Effects of annealing atmospheres on the structure and ferromagnetic properties of Fe0.12Cu0.02Zn0.86O thin films

Fe_0.12Cu_0.02Zn_0.86O thin film was deposited on a Si substrate using r. f. sputtering with no heating and an Ar/O₂ ratio of 10%. After deposition, the specimens were annealed at 400 °C for 1 h, in nitrogen and hydrogen atmospheres. The X-ray diffractometry (XRD) analysis results show that the crystallinity of Fe_0.12Cu_0.02Zn_0.86O thin film annealed in a nitrogen atmosphere is better than that of the film annealed in a hydrogen atmosphere. The X-ray photoelectron spectroscope (XPS) results show that there are more oxygen vacancies in the Fe_0.12Cu_0.02Zn_0.86O thin film annealed in a hydrogen atmosphere. The magnetic force microscope (MFM) analysis results also demonstrate that some magnetism particles are precipitated for the Fe_0.12Cu_0.02Zn_0.86O thin film annealed in a hydrogen atmosphere. This results in an improvement in the ferromagnetic properties, and the saturation magnetization is 70.2 emu/cm³, which is about 25% larger than that for the as-grown Fe_0.12Cu_0.02Zn_0.86O thin film.     

Oxygen isotope equilibration and exchange as probes for differing dioxygen interactions with pure and rhodia-promoted CeO2 and Al2O3

Comparisons are made between the catalytic activities of CeO₂, Al₂O₃ and Rh₂O₃ when pure, or in the case of CeO₂ and Al₂O₃ when promoted by rhodia dispersed thereon, in respect of: (a) activity at 290 K for homomolecular oxygen isotope equilibration of an equimolar (¹⁸O₂ + ¹⁶O₂) probe gas, the so-called R₀ process, (b) activity under T-ramp for heterophase oxygen isotope exchange between surface lattice and O₂ highly enriched in ¹⁸O, which is shown to occur predominantly by single-stay exchange of both oxygen atoms of dioxygen (the so-called R₂ process). This revised version was published online in June 2006 with corrections to the Cover Date.     

UV-Enhanced Exchange of O2with H2O Adsorbed on TiO2

Ultraviolet light dramatically increases the rate of isotope exchange between gas-phase O₂and water adsorbed on TiO₂at room temperature, but it does not affect the rate of CO₂–water exchange. Both ethanol and acetaldehyde, when coadsorbed with H₂¹⁸O, dramatically decrease the rate of O₂exchange, but not CO₂exchange, with adsorbed H₂¹⁸O. This decrease is attributed to a combination of competition for adsorbed oxygen between exchange and photocatalytic oxidation of the adsorbed organic and blocking of the oxygen adsorption sites by the organic. The same oxygen species participate in O₂-H₂¹⁸O exchange and photocatalytic oxidation.     

Isotopic Study of N2O Decomposition on an Ion-Exchanged Fe-Zeolite Catalyst: Mechanism of O2 Formation

N₂O decomposition on an ion-exchanged Fe-MFI catalyst has been studied using an ¹⁸O-tracer technique in order to reveal the reaction mechanism. N₂ ¹⁶O was pulsed onto an ¹⁸O₂-treated Fe-MFI catalyst at 693 K, and the O₂ molecules produced were monitored by means of mass spectrometry. The ¹⁸O fraction in the produced oxygen had almost half the value of that on the surface oxygen, and ¹⁸O¹⁸O was not detected. The result shows that O₂ formation proceeds via the Eley–Rideal mechanism (N₂ ¹⁶O + ¹⁸O(a) N₂ + ¹⁶O¹⁸O).     

