samples were investigated by means of excitation spectra, emission spectra and X-ray diffraction analysis.A variety of strontium aluminates, such as SrAl₂O₄, Sr₄Al₂O₇, Sr₃Al₂O₆, Sr₃Al₂(Eu, Dy, Y)O_7.5, Al₅(Eu, Dy, Y)O₁₂, Sr₄Al₁₄O₂₅, SrAl₁₂O₁₉ and (Eu, Dy, Y)AlO₃ have been identified in the samples prepared from starting precursors with Al/Sr mole ratios ranging from 0.44 to 5. The afterglow decay rate was found to be the fastest for sample with Al/Sr ratio of 4.18, in which SrAl₄O₇ phase was dominant. The afterglow decay rate for phosphor with Al/Sr ratio of 2, in which SrAl₂O₄ phase was dominant, was detected to be slow. Moreover, the emission spectra of the samples shift to yellow-green long wavelength from bluish-green-ultraviolet short wave with the increase of Al/Sr ratios resulting from the change in the composition.     

Polymers based on N,N‐diglycidylaniline. I. Investigations of the curing kinetics by dynamic differential scanning calorimetry measurements

N,N‐Diglycidylaniline was reacted with aniline (yielding polymer EP‐1) and the newly synthesized chromophore 4‐(phenylazo)aniline (yielding polymer EP‐2). The curing kinetics of these two epoxy resin systems was studied in dynamic experiments by means of differential scanning calorimetry. Kinetic parameters such as the activation energy and frequency factor were estimated with the Ozawa method [E(O) and A(O), respectively], the Kissinger method [E(K) and A(K), respectively], and the modified Avrami method [E(A) and A(A), respectively]. The activation energy and frequency factor of EP‐1 were much lower than those of EP‐2 estimated with the Ozawa, Kissinger, and Avrami methods. The activation energy and frequency factor for EP‐1 determined with the Ozawa method [E(O) = 55.8 kJ/mol, A(O) = 10 × 10³ 1/s] and the Avrami method [E(A) = 56.4 kJ/mol, A(A) = 9.2 × 10³ 1/s] were higher than those determined with the Kissinger method [E(K) = 51.0 kJ/mol, A(K) = 2 × 10³ 1/s]. In the case of EP‐2, the kinetic parameters calculated with the Ozawa model [E(O) = 140.4 kJ/mol, A(O) = 12.3 × 10¹³ 1/s] and the Kissinger model [E(K) = 139.9 kJ/mol, A(K) = 10.9 × 10¹³ 1/s] were higher than those calculated with the Avrami model [E(A) = 130.4 kJ/mol, A(A) = 7.9 × 10¹² 1/s]. The obtained polymers were characterized with Fourier transform infrared, ¹H‐NMR, differential scanning calorimetry, and ultraviolet–visible spectroscopy. The polymers exhibited low glass‐transition temperatures in the range of 57–79°C and good solubility in common organic solvents. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

CuI and H2O2 Inactivate and FeII Inhibits [Fe]‐Hydrogenase at Very Low Concentrations

[Fe]‐Hydrogenase (Hmd) catalyzes reversible hydride transfer from H₂. It harbors an iron‐guanylylpyridinol as a cofactor with an Fe^II that is ligated to one thiolate, two COs, one acyl‐C, one pyridinol‐N, and solvent. Here, we report that Cu^I and H₂O₂ inactivate Hmd (half‐maximal rates at 1 μM Cu^I and 20 μM H₂O₂) and that Fe^II inhibits the enzyme with very high affinity (K_i=40 nM ). Infrared and EPR studies together with competitive inhibition studies with isocyanide indicated that Cu^I exerts its inhibitory effect most probably by binding to the active site iron‐thiolate ligand. Using the same methods, it was found that H₂O₂ binds to the active‐site iron at the solvent‐binding site and oxidizes Fe^II to Fe^III. Also it was shown that Fe^II reversibly binds away from the active site iron, with binding being competitive to the organic hydride acceptor; this inhibition is specific for Fe^II and is reminiscent of that for the [FeFe]‐hydrogenase second iron, which specifically interacts with H₂.     

A novel CMAS-resistant material based on thermodynamic equilibrium design: Apatite-type Gd10(SiO4)6O3

Calcium-magnesium-alumino-silicates (CMAS) melt attack has been a critical issue for the thermal barrier coatings (TBCs) with ever-increasing engine operating temperature. In this study, a novel CMAS-resistant material apatite-type Gd₁₀(SiO₄)₆O₃ is developed for TBCs application based on thermodynamic equilibrium design. The chemical reaction of Gd₁₀(SiO₄)₆O₃ bulk and CMAS melt is investigated at 1300°C. The CMAS corrosion resistance of Gd₁₀(SiO₄)₆O₃ bulk is evaluated and compared with the well-studied CMAS-resistant material Gd₂Zr₂O₇ (GZO). It is found that Gd₁₀(SiO₄)₆O₃ shows a significantly enhanced CMAS resistance, including lower intrinsic CMAS infiltration rate (~1.09 μm/h^1/2) and smaller infiltration upper limit (50-62 μm) for a 20 mg/cm² CMAS deposition. More importantly, for Gd₁₀(SiO₄)₆O₃, the CMAS infiltration only alters the composition but does not change the crystal structure or destroy microstructural integrity. The reaction mechanism is elucidated as following two stages: (a) surface Gd₁₀(SiO₄)₆O₃ quickly transforms into Ca₂Gd₈(SiO₄)₆O₂ in suit by interdiffusion with CMAS melt and then is thermodynamically stable with CMAS melt, thereby effectively inhibiting the further CMAS infiltration and (b) with the ongoing interdiffusion of Gd/Ca, the CMAS-infiltrated layer slowly thickens and follows a parabolic law. Meanwhile, the CMAS melt gradually precipitates Ca₂Gd₈(SiO₄)₆O₂ and CaAl₂Si₂O₈ (anorthite) until the melt is exhausted.     