Optical properties of Eu3+/Pr3+ doped Zn4O(BO2)6 synthesized by solid-state reaction

Zn₄O(BO₂)₆ based on the [B₂₄O₄₈] sodalite-cage structure fixed by the inside [Zn₄O₁₃] clusters is expected to be a new class of solid-state lighting material with perfect thermal and mechanical stability. Herein, in the current work, we have respectively introduced non-equivalent rare-earth cations Eu³⁺ and Pr³⁺ into Zn₄O(BO₂)₆ host to design white and green emission materials by a novel solid-phase sintering method at lower temperatures. Zn₂B₆O₁₁ replacing B₂O₃ or H₃BO₃ as raw materials can effectively avoid the impure products caused by the uncontrollable volatilization of B₂O₃ or H₃BO_3. The newly designed light-emitting materials of Zn_4(1-x)O(BO₂)₆: xRe³⁺ (ReEu or Pr), including Zn₄O(BO₂)₆ host, have good absorption capacity in the ultraviolet region. Under ultraviolet irradiation, Zn₄O(BO₂)₆, Zn_4(1-x)O(BO₂)₆: xEu³⁺and Zn_4(1-x)O(BO₂)₆: xPr³⁺ emit the blue, white and green lights, respectively. In addition, all these materials can effectively degrade methylene blue, in which Zn_4(1-x)O(BO₂)₆: xPr³⁺ has the highest efficiency. The luminescence and degradation mechanisms of Zn₄O(BO₂)₆, Zn_4(1-x)O(BO₂)₆: xEu³⁺and Zn_4(1-x)O(BO₂)₆: xPr³⁺ have been adequately explained by their electronic structures based on the first principle calculations. The current study confirms that the doping of Eu³⁺/Pr³⁺ in Zn₄O(BO₂)₆ can broaden its applications as photoluminescent and photocatalytic materials.     

Decomposition of Nitrous Oxide Over Fe-Ferrierites. Effect of Deposited Oxygen on the Framework Oxygens Studied by 18O Isotopic Exchange

About 50-75% of oxygen captured during decomposition of N₂O at 200 °C over Fe-FER (Fe/Al 0.03-0.6) was exchanged by ¹⁸O at room temperature. Complete desorption of captured oxygen containing mostly ¹⁶O isotope was reached at higher temperature. The ¹⁸O deficiency was rationalized by assuming labilization of the framework oxygen in Fe-FER.     

Oxygen isotope reactions on platinum

The efficiency of a platinum filament as a catalyst for the oxygen isotope equilibration reaction ¹⁶O₂ + ¹⁸O₂ = 2 ¹⁶O¹⁸O has been measured for filament temperatures between 300 and 1400 °K. The maximum efficiency was about 11% near 950 °K. The results are compared with the initial sticking probability of oxygen in the same temperature range and with the rate of the high temperature (>1000 °K) pumping action of the filament. It is concluded that the adsorption and isotope equilibration reactions are related but that pumping proceeds by a separate process, although not through thermal accommodation of oxygen on the surface.     

Synthesis and photoluminescence characterizations of Zn2+ and Tb3+ codoped CeO2 phosphors for temperature sensing applications

Cyan light-emitting Ce_0.985-xZn_xO₂:0.015 Tb³⁺ (x = 0 to 0.2) phosphors were synthesized using the ethylenediaminetetraacetic acid-assisted hydrothermal method. The X-ray diffraction and refinement analyses of the prepared phosphors indicated that the formed face-centered cubic structure remained intact even after the doping of large quantities of Zn²⁺ ions. However, the incorporation of Zn²⁺ ions increased the Ce³⁺/Ce⁴⁺ ratio, resulting in the enhancement of oxygen vacancies in the prepared phosphors. The generation of oxygen vacancies caused the evolution of a broad photoluminescence emission band ranging from 400 to 525 nm with a characteristic Tb³⁺ emission of approximately 543 nm. Two-emission regions in Ce_0.885Zn_0.1O₂:0.015 Tb³⁺ phosphors were utilized for measuring the fluorescence intensity ratio (FIR) as a function of temperature ranging from 303 to 523 K. At 523 K, the FIR values dropped to approximately 40% of the starting temperature value. The variation of FIR values followed the Boltzmann behavior. The Boltzmann fitting demonstrated the feasibility of the present phosphors for temperature sensor applications. The optimum absolute sensor sensitivity of Ce_0.885Zn_0.1O₂:0.015 Tb³⁺ phosphors was measured to be 0.0043 K⁻¹ at 398 K with a resolution of approximately 1 K⁻¹. Moderate temperature sensitivity, negligible hysteresis loop, and excellent reversibility revealed the suitability of Ce_0.885Zn_0.1O₂:0.015 Tb³⁺ phosphors for sensing the temperature in various electronic devices.     

Phase transformation and dielectric properties of sputtering-prepared Zn–Ti–O thin films

Zn–Ti–O films were co-sputtered from Zn and Ti targets and then annealed at temperatures ranging from 600 °C to 900 °C for 2 h under an air atmosphere. The [Ti]/([Ti]+[Zn]) ratio decreased from 75.52 to 28.26 as the Zn-target power increased from 25 W to 75 W. The phase transition of the films strongly depended on the [Ti]/([Ti]+[Zn]) ratio. High [Ti]/([Ti]+[Zn]) ratios led to the coexistence of ZnTiO₃, Zn₂Ti₃O₈, and rutile TiO₂ phases. Zn₂Ti₃O₈ gradually became the major crystalline phase as the [Ti]/([Ti]+[Zn]) ratio and rutile TiO₂ and ZnTiO₃ phases decreased. The aforementioned phases disappeared when the [Ti]/([Ti]+[Zn]) ratio was especially low. In their place, Zn₂TiO₄ and even ZnO phases developed. The dielectric constant of the films increased with increasing [Ti]/([Ti]+[Zn]) ratio. However, extremely high [Ti]/([Ti]+[Zn]) ratios increased the dielectric loss of the films. The film mainly composed of the Zn₂Ti₃O₈ phase exhibited optimal dielectric properties, including a dielectric constant and loss equal to 40.1 and 0.0304, respectively, at 1 MHz.     

Build-in electric field induced step-scheme TiO2/W18O49 heterojunction for enhanced photocatalytic activity under visible-light irradiation

Artificial Z-scheme heterostructure photocatalysts, inspired by the natural photosynthesis, have been explored for water contamination owing to the efficiency of charge carriers separation and enhanced redox capacity. Herein, a novel step-scheme TiO₂/W₁₈O₄₉ heterojunction integrating TiO₂ nanosheets and spindle-like W₁₈O₄₉ was prepared via a two-step solvothermal method. The TiO₂/W₁₈O₄₉ heterojunction with the optimum ratio exhibited excellent photodegradation of RhB higher by a factor of 2.26 and TC degradation higher by a factor of 3.32 than the pristine TiO₂ when exposed to visible light. The reactive free radical trapping experiment indicated •O₂⁻ was determined to the dominant reactive species. Furthermore, XPS analysis and •O₂⁻ quantification measurements confirmed a build-in electric field induced step-scheme structure in TiO₂/W₁₈O₄₉ composites, which effectively enhanced the separation of carriers, thus improved photocatalytic activity. The present study will offer a new perception related to the formation of step-scheme heterostructure for photocatalytic degradation.     

Enhanced ferroelectric properties of (Zn,Ti) equivalent co-doped BiFeO3 films prepared via the sol-gel method