Phase composition,microstructure and thermophysical properties of the Srx(Zr0.9Y0.05Yb0.05)O1.95+x ceramics

Sr_x(Zr_0.9Y_0.05Yb_0.05)O_1.95+x (x=1.0, 0.9, 0.8, 0.7) ceramics were prepared by solid state reaction sintering. The sintered Sr_1.0(Zr_0.9Y_0.05Yb_0.05)O_2.95 is a single-phase solid solution while the sintered Sr_x(Zr_0.9Y_0.05Yb_0.05)O_1.95+x (x=0.9?0.7) are composites, and a significant grain growth inhibition is observed in the sintered Sr_x(Zr_0.9Y_0.05Yb_0.05)O_1.95+x (x=1.0, 0.9). Rare-earth elements distribution in the bulk materials indicates that Yb and Y preferentially substitute Zr-sites in SrZrO₃, and the highest solubility of RE₂O₃ in pure SrZrO₃ is ～0.8 mol%. The sintered Sr_x(Zr_0.9Y_0.05Yb_0.05)O_1.95+x have high thermal expansion coefficients up to ～11.0×10^?6 K^-1 (1200°C). Sr_0.8(Zr_0.9Y_0.05Yb_0.05)O_2.75 has the lowest thermal conductivity of 1.38 W·m^-1·K^-1 at 800°C. Sr_x(Zr_0.9Y_0.05Yb_0.05)O_1.95+x (x=1.0, 0.9, 0.8) show no phase transition from 600 to 1400°C, whereas Sr_x(Zr_0.9Y_0.05Yb_0.05)O_1.95+x (x=0.9, 0.8) have excellent high-temperature phase stability over the whole investigated temperature range. Therefore, Sr_x(Zr_0.9Y_0.05Yb_0.05)O_1.95+x (x=1.0, 0.9, 0.8) are considered as promising TBCs materials that might be operated at higher temperatures compared to YSZ.     

Relaxor nature in Ba5RZr3Nb7O30 (R = La,Nd, Sm) tetragonal tungsten bronze new system

Ba₅RZr₃Nb₇O₃₀(R = La, Nd, Sm) lead‐free relaxor ferroelectrics were prepared by a standard solid‐state reaction process, and the influence of A and B site ion occupation on the dielectric characteristics especially the relaxor nature were investigated systematically. Tetragonal tungsten bronze structure with space group P4/mbm was determined for all compositions, ion cross distribution by Ba²⁺ and R³⁺ in A1 site was observed, while A2 site was only occupied by Ba²⁺. Selected area electron diffraction patterns confirmed the existence of incommensurate superlattice modulation. Furthermore, temperature and frequency dependences of the dielectric properties showed a broad permittivity peak with strong frequency dispersion, following well the Vogel‐Fulcher relationship. The maximum dielectric constant temperature increased gradually with decreasing A1 site ion size. Slim P‐E hysteresis loops were obtained at room temperature for all compositions. Meanwhile, micro ferroelectric domains were observed in Ba₅SmZr₃Nb₇O₃₀. For Ba₄R₂Zr₄Nb₆O₃₀ and Ba₅RZr₃Nb₇O₃₀ (R = Nd, Sm), the transition from normal ferroelectric to relaxor behavior originates from the increased t_A1, which is a result of cross distribution at A1 site. Compared with Ba₅RTi₃Nb₇O₃₀, Zr substitution at B site enhances the relaxor nature.     

Oxidative Destruction of Hydrocarbons on Ca12Al14-x Si x O33+0.5x (0 ≤ x ≤ 4) with Radical Oxygen Occluded in Nanopores

Three types of calcium aluminosilicate, Ca₁₂Al₁₄O₃₃ (C₁₂A₇), Ca₁₂Al₁₄Si₂O₃₄ (C₁₂A₆), and Ca₁₂Al₁₀Si₄O₃₅ (C₁₂A₅), were prepared by calcining the respective hydrothermally synthesized hydrogarnet, Ca₃Al₂(OH)₁₂, Ca₃Al₂(SiO>₄)_1/3(OH)_32/3, and Ca₃Al₂(SiO₄)_0.8(OH)_8.8. Different amounts of superoxide (O₂^-) and peroxide (O₂^2-) were occluded in the lattice of these calcium aluminosilicates. No activity improvement was observed for the oxidation of propylene and benzene by increasing the amounts of (O₂^-) and (O₂^2-).