High-quality BiFe_1-2xZn_xTi_xO₃ (BFZTO with x = 0, 0.01, 0.02, 0.03, 0.04, and 0.05) films were successfully prepared on fluorine-doped tin oxide (FTO)/glass substrates via the sol-gel method. The influence of (Zn, Ti) equivalent co-doping on the structure, surface morphology, and ferroelectric properties of BFZTO films was investigated systematically. X-ray diffraction (XRD) and Raman spectra analysis indicate that co-doping results in structural transformations. Scanning electron microscope (SEM) images show that BFZTO films with x = 0.02 exhibit uniform fine grains and higher density, which is instrumental for the development of ferroelectric properties. X-ray photoelectron spectroscopy (XPS) analysis reveals that BiFe_0.96Zn_0.02Ti_0.02O₃ film can inhibit the conversion of Fe³⁺ into Fe²⁺, thereby greatly reducing oxygen vacancy concentration. Therefore, under the electric field strength of 150 kV/cm, BiFe_0.96Zn_0.02Ti_0.02O₃ film was found to have the lowest leakage current density, J = 1.13 × 10^?6 A/cm², which is five orders of magnitude lower than that of pure BiFeO₃ (BFO) film. Furthermore, this film exhibits the largest remnant polarization at room temperature, P_r = 131.9 μC/cm², which is more than twice as large as that of pure BFO (P_r = 52.6 μC/cm²). Additionally, by comparing P-E hysteresis loops of different regions on the surface of BiFe_0.96Zn_0.02Ti_0.02O₃ film, it was found that the film has high uniformity and stable overall performance. Dielectric and magnetic properties were also enhanced via (Zn, Ti) co-doping.     

Oxygen Isotope Transport Properties of Yttria‐Stabilized Zirconia (YSZ) in O2‐ and H2O‐Containing Atmospheres

Oxygen isotope exchange experiments, H₂¹⁸O/H₂¹⁶O (”wet” anneals) and ¹⁸O₂/¹⁶O₂ (”dry” anneals), were performed on single crystal samples of yttria‐stabilized zirconia (YSZ) at a temperature of T = 1073 K with subsequent determination of the oxygen isotope profiles in the solid by time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS). Such experiments yielded oxygen tracer diffusion coefficients (D*) and oxygen tracer surface exchange coefficients (k*), from both the polished (smooth) and unpolished (rough) sides of single crystal samples, as a function of water partial pressure pH₂O and oxygen partial pressure pO₂. Isothermal values of D* were found to depend on neither pO₂ nor pH₂O (nor surface roughness). Isothermal values of k*, in contrast, displayed a strong dependence on pO₂ or pH₂O; k*_wet was, in addition, 2–3 orders of magnitude higher than k*_dry. Surprisingly, surface roughness had little effect on k*_wet, whereas rough surfaces exhibited much higher k*_dry values than smooth surfaces. Data for k*_wet obtained as a function of temperature at pH₂O = 18 mbar show a change in activation enthalpy at T ≈ 973 K. The behavior of k* is discussed in terms of surface composition, surface area and surface reaction mechanisms.     

Role of Zeolitic Oxygens During the Decomposition of 15N 2 18 O Over Fe-ferrierite

Isotopic species of dioxygen released during the decomposition of ¹⁵N₂¹⁸O over Fe-ferrierite show that the zeolite oxygens participate in the reaction. While Fe-ferrierite alone does not exchange its oxygens with ¹⁸O₂ below 400 °C, this exchange is very rapid in the mixture of ¹⁸O₂+N₂O. The amount of participating zeolite oxygen (ca. 1–6 per iron atom) is practically the same in the latter case as in the decomposition of ¹⁵N₂¹⁸O. The time dependence of individual dioxygen isotope species released during the ¹⁵N₂¹⁸O decomposition points to the primary release of ¹⁸O₂ which is very rapidly exchanged for the zeolite oxygen by a single-step mechanism.     

Effects of the annealing atmosphere on the microstructure and properties of BiFe0.99Zn0.01O3 films

BiFe_0.99Zn_0.01O₃ (BFZO) films were annealed in different atmospheres (Air, N₂ and O₂) on ITO/glass substrates. The influences of the different annealing atmospheres on the oxygen vacancy concentration, microstructure, ferroelectric behavior, leakage current, leakage mechanism, aging and dielectric performance of the BFZO films were studied. The crystallization and grain development for the sample annealed in an O₂ atmosphere improved, and the concentrations of the Fe²⁺ and oxygen vacancies were the lowest among the samples studied herein. The BFZO film had the lowest leakage current density and the best ferroelectric performance in an O₂ annealing atmosphere among the samples studied herein, and the leakage was due to the F-N tunneling effect mechanism. From the perspective of the volume effect, the aging model was established, and the aging mechanism of the BFZO films was discussed in depth. Compared with Air and N₂, the annealed film in O₂ exhibited no obvious aging.     

Improved dielectric and non-ohmic properties of (Zn + Zr) codoped CaCu3Ti4O12 thin films

The good dielectric and non-ohmic properties of CaCu₃Ti₄O₁₂ and CaCu_2.95Zn_0.05Ti_4-xZr_xO₁₂ (x?=?0, 0.05 and 0.10) thin films prepared by a sol-gel method were determined. The enhanced dielectric properties, with a dielectric constant of ${\epsilon }^{\text{'}}$ ≈ 4357 and a dielectric loss of tan δ?≈?0.019, of the CaCu_2.95Zn_0.05Ti_3.95Zr_0.05O₁₂ (ZnZr05) thin film at 1?kHz and room temperature were investigated. The XPS spectrum showed that the ZnZr05 film can produce copper vacancies V_Cu” and mixed valence structures for Cu⁺/Cu²⁺ and Ti³⁺/Ti⁴⁺ inside the crystal. The ZnZr05 film maintained a high dielectric constant due to the large grain sizes and the presence of the mixed valence structures, while its low tan δ was attributed to an increase in the V_Cu” concentration. At the same time, the enhanced nonlinear coefficient (4.2) and low leakage current (193?μA) of the ZnZr05 film were explained in detail.     

Effect of temperature and film thickness on structural and mechanical properties of c-axis oriented Zn0.95Mg0.05O thin films

Zn_0.95Mg_0.05O solutions were synthesized by the sol-gel technique using Zn and Mg-based alkoxide. The structure, microstructure, and mechanical properties of the c-axis oriented Zn_0.95Mg_0.05O thin films were investigated as a function of film thickness and temperature. Zn_0.95Mg_0.05O thin films were grown on a glass substrate using the sol-gel dip-coating method. Then, the thin films were annealed at various temperature values (500–600 °C for 30 min) under air. X-ray diffraction of the Zn_0.95Mg_0.05O thin films results indicated that all samples had a ZnO wurtzite structure and (002) orientation. The photoluminescence (PL) measurements revealed the near-band emission (NBE), the Zn_i related emission, and the excess oxygen interstitials and their complexes with zinc vacancies. The surface morphologies and microstructure of all samples were characterized by using Scanning Electron Microscope (SEM). It was observed that surface morphologies of Zn_0.95Mg_0.05O thin film were dense, uniform, crack free and without pinhole. Effects of film thickness and temperature on stress in Zn_0.95Mg_0.05O thin films were analyzed theoretically to see whether there was any crack inside of the thin films and substrate or not. It was found that the stress component values of thin films were compressive; however, for glass substrate they were tension.     

Characterization of ceria films on α-Al2O3(0001) and polycrystalline zirconia using O2 TPD with labeled 18O2

The nature of weakly bound oxygen on ceria films was studied using temperature-programmed desorption with labeled ¹⁸O₂. For α- Al₂O₃(0001)-supported ceria, a desorption feature between 800 and 1300 K is shown to result from partial reduction of ceria. However, this oxygen accounts for only a small fraction of the total oxygen in the ceria film and isotopic labeling studies suggest that this oxygen does not exchange freely with the remaining oxygen in the film. In contrast, results for zirconia-supported ceria demonstrate that much more oxygen desorbs in the low temperature regime below 1300 K, and that there is significant isotope exchange throughout the ceria film and with the zirconia substrate. Finally, exposure of reduced, zirconia-supported ceria to water at 670 K resulted in reoxidation of the ceria film. Oxygen from ceria was then shown to react with CO adsorbed on supported Rh particles, completing the catalytic cycle for the water-gas-shift reaction. This revised version was published online in July 2006 with corrections to the Cover Date.     

Manipulation of the ratio of Li+/Zn2+ on the structure and persistent luminescence property of Li2Zn0.9992Ge3O8:0.08%Cr3+

Long persistent luminescence (LPL) materials have been widely applied and investigated in the fields of night-safe, bio-fluorescent labeling, and optical anti-counterfeiting because of their unique properties of delayed luminescence. In this work, the focus of this research is to significantly improve the LPL properties of Li₂Zn_0.9992Ge₃O₈:0.08%Cr³⁺ by adjusting the ratio of Li⁺/Zn²⁺. On the one hand, when Li⁺:Zn²⁺ < 2:1 (Li_1.97Zn_1.0292Ge₃O₈:0.08%Cr³⁺), a deep-red LPL is produced in the 650–900 nm band for more than 50 h, which is 2.5 times longer than that without regulation. From another perspective, when Li⁺:Zn²⁺ > 2:1 (Li_2.01Zn_0.9892Ge₃O₈:0.08%Cr³⁺), the intensity of LPL is enhanced about four times compared to unregulated. The relationship between traps and LPL was comprehensively investigated by analyzing thermoluminescence spectra. Biological tissue penetration experiments were performed and a set of anti-counterfeit labels was designed. This research will provide guidance for the design of a novel persistent phosphor for the desired trap depth.     

Silver cofirability differences between Bi1.5Zn0.92Nb1.5O6.92 and Zn3Nb2O8

We have investigated systematically the differences of silver cofirability and microwave dielectric properties between Zn₃Nb₂O₈ and Bi_1.5Zn_0.92Nb_1.5O_6.92 (BZN). Two type dopants: 0.29BaCO₃–0.71CuO (BC) and 0.81MoO₃–0.19CuO (MC) were used in Zn₃Nb₂O₈ and Bi_1.5Zn_0.92Nb_1.5O_6.92 ceramics so they can be cofired with silver. The BC-doped ceramics in general have better dielectric properties than those of MC-doped ceramics. The BC-doped Zn₃Nb₂O₈ exhibits better dielectric properties than those of BC-doped BZN (k = 14.7, Q × f = 8200 GHz versus k = 120.1, Q × f = 1050 GHz). For silver compatibility study, the interfacial behaviors between microwave dielectric materials and silver were investigated by using X-ray diffractometer, scanning electronic microscope, and electronic probe microanalyzer. No new crystalline phase and no silver migration behavior were found in the BC-doped Zn₃Nb₂O₈ ceramics cofired with silver, but slight silver migration was detected for BC-doped BZN. But slight silver migration was detected for MC-doped Zn₃Nb₂O₈ and BZN ceramics cofired with silver. Therefore, the good overall properties of BC-doped Zn₃Nb₂O₈ are suitable for microwave applications.     

Enhancement of energy storage and thermal stability of relaxor Pb0.92La0.08Zr0.52Ti0.48O3-Bi(Zn0.66Nb0.33)O3 thick films through aerosol deposition

Relaxor ferroelectric Pb_0.92La_0.08Zr_0.52Ti_0.48O₃ (PLZT 8/52/48) has been studied widely for applications to high energy storage capacitors because of its polarization-electric (P-E) field hysteresis. On the other hand, its energy storage characteristics are unsatisfactory because the dielectric properties deteriorate with temperature. In the present study, a dense nano-composite thick film (∼5 μm) was fabricated by the aerosol deposition (AD) of mixed powders of BZN [Bi(Zn_0.66Nb_0.33)O₃] corresponding to 0, 5, and 10 at.% with lanthanum-doped lead zirconate titanate ceramics (PLZT) at room temperature, followed by post-annealing for crystallization recovery. The composition of 0.95(Pb_0.92La_0.08Zr_0.52Ti_0.48O₃)-0.05Bi(Zn_0.66Nb_0.33O₃) PLZT-BZN5 was made artificially, which accommodates the coexistence of two different phases, demonstrating superior energy storage performance. The 550°C-annealed PLZT-BZN5 film showed a superior energy density of 14.7 J/cm³ under an electric field of 1400 kV/cm and an efficiency of 81%. The PLZT-BZN5 film also exhibited low dielectric loss and improved temperature stability.